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Home My WebLink About20012727 PLANNED UNIT DEVELOPMENT CHANGE OF ZONE APPLICATION LONGS PEAK ESTATES ERIE, COLORADO Prepared for: Propp Realty, Inc. 12600 West Colfax Avenue, Suite B-130 Lakewood, Colorado 80215 February , 2000 THE SEAR-BROWN GROUP 1726 Cole Boulevard, Suite 350 Golden, Colorado 80401 2001-2727 LANNED UNIT DEVELOPMENT CHANGE OF ZONE APPLICATION PLANNING DEPARTMENT SE ONLY: Case Number 3 Application Fee: Zoning District Receipt Number Date Application Checked By: Planner Assigned to Case: t TO BE COMPLETED BY THE APPLICANT: (Print or type only except for required signatures). I (we), the undersigned, hereby request hearings before the Weld County Planning Commission and the Board of County Commissioners concerning the proposed PUD rezoning of the following described unincorporated area of lii/e/d County. LEGAL DESCRIPTION: SEE ATTACHED (If additional space is required, attach an additional sheet of this same size or.a copy of the deed) PARCEL NUMBER: 1 4 6 7 0 9 1 0 0 0 0 4(12 digit number-.found on TAX I.D. or obtained at the Assessor's Office) NAME OF PROPOSED PUD SUBDIVISION Longs_ Peak Estates EXISTING ZONING Agricultural PROPOSED ZONING PUD-Residential 'OTAL ACREAGE 32 OVERLAY DISTRICTS None PROPOSED DEVELOPMENT GUIDE SUBMITTAL (Specific or Conceptual) Conceptual PROPERTY OWNERS OF AREA PROPOSED FOR PUD REZONING: NAME Daryll & Carol Propp, Propp Realty, Inc. PHONE ( 303 ) 233-4000 ADDRESS 1200 West Colfax Ave. , Suite B-130 , Lakewood, CO 80215 NAME PHONE ADDRESS APPLICANT OR AUTHORIZED AGENT (if different than above ') NAME Robert Gollick, LLC ADDRESS 609 S . Gaylord Street, Denver, CO 80209 HOME TELEPHONE BUSINESS TELEPHONE ( 303 ) 722-81 /1 * If agent is different from the property owner, please submit written documentation from the property owner authorizing said agent to represent the owner. Signature: Owner or Auth orized Agent 8 Table of Contents 1 Planned Unit Development Change of Zone Application 2 Conceptual Development Guide 3 Copy of Deed or Legal Instrument 4 Property Owners Within 500 Feet 5 Supporting Documents From Left Hand Water District 6 Supporting Document From Town of Erie LTC REAL ESTATE CONSULTING Ms. Monica Mika, Planning Director Department of Planning Services Weld County Administrative Offices 1400 North 17th Avenue Greeley, Colorado 80631 March 10, 2000 Re: Longs Peak Estates Dear Monica: Enclosed you will find twenty-five (25) copies of the complete PUD Change of Zone submittal for Longs Peak Estates. Checks for the PUD application fee of $2,000.00, the plat recording fee of $11.00 and the hearing notification fee of $20.00 are also included. John Rinko and Bethany Walker of The Sear-Brown Group are the project engineers and planners, I am the project coordinator. Please notify me of agency review comments, application revisions and/or any other information you may need to expedite the County review process. If you need additional copies of the application or would like to meet to discuss the development proposal do not hesitate to call. Sincerely,(-g-40 Ccd• ,\,k Robert J. Gollick, President Robert Gollick LLC cc: Daryll Propp, Propp Realty John Rinko, The Sear-Brown Group • 609 SOUTH GAYLORD STREET, DENVER, COLORADO 80209, 303-722-8771 FAX 303-744-3243 or ae1r,��. ti �,��ef' ' °` TOWN OF ERIE �'i}� 645 HOLBROOK P.O.BOX 100 ' ' ERIE,COLORADO 80516 el LOCAL(303)828.3843 �� y ...•••"- METRO(303)665.3555 0 0 0 ' / e 1ll04 - FEB 13 1997 February 10, 1997 Kathy Peterson Left Hand Water District P.O. Box 210 Niwot, CO Dear Kathy: I am writing in response to your October 15 letter regarding the Daryll Propp tap request. I apologize for not responding earlier,we were finalizing our Comprehensive Plan during that time and it got set aside in the shuffle. The Town does not object to Left Hand providing the twelve water taps to the Propp property. It is within our Comprehensive Plan Area and the number of dwelling sites on the property conform to the Plan. Again, I apologize for the delay in our response. Sincerely, • G W Direct of Community Development cc: File Leon Wurl POLICE DEPT. P.O. BOX 510 METRO (303)449-3156 LOCAL(303)828-3200 MOUNTAIN VIEW FIRE PROTECTION DISTRICT (303)772.0710 Legal Description The following real property, in the North of Erie, County of Weld, and State of Colorado,to wit: An undivided one-half interest in and to the East 1/2 of the East '/x of the Northeast '/,of the Northwest '/, of Section 9,Township 1 North,Range 68 west of the 6'h P.M., Weld County, Colorado, more particularly described as follows: Beginning at the north quarter corner of said Section 9;thence southerly along the east line of the Northwest '/,of said Section 9, a distance of 1338 feet, more or less, to the south line of the Northeast ''/of the Northwest '/of said Section 9; thence westerly along the south line of the Northeast S5 of the Northwest '/ of said Section 9,a distance of 330.16 feet to a point; thence northerly and parallel to the east line of the said Northwest 'V,of said Section 9, a distance of 1339.36 feet,more or less, to the north line of said Northwest ''/, of said Section 9; thence easterly along said north line of said Northwest ''/,of said Section 9, a distance of 329.56 feet to the POINT OF BEGINNING. Including all water rights and water taps with property with all its appurtenances,and warrant(s)the title to the same. The following real property, in the North of Erie,County of Weld,and State of Colorado, to wit: An undivided one-half interest in and to all that part of the West ''/:of the Northeast''/,of Section 9, Township 1 North,Range 68 West of the 6th P.M.,Weld County, Colorado,described as follows: Beginning at the northwest corner of said Northeast''/ of said Section 9, a point from which the northeast corner of said Section 9 bears East 2637.5 feet, more or less;thence South 0° 50' West 1094.9 feet along the West line of said Northeast'/to the TRUE POINT OF BEGINNING; thence South 0° 50' West 1582.1 feet,more or less,along the west line of said Northeast '/,to the southwest corner of said Northeast'/of said Section 9; thence East 118 feet along the south line of said Northeast '/,to an irrigation ditch; thence along the approximate center of said ditch the following courses: North 7°54' East 136.25 feet; North 59°28' East 300 feet; North 55°23' East 217 feet; North 45°23' East 471.4 feet; North 39°51' East 62.7 feet; North 6°06' West 100.4 feet; North 41°00' West 516.1 feet; North 39°05' West 273 feet to the headgate of a lateral ditch; thence North 77° 15' West along said lateral ditch 417.2 feet more or less,to the TRUE POINT OF BEGINNING; together with an undivided interest in one(1)share of the capitol stock of the Farmer's Reservoir and Irrigation Company, with all it appurtenances,and warrant(s)the title to the same. PUD Application Application Requirements PUD Change of Zone for Propp Realty 32- Acre Weld County Site — Longs Peak Estates Parcel #: 146709100004 Existing Zoning: Agricultural land or Low Density Residential (per Erie Comprehensive Plan) # of Proposed Lots: 13 Total Area: 32 Acres Water: Left Hand Water District Sewer: Private Septic System Gas: Public Service Company of Colorado Phone: US West Electric: Public Service Company of Colorado School: St. Vrain Valley School District Fire: Mountain View Fire Protection District Conceptual Development Guide Longs Peak Estates is a proposed planned unit development that is set on 32 acres of currently undevelped land located approximately 2 miles northeast of downtown Erie, in Weld County,Colorado. The proposed development will contain 13 residential building sites ranging in size from approximately 1.1 acres to 2.7 acres. Out of the 32 total acres, approximately 13 acres are located in the northeast'/,of the northwest ''/,of Section 9,Township 1 North,Range 68 West of the 6th PM. The remaining 19 acres are located in the southwest 1/4 of the northeast '/,of the same section. The 32-acre site is located between County Road#5 and County Road#7 and south of County Road#12. The site is northeast of Erie in Weld County and is west of Peak View Road. The vacant land is currently zoned as agricultural land and is taxed as"developable" land. The recently adopted Erie Comprehensive Plan of October, 1999 identifies the future use as low density residential. The following eight components are addressed per the Development Guide Requirements stated in the PUD Ordinance: 6.3.1 Component One—Environmental Impacts 6.3.1.2.1.1 Noise and Vibration 6.3.1.2.1.2 Smoke,Dust and Odors 6.3.1.2.1.3 Heat, Light and Glare 6.3.1.2.1.4 VisuallAesthetic Impacts 6.3.1.2.1.5 Electrical Interference 6.3.1.2.1.6 Water Pollution This proposal should not have any negative impacts to the above listed environmental concerns on this property or adjacent properties. The applicant is willing to address any concerns that staff or referral agencies have pertaining to the listed environmental impacts. 6.3.1.2.1.7 Waste Water Disposal Sewage Disposal for residences will be through individual private septic systems. 6.3.1.2.1.8 Wetland Removal Standing water on the property is only observed during springtime rains and snowmelt. If wetlands are found onsite, the area will be designated open space. 6.3.1.2.1.9 Erosion and Sedimentation An Erosion and Sedimentation Control Plan will be submitted as part of the subdivision construction documents and will be prepared in accordance with the Storm Drainage and Technical Criteria Regulations. 6.3.1.2.1.10 Excavating,Filling and Grading Overgrading is not anticipated in the project. Normal excavation relating to home,road&trail construction is expected. When possible, soils removed will be incorporated into the landscape plan. 6.3.1.2.1.11 Drilling,Ditching and Dredging There will be no drilling,ditching or dredging in the proposed development. 6.3.1.2.1.12 Air Pollution 6.3.1.2.1.13 Solid Waste 6.3.1.2.1.14 Wildlife Removal 6.3.1.2.1.15 Natural Vegetation Removal This proposal does not have a negative impact to the above listed environmental issues. This proposal will increase the amount of natural vegetative cover in the open space areas. There is a low impact to wildlife in the development, according to the Potential for Impact Wildlife Habitat map included in the Weld County Comprehensive Plan. 6.3.1.2.1.16 Radiation/Radioactive Material To the applicant's knowledge,there are no known radiation or radioactive materials on this site. Radon mitigation can be done on a lot by lot basis during the design and construction of each individual residence, if necessary. 6.3.2 Component Two - Service Provision Impacts 6.3.2.2.1.1 Schools The property is within the St. Vrain Valley School District. The school district has projected that the impact of the 13 lot subdivision is a total of 9 students. There is no impact to the middle/senior high school capacity,but it will impact the already over capacity elementary school. The developer is willing to form an agreement with the school district to help mitigate the impacts on the school. This agreement may include a cash in-lieu of land dedication fee to address the capacity concerns at the school. 6.3.2.2.1.2 Law Enforcement Provisions for law enforcement will be discussed between the Weld County Sheriff Department and the Town of Erie. 6.3.2.2.1.3 Fire Protection Fire protection will be provided by the Mountain View Fire Protection District. The District expressed several concerns during the sketch plan review. These concerns are addressed as follows: 1)The residences shall be constructed in accordance with the provisions of the 1994 Edition of the Uniform Fire Code and the 1994 Edition of the Uniform Building Code. 2)Fire flows will be submitted to the district to ensure that the necessary flows are available. 3)Fire hydrant spacing within the development will not exceed 500 feet. A plan will be submitted to the District for their approval. 4)The proposed road will be designed and maintained to support the imposed loads of fire apparatus and will be surfaced for all-weather driving capabilities. 5) Street signs will be placed at intersections. Any non-standard signs used will be submitted to the District for approval. 6)Approved addresses will be visibly placed on all residences. 7) There are no known gas/oil wells in the area. Should any be found on or near the property,they will be shown on the plans and the required setbacks will be used. 6.3.2.2.1.4 Ambulance Ambulance service will be provided by private or local paramedics. 6.3.2.2.1.5 Transportation Access to and from the development will be through a 60-foot road/right-of-way running south from County Road#12 and veering east towards Peak View Road. The road/right-of-way will consist of 11 foot drive lanes with 4 foot shoulders, and will encompass approximately 3.9 acres of the 32-acre site. The street will be constructed in accordance with Weld County Department of Public Works Street Construction Guidelines and will be maintained by The Homeowners Association. 6.3.2.2.1.6 Traffic Impact A traffic study will be completed before final approval. Traffic impact should be minimal. 6.3.2.2.1.7 Storm Drainage Storm water drainage features will be designed in accordance with Weld County Storm Drainage Design and Technical Criteria Regulations. The site will be regraded to allow water flow to the north-northwest into a detention pond. The water will be released into the irrigation ditch toward Coal Creek. 6.3.2.2.1.8 Utility Provisions Gas and electric service will be provided by The Public Service Company of Colorado. U.S. West will provide phone service. 6.3.2.2.1.9 Water Provisions Public water is available north of the development along County Road#12 from the Left Hand Water District. An estimated 10-inch water line located within the proposed road/right-of-way will provide water to the 13 residences and three fire hydrants along the road. Twelve taps(plus the one given with the land) have been purchased from the Left Hand Water District. See attached letter from the District for proof of service. 6.3.2,2.1.10 Sewage Disposal Provisions Sewage disposal for residences will be through individual private septic systems. Should the property be annexed into the Town of Erie or sanitary sewer service is brought to the site,the development assumes eventual hook up to the sewer collection system. In anticipation of future sanitary sewer hook up, the developer plans to install a sanitary sewer pipe through the subdivision that can be tied into a sanitary sewer main coming to the property. 6.3.3 Component Three- Landscaping Elements Seeding and watering of residence lawns,the greenspace,and undeveloped portions of the site will improve the existing vegetation on the property and the overall appearance. The current native vegetation includes: wheatgrass, intermediate wheatgrass,cheatgrass,and several other mid grasses. The residence lawns and greenspace will match the low water,"high plains"grasses. The installation of native low water plants, shrubs and trees throughout the development will dramatically increase area aesthetics. Low water and low maintenance grasses will be used along the greenspace to provide maximum beauty and low water consumption. Xeriscaping will be performed at the development's entrance to the north portion of the property. The use of xeriscaping will conserve water and protect the environment by using site appropriate plants. A Landscape Plan will be submitted during the Final Plan submittal. 6.3.4 Component Four- Site Design The site ranges from approximately 5100 ft mean sea level(MSL)in the southwest portion of the site to 5060 ft MSL in the northwest portion of the site. The site is gradually sloped towards the northwest. A north-south trending irrigation canal is present along the eastern border of the site and an apparently abandoned east-west fragment is located near the center of the property. Although considered urban in scale(more than 5 lots),the developer feels he is creating a non-urban setting by developing the land into large lots with a trail connecting all the lots with the open space. The Town of Erie Comprehensive Plan has characterized the subject property as having a land use of"low density residential". Low density residential is described as having a gross density of 0.5 units per acre(1 unit per 2 acres),or the total land area divided by the number of residential units. The gross density for the subject property is 32 acres/13 residential units, or 0.41 units per acre(1 unit per 2.46 acres). The subject property is not located within a flood plain,according to the Town of Erie Comprehensive Plan Floodplain Map. However,the property was identified as having subsidence hazard on the Geologic Hazards Map of the Town of Erie Comprehensive Plan. The property has been mined for coal from 1920 to 1953, and there are no plans for continued mining activities. According to a study performed by Amuedo and Ivey for the Colorado Geologic Survey, the area is labeled within a severe subsidence hazard zone. The area was also labeled as having a sever subsidence hazard in the Town of Erie Comprehensive Plan, and was assigned as having a land use of"low density residential". According to the Amuedo&Ivey study,a"sever"hazard area is characterized by either: 1)the presence of pillars with subsidence(pillars are assumed to be undergoing decomposition),or by 2)the absence of evidence of surface subsidence. The study also includes several plates showing adjacent property along the southwestern boundary of the subject property. There is a small southeastern portion(-25%)of the subject property that is shown as having remaining pillar support. The depth-of-cover, (or thickness of overburden above mine workings), in this portion is between 100 feet and 150 feet, which is thicker than the area of known subsidence on the adjacent property. The remaining portion of the subject property(-75%) is shown as having pillar support removed. According to the Amuedo&Ivey study, it is assumed that if the majority of the pillar support has been removed beneath an area,it is likely that subsidence occurred shortly after and is essentially complete. The Farmers Ditch running along the east property line is within its own right-of-way and is next to the proposed open space. There will be no impact to the ditch. Land uses for adjoining properties include: low density housing, dry cropland, and an adjacent urban scale subdivision, Scott's Acres. Estimated impact on the site and surrounding area is minimal. It should be noted that the northern six lots may require notification on the plat of low flying planes in the area. These planes come from a nearby private airstrip and may fly at a low altitude over these lots. Also, further study and delineation of the possible wetlands and geological hazards on the site will be performed as the project moves through the approval process. 6.3.5 Component Five - Common Open Space Usage The entrance from County Road#12 will accommodate a bus stop and mail drop. The greenspace/common space will follow the road south until it reaches the irrigation ditch. It will then follow the irrigation ditch to the southwest portion of the site,where it will end in a small"park-like"setting,or gathering area,with a gazebo. The greenspace and gathering area will provide approximately 3.3 acres of common open space. The 30-foot wide greenspace will be established along the perimeter of the lower 7 proposed lots. The greenspace will be located directly across the street from the other 6 lots to provide access to all residences in the development. The greenspace will include a 10-foot wide multiple use trail that leads to a gathering area with gazebo,and will be accessible from the residential units. The trail will be designed for walking, running, and biking. Subject to local regulations and the Home Owners Association, the trail may also be used for horseback riding. The Home Owners Association will provide long-term upkeep and maintenance. The site provides 13%open space, including the detention pond area, and does not meet the desired 15% for the development. The developer feels that incorporating the through trail to the park-like setting provides a much more enjoyable solution to the open space requirements rather than unusable areas incorporated into the design for the sake of meeting the minimum requirement. 6.3.6 Component Six - Signage All signs within the proposed subdivision will adhere to the regulations set forth in the PUD Ordinance #197. 63.7 Component Seven - MUD Impact This proposal is not located within the MUD boundary,as delineated in the Weld County MUD Ordinance or the Comprehensive Plan. There is no MUD impact. 6.3.8 Component Eight - Intergovernmental Agreement Impacts This proposal is not located within any approved Intergovernmental Agreement boundaries. This proposal is not located within the designated Urban Growth Boundary of the Town of Erie per Weld County adopted maps,however,this proposal is consistent with the low density residential area designated on the approved Town of Erie Comprehensive Plan of October, 1999. The Town of Erie has also stated the number of dwelling sites on the property conforms to the Plan. Summary This development is compatible with and compliments the existing character of the area. These lots will have custom designed homes,incorporating a variety of style and architecture. The proposed lots will complement the adjacent properties with similar lot sizes. Development of the property will allow residents of the subdivision to enjoy unobstructed mountain views in a country-like setting. Development of a common open space, or greenspace,following the community irrigation ditch along the eastern border of the development will provide a community walkway. The community walkway will be a multiple use trail. The Home Owners Association will maintain the greenspace as well as the street. The greenspace will lead to a"park-like" setting including a small gazebo and gathering area to the south end of the development. E-21 Engineering, Inc. Phone 303-277-1548 Environmental Engineering for the 21st Century Fax 303-277-1583 400 Corporate Circle,Suite K Phone 888-628-1083 Golden,Colorado 80401-5625 Fax 888-628-1084 November 14, 2000 Mr. Darryl Propp Propp Realty, Inc. 12600 West Colfax Ave., Suite B-130 Lakewood, Colorado 80215 Subject: Report of Subsurface Soil Investigation Longs Peak Estates, Weld County, Colorado E-21 Project No.347 Executive Summary Subsurface soils at the proposed Longs Peak Estates were evaluated with respect to percolation and geotechnical characteristics of the soils. Results of on-site percolation testing indicated that areas of soils are suitable for leachfield installation. Soils described by an E-21 geologist, and supported by grain size _ analyses, identified surface soils at the site to consist of interbedded fine sand, silt, and silty clay with a trace of fine gravel. Surface soils at the site are likely river terrace deposits associated with flood events of Boulder Creek overlying weathered bedrock containing thin coal and sandstone seams. Soils were tested by the geotechnical laboratory and found to exhibit low to high swelling potentials. Bedrock was observed throughout the site at depths between 4.5 and 9 feet below the ground surface and consisted of shale, with a few areas of sandstone. Thin coal seams were occasionally observed within the shale units. Groundwater was not encountered within the upper 11 feet at the site. Piezometers, installed to depths ranging from 11 to 15 feet below grade, were found to be dry at the time of their installation on September 22, 2000 and on October 2 and 3, 2000, indicating that the uppermost groundwater at the site is normally below a depth of 11 feet. Recommendations include the following: 1. Leachfield construction may be installed within areas tested and found to be within the acceptable range of 5 and 60 minutes per inch percolation rate. Leachfields should be designed by a qualified individual, and additional field testing may be required to obtain final approval. 2. Consideration of the swelling potential should be made during the construction design phase of site development and swell potential must be incorporated into foundation, pavement, landscape, and overall design. 1 Longs Peak Estates Subsurface Soil Investigation November 14,2000 Introduction This letter report includes the field activities and soils analyses associated with proposed development of the Longs Peak Estates in Weld County, Colorado (Figure 1). Field activities and soils analyses were conducted to evaluate the suitability of site soils for leachfield installation and to perform preliminary geotechnical testing and evaluation of soils. Site activities, including subsurface soil sampling and percolation testing, were performed by E-21 Engineering, Inc. (E-21) personnel. Laboratory analyses were performed by Advanced Terra Testing, Inc. (ATT) of Lakewood, Colorado. Included with this report are Attachment 1 — Figures; Attachment 2 - Subsurface Soil Boring Logs; Attachment 3 — Percolation Test Data; and Attachment 4—Geotechnical Laboratory Data. Field Activities Field activities were performed on September 21 and 22, 2000 and included the direct push sampling of soils to 15 feet depth, or method refusal; the advancement of a 6-inch solid stem auger for percolation testing; groundwater elevation monitoring; and the performance of percolation tests. Subsurface soil sampling A direct push boring was advanced at each of the seven planned lots within the area proposed for development (the Site). Direct push soil boring locations are presented on Figure 2 of Attachment 1. -- Direct push borings were advanced using a truck mounted hydraulic hammer that advanced a 2-inch I.D. stainless steel tube of 4-feet length. The interior of the stainless steel tube contained an acetate liner that allowed for extraction and field description of soils encountered. Field logs, which include the description of encountered subsurface materials, are included in Attachment 2. Subsurface soil sampling included the collection of discreet interval samples for percent moisture, density and swell/compaction analyses. Extracted samples were immediately sealed within aluminum foil to preserve the moisture and structure of the sample. Samples were hand delivered to ATT for analyses. During subsurface soil sampling, the stainless steel tube was advanced to a total depth of fifteen feet, except at the locations in Lot 3 and Lot 6 where sandstone bedrock was encountered at 10.5 and 10.7 feet depth, respectively. Because the sandstone was appreciably denser than the weathered shale bedrock encountered at each of the other site locations, advancement of the sampling mechanism beyond 11 feet depth was unfeasible. Other subsurface soil sampling performed for each proposed lot included the composite testing of the 0.5- to 4.0-foot depth soils for grain size distribution analyses. This sample was obtained during solid stem auger advancement for percolation test holes. The sample was combined and submitted as a composite sample from each lot, for a total of seven samples. Analysis was performed using American Society for Testing and Materials (ASTM) sieve Method D-422. Ground water elevation monitoring After completion of the direct push borehole a piezometer was installed to evaluate the presence and/or elevation of groundwater. Piezometers were constructed of 1-inch I.D. PVC screen with flush-threaded joints attached to a solid riser. The screen section at each location was approximately 5-feet in length with the riser portion extending to approximately 0.25 feet above grade. The purpose of the screened 2 Longs Peak Estates Subsurface Soil Investigation November 14,2000 section at the bottom of the piezometer was to allow groundwater, if present, to enter the PVC. Depth to water could be measured and surveyed to provide information with respect to groundwater elevation and flow direction. The annular space between the PVC and the borehole was backfilled with native materials extracted during advancement of the solid stem auger. Groundwater elevation monitoring included the electronic tape measuring of the depth to groundwater at each of the seven installed piezometers. Measurements were made from the top of the PVC casing. Total depth measurements were also taken to evaluate the extent of silting-in of the piezometers. Groundwater elevation monitoring was performed twice after piezometer installation. Percolation test holes Review of American Society of Testing and Materials (ASTM) methods for Comparison of Field Methods for Determining Hydraulic Conductivity of the Vadose Zone (ASTM Method D 5126-90), suggests that a wide range of test methods are available for this test, but no specific method has been promulgated by ASTM. Colorado Geological Survey representatives indicated a statewide standard for percolation testing does not exist. Therefore, percolation testing was performed in accordance to standard methodology typically acceptable to state and county health departments. The truck mounted hydraulic drilling rig was used to advance 6-inch solid stem auger borings for completion of the percolation tests for each lot. Percolation holes were advanced to a depth 2 feet beyond the anticipated depth of leachfield installation, or to approximately 4 feet below grade. Where necessary, secondary percolation test holes were advanced by hand with a soil auger. Locations were — - selected based on proposed home construction envelopes with leachfields located in areas that will not contain structures, but will be adjacent to dwellings. Prior to performing the percolation test, the holes were pre-soak by filling with tap water 24 hours prior to the start of testing to saturate the subsurface soils. Following this period,testing was initiated by filling the percolation hole with tap water and measuring the distance to the water from a consistent point. To provide a consistent measuring point,a 1-inch by 1-inch board was placed level across the hole and measurements made from the bottom edge of the board throughout the period of testing. After recording the initial depth to water from the bottom of the board, subsequent measurements were made from the same point throughout the test. The test was concluded after a 6-inch drop in the water level was observed. Measurement times are averaged and provide a soil percolation rate in inches per minute. Percolation rates between 5 and 60 minutes per inch were deemed acceptable rates. Field data sheets were used to record percolation rates throughout the period of testing and are included in Attachment 3. Field Findings Surface and subsurface soils Surface soils at the site include mostly silt and silty clays with some very fine sand, and a trace of fine gravel. Boring logs with descriptions of encountered subsurface soils are presented as Attachment 2. Based upon the structures present within the soils, site topography, and proximity of the site to Boulder Creek, it is believed that surface soils at the site are flood or overflow deposits. Structures observed within the surface soils include laminations created by alternating horizons of finer and slightly coarser units. Additional features observed within the subsurface soil samples included secondary calcium and iron based precipitates, roots, and horizontal and vertical fractures. 3 Longs Peak Estates Subsurface Soil Investigation November 14,2000 Information from the United States Department of Agriculture (USDA) Soil Conservation Service report on the Soil Survey of Weld County, Colorado, Southern Part, indicates that soils within the site consist of — the Noan Loam or the Renohill Clay Loam. The northern and central portions of the site contain the Noan Loam which is described as a clayey silty with moderate to high shrink swell and low strength. The Renohill Clay Loam is described as a moderate to high shrink swell soil with moderate strength. Both of — the soils are described as having an erosion hazard of moderate. The soils description from the USDA report compares well with the field and laboratory findings contained within this report. These surface deposits are present throughout the site and extend to a depth of between 4.2 and 7.9 feet. Below the surface soils, weathered to unweathered bedrock was observed. Bedrock at the site consists of shale, with occasional interbedded thin sandstone and coal horizons. Percolation test results Percolation tests are run to assess soil suitability to sewage discharge through a leachfield. Percolation tests for lots 1 through 7 were conducted on September 22, 2000. Percolation tests for lots 1, 5 and 7 exceeded the maximum percolation rate of 60 minutes per inch required for acceptable soil conditions. Therefore, percolation test holes at la, 5a and 7a were drilled by hand with a soil auger on October 8, 2000. Each of the on-site percolation test holes were filled with water and allowed to sit for 24 hours to ensure proper soil saturation and swelling. The percolation test holes drilled on October 8 were refilled on October 9 for re-testing. Percolation test hole locations are presented on Figure 2 of Attachment 1. Based on the percolation testing, the surface soils, though fine grained, are suitable for the installation — -- of a conventional leachfield. Percolation results suggest that the interbedded nature of slightly coarser horizons allow for ample percolation of introduced liquids. Percolation testing results ranged from 5.8 minutes per inch to 48 minutes per inch. Results are presented below on Table 1. Table 1. Summary of Percolation Testing Results Percolation UTM Coordinate UTM Coordinate Percolation Test Rate Result Hole ID North East LI 4435741 0499216 100 Minutes/Inch Fail Lla 4435741 0499209 5.8 Minutes/Inch Pass L2 4435696 0499211 14.7 Minutes/Inch Pass _ L3 4435377 0499333 20.3 Minutes/Inch Pass L4 4435369 0499406 14.8 Minutes/Inch Pass L5 4435351 0499486 200 Minutes/Inch Fail L5a 4435351 0499441 23.5 Minutes/Inch Pass L6 4435306 0499323 30.7 Minutes/Inch Pass L7 4435282 0499386 80 Minutes/Inch Fail L7a 4435200 0499386 48.0 Minutes/Inch Pass Groundwater levels Groundwater was not observed during installation of the piezometers on September 22, 2000. Groundwater was not observed to be present at the site during either of the groundwater elevation _ monitoring events of October 2 and October 9, 2000. 4 Longs Peak Estates Subsurface Soil Investigation November 14,2000 Laboratory Results The boring locations, depths of encountered weathered bedrock and bedrock, as well as the grain size distribution results, are presented below in Table 2. Analytical results are contained in Attachment 4. The coarsest material appears to be present within the area of L4B as the proportion of sand and coarser grain sizes are nearly twice that observed at other areas of the site. Based upon this and observations made during subsurface soil sampling, if a sand-rich horizon is encountered during borehole advancement then the overall distribution will include a greater proportion of sand. Because the sand horizons are thin, correlation of the units across the site was not feasible. Table 2. Summary of Field Soil Boring and Grain Size Distribution Data Soil UTM UTM Depth To Depth Percent Percent Boring Coordinate Coordinate Weathered To Silt and Sand and ID North East Bedrock Bedrock Clay Coarser L1B B 4435741 0499216 7.9 feet 8.0 feet 71.6 28.4 L2B 4435696 0499211 8.2 feet 9.2 feet 72.1 27.9 L3B 4435373 0499328 6.7 feet 7.1 feet 73.8 26.2 L4B 4435369 0499406 8.2 feet 9.2 feet 57.1 42.9 L5B 4435323 0499486 6.7 feet 8.5 feet 84.4 15.6 L6B 4435306 0499315 6.7 feet 7.0 feet 86.2 13.8 L7B 4435278 0499366 4.2 feet 4.5 feet 85.4 14.6 Density and compaction/swell testing results indicate moderate densities and swell potentials that range from low to high. The compaction results appear average. Results are presented below in Table 3. Results of soil swell tests ranged from less than 2% to greater than 5%. Soils with greater than 5% swell are classified as high swelling and soils with 3% to 5% swell are considered to be moderate swelling soils in the Colorado Front Range Area. Consideration of swell potential must be incorporated into foundation, pavement, landscape, and overall design. Table 3. Summary of Subsurface Soil Sampling, Moisture, Density and Compaction/Swell Data Soil Sample Moisture Wet Swell Compaction Boring Depth % Density (Under 336 Under 336 ID Lbs/ft3 Lbs/ft3) Lbs/ft3) LIB 2.0—4.0 feet 7.5 Not Analyzed Not Analyzed Not Analyzed L2B 2.0—4.0 feet 9.2 Not Analyzed Not Analyzed Not Analyzed L3B 2.0-4.0feet 17.1 116.0 1.26 % 1.8 % L4B 2.0—4.0 feet 6.3 Not Analyzed Not Analyzed Not Analyzed L5B 2.0—4.0 feet 12.8 1263 3.69 % 1.1 % L6B 2.0—4.0 feet 13.0 Not Analyzed Not Analyzed Not Analyzed L7B 2.0—4.0 feet 13.4 130.8 5.87 % 0.95 % 5 Longs Peak Estates Subsurface Soil Investigation November 14,2000 Conclusions 1. Subsurface soils within the area proposed for development of the Longs Peak Estates consists mostly of interbedded fine sand, silt, and silty clay that ranges in thickness from 4.7 to 9.4 feet. 2. Bedrock, in variable stages of weathering, is found below the surficial soils. The majority of the site is underlain by shale, but the very southwestern portion of the site is underlain by a sandstone layer that is not substantially weathered. 3. Groundwater was not observed within 11 feet of the ground surface throughout the site and was not observed within the upper 15 feet of materials in the northern and southeastern portions of the site. 4. Percolation testing of soils from a depth of 2 to 4 feet below the surface identified areas of on-site soils to be suitable for leachfield installation. Percolation is likely assisted by the coarser sand seams within the silt and silty clay soils present throughout the site. 5. Swelling potential of soils from 2-4 feet depth throughout the site vary from low to high. Soils within the southeastern portion of the site, proximal to proposed lot#3, were tested and results indicate low swell potential. Other soils tested were within the moderate to high swell potential range. These areas likely contains clay soils of the montmorillinite group that enlarge due to incorporation of water — — molecules into their structure. Recommendations 1. Leachfield construction may be installed within areas tested and found to be within the acceptable range of 5 and 60 minutes per inch percolation rate. Leachfields should be designed by a qualified individual, and additional field testing may be required to obtain final approval. 2. Consideration of the swelling potential should be made during the construction design phase of site development and swell potential must be incorporated into foundation, pavement, landscape, and overall design. Limitations These services were performed in accordance with the scope of work requested by Rinko LLC. This evaluation of subsurface soil and groundwater conditions has been performed to evaluate the suitability of the subject property for subdivision and development with respect to soil characteristics and groundwater conditions only. Detailed structure and foundation design for construction must be performed by a qualified soil and foundation engineer. This report has been prepared with the level of care ordinarily exercised by members of the profession currently practicing under similar conditions. Some uncertainty will always exist concerning the presence, or absence of, potentially adverse conditions at any particular property, irrespective of the rigor of the investigation. Accordingly, the Consultant offers no warranty, either expressed or implied, that adverse environmental or geologic 6 Longs Peak Estates Subsurface Soil Investigation November 14,2000 conditions, other than those identified in this report, do not exist at the Site, or that such adverse conditions will not exist there in the future. Sincerely, E-21 ENGINEERING, INC. ()(2)./431 Serb's anson, P.E., P.G. Paul F. Gottler, P.G. ngineering Geologist/Environmental Engineer Project Geologist c-21 shared/projects/347-Propp Really—subsurface Soil Letter Report 7 Attachment 1 Figures ' plulu�bs .(---- - _ 4982 / _. —.J 1 I / A\ MINER(AL ----) ono• (,/ 500 A \ ( \) /I- 'I \ 4) \\\,,. I • i NO/47 I�J ( J © �,..r• te�, I I $oq so< I std I/ QTLo } , � / �� - • SITE ..� _ Z :. \'1/4 .__._./ I. (i �" � - / ) { 7 �� ©\� A 1 v i l = • y • ‘2J I___ NT IIof I \___/----- u,. ''.. !� . ) I I M . 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W - _ �_ ,� �i� r ioo o tw 200 I N I I W IN MI LEGEND G`B SOIL &WCPIG LOCATION LONGS PEAK ESTATES °I P000tATION TEST °��" WELD COUNTY, COLORADO PRIMARY SEPTIC LOCATION FIGURE 2: SITE MAP 1 SECONDARY SEPTIC EOCATION PROJECT NO: 34] ME: L -- - DEEM BY* DRMVN EPP CHECKED BY: ISSUE DATE 11/14/00 REVISION: SHEET 1 Of 1 Figure 2 : Site Map is an oversized map See Original File PLANNED UNIT DEVELOPMENT CHANGE OF ZONE APPLICATION LONGS PEAK ESTATES WELD COUNTY, COLORADO SUPPLEMENTAL INFORMATION August 23, 2000 Prepared for: PROPP REALTY, INC.. 12600 West Colfax Avenue Suite B-130 Lakewood, Colorado 80215 Prepared by: RINKO, LLC P.O. Box 28218 #16 Lakewood, Colorado 80228 (303) 601-9230 RINKO, LLC Phone:303-601-9230 Fax:303-277-1583 nko,LLC E-Mail:johnrinko@yahoo.com r.O.Box 28218#16 Lakewood,Colorado 80228 August 23, 2000 Julie Chester Lead Planner Weld County Department of Planning Services 1555 North 17th Avenue Greeley, Colorado 80631 Subject: Response to Request for Additional Information Longs Peak Estates, Case#Z-543 Dear Julie: Introduction This Supplemental Information Report has been prepared to address the issues presented in your Memorandum dated May 8, 2000 to the Weld County Planning Commission in reference to a request for continuance of Case Z-543 (Attachment 1). This letter report is organized in accordance with the issues presented in the Memorandum as listed below: Public Meetings Proposed Changes Project Meeting Technical Issues: 1. Site evaluation for septic systems 2. Drainage study 3. Traffic study 4. Geological subsidence study 5. Wetlands study 6. Soils study The basis for this letter report includes our response to the issues,the results of our extensive work with the neighboring landowners to achieve a harmonious program,and the discussions from our project meeting held in your office on Tuesday,July 25,2000. The most important issue was the negative response of the neighboring landowners, followed by the technical issues listed above. Longs Peak Estates—Case Z-543 Julie Chester August 23, 2000 Page 2 Public Meetings Based on the feedback received from the original Planned Unit Development—Change of Zone Application dated March 10, 2000, it became apparent that the proposed plan did not meet the expectations of the neighboring landowners. The first course of action undertaken by Propp Realty was to convene meetings with the neighbors in order to obtain their input first hand. A series of three meetings were held during the time of this continuance in order to address their concerns and fine tune the proposed development. The first meeting was held in Lakewood, Colorado on July 18, 2000. A second and third meeting were held on August 3 and 17 in Erie,Colorado at the home of a neighboring landowner in order to increase the opportunity for public participation. Attendance sheets are included as Attachment 2. The three main concerns expressed by the neighbors included the number of lots,preserving the country and farming lifestyle of the area,and the flow of traffic for the new development. The original proposal of 13 lots over 32 acres, at a bulk density of 2.5 acres per unit,was viewed as too small to promote the country, agricultural lifestyle shared by the neighboring landowners. Similarly, the new landowners needed to be aware that the lifestyle of the immediate community was agricultural, with several neighboring landowners supporting themselves through agricultural businesses. Promoting the new development as supportive to animals,specifically promoting the raising or owning of animals would provide a better match for the community as a whole. The traffic flow issues revolved around the originally proposed through road, connecting Weld County Road#12 and Peak View Road with a new,paved county road. This was viewed as potentially disruptive to the country-like setting of the area,and promoting increased traffic beyond that of the new land owners due to the paved road,generating a"highway"effect for the neighbors. Other issues discussed and addressed included the proposed building envelopes,water line design and placement of fire hydrants, Peak View Road maintenance issues and traffic loading, intersection signage, construction traffic flow and control,placement of septic fields,utilities,building heights and property line offsets, open space/trail systems and locations of pathways,protection of irrigation ditches,the role of the homeowners association and commitments of maintaining open spaces,road surface design, landscaping elements,and various other minor details regarding the proposed development. The goal of these public meetings was to revise the proposed development to meet the needs and expectations of the neighboring landowners and gain their support for the project. This Submittal includes the results of the close interactions with the neighbors. Based on the response received and the proposed minor changes described herein,we believe we have succeeded in obtaining this goal. Longs Peak Estates—Case Z-543 Julie Chester August 23, 2000 - Page 3 Proposed Changes We intend to offer a reduced number of lots for Longs Peak Estates as a result of and the feedback from the neighboring landowners. In order to provide a development that best suites the area, the local land use, and meets the desires of the neighbors, we intend to reduce the proposed number of lots in the development by almost 50%, offering 7 lots instead of the originally proposed 13 lots. This reduction will occur through the combination of lots, keeping the original design of the development intact so that this will be considered a minor change. The reduction of lots will provide for a bulk density reduction for the 32-acre site from 2.5 acres/unit to 4.6 acres/unit. The configuration will have the northern 6 lots reduced to 2 lots, and the southern 7 lots reduced to 5 lots. This reduction in lots will satisfy the immediate concerns regarding the identified issues at this time, with flexibility to fully address each concern during final design and platting. We also propose to break the continuous road into two individual cul-de- sacs to address traffic flow concerns. These minor changes have received the support of the neighboring landowners. We will promote the use of the land for animals through specific language in the homeowner's covenant, and inform the new owners of the country, agricultural nature of the area through the inclusion of the right to farm covenant already appearing on the Conceptual Change of Zone Plat. The right to farm covenant will also be included in the homeowner's covenant. The text of the language to promote the lifestyle in the homeowner's covenant appears below: Intent Statement The intent of the proposed Longs Peak Estates PUD is to provide an opportunity for a rural residential lifestyle in an area that is experiencing strong development pressure. The seven large single family lots will permit a variety of livestock, domestic and exotic animals including horses, sheep, llamas, goats, swine, chickens, etc. the number of which is controlled by the limits established in this PUD. Buyers of these lots need to be aware of the unique lifestyle that exists in the area, which includes working farms and ranches, dairy production, a wide variety of livestock, domestic animals and show animals that range from pets to agricultural production. This is the predominant lifestyle for the neighborhood and it is anticipated that the residents of Longs Peak Estates will be integrated into the rural fabric of the area. The proposed PUD limits for animal units are the Weld County agricultural zone district requirements, appearing in Attachment 3. Using these limits will allow the new lots to have the option to raise animals that best matches the neighboring land uses. Longs Peak Estates—Case Z-543 Julie Chester August 23, 2000 Page 4 Other minor changes include the placement of a fire hydrant at the southernmost end of the new water line, so that firewater is available to the nearby landowners on Peak View Road. Based on preliminary feedback from Left Hand Water,we will connect the new water line to the existing line at the southern end of Peak View Road which will increase water pressure and water quality for neighboring water users. The proposed open space/trail system has been modified to include additional trail loops to promote the raising of horses for recreational purposes. The design of these loops provides additional offsets for neighboring landowners. We will continue to work with the neighboring landowners during final design stages to obtain their input on building envelopes and septic field envelopes to best possible maintain their mountain views. Offsets, setbacks, and height limitations per Weld County requirements will be enforced. The irrigation ditches that cross the property are protected under Colorado Law and will be preserved during site design. The revised roadway design breaks the continuous road into two cul-de-sacs designed to Weld County Department of Transportation standards. This will eliminate the potential of a"highway" effect for the neighboring landowners while fairly dividing the traffic flow to the north and south. Existing roadway traffic loading thresholds will not be exceeded. The new roads will be paved to minimize dust and to meet County standards. Signage will be added to the intersection of the new road with Peak View, including stop signs, and"no outlet" signage. We will work with Weld County DOT, the neighboring landowners, and other agencies as needed to address the issues regarding the maintenance of Peak View Road during the final design stages so that these issues are resolved before the initiation of construction activities. Finally,the proposed utilities for the site will be underground which will provide an aesthetically pleasing site design. The homeowner's association will be responsible for maintaining the open space in accordance with the Weld County PUD Zoning Ordinance. The association will also maintain the new roadways, enforce the covenant, maintain the open space trails, and provide an avenue for the neighboring landowners to interact. Project Meeting A project meeting was held with representatives of Weld County after the initial public meeting to review the proposed changes. A letter was prepared to document the discussions and direction from this meeting held in your office on Tuesday, July 25,2000 and appears as Attachment 4. In attendance at the meeting were: • Julie Chester, Weld County Department of Planning Services • Diane Houghtaling, Weld County Public Works Department • John Rinko, representing Daryl'Propp,Property Owner The purpose of the meeting was to discuss the additional information requests of Weld County Department of Public Works,Weld County Department Public Health and Environment, and the Longs Peak Estates—Case Z-543 Julie Chester August 23, 2000 Page 5 Colorado Geological Survey as detailed in your Request for Continuance Memorandum dated May 8, 2000. We understand that our direction for the project does not constitute a major change based on our conversation after your staff meeting on July 28, 2000. We intend to continue to work with you and your staff to maintain minor change status,with the goal of providing a concept design that meets the expectations of the neighboring landowners. Technical Issues Our response to the technical issues is predicated on the reduction of the number of proposed lots for Longs Peak Estates from 13 to 7,which nearly doubles the average lot sizes. A revised Conceptual Change of Zone Plat for Longs Peak Estates PUD is provided in Attachment 5. This change was discussed in detail in the project meeting and as a result, found to alleviate the concerns listed in the continuance memorandum. The requests for more detailed studies were agreed to be of lesser immediate concern,and could now be addressed in final design. The purpose of this section is to present an overview of the issues and how the new layout serves to minimize the immediate concerns of your staff, and to provide you with our proposed approach for addressing each issue during final design. We intend to work closely with you and your staff during final design to address the original concerns or other concerns that may arise. The revised layout with the reduction in the number of lots from 13 to 7 provides the following benefits: • Provides a site layout favorable and acceptable to the neighboring landowners; gains their support for the project, • Allows increased individual lot sizes to better arrange building and septic fields envelopes to meet County requirements, • Increases open space to meet the County minimum of 15%, • Allows for a trail network to increase recreational use and promote horse activity, • Provides for flexibility to better arrange units to avoid geological subsidence hazards, and helps to minimizes subsidence issues by decreasing housing density, • Reduces traffic loadings and impacts on local roads; minimizes a perceived"highway" effect for the neighbors, • Allows for more animal units per lot to better conform with the neighboring land uses, • Minimizes impacts to mountain view for neighbors by reducing number of houses, • Improves the existing empty lot into an attractive,high quality use which will be attractive to neighboring landowners, • Increases the points for drainage control from one to potentially three with new lot arrangement, and • Encourages the rural lifestyle for the new lots to match the surrounding lifestyle which meets the expectation of the neighbors and gains their support. Longs Peak Estates—Case Z-543 Julie Chester August 23, 2000 Page 6 Detailed responses to the issues in the Memorandum appear below. 1. Site evaluation for septic systems The Weld County Department of Public Health&Environment presented issues with the original 13 lot development as documented in the comment package on the March change of zone submittal. The primary issue was the relatively small lot sizes for arranging septic field and backup field envelopes in potentially tight soils while maintaining offsets from irrigation features,property lines,and potential wetland areas. An informal,brief discussion was held with a Department Representative, Pam Smith, to review these concerns at the continuance hearing. The reduced number of lots will increase lot sizes and provide ample building and septic envelopes to meet the Weld County requirements for individual septic systems. The first area of concern was the southern end of the northern 10 acre portion of the site, where the potential wetland encroachment onto the site and the irrigation ditch generated limitations for Lots 5 and 6 of the former 13 lot configuration. The new lot design reduces the 6 lots proposed for the northern 10 acre portion to 2 lots. The proposed layout of the two lots provides for ample setbacks from the potential wetlands area and the irrigation ditch. The septic absorption envelopes,both primary and secondary per site, will be to the north of the ditch, out of the suspect areas. We still intend to provide a detailed site evaluation for each lot during final design, and if necessary, provide engineered absorption fields to meet county requirements. Secondary field envelopes will be provided and incorporated into each lot design. The revised lot design indicates envelopes on each lot where buildings and septic fields would be arranged in order to demonstrate the ample space available for each lot while maintaining setbacks and offsets. The development covenant will provide protection of the envelopes from structures, shrubs,trees,and other activities which would potentially impact the primary and secondary absorption fields. The scope of work for final design will include the following: • A site evaluation on each lot conducted at the location of the primary and secondary absorption fields • Demarcation of these fields on the drawings as no build or development areas • Borings to establish ground water depth • Test holes to assess soil types to at least 10 feet • Percolation tests for primary and secondary fields • Septic system and leach field designs to County and State standards, including maintaining minimum intervals between base of a leach field and the water table. • Should the field testing indicate unacceptable findings, engineered systems will be designed and installed per County and State standards. Longs Peak Estates—Case Z-543 Julie Chester August 23, 2000 Page 7 2. Drainage study The issues regarding the drainage study were discussed in the project meeting with Weld County DOT representative Diane Houghtaling. The primary concern for the site drainage was the feasibility and success of directing the surface flow entirely to the northern portion of the site. Engineered solutions would have been required to address the irrigation ditch crossings, along with the concerns for the final destination of the surface water to Weld County Road#12. The new site design with reduced number of lots will allow the incorporation of additional drainage fields for the various areas of the property. Under the new design,the northern portion of the site will drain to the original drainage field shown in the submittal,while one or two additional drainage fields will be added to the west central portion of the southern portion of the site to address drainage. Specifically, the new layout calls for the area north of the irrigation ditch crossing the property to be directed to the north, following the natural land contours,to a detention pond at the northern boundary of the property. The central portion of the site would be directed to the potential wetlands area for detention, and the southern portion of the site would be directed to a third detention pond located at the central western boundary of the lower section of the site. This arrangement best matches the existing drainage occurring at the site with the natural contours and allows for flexibility during final design to meet the County's requirements. A detailed drainage report will be included in final design for the site, including these new drainage fields, and will be prepared and signed by a Colorado licensed engineer. The drainage report will be completed in accordance with the current Weld County requirements. The report will address the design of drainage facilities on the north and south portions of the property. Possible drainage facility improvements for the site include storm sewers, roadway culverts, drainage swales and detention ponds, if necessary. The proposed site layout and associated drainage improvements will be designed to minimize the development's impact on the surrounding area by maintaining existing drainage patterns on and off site. We will work with the neighboring landowners during final design to establish water needs and other issues. Easements will be established for irrigation ditches. 3. Traffic study The input from the neighboring landowners focused on the proposed through road and the effects of generating excessive traffic to the area. Our proposed reduction in the number of lots will ease the overall traffic burden through close to a 50%reduction in traffic impacts to the surrounding area. However,the neighbors required a solution to the through road. Similarly,the Weld County DOT was concerned with traffic loading onto Peak View Road,which by State regulations,can not exceed a traffic county of 200 without major improvements. Our design must propose a way to limit the traffic onto Peak View Road while meeting the neighbors concerns with traffic flow. Longs Peak Estates—Case Z-543 Julie Chester August 23, 2000 Page 8 Our revised plan addresses these issues by providing a break in the through road with two separate cul-de-sacs. The two northern lots are accessed from Weld County Road#12,and the south 5 lots are accessed through an extension of Peak View Road. This arrangement provides for controlled traffic loading onto Peak View Road so as not to exceed the 200 trips per day design number. This is established through a theoretical maximum loading based on the number of lots with access to Peak View Road. Specifically,there are currently 16 lots which border Peak View Road and the connected side road of Bruce Road. These lots are listed in Attachment 6. Using the theoretical design maximum factor of 9.57 trips per day per lot,the total existing loading onto Peak View Road is 153.12 trips per day. Adding 5 lots,or 47.85 trips per day,brings the total to approximately 200 which is within the guidance value maximum. It should be noted that 2 lots that are included in this count do not use Peak View Road(the Mullen lot has their driveway off of Weld County Road#12 and the Favela lot uses access from Weld County Road#7). Thus this provides a safety factor to the maximum traffic loading calculations. The proposed new roads will be paved and designed to meet current Weld County DOT standards, including two 12 foot wide paved lanes and two 4 foot shoulders,and 55 foot radius cul-de-sacs. We will work with the Weld County Department of Public Works during final design to address concerns for traffic flow and limiting traffic on Peak View Road,maintenance of Peak View Road,adjust road alignments, signage,discuss emergency access routes between the two cul-de-sacs if necessary and required by the fire department,and other issues as necessary. 4. Geological subsidence study The issue of potential geologic subsidence will be fully addressed as per the requirements of the Colorado Geological Survey and Weld County regulations. We intend to perform a detailed study during final design to address this issue prior to any lots being sold. The reduction in the proposed number of lots allows for better management of this potential situation. By increasing the acreage per lot,we are able to better site the building envelopes to avoid areas of potential subsidence. Reducing the housing density also reduces the potential impacts as compared to the original 13 lot plan. Included in Attachment 7 is a preliminary analysis of the issues presented in the Amuedo and Ivey study regarding the Morrison and Clayton Mines. Also included is a preliminary scope of work prepared by E-21 Engineering Inc. which details the assessment to be performed during final design. Although regional in nature,the Amuedo and Ivey study suggests that the northern portion of the site may be free from mining due to the existence of the fault line crossing the property. This helps to minimize potential impacts for lots 1 and 2. The majority of the site may have had the pillars removed during historic mining activity,which could be supported by the ponding of water at topographic low points in the central portion of the site. If this occurred,the severity of potential Longs Peak Estates—Case Z-543 Julie Chester August 23, 2000 Page 9 subsidence is minimized for Lots 3,4 and 5. The southern portion of the site is indicated to potentially have pillars remaining,and does not readily show surface evidence such as water ponding. In this area we have located only 2 lots, so that the design of the building envelopes can be varied within the envelope shown to address potential subsidence. Regardless, we will perform the scope of work, employ engineering solutions if necessary, and obtain approval from the Colorado Geologic Survey prior to final plat to fully address potential geologic subsidence hazards. We will work with experts from Colorado Geologic Survey to fine-tune the study's scope and depth to meet their approval prior to any lots being sold. 5. Wetlands study We intend to provide a complete wetlands study,performed by a qualified contractor,and if necessary,provide methods to preserve wetlands. The revised site design reduces the number of units on the northern portion of the site from 6 lots to 2 lots, so that we can avoid the suspect wetlands areas near former lots 5 and 6. For the northern portion of the site,no building or sewer system envelopes will be south of the drainage ditch crossing the site so that the potential wetlands area can be protected. Lot 3 is arranged so that the building and septic system envelopes can be kept away from the suspect wetland area. Options to include and maintain a wetland area by the homeowner's association may be considered in order to enhance the rural appeal of the property. 6. Soils study We intend to perform a complete soils study as part of the site study,and provide engineering solutions to address potential expansive soil issues for building foundations, absorption fields, and other potential issues such as inconsistent soil compaction due to historic subsidence. This information will be used in the design of the septic system envelopes, site drainage control, roadway design, foundation design, and design of bridges. Depth to ground water will be established, and the occurrence of bedrock(to a depth of 15 feet). Final design will include fieldwork and note the locations of all site tests on the site drawing. Geotechnical testing and evaluations will be performed for structures, including a minimum of five boreholes across the site to collect samples for analysis (density,moisture content, strength and swell-consolidation potential). Summary This Supplemental Information Report has been prepared to address the issues presented in your Memorandum dated May 8, 2000 to the Weld County Planning Commission in reference to a request for continuance of Case Z-543 (Attachment 1). Based on your feedback,we understand that these Longs Peak Estates—Case Z-543 Julie Chester August 23, 2000 Page 10 adjustments constitute a minor change and will allow for the case to proceed to hearing on September 5, 2000. We feel that the involvement and interaction with the neighboring landowners along with our reduction in the proposed lots provides Weld County with an exemplary solution for this site which meets the needs and expectations of the neighbors and community. We look forward to proceeding with this program with you and your staff. Please feel free to contact me (303)601-9230 with any questions or concerns. Sincerely, Xj\LI Jk7\ John Rinko,Jr., P.E. cc: Bob Gollick Daryll Propp ATTACHMENTS 1. Memorandum dated May 8,2000 to the Weld County Planning Commission in reference to a request for continuance of Case Z-543 2. Public Meetings Attendance Sheets 3. Agricultural Zone District Animal Unit Basis 4. Conceptual Summary Letter,July 27, 2000,to Julie Chester regarding information request 5. Revised Change of Zone Plat for Longs Peak Estates(Drawing) 6. Lots with access to Peak View Road 7. Geological Subsidence Overview and Scope of Work prepared by E-21 Engineering Inc. Longs Peak Estates—Case Z-543 E-21 Engineering, Inc. Phone 303-277-1548 Engineering for the 21st Century Fax 303-277-1583 400 Corporate Circle,Suite K Phone 888-628-1083 Golden,CO 80401 Fax 888-628-1084 Mr. Daryll Propp Propp Realty,Inc. 12600 W. Colfax Ave., Suite B130 Lakewood, CO 80215 August 21, 2000 Subject: Scope of Work-Geologic Hazard Evaluation Longs Peak Estates Dear Mr.Propp, E-21 Engineering, Inc. (E-21) is pleased to submit this scope of work in association with a required geologic hazard evaluation for the Longs Peak Estates in Weld County Colorado. The geologic hazard evaluation is required for receipt of a Geologic Hazard Overlay District Development Permit. This permit is required before final approval by the Weld County Board of Commissioners. The scope of work has been developed at the request of Mr.John Rinko. Scope of Work: Based on documentation available from the Weld County Department of Planning Services a Geologic Hazard Overlay District Development Permit must be received before final development authorization is granted. This permit requires a geologic hazard evaluation be performed on the subject site. The hazard evaluation should provide information regarding the potential for structural damage to new homes during land subsidence due to mine collapse. To evaluate the subsidence potential E-21 proposes the following scope of work: • Perform a literary search covering the Morrison Mine and related topics for information on subsidence potential at the site. Information sources are expected to include publications at the Colorado School of Mines, Association of Engineering Geologists, Colorado Division of Minerals and Geology,and the US Geological Survey. • Evaluate the extent of mining under the site (Morrison Mine, and potential others). According to published information the existing coal mines have been plotted to within 500 ft on 90% of the published maps. Large-scale maps are available at the Colorado Division of Mines that may allow more detailed evaluation of the extent of the mines at, or below, the area proposed for development. Additional data may also be made available from the well logs from natural gas wells located in the vicinity of the site. • Evaluate the potential for"poaching"of coal within the Morrison Mine. Published information suggests that mines where high royalties were paid were often excavated beyond the known boundaries. This activity, called poaching, often extended the boundary of a mine beyond that published. Review of royalty information and the potential that the Morrison Mine has been one where poaching has occurred may be found during review of Colorado Division of Mines records. • Published information on overburden thickness was rounded off to the nearest 50 feet. Since overburden thickness is related to mine collapse, additional evaluation of overburden thickness at the site is warranted. Information on overburden thickness can be evaluated from well logs of proximal wells, or from information contained at the Colorado Division of Minerals and Geology. • Information derived from a countywide report indicates that the Morrison Mine in the area of the site does not contain remaining pillars. Information regarding the presence of pillars is based on information review and may not have been accurately transcribed. Information available at the Colorado Division of Minerals and Geology can be reviewed for the site to better evaluate the potential for site subsidence. • Published information regarding coal bed thickness at the mine was reported to be 5-10 feet at the site. Information regarding the exact thickness should be reviewed so that a better understanding of the hazard is known. The literature search may provide supporting information regarding the low likelihood of collapse when less than 8 feet of coal has been removed. • Information regarding the geologic strata immediately above and below the mined coal should be reviewed to assist in evaluating the subsidence potential for the site. Published information suggests that "ironstone" layers provide sufficient support in some areas if present immediately above the voids left after removal of coal seams. • Information derived from a countywide report on coal mining indicates that a normal fault is located across the northern portion of the site. A more precise location of the fault relative to the site should be undertaken. By locating the fault more precisely, the limit of the Morrison Mine in the area of the site can be located. This information can be attained at the Colorado Division of Minerals and Geology and/or from well logs of proximal oil/gas exploration, or through review of aerial photographs held at private and public entities. • If information gathered from any of the aforementioned sources still indicates that a land subsidence hazard exists then more cost effective non-invasive methods of investigation, such as various geophysical tools, can be evaluated as a means to detect the absence or presence of voids in the area below that proposed for development. Propp-Scope of Work 2 E-21 Engineering, Inc. Amudo and Ivey Map Report Project# 336 Re: Longs Peak Estates To: John Rinko From: Paul Gottler Date: August 21, 2000 Map 1:Mine Limits. The mine limits have been incorporated onto the aerial photograph of the site. The presented limits of the Morrison Mine included most of the area proposed for development except approximately the northern 500 feet of the north parcel. Map 2:Overburden Thickness. Overburden thickness as evaluated through elevational data from the mine was incorporated into map 2. Based on the northeast-southwest trend of the line separating the 50-100 feet from the 100-150 feet cover the thickness of overburden material apparently is greatest in the eastern and southern portions of the site. Map 3:Pillars Removed and In-Place. Based on the maps included with the Amudo and Ivey report a portion of the site proposed for development includes area that remains underlain by pillars. The southern portion of the southern parcel appears to be completely underlain by an area still containing pillars. The north-central area within the southern parcel also contains pillars. It appears the area immediately west of the site that has experienced some subsidence appears to have had the pillars removed. Map 4: Coal Thickness. Based on the maps provided with the report the entire area of mining within section 9 appears to have contained between 5 and 10 ft thickness of coal. Map 5:Subsidence Areas. The area immediately west of the site has been identified as an area of mine subsidence. The extent of the subsidence on the map included with the report appears much greater than that apparent on the aerial photograph. The reason for this difference is unknown. Map 6:Subsidence Hazard. Based on the report map the entire site is within the area defined with a severe subsidence hazard. Included with the map drawn atop the subsidence map are the locations of two fault lines in the area around the site. The U on one-side of the fault is meant to represent the up-block;the D, or down-side block, is also represented. The fault does cross the center portion of the north parcel. It is not known whether this fault is active. e-11 sMr�proiects336-Map Renew Report t 7 f�+.. t, .! ,> Y' wvT1i. 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Longs Peak Estates Golden, Colorado 80401 Figure 5 E-21 Project#336 August, 2000 Weld Ceu,'Y Planning cep, RINKO, LLC Phone: 303-601-9230 4 /1 71 2QQQ Fax: 303-277-1583 Rinko,LLC E-Mail:johnrinko@yahoo.com P.O.Box 28218#16 RED Lakewood,Colorado 80228 F� K " August 16, 2000 Julie Chester Lead Planner Weld County Department of Planning Services 1555 North 17th Avenue Greeley, Colorado 80631 Subject: Updated Mailing List Longs Peak Estates, Case#Z-543 Dear Julie: Attached please find the updated mailing list for the above referenced project. I have also included three copies of the mailing list on mailing labels for your convenience. I look forward to our meeting on Wednesday, August 23, 2000 at 10:00 at your office. Sincerely, ja1/4, John Rinko, Jr., P.E. cc: Bob Gollick Daryll Propp RINKO, LLC Weld County Planning Dept Phone: 303-601-9230 Fax:303-277-1583 - Rinko,LLC E-Mail:johnrinko@yahoo.com P.O. Box 28218#16 n' IC, 01 2000 Lakewood,Colorado 80228 RECEIVED July 27, 2000 Julie Chester Lead Planner Weld County Department of Planning Services 1555 North 17th Avenue Greeley, Colorado 80631 Subject: Conceptual Summary of August 15, 2000 Submittal Longs Peak Estates, Case#Z-543 Dear Julie: This letter has been prepared to document our discussions and direction from our meeting held in your office on Tuesday, July 25, 2000. In attendance at the meeting were: • Julie Chester, Weld County Department of Planning Services • Diane Houghtaling, Weld County Public Works Department • John Rinko, representing Daryll Propp, Property Owner The purpose of the meeting was to discuss the additional information requests of Weld County Department of Public Works, Weld County Department Public Health and Environment, and the Colorado Geological Survey as detailed in your Request for Continuance Memorandum dated May 8, 2000. This information is due to you August 15, 2000 in order to prepare for the hearing date of September 5, 2000. The issues can be summarized into six (6) issues as presented below: Issues: 1. Site evaluation for septic systems 2. Drainage study 3. Traffic study 4. Geological subsidence study 5. Wetlands study 6. Soils study As presented in the meeting, we intend to offer a reduced number of lots for Longs Peak Estates as a result of and the feedback from the neighboring landowners. Our meeting of July 18, 2000 with representatives of the adjacent landowners resulted in their wish to have larger lots to promote the Julie Chester July 27, 2000 Page 2 country lifestyle including raising or owning animal. Eight neighbors attended the informal public meeting. In order to provide a development that best suites the area, the land use, and meets the desires of the neighbors, we intend to reduce the proposed number of lots in the development by almost 50%, offering 7 lots instead of the originally proposed 13 lots. This reduction will occur through the combination of lots, keeping the original design of the development intact so that this can be considered a minor change. The reduction of lots will provide for a bulk density reduction for the 32-acre site from 2.5 acres/unit to 4.6 acres/unit. The configuration will have the northern six lots reduced to two lots, and the southern 7 lots reduced to 5 lots. This reduction in lots will satisfy the immediate concerns regarding the identified issues at this time, with flexibility to fully address each concern during final design and platting. We intend to meet with the neighbors again to present this reduction and obtain their support for the program. Specifically, we will provide the following for the August 15, 2000 submittal: Issue Response: 1. Site evaluation for septic systems The reduced number of lots will increase lot sizes and provide ample building and septic envelopes to meet the Weld County requirements for individual septic systems. We intend to incorporate the area near former lots 5 and 6 into open space to address setback limitations and seasonal high water occurrences. We still intend to provide a detailed site evaluation for each lot during final design, and if necessary,provide engineered absorption fields to meet county requirements. Secondary field envelopes will be provided and incorporated into each lot design. 2. Drainage study The reduced number of lots will allow the incorporation of additional drainage fields for the design. The northern portion of the site will drain to the original drainage field shown in the submittal, while one or two additional drainage fields will be added to the west central portion of the southern portion of the site to address drainage. A complete drainage study will be included in final design for the site, including these new drainage fields. 3. Traffic study The reduction in lots will mean close to a 50%reduction in traffic impacts to the surrounding area. We will work with the Weld County Department of Public Works during final design to address their concerns for limiting traffic on Peak View Road. Road alignment will be adjusted to meet their requirements. Julie Chester July 27, 2000 Page 3 4. Geological subsidence study By reducing the number of lots, we are able to better site the building envelopes to avoid areas of potential subsidence. We will provide a detailed scope of our proposed full subsidence investigation for the August 15, 2000 submittal, including detailed research and if necessary, field borings. 5. Wetlands study We intend to provide a complete wetlands study and if necessary, provide methods to preserve wetlands. By reducing the number of units on the northern portion of the site from 6 to 2, we can avoid the suspect areas near former lots 5 and 6. 6. Soils study We intend to perform a complete soils study as part of the site study, and provide engineering solutions to address potential expansive soil issues for building foundations, absorption fields, and other potential issues. This conceptual summary is provided to you so that you can understand the package we intend to submit to you on August 15, 2000 and to ensure that the changes noted,primarily the reduction in number of proposed lots to meet the wishes of the neighbors, constitute a minor change so that we may continue to proceed with this project. Please feel free to contact Bob Gollick(303-722-8771) or me with any questions or concerns. Sincerely, John Rinko, Jr., P.E. cc: Bob Gollick Daryll Propp Longs Peak Estates • Weld County, Colorado Lots with Access to Peak View Road Traveling from WCR#12 (North to South) Weld County Tax Count Account# Parcel Number Name Street Address City State Zip Current access point 1 R0095395 1467-09- 1- 00- 019 MUI_I_EN WILLIAM & LUCILLE 2734 Weld CO Road 12 Erie CO 80516 Weld County Road # 12 2 85708586 1467-09- 1- 01- 001 POMASL JOSEPH C & CYNTHIA L 4932 Peak View Road Erie CO 80516 Peak View Road 3 R0095295 1467-09- 1- 00- p18 KOVETS KEVIN & KAREN M 4887 Peak View Road Erie CO 80516 Peak View Road 4 R5708986 1467-09- 1- 01- 008 MC CULLY EVERETTE R & LINDA M 4772 Peak View Road Erie CO 80516 Peak View Road 5 R5709886 1467-09- 1- 02- 009 TIETZE DAVIS A 4831 Peak View Road Erie CO 80516 Peak View Road 6 R5709986 1467-09- 1- 02- 010 ROSE RANDY D 4801 Peak View Road Erie CO 80516 Peak View Road 7 R5709086 1467-09- 1- 01- 009 MC CULLY EVERETTE R& LINDA M 4772 Peak View Road Erie CO 80516 Peak View Road 8 R5709686 1467-09- 1- 01- 003 THEEDE RONALD E & JEANNE D 2845 Bruce Road Erie CO 80516 Peak View via Bruce Road 9 R0077089 1467-09- 1- 03-012 FAVELA MANUEL&ANGELINA 3837 Umatilla Street Denver CO 80211 Weld County Road#7 10 R5709686 1467-09- 1- 02- 008 LAFFERTY MICHAEL E 4702 Peak View Road Erie CO 80516 Peak View Road 11 R5709386 1467-09- 1- 02- 005 NELSON BARBARA JEAN 4701 Peak View Road Erie CO 80516 Peak View Road 12 R5709586 1467-09- 1- 02- 007 LAFFERTY ANNA M 4652 Peak View Road Erie CO 80516 Peak View Road 13 R5709486 1467-09- 1- 02- 006 LEASE ADDISON E & BEATRICE A 4651 Peak View Road Erie CO 80516 Peak View Road 14 R5710086 1467-09- 1- 03- 004 ROLOFF JOAN A 10935 Verna Lane Northglenn CO 80234 Peak View Road 15 R5710486 1467-09- 1- 03- 009 RHODES TERRANCE E &JOAN P 4590 Peak View Road Erie CO 80516 Peak View Road 16 R5710586 1467-09- 1- 03- 010 DEMING ROBERT W& BOWER RICHARD 4471 Peak View Road Erie CO 80516 Peak View Road PROPP REALTY MANAGEMENT LLC -12600 West Colfax Ave., B-130 3kewood, Colorado 80215 Weld County Planning Dept Tel: (303) 233-4000 Fax: (303) 233-3100 JUN 30 2000 www.propprealty.com June28, 2000 RECEIVED Julie A. Chester Lead Planner Department of Planning Services Weld county Administrative Offices 1555 N. 17` Avenue Greeley, Colorado 80631 Re: Longs Peak Estates, Z-543 Request for Continuance Dear Ms. Chester: The Longs Peak Estates Site, Case Z-543, is scheduled for a zoning hearing on July 6, 2000 from the continuance of the original hearing date of May 16, 2000. The basis for this original continuance is the additional requested information documented in your May 8, 2000 Memorandum to the Weld County Planning Commission. The purpose of this correspondence is to request a continuance from July 6, 2000 to a later date in order to review and/or complete the tasks requested. Your conversation with Mr. John Rinko on June 28, 2000 indicated that you are recommending a continuance to September 5, 2000, with information due to your office in Mid August. We concur with this communication and will assume that the hearing scheduled for July 6, 2000 will be rescheduled for September 5, 2000 unless we hear otherwise. We will have a representative attend the 1:30 PM, July 6, 2000 hearing. We look forward to completing this step of the process with you and your office. Sincerely, Daryll Propp cc: Bob Gollick John Rinko PROP REALTY MANAGEMENT L. ,C; 12600 West Colfax Ave., B-130 Lakewood, Colorado 80215 T 303) 233-4000 Fa N: (303) 233-3100 www.propprealty.com June 23, 2000 John Rinko, Jr., P.E. E-21 Engineering Inc. 400 Corporate Cr. # K Golden, CO. 80401 ,. Re: Case # Z-543 Daryll & Carol Propp (Long's Peak Estates) Dear John Rinko, Jr., P.E.: In a continuing effort to inform those, concerned with the above-mentioned project we have set up a meeting to openly discuss this project. The meeting will be held on July 18, 2000 at 7 p.m. the location is 3000 Youngfield St. # 100, Lakewood, CO. 80215. (From Erie go South on 1-25 to 1-70 West then exit#264 (W 32nd Ave.) turn Left on to 32nd Ave., then Right on to Youngfield St., 3000 Youngfield St. will be on your left (next to Taco Bell). We feel it is essential to get together to resolve any issues and hopefully work out a plan that is acceptable to everyone. We eagerly encourage you to attend the meeting if you have any concerns. Feel free to call me if you have any questions at (303) 233-4000. Sincerely, Daryll Propp Propp Realty, Inc/Long's Peak Estates cc: Barbara Kirkmeyer—Weld County Commissioner Julie Chester—Weld County Lead Planner Robert Gollick— Robert Gollick LLC John Rinko —Sear-Brown Group Evan Lipstein —Attorney at Law 6\1C\ 2 �H`L0 303 Coo( 813O /013 Lakew0 ( l s k-VC•i` 12z nn( (&C0. Sc .ZL\ CoAAc.totc40 J £et/T V(NrzEz. 3o3-82Y-x.'677 /274,jo tv . 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Phone:303-601-9230 Fax: 303-277-1583 Rinko,LLC 'IT 25 2000 E-Mail:johnrinko@yahoo.com P.O. Box 28218#16 Lakewood,Colorado 80228 RECEIVED September 21, 2000 Julie Chester Lead Planner Weld County Department of Planning Services 1555 North 17th Avenue Greeley, Colorado 80631 Subject: Letter of Understanding Longs Peak Estates, Case #Z-543 Dear Julie: In an effort to maintain communication with your office, we have prepared this letter to address the remaining issues associated with the proposed Longs Peak Estates project. Both Bob Gollick and I have been unable to contact you directly over the last couple of weeks; however,we understand your current workload and commitments. We intend to expend resources to address the issues noted below, and prior to this wish to make certain we are in agreement that these are the only remaining outstanding issues. Your concurrence with this letter after review would be appreciated. The purpose of this letter is to establish an understanding of Weld County Department of Planning Services' expectations and conditions for support of the above referenced project. Based on the presentation to the Weld County Planning Commission for request of continuance at the September 5, 2000 meeting and your conversations with Mr. John Rinko and Mr. Bob Gollick, we understand that there remains four issues that you require additional information prior to consideration for approval. These issues and their conditions for approval are: 1. PUD Coherency The modification of the through road to two cul-de-sac entrances for the development requires additional detail to depict the overall coherency of the Planned Unit Development as one development. Details of the features linking the seven lots as one system must be provided, such as detail on the trail system, gathering areas, placement of the gazebo, and other amenities which bring the design together as one development from a planning sense. The estimated open space acreage will be provided in this task. Demonstration that the proposed centrally located open space will function as the area which ties the development together, shown through additional figures and/or drawings, will favorably satisfy this issue. Longs Peak Estates—Case Z-543 Julie Chester September 21, 2000 Page 2 2. Health Department Approval of Proposed Septic Systems Performance of a soil study, with borings advanced to at least 10 feet, establishment of ground water levels if within this zone, and a percolation test at the septic envelope proposed for each of the seven lots is required to obtain preliminary approval from the Weld County Health Department. Boring logs will be generated and the locations of the fieldwork will be marked with a semi- permanent market. The site plan will be updated to show the locations of the field tests. The field results will be used to establish the size for two septic system envelopes for each site. Demonstration that the lots have favorable soils and surface and subsurface conditions for septic system, and preliminary approval by Weld County Department of Health, will favorably satisfy this issue. 3. Colorado Geological Survey Approval of Geologic Subsidence Hazard The detailed subsidence study as outlined in the Supplemental Information letter report dated August 23, 2000 will be performed. Demonstration that the potential for subsidence with recommended design parameters are acceptable, and preliminary approval by the Colorado Geological Survey, will favorably satisfy this issue. 4. Mountain View Fire Protection District Approval of Road Configuration The recent correspondence from Mountain View Fire Protection District approves of the new road configuration. We will provide additional information to address other Fire issues, such as the maximum fire water flow rates and/or the need for sprinkler systems in homes in our response. Receipt of our acceptance of these conditions in writing to you will favorably satisfy this issue. We are initiating the engineering and scientific studies per your request to gather the information and address these issues. If the results of the additional technical and engineering reports are favorable as defined above, we understand that the Weld County Department of Planning Services will recommend approval for the change of zone for the above project. Please contact Bob Gollick (303-722-8771), John Rinko (303-601-9230), or Daryll Propp (303- 233-4000) should you have questions, concerns, or disagree with this understanding. Sigcerely, I Rinko, Jr., P.E. cc: Bob Gollick Daryll Propp Longs Peak Estates— Case Z-543 RINKO, LLC Phone: 303-601-9230 Fax:303-277-1583 Rinko,LLC E-Mail:johnrinko@yahoo.com P.O.Box 28218#16 Lakewood,Colorado 80228 Weld County Planning Dept. Memorandum 2601 RECEIVED To: Daryll Propp cc: Bob Gollick Julie Chester, Weld From: John Rinko Date: May 9, 2001 Re: Weld County Planning Department Meeting/ Status A project meeting was held with Julie Chester, Lead Planner, Weld County Department of Planning Services, on Wednesday, May 09, 2001 from 1:00 to 2:30 PM to discuss the submittal requirements and schedule for the Longs Peak Estates Project. Resolution of Issues Prior to the continuance of the submittal, case#Z543, there remained four(4) issues of concern as detailed in the letter from the author to Ms. Chester on September 21, 2000 (attached). The issues with the fire department have been addressed. The issue associated with the coherence of the PUD will be addressed through presentation of a colorized site plan showing the features that link the development together, such as the trail system,the gazebo/meeting area, etc. When asked if this was sufficient to address the coherency issue, Julie deferred response until reviewing the submittal and obtaining input for other staff members. The issue involving the site soils/septic systems is addressed through the on-site percolation and soils testing work performed last fall, and will be submitted to Weld County Health Department with the upcoming submittal. This final issue is the geologic hazard/subsidence issues which we are currently addressing and is further discussed below. Julie mentioned that the newly passed zoning regulations have adjusted the definition of a non- urban development to a development with less than or equal to 9 lots, up from 5 lots. This is a key and positive element since this removes a condition of denial for Weld County Planning for our site. Technically, Julie had to recommend denial in the past since our site was over the arbitrary limit. The zoning regulations have changed, replaced by a County Code. However, since we are already under consideration, we are effectively grandfathered from the new regulations. It should be noted Memo to: Daryll Propp Longs Peak Estates Weld County Meeting May 9, 2001 Page 2 of 2 that Julie did not think this change would have effected our site plan. Regardless, we went on record as understanding that we are grandfathered from the new regulations. Scheduling We have been tentatively scheduled for the Tuesday, June 19, 2001 Planning Commission Hearing based on previous conversations between the author and Ms. Chester. The request for a meeting was formalized in the attached letter. However, this schedule presents potential issues, contingent on the timely resolution of the subsidence issue with Colorado Geological Survey and the review requirements of Weld County. The time line to meet this meeting date, working backwards, is as follows based on the Weld County requirements for notification and posting: Tues, June 19th Scheduled Hearing date Tues, June 12th Submittal from Planning staff to Planning Commissioners due Fri, May 186 Our complete submittal due to Planning for referral and review Wed, May 16th Commitment to meet schedule notification to Planning The difficulty in meeting this schedule is the requirement to have,the complete package delivered to Weld by next Friday, which implies a resolution of the subsidence issues. Since this work is not scheduled to be complete until the end of May(technical review, negotiations with Colorado Geological Survey, written resolution, and written referral from CGS), this schedule may be difficult to meet. Therefore, as a backup plan, I tentatively scheduled a time slot for the next available Hearing, Tuesday, July 17th so that if we can not meet the current schedule, we would not be rescheduling into September. To compensate for this potential delay, we will pre-advertise for the County Commissioner's Hearing and schedule that meeting for Wednesday, August 1s`. The standard time between the Planing Commission Hearing and the County Commissioner's Hearing is 45 days; thus we can still maintain the overall schedule (June 19th plus 45 days is August 31.6). We will be able to make a final call on the scheduling next week, prior to the Wednesday, May 16`h commitment date. RINKO, LLC Phone: 303-601-9230 Fax: 303-277-1583 Rinko,LLC E-Mail:johnrinko@yahoo.com P.O.Box 28218#16 Lakewood,Colorado 80228 May 9, 2001 Julie Chester Lead Planner Weld County Department of Planning Services 1555 North 17th Avenue Greeley, Colorado 80631 Subject: Request for I-Tearing Longs Peak Estates, Case#Z-543 Dear Julie: The purpose of this letter is to establish a hearing date with the Weld County Department of Planning Services for the above referenced project. A request of continuance was made at the September 5, 2000 Weld County Planning Commission meeting in order to perform engineering studies to obtain additional information prior to consideration for approval. These studies are at or near completion and will be available shortly for review. Thus,we request that a date be set for the hearing as soon as possible. Please contact Bob Gollick (303-722-8771), John Rinko (303-601-9230), or Daryll Propp (303- 233-4000) should you have questions or concerns. We look forward to successfully achieving the change of zone request. Si cerely, John Rinko,Jr.,P.E. cc: Bob Gollick Daryll Propp Longs Peak Estates—Case Z-543 WESTER ENVIRONMENT D EQOLO T, INC), ornate IN DENVER AND GRAND nwarzoN June 13, 2001 John Rinko, Jr., P.E. Rinko, LLC P.O. Box 28218 #16 Lakewood, Colorado 80228 Subject: Review of Mine Subsidence Investigation, Longs Peak Estates Subdivision Erie, Colorado. Western Environment and Ecology, Inc Project Number 258-001-01. Dear Mr. Rinko: At your request, Western Environment and Ecology, Inc. (Western Environment) reviewed the report prepared by E-21 Engineering, Inc. (E-21) entitled "Report of Coal-Mine Subsidence Evaluation for Longs Peak Estates Subdivision Weld County, Colorado" dated May 3, 2001. Of particular interest to our review was the lithographic and geophysical logs of 11 borings completed on the project. The data developed by E-21 from these borings is used in Western Environments' assessment. The following discussion presents a likely scenario for potential collapse and subsidence occurring within the Boulder-Weld Coal Field. This scenario is based upon research and experience from other projects conducted by Western Environment personnel, but it must be emphasized that the explanations are theoretical. The results of numerous studies conducted by Western Environment show that when coal was removed, often no significant stratigraphic displacement of overlying beds occurred. There are two possible explanations for this observation: 1) after mining there was enough natural roof strength across the span of rooms to support the load and not fail, or 2) after roof failure the collapse is somehow confined to a specific interval. In the majority of Western Environment projects, the caliper logs show that the rooms are not open and that the "back" or roof of the mine is down. Therefore, the collapse and subsequent bed deflections are somehow limited to a specific horizon. The idea of progressive collapse of overlying units continuing until a"pressure arch" or dome is formed above the collapsed workings is well documented (U.S.G.S. Prof Paper 969). Bell (1975) states that from his experiences in rock of similar character as those present in the Boulder-Weld Coal Field, upward migration is commonly one to two times the width of the intervening room. Matherson and Bliss (1986) and Ackenheil and Doughtery(1970) use a figure of twice the distance between supports for an approximation of arch development. Both of these estimates fit well with the observed results from drilling on the Longs Peak project that show that collapse is confined to an interval of 20 to 40 feet above the workings. In addition, to the "pressure arch"the caliper log indicated that no void is present within the mined zone or at the top of the arch. It is then necessary to increase the volume (decrease the density) of the overlying material in order that the void and developing arch is filled, potentially resulting in additional support (Bell 1975). Testing performed on the claystone bedrock show that it can"swell"upon wetting in excess of 20% (ATEC 1985). Therefore, a five foot void could be filled by the 93117 WEST POWERS AVENUE • TM- -ETON,COLORADO 50130 PRONE (303)730-345* ° VOX (303) 730-4484 • E-EAffi - WESTERNLTGAOL.COX W Ww WES ENVm NT.COX fracturing, wetting and swelling of 25 feet of claystone. Jeff Hynes, former senior engineering geologist with the CGS, has expressed his opinion that the "swelling" of the claystone observed by Western Environment may actually be a result of expansion of the clays when the isostatic confining pressure is removed during drilling. Additionally, Mr. Hynes had commented on his observation that floor"heave" is prevalent in operating Boulder-Weld coal mines. This is likely due to the higher uniaxial compressional strength of the coal (ATEC, 1985) in relation to the claystone that commonly makes up the floor of the mine. Regardless of the exact mechanism, it is evident that the following process involving collapse confinement and support are likely to occur within the Boulder -Weld Coal Field: 1) Formation of pressure arches approximately 20 to 40 feet above the mined seam, and 2) Increase in volume (by swelling , depressurizing, or floor heave) of claystone roof and floor rock. The caliper logs contained in the E-21, May 3, 2001 report indicated that no open voids existed in the rubble zone of the intersected mine workings. This is consistent with the previous explanation of void filling. However, due to the uncertainly associated with subsidence and strain prediction of abandoned mines, Western Environment has adapted a conservative strain prediction method utilizing the United Kingdom National Coal Board's graphical strain profiling system. This method of strain prediction was developed for on-going long wall mining operations. To make the method applicable to abandoned room and pillar mines, several modifications and assumptions were made by Western Environment. The first modification is to define the thickness of the void space. The standard method is to use the actual mineable thickness of coal. However, the drill holes completed on the Longs Peak Estates subdivision show collapse to be complete. Therefore, to proceed with a"worst case"theoretical analysis, the following assumption was made: any increase in hole diameter greater than 50% (9.0 inches)will be treated as an open void, the vertical amount of"theoretical" void for all holes intercepting the mine was then averaged. This results in a theoretical void space of 1.0 feet (Table 1). Profiles developed by the United Kingdom National Coal Board (1966), differentiates maximum subsidence (Smax) for varying width to depth ratios, between solid stowing(filling the mine void) and caving. In applying this method to modern room and pillar(room and board) mines, Western Environment assumed that with extraction rates of near 50%, an Smax value taken halfway between the stowing and caving limits would be conservative. This produces an Smax of 0.60 feet. The width of the extraction is also critical. Western Environment chose to use a width of workings that would produce the maximum surface subsidence. This value is approximately 120 feet. The average depth to the top of the mined interval (90 feet) was also incorporated into the analysis. The reader is here encouraged to review both the United Kingdom National Coal Board's Subsidence Handbook, and the previous studies for the mechanics of the process. By using this information, it is assumed that maximum"worst case"theoretical horizontal strains would be 0.46%. i Figure 1 relates foundation length to damage category. The 0.46% strain calculated will allow for construction of buildings with a maximum foundation length of 42 feet. This size structure would be subject to LESS l'HAN APPRECIABLE damage in a"worst" case subsidence event. Table 1 Hole Top of Mine Theoretical Void Thickness (feet) (feet) E-1 99 log did not penetrate mine E-2 log did not penetrate mine log did not penetrate mine C-1 85 N/M C-2 89 0.0 C-3 97 2.5 C-4 102 N/M W-1 95 1.5 W-2 84 N/M W-3 82 N/M W-4 90 0.0 NL-1 82 N/M AVERAGE 90.5 1.0 N/M- not mined During our review of the E-21 report a reference to multi-level mining beneath the Morrison Mine from workings of the Clayton Mine was made. The attached Figure 2 indicates those areas of the Longs Peak Estates subdivision that are overlain by workings of both the Morrison and Clayton Mines. Due to the lack of direct data on the condition of the Clayton Mine and the likelihood that the potential strains from a"theoretical" collapse of both the mines would be greater then that which would allow home construction, Western Environment recommends that no occupied structures be built above any multi-level mining. To determine the approximate magnitude of the soil pressures on below-grade walls due to the theoretical strains resulting from subsidence, Western Environment assumed all pressures to be passive (NTIS PB81-174690). The following formula was used to calculate the maximum passive lateral pressure assuming cohesion less soils (Rankine 1857): Pp = '/ KpVH2 where: Pp =Maximum Passive Pressure Kp = Coefficient of Passive Earth Pressure V= Soil Density (120 pet) H=Foundation Depth The coefficient of passive earth pressure (Figure 3) can also be determined using the following formula: Kp=Tan2 (45+Phi/2) Where: Phi = Angle of Internal Friction of the Soil = 30 degrees Using this information, the maximum passive earth pressure on an 7 foot foundation wall was estimated to be 11,520 pounds per lineal foot (phi) of wall. However, to produce this force a strain of 20% is required (Figure 3). The following table relates passive earth pressures to the maximum calculated"theoretical" strain for the site using 7 foot (below grade) wall depths and compares these values and the resultant tensional stress with the tensional strength of concrete. Subsidence Induced Earth Pressures Tensional** Maximum Strain Earth Pressure Tensional* Strength of Concrete 7 foot foundation lbs per lineal foot Stress (psi) (psi) 0.46% 3,600 230 300 * T=MY/1 where T = Tensional Stress M=Maximum Moment (Earth Pressure) I= Section Modulus Y= Distance from Neutral Point to Surface (0.33 feet) ** ASSUMPTIONS - Uniform Pressure Distribution - 3,000 psi Concrete - 8 inch thickness -No Internal Reinforcement for Foundation Wall The previous table indicates that the mine subsidence induced "theoretical worst case" lateral passive soil pressure and the resulting overturning moments calculated for the Longs Peak Estates Subdivision are not sufficient to cause failure of 7 foot (below grade) foundation walls. Based upon the review of the E-21 report, Western Environment and Ecology, Inc. makes the following conclusions: 1) Maximum mine subsidence related worst case "Theoretical" Strains calculated for the Longs Peak Estates Subdivision(0.46%)would allow for construction of buildings with maximum foundation lengths of 42 feet. Larger structures could be built following additional site specific geotechnical investigations. 2) The lateral earth pressures developed during a worst case subsidence event would allow for standard 7 foot below grade foundation walls. 3) No occupied structures should be built on those area shown on Figure 2 to be underlain by both the Morrison and Clayton Mines. Please feel free to contact us with any questions you may have or should you require clarification of our findings. Sin erely, Crre D. erma . Pr s ent 0.6 I ) - 7 I I I I I 0.5 1 0.46% 0.4 • `li a Z 0.3 Nt GC I 9F 0 e'4F l I 0.2 to I `e I o.l s�cy I .I I I rioii 0 meters 0 25 50 75 100 125 150 175 feet 0 50 100 200 300 400 500 60C 42 TOTAL LENGTH OF STRUCTURE CLASS OF DAMAGE DESCRIPTION OF TYPICAL DAMAGE VERY SLIGHT OR NEGLIGIBLE SLIGHT CRACKS SHOWING IN WALLS AND CEILINGS INSIDE BUILDINGS, BUT NOT VISIBLE ON OUTSIDE. SLIGHT SLIGHT CRACKS SHOWING INSIDE THE BUILDING. DOORS AND WINDOWS WILL NOT CLOSE. APPRECIABLE SLIGHT CRACKS SHOWING BOTH OUTSIDE AND INSIDE BUILDING, DOORS AND WINDOWS WILL NOT CLOSE. DRAINS, SEWERS, AND GAS PIPES FRACTURE. SEVERE DRAINS. SEWERS, AND GAS PIPES FRACTURE. OPEN FRACTURES THROUGH WALLS or BUILDING. WINDOW AND DOOR FRAMES DISTORTED. FLOORS NOTICEABLY SLOPING, WALLS LEANING OR BULGING NOTICEABLY. SOME LOSS OF BEARING OF BEAMS ON WALLS. PORTICOES AND FLOORS BUCKLE. • VERY SEVERE WORSE THAN ABOVE ANO REQUIRING PARTIAL OR COMPLETE REBUILD- ING. ROOF ANO FLOOR BEAMS LOSE BEARING AND WALLS LEAN BADLY ANO NEED EXTERNAL SUPPORT. WINDOWS BROKEN AND DISTORTED. SEVERE SLOPES, BUCKLING ANO BULGING OF ROOFS AND WALLS OCCUR. (FROM N.C.B.) 11,1118 TERN *TaR®N7iSN? Figure 1 AND ECOLOGIC INCA Strain Percent to Length of Structure 2217 West Powers Avenue Longs Peak Estates Littleton,Colorado 80120 LATERAL STRAINS FOR ACTIVE AND PASSIVE STRESSES I I � Kp Ka E E -5 0 +10 +20 HORIZONTAL STRAIN (from Lambe and Whitman, 1969) WEST ENVIRONMENT Figure 3 AND ECOLOGY INC. Lateral Strains 2217 West Powers Avenue Longs Peak Estates Liitleton, Colorado 80120 RINKO, LLC Phone: 303-601-9230 Fax: 303-277-1583 Rinko, LLC E-Mail:johnrinko@yahoo.com P.O. Box 28218#16 Lakewood,Colorado 80228 June 20, 2001 Celia Greenman Colorado Geological Survey Room 715 1313 Sherman Street Denver, Colorado 80203 Subject: Longs Peak Estates Erie, Weld County, Colorado Subsidence Investigation Results Dear Celia: A subsidence investigation was undertaken at the Longs Peak Estates site located near Erie, Weld County, Colorado to assess the issues presented by the historic coal mining. The results of this investigation are contained in the attached reports. From these reports, the following is observed. SUBSIDENCE INVESTIGATION SITE AND PUBLISHED DATA INVESTIGATION Report of Coal-Mine Subsidence Investigation for Longs Peak Estates Subdivision, Weld County, Colorado, E-21 Engineering, Inc., May 3, 2001 The purpose of this Site Investigation Report was to summarize the work efforts to collect site data and observations. The findings of this report include the following: 1. A majority of the area in the southern portion of the site has been mined through the historic Morrison Mine activities. 2. Some of the area above has also been mined through the historic Clayton mine. 3. A total of eleven(11) borings were completed, on the average of two (2) per lot in the southern area with one completed in the northern area. 4. The investigation included the borings and associated boring logs, the geophysical logs, site observations, and historic aerial photograph reviews. Celia Greenman June 20, 2001 Page 2 GEOLOGICAL EVALUATION Review of Mine Subsidence Investigation, Longs Peak Estates Subdivision, Erie, Colorado. Western Environment and Ecology, Inc., June 13, 2001 Using the Site Investigation Report, Mr. Greg Sherman of Western Environment and Ecology, Inc. (Western Environment)reviewed the Site Investigation Report with respect to the potential for subsidence. Western Environment's recommendations, based on the data collected, include the following: 1. Maximum mine subsidence related worst case "Theoretical" Strains calculated for the Longs Peak Estates Subdivision(0.46%) would allow for construction of buildings with maximum foundation lengths of 42 feet. Larger structures could be built following additional site specific geotechnical investigations. 2. The lateral earth pressures developed during a worst case subsidence event would allow for standard 7 foot below grade foundation walls. 3. No occupied structures should be built on those areas shown on Figure 2 [of the Western Environment report] to be underlain by both the Morrison and Clayton Mines. ENGINEERING ANALYSIS Subsidence Predictions and Surface Strain Analysis, Longs Peak Estates, John F. Abel, Jr., Mining Engineer,June 20, 2001 Using the Site Investigation Report and the original mine maps, Dr. Abel provided engineering analyses, conclusions and recommendations for the subsidence issues and surface strains at the site. His work included the identification of areas at the site where the predicted maximum surface strain is less than 1,000 micro-strain (vs). In these areas, residential development should be acceptable. Outside of these areas, Dr. Abel categorized the potential for surface strain using a gradient scale of A (1,000 to 2,000 vs)to E (>5,000 vs). Properly designed utilities and roadways should be acceptable in areas denoted A and B. The potential for chimney collapse was also assessed in his report and concluded that although possible,the occurrence of this event is not likely for the site and correlates to areas outside of the less than 1,000 vc areas previously denoted. THIRD PARTY REVIEW Third Party Review Report, John B. Ivey, Amuedo and Ivey, Inc., June 2001 Dr. Ivey will be reviewing the attached reports concurrently and will provide independent feedback to the Colorado Geological Survey. This report will be separately submitted directly to you when complete. Rinko, LLC Celia Greenman June 20, 2001 Page 3 PROPOSED BUILDING ENVELOPES Using the work of Western Environment, acceptable building envelopes can be established for each lot with the conditions that these envelopes are not placed over areas of the Clayton Mine, and the occupied structures are limited to 42 feet in length. Under these restricted conditions, the acceptable building envelopes for each lot appear in Figure 1. Adapting the work of Dr. John Abel, acceptable building envelopes can be established for each lot within the areas projected to have surface strains less than 1,000 vs. Occupied structures within these boundaries should not be limited in length. Using these conditions,the acceptable building envelopes for each lot appear in Figure 2. Combining the work of these experts, acceptable building envelopes for occupied structures without building length limits appear in Figure 3. The conclusions of these experts were based on the site data collected and summarized in the Subsidence Investigation Report. In accordance with Western Environment's recommendations, the future owner of a lot may wish to perform additional investigations (borings)to deviate from the above building envelope restrictions. Based on the investigative work performed and submitted herein, we request approval from the Colorado Geological Survey to proceed with the Change of Zone for the Longs Peak Estates subdivision. Weld County has received this package, and through referral,this subsidence investigation package is submitted for your review and comment. Please do not hesitate to contact Julie Chester of Weld County Planning(970) 353-6100, ext. 3540, the authors listed above, or me should you have any questions, comments, or concerns. On behalf of the owner, Mr. Daryll Propp of Propp Realty, Inc., we appreciate your continued involvement in this site. Sincerely, John Rinko, Jr. Principal cc: ✓Iulie Chester, Weld County Planning Greg Sherman, Western Environment and Ecology, Inc. John Abel, Mining Engineer John Ivey, Amuedo and Ivey Serge Hanson, E-21 Engineering, Inc. Daryll Propp, Propp Realty Inc. attachments Rinko, LLC ATTACHMENTS - TABLE OF CONTENTS ATTACHMENT 1: Figures Figure 1: Recommended Building Envelopes Per Western Environment And Ecology, Inc. Report Figure 2: Recommended Building Envelopes Per John F. Abel Report Figure 3: Recommended Building Envelopes Per John F. Abel And Western Environment Report ATTACHMENT 2: Report of Coal-Mine Subsidence Investigation for Longs Peak Estates Subdivision, Weld County, Colorado, E-21 Engineering, Inc., May 3, 2001 [SEPARATELY BOUND REPORT] ATTACHMENT 3: Review of Mine Subsidence Investigation, Longs Peak Estates Subdivision, Erie, Colorado. Western Environment and Ecology, Inc., June 13, 2001 [SEPARATELY BOUND REPORT] ATTACHMENT 4: Subsidence Predictions and Surface Strain Analysis, Longs Peak Estates, John F. Abel, Jr., June 20, 2001 [SEPARATELY BOUND REPORT] ATTACHMENT 5: Third Party Review Report, John B. Ivey, Amuedo and Ivey, Inc., June 2001 [SEPARATELY BOUND REPORT] [TO BE COMPLETED] RINKO, LLC Phone: 303-601-9230 Fax: 303-277-1583 Rinko, LLC E-Mail:johnrinko@yahoocorn P.O. Box 28218#16 Lakewood,Colorado 80228 June 20, 2001 Pam Smith I.S.D.S. Program Coordinator Weld County Department of Public Health& Environment 1555 N. 17th Avenue Greeley, Colorado 80631 Subject: Longs Peak Estates Erie, Weld County, Colorado Soils Testing and Percolation Testing Results Dear Pam: An investigation was undertaken at the Longs Peak Estates site located near Erie, Weld County, Colorado addressing the site soils and percolation testing. The purpose of this investigation was to identify the presence of acceptable soil conditions for on-site septic systems for each of the seven proposed lots, and to obtain data regarding the surface and subsurface soils. The results of this investigation are contained in the attached report. From this report, the following is observed. Report of Subsurface Soil Investigation, Longs Peak Estates, Weld County, Colorado E-21 Engineering, Inc., November 14, 2000 The purpose of this Soil Investigation Report was to collect site data regarding the surface and subsurface soils on each lot, and identify potential areas where conditions were acceptable for on-site septic systems. The conclusions and recommendations of this report include the following: Conclusions 1. Subsurface soils within the area proposed for development of the Longs Peak Estates consists mostly of interbedded fine sands, silt, and silty clay that ranges in thickness from 4.7 to 9.4 feet. 2. Bedrock, in variable stages of weathering, is found below the surficial soils. The majority of the site is underlain by shale, but the very southwestern portion of the site is underlain by a sandstone layer that is not substantially weathered. 3. Groundwater was not observed within 11 feet of the ground surface throughout the site and was not observed within the upper 15 feet of materials in the northern and southeastern portions of the site. 4. Percolation testing of soils from a depth of 2 to 4 feet below the surface identified areas of on-site soils to be suitable for leachfield installation. Percolation is likely assisted by the coarser sand seams within the silt and silty clay soils present throughout the site. Pam Smith June 20, 2001 Page 2 5. Swelling potential of soils from 2-4 feet depth throughout the site vary from low to high. Soils within the southeastern portion of the site, proximal to proposed lot#3, were tested and results indicate low swell potential. Other soils tested were within the moderate to high swell potential range. These areas likely contains clay soils of the montmorillinite group that enlarge due to incorporation of water molecules into their structure. Recommendations 1. Leachfield construction may be installed within areas tested and found to be within the acceptable range of 5 and 60 minutes per inch percolation rate. Leachfields should be designed by a qualified individual, and additional field testing may be required to obtain final approval. 2. Consideration of the swelling potential should be made during the construction design phase of site development and swell potential must be incorporated into foundation, pavement, landscape, and overall design. The conclusions were based on the site data collected and summarized in the report. In accordance with the report's recommendations,the future owner of a lot will have to perform additional investigations (geotechnical borings, additional percolation testing)to obtain final approval for the site specific septic systems and building foundation designs. Based on the investigative work performed and submitted herein, we request approval from the Weld County Department of Public Health& Environment to proceed with the Change of Zone for the Longs Peak Estates subdivision. Weld County has received this package, and through referral, this Soil Investigation Report package is submitted for your review and comment. Please do not hesitate to contact Julie Chester of Weld County Planning(970) 353-6100,ext. 3540, or me should you have any questions, comments, or concerns. On behalf of the owner, Mr. Daryll Propp of Propp Realty, Inc., we appreciate your continued involvement in this site. Sincerely, John Rinko, Jr. Principal cc: 'iulie Chester, Weld County Planning Serge Hanson, E-21 Engineering, Inc. Daryll Propp, Propp Realty Inc. attachment Rinko, LLC RINKO, LLC Phone: 303-601-9230 Fax:303-277-1583 Rinko,LLC E-Mail:johnrinko@yahoo.com P.O.Box 28218#16 Lakewood,Colorado 80228 June 20, 2001 Julie Chester Lead Planner Weld County Department of Planning Services 1555 North 17th Avenue Greeley, Colorado 80631 Subject: Supplemental Information Second Submittal Longs Peak Estates, Case#Z-543 Dear Julie: This Supplemental Information Report, Second Submittal has been prepared to address the remaining issues as noted in your Memorandum dated August 29, 2000 to the Weld County Planning Commission in reference to a request for continuance of Case Z-543 (Attachment 1). Longs Peak Estates is a proposed Planned Unit Development(PUD)of seven(7)lots over approximately 32 acres,with a bulk density of 4.6 acres per lot. The intent of the proposed Longs Peak Estates PUD is to provide an opportunity for a rural residential lifestyle. The seven large single family lots will permit a variety of livestock, domestic and exotic animals. This is the predominant lifestyle for the neighborhood and it is anticipated that the residents of Longs Peak Estates will be integrated into the rural fabric of the area. Introduction The Longs Peak Estates project was initiated with the submittal of a Sketch Plan to Weld County Planning in March 1998. An initial Change of Zone for a Planned Unit Development for thirteen (13)residential lots and 3.3 acres of common open space was presented in March 2000. After addressing many substantial issues as discussed in our July 25, 2000 meeting (July 27th letter, Attachment 1), including extensive work with the neighboring landowners to achieve a harmonious program, a report entitled"Planned Unit Development, Change of Zone Application,Longs Peak Estates, Weld County, Colorado—Supplemental Information"was submitted on August 23, 2000. This document presented the layout of the proposed Longs Peak Estates in its current configuration. Please refer to this submittal for a more complete summary of the currently proposed PUD and the issues resolved to date. Julie Chester June 20, 2001 Page 2 As noted in your August 29, 2000 Memorandum, a few issues remained unresolved which lead to the continuance of this case at the September 5, 2000 Weld County Planning Commission Meeting. The four remaining issues were documented in the Letter of Understanding dated September 21, 2000 (Attachment 1), and included the issues listed below. We understand that Weld County Planning may review other issues as well, as noted in your October 4, 2000 response letter(Attachment 1). Issues 1. PUD Coherency 2. Health Department Approval of Proposed Septic Systems 3. Colorado Geological Survey Approval of Geologic Subsidence Hazard 4. Mountain View Fire Protection District Approval The purpose of this Supplemental Information Second Submittal document is to provide the necessary information to address these issues so that the Change of Zone may be brought to the Weld County Planning Commission. Each topic is presented below with reference to attached or separately provided support documentation. Issues and Resolution 1. PUD Coherency The currently proposed road configuration was the result of detailed negotiations with the neighboring landowners,where a compromise was reached between the previously proposed alignments and other roadway alternatives. We feel the importance of providing a project that is acceptable to the neighboring landowners is a high priority for the long-term harmony of the neighborhood. We have also provided a complete circuit trail system, open to all in the neighborhood, for use as a hiking,jogging, bicycling, and horseback riding trail. This trail system is part of the open space area, increased in size from previous submittals to 17.2% of the land area, or approximately 5.5 acres. The open space area and trail system provides a key coherent feature to Longs Peak Estates. At the heart of the open space is a Community Focal Point, including a gazebo,meeting area,picnic area,hitching posts, and other amenities overlooking the area's farms, fields and mountains. The open space and trail system has been designed to run along the entire property boarder common with the Community Irrigation Ditch, with access at County Road 12 to the north, Peak View Road to the east, and the unnamed road to the south. It is envisioned that this trail can become a link in an area-wide trail system, providing access to the surrounding area for horseback riding, bicycling, or hiking. The features described above have been incorporated into the revised site drawing entitled "Change of Zone for Longs Peak Estates"dated June 15, 2001 and appearing as Attachment 2. Rinko, LLC Longs Peak Estates—Case Z-543 Julie Chester June 20, 2001 Page 3 2. Health Department Approval of Proposed Septic Systems Additional site data specific for each lot was requested by the Weld County Department of Public Health and Environment as listed in the September 5, 2000 Letter of Understanding. This included the performance of a soil study,with borings advanced to at least 10 feet, establishment of ground water levels if within this zone, and a percolation test at the septic envelope proposed for each of the seven lots. This work effort is required to obtain preliminary approval from the Weld County Department of Pubic Health and Environment, and has been completed as documented in the attached report entitled"Report of Subsurface Soil Investigation"dated November 14,2000. The report is summarized in the accompanying transmittal letter. The report identified envelopes with acceptable conditions for septic systems for each of the proposed 7 lots. We recognize that we still may be required to provide a detailed site evaluation for each lot during final design, and if necessary,provide engineered absorption fields to meet Weld County requirements. 3. Colorado Geological Survey Approval of Geologic Subsidence Hazard In order to address the potential for geologic subsidence, a series of detailed studies have been performed and submitted to Ms. Celia Greenman of the Colorado Geologic Survey for review and comment. The work effort undertaken has been thorough, including a study of the historic mining activity, review of aerial photographs for subsidence features, completion of eleven exploratory borings (two per lot in the southern area and one in the northern area of the parcel), collection of subsurface data related to the mining activity and its effects on the subsurface soils, and collection of subsurface geophysical data. The data collected at the site are summarized in a report prepared by E- 21 Engineering, Inc. dated May 3, 2001 (attached). Using these data, Western Environment and Ecology,Inc. prepared a report entitled"Review of Mine Subsidence Investigation"dated June 13, 2001 (attached). Western Environment and Ecology concluded that development could occur on the parcel over mined areas with minor restrictions, based on a worst case analysis of the collected data. A detailed engineering analysis was performed by Dr. John F. Abel, Mining Engineer, using the data collected and the original mine workings maps. Dr. Abel identified areas within each lot that were suitable for development without restrictions as noted in his report entitled "Subsidence and Surface Strain Analysis"dated June 20, 2001 (attached). The conclusions of these experts suggest that residential development can proceed with the parcel. This package of reports, with a transmittal letter, has been provided to Ms. Greenman for consideration. We have also requested a third party review of the report package from Dr. John B. Ivey of Amuedo and Ivey, Inc. Dr. Ivey's review will occur concurrently with Ms. Greenman's review of the material. Rinko, LLC Longs Peak Estates — Case Z-543 Julie Chester June 20, 2001 Page 4 We intend to hold a project meeting with the Colorado Geologic Survey shortly to present the findings and discuss the issues at the site. Weld County Planning will be informed of all meetings and the outcomes. 4. Mountain View Fire Protection District Approval Mountain View Fire Protection District provided approval in their correspondence dated August 31, 2000 to you from LuAnn Penfold,Fire Marshal (Attachment 1). All applicable codes will be met as they pertain to water supply, fire hydrant locations, fire department access, and street widths and designs. We concur with Ms. Penfold's comments,including the requirement for residential fire sprinkler systems if the required water supply for fire protection is not available. Fire hydrant locations and spacing as requested will be met, and the site's roads will be designed to meet imposed loads of fire apparatus. Detailed maps will be provided to the Fire District upon completion. It should be noted that our water line design, as requested by Left Hand Water District,will be a loop design, linking the water main on County Road 12 with the water line along the southern end of Peak View Road. This configuration will not only improve the water quality and pressure for the users on the southern end of Peak View Road,but also provide fire hydrants for those existing residential homes. Summary Based on the extensive work effort put forth to date, the additional work effort documented herein, and the discussion of the remaining issues as documented in our Letter of Understanding, we trust the proposed Change of Zone for Longs Peak Estates will be favorably considered. The coherency of the PUD is demonstrated through the lot and open space design, with the proposed centrally located Community Focal Point which will function as the area which links the development together. The attached soils report demonstrates that the lots have favorable soils and subsurface conditions for septic systems, so that preliminary approval by Weld County Department of Health can be obtained. The detailed subsidence investigation is being reviewed by the Colorado Geological Survey, and should favorably satisfy this issue. Finally, receipt of our acceptance of the conditions set forth by the Mountain View Fire Protection District should favorably satisfy fire safety issues. We are awaiting the approvals of the engineering and scientific studies from Weld County Department of Public Health and Environment and the Colorado Geological Survey. If the results of the technical and engineering reports are favorable, we trust that the Weld County Department of Planning Services will recommend approval for the change of zone for the above project. Rinko, LLC Longs Peak Estates— Case Z-543 Julie Chester June 20, 2001 Page 5 Please contact John Rinko (303-601-9230), Bob Gollick (303-722-8771), or Daryll Propp (303- 233-4000) should you have comment, questions, or concerns with regards to this submittal. We appreciate your continued efforts in this case, and look forward to a favorable outcome. Sincerely, John Rinko,Jr., P.E. cc: Bob Gollick Daryll Propp ATTACHMENTS: Attachment 1: Correspondences Attachment 2: Change of Zone Drawing Attachment 3: Subsidence Investigation Report Package(separately bound documents) Attachment 4: Soils Study Report(separately bound documents) Rinko, LLC Longs Peak Estates— Case Z-543 AMUEDO AND IVEY, INC. WORLDWIDE GEOLOGICAL CONSULTANTS 15554 W.67TH AVENUE ARVADA, COLORADO 80007-7041 , '° U.S.A. -- TEL: 303/456-5848 •• " ' FAX: 303/456-5890 Established 1953 PETROLEUM AND MINERAL EXPLORATION JOHN B. IVEY, CPG, RG, PE ENGINEERING GEOLOGY AND PHOTOGEOLOGY June 28, 2001 Ms. Celia Greenman Geologist Colorado Geological Survey Room 715 1313 Sherman Street Denver, Colorado 80203 Re: Third-party Review, Subsidence Potential, Proposed Longs Peak Estates Weld County, Colorado Dear Celia: This letter report is a third-party review of the work that E-2I Engineering, Inc. has undertaken in assessing the coal mine subsidence hazard for the referenced proposed subdivision. In essence my assignment is to act in a review and advisory capacity and to comment on the adequacy and pertinence of the report "Report of Coal-Mine Subsidence Investigation for Longs Peak Estates Subdivision, Weld County, Colorado." This report is dated May 3, 2001 and was prepared by E-21 Engineering, Inc (E-21). My review did not include any editorial functions. Mr. Serge Hanson, president of E-21, has directed me to address this letter-report to you. Third-party Tasks The primary tasks included the following:. 1) Comment as an unbiased reviewer on E-21 Engineering, Inc. (E-21) work, but not to participate in the project. 2) Review the E-21 data-collection effort for adequacy and pertinence. 3) Compare subject study with Colorado Geological Survey (CGS) requirements. 4) Comment on CGS concerns. .The scope of this third-party review was established on April 10, 2001 in a meeting in the offices of E-21.Engineering, Inc. Serge Hanson ( SH), Paul Gottler (PG), John Rinko (JR), and I were in attendance. In consideration of the contact the E-21 staff and Rinko LLC had already had with you as the designated party in the Colorado Geological Survey (CGS) for coalmine subsidence projects it, was determined that you and I could copy each other on any correspondence and that we could enter into discussions, as appropriate, concerning the subdivision. I made several comments in this meeting about collection and interpretation of data relating to undermining and the EXHIBIT 2 MIB\ WTT Ul potential for subsidence. I also suggested that it would be well to review historical aerial photography of the area. In a telephone conversation with you on April 17, 2001 I discussed my role as a third-party reviewer and advisor to E-21. In this role my work was to comment on various aspects of the work that E-21 had undertaken in order to prepare a draft report dated February 22, 2001. I explained that my work was limited to an advisory role and did not include consulting or participating in project activities. You accepted the explanation of my role and agreed to copy me on any correspondence relating to this project. Comments as an Unbiased Reviewer After the April 10th meeting I began a review of a draft report prepared by E-21 and dated February 22, 2001. On May 3`d I received a second draft report of that date, and on May 8th I met with Messrs. Hanson, Gottler, and Rinko. I made a number of suggestions as to how the report and maps could be referenced to make the report more readable. Suggestions were made as to changes in map formats including use of the Morrison and Clayton original mine maps to ensure as close and accurate correlation as possible between surface and subsurface features. Adequacy and Pertinence of Data In my opinion the data collected was pertinent and adequate to make decisions as to development of the proposed subdivision. E-21 has made a logical collection of data, and has acquired consultant help in the interpretation of that data. The natural tendency for scientists and engineers is to want more data than is available; however, the data suite collected was reasonably comprehensive for the subdivision area. At some point, given the requirement for disclosure in Colorado,the burden of proof rests with the buyer. He must consider, with his foundation design engineer and his architect, what restrictions are placed on a building site and whether meeting these restrictions is within an acceptable budget. Where coalmine subsidence is a concern the potential zero subsidence line and other surface strain data are needed by the engineer and the architect. As work proceeded it became evident to me that E-21 could benefit from technical inputs by a rock- mechanics engineer with experience in coal mine subsidence. I recommended discussing this with Dr. John Abel who is an acknowledged expert in the field. On May 10, Messrs. Hanson, Gottler and I met with Dr. Abel who is Emeritus Professor of Mining Engineering (JFA), Colorado School of Mines. We discussed the project and Dr. Abel provided insights on surface development and undermined areas. He was subsequently retained by E-21 to work on the project and develop surface strain data. He submitted a report "Subsidence and Surface Strain Analysis, Longs Peak Estates"on June 20, 2001. In this report he defined the zero subsidence line and the 1000 micro-strain line. elitax 3 SIS VIII W 1111 itVVOS John Rinko also arranged with Mr. Greg Sherman of Western Environment and Ecology, Inc. (WEE)to review the E-21 report dated May 3, 2001. Mr. Sherman's ultimate recommendation was that no building greater than 42 feet long be erected in the area. He prepared a map showing recommended building envelopes on the seven lots. Dr. Abel's work defined the zero subsidence line, the 1000 micro-strain line, and designated areas in which increments of 1000 micro-strains up to 6000 could be expected. The Abel and Sherman maps were combined into a third map showing limits of subsidence, the 1000 micro-strain line, and the building envelopes. These maps were transmitted to you by JR with a letter dated June 20, 2001. In my opinion the data acquisition program conducted by E-21 conducted was adequate and pertinent. The retention of two consultants increased that adequacy and pertinence. The test of the approach taken is that using both sets of consultant data has enhanced the value of the investigation Comments on the Report of June 20, 2001 A cursory reading of JFA's report dated June 20, 2001 indicates that it is more pertinent and applicable to the Longs Peak Estates property than the WEE report (of June 13, 2001). However, the WEE report provides usable information of a more specific nature based on one type and size of house foundation in a worst-case situation. Data from the two reports enhances the overall E-21 program as noted by the maps accompanying JR's letter of June 20th to you. The JFA report (June 20, 2001) presents data and defines the 1000 micro-strain, and limit of subsidence lines with respect to the subdivision. These factors in turn should be used in the design of foundations either before or after a foundation design engineer and architect have reviewed the owner's building site plans. Several points should be made concerning the E-21 report of May 3, 2001: 1) On Figure 3 (Boring Locations) the source of the topographic mapping should be stated for the record. This could be provided in an addendum. 2) A legend should be included in Appendix 2 for symbols used in the boring logs and cross sections. 3) Total footage drilled (1277 feet) in the 11 borings should be stated for the record. This could be stated under the heading "Results of Test Boring and Logging" on p. 10 or in an addendum. 4) A page-size map could illustrate the verbal descriptions of features observed on the historical aerial photography This will make it much easier for a reader to follow the discussion If it is determined that this is needed it could be prepared as part of an addendum. 5) Surface elevations for borings W-3, C-1, C-4, and NL-1 do not agree with elevations given on the boring logs. The correct elevations could be furnished in an addendum. 6) Two sets of"Findings" are noted on p. 2 in the Executive Summary, and on p. 20 of the main body of the report. Some of the findings are duplicated directly, and others 4 fls s'U an saw ‘t.4,5" are combinations. The two sets should be the same since the Executive Summary is generally a shortened version of the main report. It would be helpful to the reader if both sets of Findings were numbered. Comparison of Subject Study with CGS Requirements Hopefully, upon review of the report of May 3r°and several related reports dated June 20th, you will find that the data collection and analysis provided will allow you to take a different approach to development of the subdivision. You have a computer program developed in-house at the CGS; however, this program apparently is not in wide use, and with some limitations in input data it may prove to be more useful. Apparently Greg Sherman has found it useful in certain instances I understand that he used the program in developing his report of June 13`s. The reports by Dr. Abel and Mr. Sherman should satisfy the concerns expressed previously by you. There do not appear to be any hard and fast requirements for subsidence investigations imposed on the development of undermined land.. FIB 1041 (CGS, Special Publication No. 6, 1974)presents very generalized comments on the recognition and mitigation of subsidence. It is probably well that there are no rigid rules established since, as things stand now, each case must be considered on its own. There apparently are informal rules governing the requirements for land development in undermined areas. Serge Hanson provided me with a copy of a letter E-21 had received from you that generally stated procedures for subsidence studies. You wrote this letter to Mr. Andrew Suedkamp on September 5, 2000. The procedures included in this letter were followed by E-21 in its preparation for its report of May 3, 2001. Colorado Geological Survey The most recent comments from the CGS is a letter of May 2, 2001 from you to Paul Gottler of E-21. The consulting reports by Dr. Abel and Mr. Sherman have defined buildable space suitable for construction of residential structures on each of the lots. . Because there are surface areas with significantly higher strains it would be necessary to further define strains higher than 1000 micro-strains if those areas are desired for construction of buried utilities or rigid structures. It will be necessary to develop boundaries between different general areas designated A, B, C, etc. on Plate 2B (Abel report). The net effect of this situation is that site-specific strain evaluation should be required on each lot and in utility corridors. These aspects of the subdivision should also be a part of the disclosures made to buyers. It is well established, and I would surmise, agreed by CGS, that development should only be above the Morrison Mine. Surface development should not be undertaken above the Clayton Mine. Messrs Hanson, Rinko and Gottler, after review of the Abel and Sherman consultant reports, have suggested that an appropriate approach to assure that proper steps are taken in building residential structures would be to impose the following rules IM'A I \lt All or conditions which could be incorporated into subdivision covenants, or in some manner be imposed on the owners of the lots. Based on the consulting reports prepared for the subdivision the site is developable with the following conditions: 1) Residential structures are limited to the 1000 micro-strain and less areas (shaded areas) identified on Plates 2B and 6 of the Abel report. 2) Underground utilities are limited to the shaded areas identified above with standard design, or in "A" and "B"areas with flexible design. The "B" area will be further defined to identify this area prior to design of utilities. 3) If the design of a lot deviates from 1 and 2 above, the residential structure will be limited to 42 feet in length with a 7-foot basement, and not located over the Clayton Mine workings as identified in the WEE report. 4) Any other deviation from 1 through 3 above will require additional investigations. I agree with the imposition of these conditions as a means of taking progressive steps in the development of the site. In essence, the greater the potential risk taken, the more far-reaching the investigations should be. If there are questions about my inputs to this project please contact me. Sincerely, AMUEDO AND IVEY, INC. ,,)zu John B. Ivey, C.P.G . .G ' Presid . c-: QtN B• 1 frF. 1pA \6M RROFFsso7,- 1 pfc019TEgto ``'y1 f ardrl Al Zt. Cc: Serge Hanson }`y� 896 +ti 9050 Paul Gottler I( MPG r o -/ John Rinko ""l ,.. .PJ. �esiorveL E°'G )' c\> l f Of COVC-- N ,57,-.2) k^ RINKO, LLC Phone:303-601-9230 Fax: 303-277-1583 Rinko,LLC E-Mail:johnrinko@yahoo.com P.O.Box 28218#16 Lakewood,Colorado 80228 Weld County Planning Dept. July 2, 2001 UL 0 6 2001 RECEIVED Julie Chester Lead Planner Weld County Department of Planning Services 1555 North 17th Avenue Greeley, Colorado 80631 Subject: Supplemental Information Second Submittal Subsidence Third-Party Review Longs Peak Estates, Case#Z-543 Dear Julie: Attached please find the results of the third-party review of the subsidence issues for the above referenced site. This attached final letter from Mr. John B. Ivey of Amuedo and Ivey, Inc. to Ms. Celia Greenman of the Colorado Geological Survey dated June 28, 2001 supercedes the advance copy dated June 27, 2001 distributed by facsimile. Please discard the earlier facsimile version and replace with this letter. The third-party review was requested to provide an independent review of the assessment of the potential subsidence issues for Longs Peak Estates. The letter outlines the task performed by Mr. Ivey and his conclusions regarding the project. Mr. Ivey agrees that the site is developable with the conditions for development detailed on page 5 of his letter,based on his independent review of the subsidence reports. Please contact me if you have any comment, questions, or concerns with regards to this submittal. We appreciate your continued efforts in this case, and look forward to a favorable outcome. Sincerely, c:=3\--A•—(21/4 t_ John Rinko,Jr. Principal cc: Bob Gollick Daryll Propp attachment E-21 Engineering, Inc. Phone 303-277-1548 — Environmental Engineering for the 21st Century Fax 303-277-1583 400 Corporate Circle,Suite K Phone 888-628-1083 Golden,Colorado 80401-5625 Fax 888-628-1084 May 3, 2001 Mr. Darryl Propp Propp Realty, Inc. 12600 West Colfax Avenue, Suite B110 Lakewood, Colorado 80215 Subject: Report of Coal-Mine Subsidence Investigation for Longs Peak Estates Subdivision Weld County, Colorado E-21 Project No. 349 Executive Summary A coal mine related land subsidence investigation has been performed by E-21 Engineering, Inc. (E- 21), at the proposed Longs Peak Estates subdivision site in Weld County Colorado. The investigation was initiated to evaluate site characteristics related to the potential for land subsidence due to coal mining below the site. Surface subsidence in the area of the site has been identified. Initial subsidence investigation activities included the review of published information regarding mine subsidence and information regarding the mines present below the area proposed for development. Subsequent activities included field analyses and verification of published information through the installation of test borings and geophysical logging of the boreholes. Two mines exist under the subject property at two different levels. The upper mine, the Morrison Mine lies at interpreted depths of 79 to 107 below the existing ground surface. The lower mine, the Clayton Mine, lies at depths estimated at 190 to 230 below the existing ground surface. Test borings were advanced within the areas underlain by mines and confirmed the presence of pillars and collapse zones within each of these areas. Eleven test borings were conducted to depths between 88 to 212 feet below ground surface (bgs). Each of the test borings were advanced to below the Morrison Mine level. One test boring was conducted to a greater depth than the others to evaluate the deeper Clayton Mine. Results of the deeper boring found the Clayton Mine to be collapsed and water-filled at the test location. Investigation results from test borings found the site to have, for the most part, experienced differing levels of mine collapse. The collapse and bulking of roof materials, as suggested by geophysical logging, indicates that void space, and remaining potential subsidence, ranges from zero (0) to approximately 2.5 feet at the site. 1 349-Longs Peak Estates Subsidence Investigation In each of the borings where loss of drilling circulation occurred subsequent geophysical logging of the hole confirmed that the unfilled areas are of limited lateral, and/or vertical extent. The limited extent of remaining collapse, and lack of significant void space, indicate that additional land subsidence, if it occurs, will be minimal. Findings Proposed Lot I is not underlain by areas that have been mined. Approximately one-half of proposed Lot 2 is within an area that has not been undermined. Proposed Lots 3 through 7 lie over areas mined using room and pillar methods. The Morrison Mine is present in portions of lots 3 through 7 and some areas of these lots were also mined by a second, deeper mine, the Clayton Mine. Based on test borings and estimated coal bed thickness, the upper mine, the Morrison Mine, is present at depths ranging from 82 to 102 feet below ground surface (bgs). Test drilling found the thickness of the coal mined by the Morrison Mine to be between 8 to ten feet. Based on maps of the Morrison Mine it appears that large numbers of the pillars were removed during final retreat mining. Surface contours suggest that collapse of roof materials into the mine has occurred and supports the fact that pillar removal, though not likely complete, was undertaken at the site. Based on published information the amount of coal extraction within the mine was likely 50-65 %. Test drilling indicates that an unknown number of pillars in areas of retreat mining were not removed. Ten test borings were conducted in areas identified as having been completely mined by room and pillar methods. Of these ten test borings, 4 encountered pillars and 6 encountered mined-out zones. Test borings indicate the majority of the mined areas have experienced collapse. The collapse, and subsequent bulking of collapsed materials, appears to have filled most of the void space under the site in the Morrison Mine. Throughout caliper testing of the boreholes none of the voids encountered provided space for the full 18-inch possible extension limit of the down-hole caliper tool. The limited caliper extension throughout the investigation suggests that the borehole excursions observed are of limited lateral extent. The ground surface topography in the area of Lots 3 through 7 show indications of low ridges overlying lines of pillars and shallow depressions in some of the mined areas. Groundwater was not observed during investigation of the Morrison Mine, or above a depth of approximately 105 feet below ground surface (bgs). Groundwater was observed at the site during the advancement of a deeper boring in the northwest portion of the south parcel. Groundwater was observed at a depth of approximately 112 feet bgs, or approximately 17 feet below the bottom of the Morrison Mine at this location. The review of a report on the parcel immediately northeast of the site identified the depth to groundwater as approximately 97 feet bgs. Based on the USGS topographic map the ground elevation in this area is approximately 15 feet lower than the site indicating a nearly flat upper groundwater surface approximately 15 feet below the bottom of the Morrison Mine at the site. 2 349-Longs Peak Estates Subsidence Investigation Aerial photographic review for the period between 1949 and 1994 indicated that potential subsidence related features are present at, or adjacent to, the site. Features were observed to be consistently present suggesting an unchanging nature to the land surface. The consistency of the land surface over the 50-year period of photographic review suggests that subsidence is not an active phenomena and observed subsidence features likely occurred within the decade following coal extraction. Data developed from this investigation may be useful in evaluating site strains to identify specific building envelopes within the site. Mine maps and evaluation of site topography indicate there are no vertical shafts or former adits on the subject site. Conclusions I. Most areas mined by the Morrison Mine have been filled by collapse of roof rock, bulking of the collapsed material, and/or sagging of the overlying strata creating some shallow subsidence topographic features at the site. 2. Based on the observed remaining void space and published information, it appears that the majority of the subsidence has reached completion and therefore should not pose a significant threat to site development. 3. The limited amount of void space present at the site indicates that evaluation of surface strains may identify areas of the site suitable for development. 4. Based on review of aerial photographs for the site and the surrounding area depressions have been present since 1949. The development of newer surface depressions were not observed during aerial photographic review through 1994. 5. Based upon the depth to observed groundwater, depth to the mine, length of time since mining activities have been performed and observations made during the drilling program suggest the likelihood of sudden ground failure at the surface is minimal. Recommendations 1. Based upon the findings of this investigation, it appears suitable areas for development are present at the site. Site-specific strains should be evaluated to assess specific development sites. 2. Colorado statutes require disclosure of geologic and other natural hazard risks or problems to property buyers. Property buyers must be informed of the past mining activities at the site and the risk of subsidence and should be provided with appropriate technical documentation and reports. 3 349-Longs Peak Estates Subsidence Investigation Introduction This report includes the results of a scientific investigation of potential land subsidence due to underground coal mining at the proposed Longs Peak Estates subdivision (site). Longs Peak Estates subdivision consists of approximately 32 acres of land located within the NE and NW quarters of Section 9, Township 1 North, Range 68 West within Weld County, Colorado. The area surrounding the site is developed as rural residential properties with greater than two-dozen residential homes within the same quarter section. The site location is presented in Figure 1 of Appendix 1. Activities performed as part of this land subsidence investigation included: review of subsidence- - related publications, review of mine maps of the Morrison and Clayton Mines which underlie the subject site, review of subsidence report for Scotts Acres which is located immediately northeast of the site, a site reconnaissance to identify existing on-site areas of potential subsidence, and drilling and geophysical logging of test borings. Records, including coal mine maps, and published documents were reviewed at the Colorado Geological Survey (CGS), Colorado Department of Natural Resources Division of Minerals and Geology, Colorado School of Mines, and at the United States Geological Survey. A subsidence engineering control study to evaluate potential methods for building and utility construction in an area of subsidence has not been undertaken. However, review of information retrieved during this investigation has been forwarded to other professionals experienced with mine subsidence issues. Results of these reviews are included in separate reports. REVIEW OF PUBLISHED INFORMATION Review of Mining Information—Morrison Mine Information regarding the Morrison Mine included the extent of subsurface mining, thickness of the coal seam mined, and overburden thickness (Reference 1). Based on historical maps depicting the extent of the coal mining, the Morrison Mine extracted coal from areas under proposed lots 3 through 7 and under portions of proposed lot 2 (see Figure 2 of Appendix 1). An evaluation of the accuracy of the mine map was undertaken using surface features for orientation and correlating the published Morrison Mine map with results of the boring activities. The findings found, the published Morrison Mine map to be generally accurate. Surface features present on the map which were used for orientation, included an irrigation ditch, the Union Pacific Railroad right of way, and the fault at the northwestern limit of mining. These features provide reasonable mapping control points. The information reviewed included a number of faults that limited the extent of mining in the area of the site. The northwestern limit of the Morrison Mine lies at a northeast-southwest (NE-SW) trending fault, which caused displacement of the coal horizon being mined. This fault apparently displaced the coal seam so that continuation of mining of the seam across the fault was not feasible. In addition to this major NE-SW trending fault that is depicted on both the Morrison Mine and Clayton Mine maps (References 1 and 2), a smaller north-south fault is depicted on the final mining extent map for the Morrison Mine of 1966. This secondary fault, which appears to be an adjustment or growth fault, extends from nearly the large NE-SW fault, discussed above, southward for approximately 900 feet. It ends within the central-north portion of the southern area proposed for development (proposed lot 3). The secondary fault may also have been observed within the deeper Clayton Mine as the eastern-most 4 349-Longs Peak Estates Subsidence Investigation extent of the mine identified "rock" at the limit of mining. Growth faults of this type are not uncommon in this area (Reference 11). Mining within both the Morrison and Clayton Mines was reportedly performed using room and pillar technique with removal of pillars from mined-areas during retreat. Available documents suggest that greater than 50% of the pillars were removed from the Morrison Mine. The removal of pillars is generally reported to induced rapid or immediate collapse and associated land subsidence (Reference 2). Based on the observed overburden lithology, reports developed during mining within the area, aerial photographic review, and test boring results subsidence at the site was likely near immediate. Information from the Morrison Mine map of limits of mining suggests that pillars were left in-place at a number of locations, including the central portion of the proposed subdivision and along main haulage ways throughout the mine. (Reference 4). Turney and Murray-Williams (Reference 11) report that the coal seam mined in the Morrison Mine was between 6.0 and 8.0 ft in thickness during mining activities performed between 1935 and 1953. In total, approximately 2,139,000 tons of coal was produced from the Morrison Mine. Roger Colton identified the mine adit, or entranceway, as being located at the eastern-most extent of mining, or very close to Weld County Road 7 and approximately 1,500 feet east of the site. Overburden thickness, as presented on maps in the Turney and Murray-Williams report, decreased towards the northwest and ranges in the area of the subject site from approximately 107 to 79 feet below ground surface (bgs) at the site. Review of Mining Information —Clayton Mine The second mine underlying the proposed subdivision, the Clayton Mine, lies at greater depths than the Morrison Mine. Information regarding the Clayton Mine was attained from the maps held at the Colorado Geological Survey and the Turney and Murray-Williams paper cited above. Based on the mining extent maps reviewed, the Clayton Mine underlies portions of lot 2 and 3, and lesser portions of lots 4, 5, 6, and 7. The location of the Clayton Mine relative to the site is also presented on Figure 2 of Appendix 1. The Clayton Mine removed a seam of coal reportedly 9 feet thick, however, the depth to the mine under the site is not accurately known. This information, obtained from The Colorado Geological Survey publication (Reference 11) indicates the mine lies under 350 feet of overburden. The final survey map of the mine indicates a shaft depth of 314 feet at a location about one mile south of the proposed subdivision. The coal seam rises approximately 8.8 feet per thousand feet to the north and the USGS topographic map indicates a drop in topography of approximately 80 feet, suggesting a depth to the Clayton Mine of approximately 180 feet under the proposed subdivision. Test boring W-1 drilled by E- 21 to 212 feet bgs identified the mine at a depth of 202 ft bgs. Based on this information it is estimated that the Clayton Mine lies at depths at 190 to 230 below the existing ground surface at the site. Mining was also reportedly performed in the Clayton Mine using the room and pillar technique. Data and maps suggest that the pillars were removed from the mine in the western portions during mining operations, but pillars remain in the eastern section of the mine, which is below the area proposed for development. The pillars were reportedly removed under proposed lot 2 where subsidence features are prominent however, the subsidence is likely due to collapse at the overlying Morrison Mine. The eastern 5 349-Longs Peak Estates Subsidence Investigation portion of the Clayton Mine, also present under the area proposed for development, underwent limited mining (16% of the site). The eastern limit of the Clayton Mine, as discussed above, is likely bounded in part by the north-south fault identified on the Morrison Mine map. Since mining activities within the Clayton Mine were halted at the fault, it is not delineated or identified as a fault on the Clayton Mine map. A table summarizing the mining activity below the area proposed for residential development is presented below. Table 1. Summary of Proposed Development Area Mine Data Lot ID Total Est. % Acres Over Est. %of Total Est. Acres Est. %of Total Est. Acres-% Acres Not Morrison Morrison Mine Over Both Over Both Underlain Mined Mine Mines Mines By Pillars 1 2.87 100 0 0 0 0 0-N/A 2 4.28 43.8 2.41 56.2 0.57 13.4 0.13 -3.0% 3 3.49 0 1.35 38.7 2.14 61.3 0.91 -26.1% 4 3.36 0 3.17 94.5 0.19 5.5 0.36- 10.7% 5 3.15 0 3.15 100 0 0 0.624- 19.8% 6 3.40 0 2.28 67 1.11 33 0.369- 10.8% 7 3.35 0 2.63 78.5 0.72 21.5 0.587- 17.5% Total 23.90 16.4 13.3 55.6 5.32 22.2 2.795- 11.7% Note: Acreages based on Coal Mining Extent Map of 1983 Turney and Murray-Williams Report. The table above does not account for pillars that were likely left in place during the removal of support pillars. As publications suggest, the room and pillar method of mining employed in the Boulder Weld County Coal fields included regularly leaving some percentage of coal (30-70%) in place as pillars to support the roof, keep access to the mine working open, ventilation, and so forth (Reference 9). Later these pillars, or a portion of them, would be pulled as miners retreated from the area. The location of pillars not scavenged during retreat was not generally recorded. Review of Scotts Acres Subsidence Potential Report The Scotts Acres subsidence report was reviewed to evaluate conditions and findings associated with a parcel of land located proximal to the subject site. Activities performed as part of the Scotts Acres report included the advancement and geophysical logging of three test borings to depths ranging from 130 to 201 feet. The report was published in March, 1985 by Deuel and Associates, Inc. for Mr. William Whitacre (Reference 7). Test borings were located over a reported pillar associated with a haulage way and within two rooms. Results of the test borings identified the top of the Morrison Mine at depths ranging from 112 to 123 ft bgs. The thickness of the Morrison Mine coal seam was observed within the encountered pillar to be 7 feet. Results from the two borings where coal had been extracted found that the mine had collapsed at both sites. The recommendations presented in the report, based on strain analyses using the methods of the National Coal Board (NCB) of Great Britain, identified areas within the Scotts Acres subdivision that may be developed. 6 349-Longs Peak Estates Subsidence Investigation Groundwater was observed in one borehole at a depth of 97 feet below grade. The groundwater depth was presented in the geophysical log and was not discussed in the body of the report. It is unknown whether groundwater was encountered in the other two test borings. The encountered lithology appeared similar to that observed during test boring advancement at the subject site. Geophysical logs for the test borings indicate the presence of sandstone/siltstone units and thinner coal seems similar to that observed at the subject site. 7 349-Longs Peak Estates Subsidence Investigation FIELD ACTIVITIES Site Evaluation Test Methods Test methods used to evaluate site subsurface conditions included a site reconnaissance to evaluate land subsidence features, and the drilling and geophysical logging of eleven test borings advanced at selected locations across the subject property. The site reconnaissance was performed to evaluate the presence of land subsidence features. Activities included a site walkover with additional review of a previously- developed topographic map of the site. A copy of the site topographic map is included as Figure 3 of Appendix 1. A total of 11 test borings were conducted to evaluate subsurface conditions at the site. Test borings were advanced using an air-rotary Ingersol-Rand T-4W drill rig with a 750 cubic-feet-per-minute (CFM) air compressor. A 6 5/8-inch drag bit was used to drill the hole with cuttings removed from the borehole using 250 pounds-per-square-inch (psi) of down-hole air pressure. If loss of air pressure and loss of surface return of cuttings occurred, the drill string was pulled in an attempt to regain circulation. If after two attempts circulation was not re-established, continued advancement of the borehole was performed. The drag bit was used throughout borehole advancement, except for the deeper materials within boring W-1, which were harder and/or more consolidated and required the use of a carbide-button bit. Boring advancement rates were recorded during drilling by keeping a time/progress log and were used to evaluate subsurface conditions. Generally, the rate of advancement was related to the hardness of materials encountered. Down pressure in excess of the weight of the drill string was required only during drilling through the occasionally encountered siltstone and sandstone layers. The size and texture of the drill cuttings from the discharge pipe were found to be directly related to the hardness of the material with the hardest bedrock exiting the hole as "dust" or very fine particles. Borings were advanced by Precision Water Well, Inc. under the direction of E-21 project geologist Paul Gottler. Mr. Gottler was on-site throughout boring activities to locate boring sites, log the borings, log the returned cuttings with respect to color, hardness and lithology, and monitor advancement rate as well as air returns. Additional data collected during borehole advancement included driller's reports regarding soft or easy drilling layers, driller's reports of hard layers, loss of air circulation, voids, and discharge of air at proximal boreholes. The discharge of air at proximal boreholes was evaluated only during the later stages of the project after identification of the venting by the downhole geophysical logging company. Copies of the boring logs are presented in Appendix 2. Borings were sited throughout the southern portion of the proposed subdivision. As indicated above, the northern area is not, for the most part, underlain by former mines. Results of the boring and geophysical logging allowed for evaluation of the thickness of the coal seam mined when encountered at pillars, thickness of overburden, the accuracy of the produced mine maps and other data previously reviewed. Boring sites were identified using W, C, and E prefixes to denote western, central, and eastern locations, respectively, with respect to the subject site area. Number suffixes were used with increasing values towards the south. A single boring advanced within the northern lot of the site was identified as NL-l. In all, 11 borings were advanced at the site at depths ranging from 99 to 212 feet below the ground surface. Boring locations were located in the field using a 12 channel Global Position System (GPS). Three readings were taken at each location and averaged. Based on the variation between readings, generally 1 or 2 meters, the locations as plotted are within 10 ft of plotted sites. Field measurement from known map points also indicated the borings to be within 10 ft of the map. Boring locations are presented on Figure 3 of Appendix 1. 8 349-Longs Peak Estates Subsidence Investigation Geophysical logging of the holes was performed immediately after borehole completion to reduce the chance of collapse. Logging tools included: one and three arm calipers, electro-magnetic(EM) induction, natural gamma, and focused gamma density. The objective of geophysical logging was to identify the presence of voids, if present, evaluate the lithology of materials over the mine, and to more precisely provide the thickness of overburden and where encountered, coal seams. Geophysical logging was performed by COLOG, Inc. Geophysical logs are included in Appendix 3. Focused density logging of the borehole was complicated by the irregular borehole diameter likely created through use of the drag bit. The irregular, or rugose, character of the borehole did not allow the focused density probe to lie flat against the formation thus incorporating some open borehole densities into the result. To reduce the effect of borehole rugosity compensated density results were provided. In general, the field evaluation of cuttings agreed with geophysical logging results. The natural gamma tool was found to be the best in identifying the coal as it is naturally depleted of gamma-emitting particles. The harder siltstone and sandstone beds deflected the density tool with coincidental increase in resistivity, with coincidental decrease in natural gamma. Dirty, or organic-rich, shale can be delineated from siltstone and sandstone through use of the resistivity log. Observations made during test borehole advancement, including loss of circulation, the reporting of easy or hard drilling, and the discharge of air through previously completed boreholes can also be used to characterize the borehole site. The discharge of air from other boreholes was found to contain a methane, or explosive gas, component and was monitored with an on-site combustible gas monitor. The readings were correlated to air volume discharge so that the level of inter-borehole communication could be evaluated. 9 349-Longs Peak Estates Subsidence Investigation FIELD RESULTS Results of Site Reconnaissance The site reconnaissance identified potential subsidence features within the southern portion of lot 2, and the northern portions of lots 3, 4 and 5. Subsidence features are not clearly definable along the southern portions of lots 3 and 4, and do not appear to be present on lots 6 and 7. The subsidence feature within the northern portion of lots 3 and 5 were drilled with results discussed below. The subsidence feature within the southern portion of lot 2 was not evaluated, but also appears to be the result of mining-induced subsidence. Current plans for the portion of lot 2 that has experienced subsidence do not include the development of structures. An area immediately west of lots 3 and 6 also appear to contain subsidence features. These features were identified in published documents (Reference 1). Results of Test Boring and Logging Test boring and geophysical logging results are presented on a boring by boring basis below. Caliper log evaluation for site subsurface conditions was performed using the three-arm caliper logs with an 18-inch maximum extension. Test Boring W-1 - Soil boring W-1 was advanced to a total depth of 212 feet bgs within the northern portion of proposed lot 3. The boring at this location was extended greater than 100 feet deeper than other borings so that information regarding the lower Clayton Mine could be retrieved. According to the Morrison Mine map, this location was not within 50 feet of a remaining Morrison Mine pillar. The boring did not encounter a thick coal seam, or pillar, at the depth of the former Morrison Mine, suggesting that extraction of the coal had been performed at this location and the map was correct. Based on the drilling and geophysical logs the mine floor was encountered at 97 feet bgs. It appears that the "back is down" at this location, or that collapse of the mine roof has occurred and the area of interstitial collapse material observed represent spaces between fallen blocks as they are of limited lateral extent. During drilling easy, or soft, materials were encountered in W-1 from approximately 42 to 49 feet bgs. The loss of cuttings return and air pressure occurred at a depth of 75 ft bgs and continued until encountering a very hard substrate at 105 feet bgs. This loss of air return suggests that voids are present between 75 and 97 feet bgs and that circulated air and/or cuttings are being lost to the voids. The return of circulation and cuttings at 105 feet depth, along with a decreased advance rate for the drill stem, indicate that the encountered voids are of limited extent. Groundwater was encountered at a depth of approximately 112 feet depth, or 15 feet below the bottom of the mine, and was observed through the duration of drilling below this depth at this location. After attainment of the total depth and removal of the drill string, the borehole was found to have collapsed to a total depth of 202 feet bgs. At the time of borehole abandonment and closure, approximately 5 days after drilling, the borehole had collapsed to 109 feet bgs. The deeper Clayton Mine was encountered at approximately 192 feet bgs. Drilling at that depth was very easy and "hold back," or upward, pressure was maintained on the drill string to slow the advance rate. Loss of circulation occurred between 160 to 202 feet bgs. A hard zone, suggesting the bottom of the mine, was encountered at 203 feet. Circulation return was coincidental with the encounter with this hard layer suggesting advancement through competent bedrock. The loss of circulation in the zone from 160 10 349-Longs Peak Estates Subsidence Investigation to 202 feet is consistent with drilling through a collapse zone and was experienced throughout the boring program. The height of materials of lower density above the mine floor, suggesting the upper limit of collapsed rock, was found to be 36 feet. This elevation is consistent with other test borings into mine collapse areas. Collapse of the borehole to 180 feet bgs occurred shortly after drilling so evaluation of the deeper mine with geophysical logging could not be undertaken. Geophysical logs for the upper portion of the borehole, or that associated with the Morrison Mine, indicate irregular borehole diameter from 76 to 97 feet bgs. The caliper logs show the borehole diameter to extend to nearly 11 inches at 96.7 feet bgs. Caliper deflections are limited and do not suggest the presence of large cavities Resistivity logs through the zone from 76 to 97 feet bgs do not indicate the presence of cavities as the log appears similar to boreholes where mining has not occurred. The similarity between the log from this location and locations where subsidence has not occurred suggests a very limited lateral extent to the areas of enlarged borehole identified by circulation loss. The density log for the zone from 76 to 97 feet bgs is also very irregular further indicating that mine roof collapse and/or material bulking has occurred. Increased, and more regular, rock density above the mined zone indicates the vertical limit of collapse, or the area where stabilization has likely been attained. Caliper logs are also more consistent from 75 feet bgs to the surface. The deeper portion of test boring W-1 was drilled with a button bit due to the hard, or more lithified, nature of the rock. Geophysical logs for the deeper portion of the mine, beyond 120 feet, were done within a saturated zone that had been drilled with the button bit. The rugosity, or "wrinkled" nature, of the borehole was greatly decreased by the use of the button bit in harder rock, allowing for the recovery of a better focused-density signal. Consistent and average rock densities move to above 2 g/cc above 152 feet bgs indicating that the rock above this depth have been unaffected by mine collapse. The caliper log shows the borehole widened to 11-inches at 192 and 201 feet bgs. Resistivity between 194 and 201 feet is low, indicating that the void interval away from the borehole is minimal. The caliper log deflects to an 11-inch maximum within the mined zone at 193.5 to 195.5 and from 199 to 201 feet bgs. Between these noted caliper deflections the borehole was observed to be within approximately 5% of the drill bit diameter. Test Boring W-2 - Test boring W-2 was advanced to a total depth of 99 feet bgs within the southern portion of proposed lot 3. Drilling was halted approximately 5 feet past the bottom of a 9-foot thick coal seam. This seam is located at the approximate depth of he Morrison Mine and is therefore interpreted to be a mine pillar. Based on the Morrison Mine map a pillar was not anticipated at this location. The reason that an unmapped pillar remains at this location is unknown, but may be related to the presence of a map-depicted north-south trending fault located adjacent to the boring site. Materials overlying the pillar appear unaffected by the removal of the coal in adjacent areas as caliper, density, and resistivity logs are within the range anticipated for the logged lithologies. Caliper logs of the borehole show the borehole to be consistently within 0.5" of the 6 5/8" bit size. The rock density is irregular, but is generally greater than 2 grams per cubic centimeter (g/cc) except within the coal seams. Resistivity is consistent throughout the hole except at the coal seams where a strong "kick" is observed and at thicker siltstone beds, which also exhibit higher resistivity values. Harder drilling, requiring the use of down-pressure, was reported by the driller at approximately 49 feet bgs. This depth coincides with a harder and denser sandstone/siltstone horizon observed on the geophysical logs. 11 349-Longs Peak Estates Subsidence Investigation Test Boring W-3 - Test boring W-3 was advanced to a total depth of 110 feet bgs within the very north limit of proposed lot 6. Drilling was also terminated past the bottom of a 10-foot thick coal seam, which was interpreted to be a mine pillar in the Morrison Mine. The Morrison Mine map indicated that a pillar should have been encountered at this location. Materials over the coal seam appear unaffected by coal extraction in the areas immediately south, and north, of the test boring site. Geophysical logs of the borehole show the borehole to be consistently within 1" of the 6 5/8" bit size. Like test borehole W-2, the rock density is irregular, but is generally greater than 2 g/cc except within the coal seams. Resistivity is consistent throughout the hole except at the coal and siltstone beds. Softer drilling, requiring the use of hold-back pressure, was reported by the driller at approximately 78 feet bgs. Test Boring W-4 - Test boring W-4 was advanced to a total depth of 102 feet bgs within the central portion of proposed lot 6. Small cavities, coal, and pieces of wood believed to be remnant mine support beams were observed below a depth of 85 feet bgs. The presence of cavities and coal suggests that extraction of the majority of the coal seam had been complete at this location. Published reports for the Morrison Mine indicate that extraction width ranged from 6-8 feet. This would allow a one foot-thick floor and ceiling during mining to reduce floor heave and ceiling collapse. Soft, or very easy, drilling was reported from 87 to 95 feet bgs. Loss of some circulation occurred at 75 feet bgs and air was reported to be discharging from proximal borehole C-3 (no air was observed exiting W-3 also located near this borehole). Materials discharging from the borehole during the soft drilling were inconsistent and included coal and shale. A hard layer, identified using geophysical logs as the bottom of the former mine, was encountered at a depth of 95 feet bgs. Geophysical logs indicate that the mine has collapsed and there is no remaining void, or the back is down at this location. Based on the erratic density logs and caliper fluctuations the zone of collapse extends to an elevation approximately 35 feet above the bottom of the former mine, or from 95 to 60 feet bgs. Resistivity values increase and density values decrease from 90 to 95 feet bgs also indicating that collapsed material has in-filled the mine. Resistivity values appear consistent relative to the materials encountered above 75 feet bgs. Density values are very erratic from the bottom of the mine to an elevation of 62 ft bgs, or 23 ft above the top of the mine suggesting that collapse structure extends to this elevation. The caliper log is also consistent above 60 feet. Soft, or very easy, drilling was reported from 87 to 95 feet bgs. Loss of some circulation occurred at 75 feet bgs and air was reported to be discharging from proximal borehole C-3 suggesting that interconnected cavities, observed within each of the mined zones, exist at this location. Air was not observed exiting test boring W-3 also located near this borehole indicating that there is no borehole to borehole communication between these locations and the suggestion that near complete collapse has occurred is likely correct. Test Boring C-1 - Test boring C-1 was advanced to a total depth of 119 feet bgs within the northern portion of proposed lot 4. A 10-foot thick coal seam, or pillar, was observed at 84 to 94 feet bgs. The map of the Morrison Mine did not identify a pillar at this location. Bedrock above the pillar does not appear to have been affected by the fault or the extraction of coal immediately surrounding the pillar. Geophysical logs show caliper measurements, density, and resistivity to be regular and consistent with the encountered lithology. Compensated densities appear regularly above 2 g/cc and increase to nearly 2.5 g/cc below the mined zone. 12 349-Longs Peak Estates Subsidence Investigation Test Boring C-2 - Test boring C-2 was advanced to a total depth of 103 feet bgs at a location within the southern portion of proposed lot 4. The map of the Morrison Mine did not identify a pillar at this location, nor was a pillar encountered. Air circulation and cuttings return were limited after 78 feet bgs, probably due to the presence of soils associated with roof collapse. Caliper logs indicate the presence of very small voids centered at 90.5 and 94.5 feet bgs, or within the mined zone that was present from approximately 88 to 97 feet bgs. The maximum extension of the calipers was 8.4 inches, indicating that the voids were of limited lateral extent. The largest borehole diameter observed was 8.3-inches present within the former mined zone. The location of remaining open space, as indicated by the presence of enlarged borehole, are within the floor and ceiling of the former mine. The remaining open space at this location may be a reflection of coal cleating, or fracturing, that enlarged the borehole during drilling. Other instances of larger borehole diameters within coal seams has been observed in this study. A portion of the range between 86.5 and 95 feet bgs, or within the minded zone, is at the normal borehole diameter. This suggests that a void is not present within the old mine, but collapsed material derived from immediately above the mine has collapsed and nearly filled the mine. The caliper logs above 86.5 feet are consistently within 0.5 inches of the bit diameter and are 100% within 5% of drill bit diameter suggesting that collapse has not impacted these materials. The natural gamma log within the mined zone suggests that the floor and roof of the mined zone contained coal. Natural gamma decrease within coal and other organic-rich zones as well as the sandstone/siltstone layers. Like location W-4 discussed above, the mine roof and floor at this location contain a one-foot buffer against roof collapse and floor heave. Density and resistivity logs appear consistent with logs developed by the on-site geologist as the correlate well with the encountered lithology. Density logs through the mined depth of 88 to 97 feet are very erratic and are regularly below 2 g/cc. Above 88 feet depth, the densities remain erratic, but are consistently above 2 g/cc. Resistivity values from 88 to 97 feet are high, but decrease and appear related to lithology above this zone. Density values for four siltstone horizons, present at 42, 55, 71 and 79 ft bgs, are higher than most of the other logged siltstone horizons and even approach a density of 5 g/cc. The presence of numerous siltstone layers makes interpretation of the other rock-type densities difficult. However, the average rock densities and caliper measurements for the zone above the mined zone do not appear significantly different from C-I where voids were not observed. Drilling was reported as easy, or soft, below 78 feet to the bottom of the mined zone at 102 feet bgs. In addition, the driller reported a void from 89.5 to 91 feet bgs. During the drilling of borings E-1, E-2, and C-3, air was observed to be venting from this boring indicating that the mined zone, though nearly completely collapsed, does provide a pathway for the high pressure air used during drilling. Test Boring C-3 - Test boring C-3 was advanced to a total depth of 112 feet bgs within the north-central portion of proposed lot 7. The Morrison Mine map shows an east-west trending pillar along a mine haulage way present approximately 35-40 feet south of the boring location, but no pillar at this specific drilling location. A pillar was not encountered during borehole advancement. Repeated drilling of the borehole after loss of circulation at 96 feet bgs did not result in air circulation return, suggesting that a void is present at this location. The driller reported easy and soft drilling from 97 to 99 feet bgs and indicated a void was present at 99 to 100 feet bgs. The former mine floor, or a hard substrate, was encountered at 105 feet bgs. Drilling continued until 112 feet without circulation return. The borehole immediately collapsed/filled to 102 ft bgs after the rig pulled off of the hole. 13 349-Longs Peak Estates Subsidence Investigation Caliper logs within the mined zone show irregular borehole diameter present between 97 and 102 ft bgs. Above 97 feet the caliper is consistently within 0.5" of the drill bit size. Density and resistivity logs above 97 feet are also consistent with undisturbed shale and siltstone bedrock, indicating that the strata overlying the mine has not collapsed extensively. During the subsequent drilling of E-2 and C-4, air was observed to be venting from this borehole. The presence of the haulage way pillar, estimated to be 35 feet south of this location, may explain the incomplete collapse at this location as the pillars may be providing sufficient support for overburden materials, thus preventing collapse. The driller reported easy/soft drilling from 97 to 99 feet and indicated a void was present at 99 to 100 feet. Air to 8% LEL was observed to be discharging from this hole during the advancement of test boring E-2. Air discharge at this location during advancement of test boring C-4 was also observed suggesting that an interconnection exists between materials collapsed into the former mine. Test Boring C-4 - Test boring C-4 was advanced to a total depth of 116 feet bgs within the southwestern portion of proposed lot 7. An existing mine pillar of 9 feet in thickness was encountered at 102 feet bgs. The map of the Morrison Mine did not identify a pillar at this location, but haulage ways are present approximately 60 feet south and 110 feet east of this site. Overburden materials do not appear to have been impacted by proximal mining activities. Geophysical logs for this borehole are consistent with undisturbed overburden materials and indicate that it has not been impacted by mining activities. Interestingly, the average rock density approaches 3 g/cc at this site. Circulation loss did not occur during advancement of this boring. Air was observed to be discharging out of borehole W-4 and C-3 with general consistency after 45feet bgs depth had been reached. The combustible gas level of the air emanating from these boreholes remained consistent at nearly 3% of LEL at either location. Test Boring E-1 - Test boring E-1 was advanced to a total depth of 105 feet bgs within the north-central portion of proposed lot 5. This boring was located within an identified closed depression indicative of a collapse structure. According to the Morrison Mine map, no pillars or haulage ways were located within 75 feet of this site. Loss of circulation and cuttings return occurred at 95 feet bgs. Geophysical logs identify a large decrease in natural gamma radiation with increased electrical resistivity, both of which occur in coal beds, at 100 feet bgs, suggesting that remnant coal from the mined zone was present at this depth. Coal was circulated out of the hole at 87 feet bgs and may have been present immediately above the mined zone from 92 to 102 feet bgs. Hard drilling was encountered at 105 feet bgs and circulation return occurred. The hole collapsed from 105 feet to 102 feet depth after removal of the drill string. Caliper logs do not identify voids within the mined zone, but show a slightly larger borehole diameter from 66-67 feet bgs. These voids are the only observed voids at this location suggesting near complete collapse at this location. Except for the last 0.25 feet the caliper log was completed through the mined zone suggesting that the limit of cavities was fully evaluated with the caliper tool. Density logs suggest that collapse associated with coal extraction impacted overburden materials to a depth of 69 feet bgs, or 23 feet above the top of the mine. This depth, or elevation above the top of the mine, appears consistent with borings at mine extraction sites that have undergone complete collapse. 14 349-Longs Peak Estates Subsidence Investigation Subsequent drilling at E-2 found that only small volumes of air were being vented from this borehole indicating that larger openings, or voids, are not present at E-1. During the drilling at E-2 more air was discharging from C-2 and C-3 than E-1 even though E-1 was closer. Test Boring E-2 - Test boring W-1 was advanced to a total depth of 100 feet bgs within the south-central portion of proposed lot 5. This boring was advanced at a location approximately 230 feet south and approximately 8 ft higher in elevation than the depression evaluated at boring E-1. According to the Morrison Mine map, a pillar is located approximately 30 feet south of this test hole location. Circulation loss occurred at 78 feet bgs and did not return throughout the rest of borehole advancement. Immediately after the rig pulled off of the hole it collapsed to 88 feet bgs. Caliper logs show borehole expansion to 10.7 inches at 72 feet bgs. The large borehole diameter is observed within a 4-feet thick coal seam from 67 to 71 feet. The caliper fluctuation at this depth interval may be related to cleats within the coal. Caliper results from 71 feet to the bottom of the log at 92 feet do not indicate the presence of open borehole. Because collapse of the borehole occurred and return of circulation beyond 78 feet could not be established it is likely that materials, including the coal at 67 to 71 feet, have collapsed into the mine and have reached a stabilization point where no further collapse is likely. Density logs show low density materials from 76 feet to the siltstone layer at 78 feet suggesting that the siltstone layer has likely collapsed and is supporting the overburden. An erratic caliper is observed from 67 to 81 feet depth. Density values are also erratic from 40 feet bgs to the total logged depth. Resistivity values are higher than normal for the range between 68 and 80 feet and appear to be related to lithology above the mined zone. The lack of circulation return and the collapse of the borehole to 88 feet bgs suggests that open space may be present at this location. Like borehole C-3, the incomplete subsidence at this location is likely related to support provided by the proximal pillar. Hard, slow drilling, indicative of a hard substrate, was reported by the driller at 96 feet bgs. Discharge of air at C-3 and C-2 were observed at 70 and 80 ft bgs. The combustible-gas value was twice as high at a depth of 80 feet when compared to the air discharging while drilling at 70 feet bgs. Air with combustible gas at 25% of the LEL of C-3 was observed emanating from E-1 at 80 feet during the advancement of E- 2. Test Boring NL-1 - Test boring W-1 was advanced to a total depth of 99 feet bgs within the southern portion of proposed lot 2. The location of the boring was intended to evaluate the depth and thickness of mined material at this location as the Morrison Mine map identified the location as within the mined zone and approximately 90 ft west of any pillars. A 10-foot thick coal seam was encountered at this location at 83 feet bgs. The elevation of the top of the coal is at 5000 feet MSL, which is consistent with other borings in this area. Geophysical logs indicate lithologically-dependent changes in resistivity, density, and natural gamma. No irregular patterns are present, and the average density is consistently above 2.2g/cc, thus, the overburden materials do not appear to have been impacted by proximal mining activities. The driller did not report any periods of easy drilling in test boring NL-1. Air discharge was not monitored as the borehole was not located proximal to any other borings. 15 349-Longs Peak Estates Subsidence Investigation DISCUSSION OF TEST BOREHOLES AND LOGGING RESULTS Test boreholes and geophysical logging of the test borings identified important site characteristics including: the elevation of the top of mined coal seam, the elevation of the bottom of the mined coal seam, and the thickness of the mined coal seam when encountered. Each of the findings associated with the test borings are contained in Table 2,below. TABLE 2 - Test Borehole Mine Elevations, Coal Seam Thickness, and Findings Boring Ground Top Coal/Mine Bottom Coal/Mine Coal Depth to Top of I.D Elevation MSL Elevation MSL Elevation MSL Thickness in Feet Mine W-1 5086.5 4991.5 4981.5 10.0 -Estimated 95 feet W-2 5085.5 5000.5 4991.5 9.0 - Encountered 85 feet W-3 5086.0 5005.0 4995.0 10.0 - Encountered 81 feet W-4 5088.0 5003.0 4993.0 10.0 -Estimated 85 feet C-I 5087.0 5002.0 4993.5 8.5 - Encountered 85 feet C-2 5090.0 4997.0 4988.0 9.0 -Estimated 93 feet C-3 5089.0 4994.0 4984.0 10.0 -Estimated 95 feet C-4 5092.5 4990.5 4980.5 10.0 - Encountered 102 feet E-1 5088.1 4993.1 4983.1 10.0 -Estimated 95 feet E-2 5096.5 5010.0 5000.0 10.0 -Estimated 86.5 feet NL-1 5082.8 5000.8 4990.8 10.0 - Encountered 82 feet The top of coal elevation ranged from 4991.5 to 5009.0 ft MSL. The observed trend in the top of coal elevation does not appear to correlate with the Morrison Mine map, which showed decreasing floor, or ceiling, elevations to the southwest. At the site, the highest top of coal elevation was located at test boring E-2, located in the northeastern portion of lot 5 within the south parcel. According to the published map the lowest elevation of the top of coal should have been observed within the southeastern portion of the site. The observed location was at test boring C-4 where it was found to be nearly 7 feet lower than test boring E-2 located in the southeast portion of the site. Geologic cross sections developed from lithologic and geophysical logs are difficult to correlate (Appendix 2). The north to south trend of the mined coal, or any of the other marker beds, provided poor correlation. As indicated previously, the development of growth faults during deposition of the coal, or along any portion of the delta front, likely has erased the existing time/distance correlation present during the period of deposition. In addition, the regularly reported heaving of mine floors and bowing of coal seams left after mining further complicate the stratigraphy. Test boring results identifying the amount of soil over the bedrock, thickness of bedrock over the top of the mine, thickness of bedrock impacted by mine collapse, coal seam thickness, and total boring depth are provided in Table 3 below. 16 349-Longs Peak Estates Subsidence Investigation TABLE 3—Summary Structural Thickness in Test Borings Estimated Boring Soil Bedrock Collapse Zone Actual Removed Total Boring Number Thickness over Mine Thickness Coal Coal Depth (feet) Thickness (feet) Thickness Thickness (feet) (feet) (feet) (feet) W-1 11 84 20 10 212 W-2 14 71 None 9.0 feet 99 W-3 5 78 None 10.0 110 W-4 6 79 35 10 102 C-1 9 75 None 8.5 119 C-2 8 79 1.5 9 103 C-3 7 89 0 10 112 C-4 11 91 None 10.0 116 E-1 5 87 87 10 105 E-2 7 79 +/- Unknown Unknown 100 NL-1 5 78 None 10.0 99 The thickness of bedrock over the mine appears greatest at C-4, located at the southeast portion of the south parcel. Aerial Photographic Review Aerial Photographs of the site covering the years 1949 through 1994 were reviewed to evaluate changes potentially related to the development of subsidence features. Photos were reviewed at the Colorado Aerial Photography facility in Denver Colorado. Photographs at 4—year intervals between the years 1974 and 1990 were reviewed by Paul Gottler of E-21 using stereoscopic magnification. Prior to 1974 photo availability at appropriate scale were unavailable. Photographs at a good scale were later acquired through the United States Geological Survey. These photos included the years 1949, 1966, and 1971. Photographic scale ranged from 1" = 0.28 mile to 1" = 1.12 mile. Following, presented as a photo-by- photo analysis, are the results of aerial photographic review: 1949 —The 1949 aerial photograph was taken July 13, 1949 and was taken at a scale of I" = 0.28 mile. The most prominent on-site feature includes a square-like feature in the western portion of lot 6. This feature is located towards the northern portion of the lot and is approximately 150 feet by 150 feet with an elevated center area. A connected more linear feature is present at the southeast corner of the square. This feature extends to, and across, the farmers ditch. Mid-sized depressions are present at the southern end of lot 7 and the northern end of lot 5. Smaller features are present near the southwest corner of lot 3, very north end of lots 4 and 5, and the south-center portion of lot 7 near the farmers ditch. Off-site visible features include a large depression approximately 400 feet north of the north border between lots 3 and 4. This feature contains a small pond and is adjacent to the Stegall residence. This feature is present throughout the aerial photo review and was observed in subsequent aerial photos to have been modified over time. Other off-site depressions are smaller than the depression noted above 17 349-Longs Peak Estates Subsidence Investigation and are present along the farmers ditch north of the site. These depressions also appear in later photos. Other prominent and remaining depressions observed in this photo include the four depressions west of the center of the south parcel. These depressions are still present today and though they change shape through time remain consistently at, or near, the location observed in this photo. 1966 — The 1966 aerial photograph was taken October 10, 1966 and was taken at a scale of I" = 0.42 mile. Features present on-site include a kidney-shaped feature at the center of the western margin of lot 3. Two smaller features are present approximately 175 and 225 feet east of this depression. Three smaller features are equally spaced and aligned north-south approximately 250 feet west of the eastern- most limit of the site. A medium sized feature is present within the center area of the southern limit of lot 2. Off-site visible features include the large depression approximately 400 feet north of the north border between lots 3 and 4. Two aligned north-south features east of this large depression are present on this photo. These features were more circular in shape when observed in the 1949 photo, but are in the same location. Other off-site depressions are smaller than the depression noted above and are present along the farmers ditch north of the site. Other prominent and remaining depressions observed in this photo include the depressions west of the center of the south parcel. At this time one very large feature appears to encompass the area of two of the features observed in the 1949 photo. Smaller depressions are also present near this area. 1971 — The 1971 aerial photograph was taken August 7, 1971 and was taken at a scale of 1" = 0.42 mile. Features present on-site include an oval-shaped feature at eastern margin of lot 5 approximately 150 feet north of the southern lot limit. The only other on-site feature is the consistently observed depression within the center area of the southern limit of lot 2. Off-site visible features include the large depression adjacent to the Stegall residence. At this time the pond is bifurcated by an isthmus-like land-mass that divides the pond into a larger eastern and smaller western sections. The depressions west of the center of the south parcel are also prominent in this photo. 1974 — The 1974 aerial photograph was taken on November 7, 1974 and was available at a scale of 1" = 2.1 miles. The striking north-south and east-west alignment of observed features was observed even though the photo was at a larger scale than preferred. Of the photos reviewed only the most recent, 1994, was at a scale more conducive to deciphering subsidence structures. Results presented here reflect the best interpretation possible. Features present on-site included the oval shaped structure observed on the western edge of the south parcel near the southwestern corner of lot #3. The other on-site feature was an oblong discoloration present within the northeastern limit of parcel #2 in the north area of the subject site. These features had been observed previously. Off-site structures include three features adjacent to the Stegall residence. Immediately west of the larger depression is a smaller one that also appears to contain standing water. Further to the east, and east of the farmer's canal, is a smaller depression that may also represent a subsidence feature. Each of these features had been observed previously. 18 349-Longs Peak Estates Subsidence Investigation Numerous circular to oval depressions are again present west of the center-north portion of lot #3. These depressions were observed in each of the aerial photos and may represent surface subsidence features. Three of the four features align in a north-south direction. The fourth feature, observed just west of the other features is larger than the others and is oval with the longer east-west axis. 1978 — The 1978 aerial photograph was at a scale of 1" = 0.68 mile and was taken on October 4, 1978. The photograph appeared to contain most of the features identified in the 1974 photo and also a few others of note. A small circular feature was present approximately 1,000 feet west of the oval subsidence structure noted above (west of the site lot #3). This feature is present within an area not underlain by the Morrison Mine and may be a feature associated with a different mine, or may be unrelated to subsidence. The presence of features that are reported, but unrelated to subsidence, should be noted. The first observance of an additional north-south feature, located approximately 300 feet west of the southern-most portion of the site (lot #6), was noted. This feature was moderately large (to approximately 100 feet in the north-south direction). According to the Morrison Mine map it would be approximately 100 feet west of a remaining chain pillar. This feature does not appear in the later 1982 photo, but was observed in the 1986 and 1994 photos. The proximity of the feature to existing pillars suggest that it may be related to farm activity as it is adjacent to the farmhouse just off-site at the southwest corner of the site. 1982 — The 1982 aerial photograph was at a scale of 1" = 0.68 mile and was taken on October 4, 1982. On-site features included the small circular item at the northeastern portion of lot #5. Two additional structures were observed in the northern half of the site near the central area at the southern boundary of lot #1. These features are north of the Stegall residence structure and appear only on the 1986 photo. Both features are less than 100 feet diameter and look like discoloration as apposed to subsidence features. Previously identified off-site structures remained visible. - 1986 — The 1986 aerial photograph was at a scale of 1" = 0.68 mile and was taken on October 7, 1986. The features present on this photo were identified in each of the previous photos. 1990— The 1990 aerial photograph was at a scale of 1" = 0.68 mile and was taken on October 16, 1990. The only on-site feature observed in this photo was the elongated oval structure located along the western edge of lot#3. Off-site features were prominent, but had been observed and discussed previously. 1994 — The 1994 aerial photograph was at a scale of 1" = 0.34 mile and was taken on October 8, 1994. On-site features include three north-south aligned features along the center of Lot #3 and three features also aligned north-south that extend from the center of lot #5 to the northern portion of lot $7. Off-site features had been observed and discussed previously. Aerial Photographic Review Results Aerial photographic review indicated that many subsidence related features were observed to be consistently present in the area at, and proximal to, the site. The unchanging nature of the land surface suggests that most subsidence likely occurred within the decade following coal extraction. 19 349-Longs Peak Estates Subsidence Investigation Findings Proposed Lot 1 is not underlain by areas that have been mined. Approximately one-half of proposed Lot 2 is underlain by mined-out areas. Proposed Lots 3 through 7 lie over mined areas. All of the area under Lots 3 through 7 where mined by the Morrison Mine and, in addition, some areas were also under-mined by a second, deeper mine, the Clayton Mine. The mined areas under the site were mined by room and pillar methods and it appears that a number of pillars were left during final retreat mining. Based on test borings and estimated coal bed thicknesses, the upper mine, the Morrison Mine, originally was at depths ranging from 82 to 102 ft bgs. The map of coal mine workings and coal removal for the Morrison Mine indicates approximately 40 to 50% of the coal was removed room and pillar methods and more coal was removed by retreat mining of pillars. Test drilling indicates numerous pillars in areas of retreat mining were not removed. Ten test borings were conducted in areas mined by room and pillar methods and which were believed to be further mined by pillar removal, of these ten test borings, 4 encountered pillars and 6 encountered mined-out and collapsed zones. Based on the mine map and test borings conducted for this report, it is estimated that approximately 40 to 60 % of the coal bed mined by the Morrison Mine was removed and, therefore, pillars underlie approximately 40 to 60 % of the area. The ground surface topography in the area of Lots 3 through 7 show indications of low ridges overlying lines of pillars and shallow depressions in some of the mined areas. Results of the test borings found that the unmapped pillars also appear to correlate with topographic highs or other surface expressions. Test drilling determined the thickness of the coal seam mined by the Morrison Mine is generally 8 to ten feet thick under the site. Geophysical logs indicate the presence of one-foot thick coal at the floor and ceiling at some locations. This observed remaining coal correlates with published reports that suggest 6- 8 feet of coal was extracted during mining of the Morrison Mine. Test borings indicate the mined areas have experienced complete, or near complete collapse. The collapse appears to have filled most of the void space under the site in the Morrison Mine. No areas were encountered with voids larger than the 12-inch horizontal reach of the down-hole caliper tool. This indicates that mine openings are essentially filled with collapsed material. Observed possible voids are believed to be localized voids within the collapsed rock mass, likely associated with chimney structures, or interstitial voids. Mine maps and evaluation of site topography indicate there are no vertical shafts or former adits on the subject site. 20 349-Longs Peak Estates Subsidence Investigation Aerial photographic review indicated that many subsidence related features were observed to be consistently present in the area at, and proximal to, the site. The unchanging nature of the land surface suggests that most subsidence likely occurred within the decade following coal extraction. Data developed from this investigation may be useful in evaluating site strains to identify specific building envelopes within the site, if they exist. Conclusions 1. Most areas mined by the Morrison Mine have been filled by collapse of roof rock, bulking of the collapsed material, and/or sagging of the overlying strata creating some shallow subsidence topographic features at the site. 2. Based on the observed remaining void space and published information, it appears that the majority of the subsidence has reached completion and therefore should not pose a significant threat to site development. 3. The limited amount of void space present at the site indicates that evaluation of surface strains may identify areas of the site suitable for development. 4. Based on review of aerial photographs for the site and the surrounding area depressions have been present since 1949. The development of newer surface depressions were not observed during aerial photographic review through 1994. 5. Based upon the depth to observed groundwater, depth to the mine, length of time since mining activities have been performed and observations made during the drilling program suggest the likelihood of sudden ground failure at the surface is minimal. Recommendations I. Based upon the findings of this investigation, it appears suitable areas for development are present at the site. Site-specific strains should be evaluated to assess specific development sites. 2. Colorado statutes require disclosure of geologic and other natural hazard risks or problems to property buyers. Property buyers must be informed of the past mining activities at the site and the risk of subsidence and should be provided with appropriate technical documentation and reports. 21 349-Longs Peak Estates Subsidence Investigation Limitation of Liability These services were performed in accordance with the scope of work requested by Rinko LLC. This report is a scientific report and has been prepared exclusively to evaluate publicly-available printed information and findings related to the installation and logging of test boreholes with respect to the presence of underground coal mines and related physical land-surface subsidence. This report has been prepared for use of Rinko LLC, Propp Realty, and others to aid in the evaluation of potential future use of the property. This report has been prepared with the level of care ordinarily exercised by members of the profession currently practicing under similar conditions. Some uncertainty will always exist concerning the presence, or absence of, potentially adverse conditions at any particular property, irrespective of the rigor of the investigation. Accordingly, the Consultant offers no warranty, either expressed or implied, that adverse environmental or geologic conditions, other than those identified in this report, do not exist at the Site, or that such adverse conditions will not exist there in the future. Final siting and design of buildings and other structures for the development will need to be based on building-specific geotechnical investigations by a qualified soil and foundation engineer. Actual pillar extent and subsurface foundation conditions must be determined by geotechnical/soil and foundation investigations for any specific structure. Sincerely, E-21 ENGINEERING,INC. --c) (41A-0 y /ebb ergius anson, P.G. Paul F. Gottler Princ'.al Geologist Project Geologist Cc: John Rinko, Rinko LLC Appendices 1 - Figures 2- Logs of Test Borings and Cross-Sections 3—Geophysical Logs 4 — Copy of 1966 Final Morrison Mine Map of the area of Longs Peak Estates 5 —Copy of 1964 Final Clayton Mine Map of the area of Longs Peak Estates KeitI'e-2I shared/pgens049-Propp049-Longs Peak[states Subsidence Investigation Report 22 Bibliography and References 1. Amuedo and Ivey, et al, 1975, Coal Mine Subsidence and Land Use in the Boulder- Weld Coalfield: Boulder and Weld Counties, Colorado, Colorado Geological Survey Engineering Geology and Land Use publication EG-09. 2. Bell, F.G. 1988, The History and Techniques of Coal Mining and the Associated Effects and Influence on Construction. In Bulletin of the Association of Engineering Geologists, Vol. XXV, No. 4, pp. 471 — 504. 3. Colorado Division of Mines — Department of Natural Resources, Final Morrison Mine Map, Dated February 3, 1967. 4. Colorado Division of Mines — Department of Natural Resources, Final Clayton Mine Map, Dated December 16, 1942. 5. Colton, Roger B. and Lowrie, Raymond L., 1973, Map of the Mined Areas of the Boulder-Weld Coal Field, Colorado, US Geological Survey Miscellaneous Field Studies Map MF-513. 6. Dames and Moore (company), 1986, Boulder County Subsidence Investigation, Volume I — Executive Summary, prepared for State of Colorado, Department of Natural - -- Resources, Mined Land Reclamation Division 7. Deuel and Associates (later ATEC Associates, now ATC Associates), March 1985, Subsidence Potential of 9 Acres of the Scotts Acres Subdivision. Available at Colorado Geological Survey. Includes 3 Geophysical Logs, Lithology Log, and 1 Structure Map. Map Reference #7, CMLRD I.D. # 1230432932801. (CMLRD=CO Mined Land Reclamation Division) 8. Hatton, Tom, and Turney, J. E., 1984, Annotated Bibliography of Subsidence Studies over Abandoned Coal Mines in Colorado, Colorado Geological Survey Information Series publication IS-22. 9. Hynes, Jeffrey L., 1984, Tri-towns subsidence Investigation, Weld County, Colorado — A Community-Wide Approach to Hazard Evaluation and Land Use in Undermined Areas, Colorado Geological Survey Open File Report 87-3. Available at Colorado Mined Lands Reclamation Division, Inactive Mine Program, Colorado Geological Survey. 97 drill holes with lithologic logs. 10. Johnson, Erin J., and Himmelreich, John W., 1998, Geologic Hazards Avoidance or Mitigation — A Comprehensive Guide to State Statutes, Land Use Issues, and Professional Practice in Colorado, Colorado Geological Survey Information Series 47. 11. Turney, J.E. and Murray-Williams, L., 1983, Colorado Front Range Inactive Coal Mine Data and Subsidence Information, -Weld County, Colorado Geological Survey. 12. Turney, J.E., 1984, Subsidence Above Inactive Coal Mines, Information for the Homeowner, Colorado Geological Survey, Special Publication 26. 13. Weimer R.J. A Guide to Uppermost Cretaceous Stratigraphy, Central Front Range, Colorado; Deltaic Sedimentation, Growth Faulting and Early Laramide Crustal Movement in The Mountain Geologist, Volume 10, #3. July, 1973, pages 53-97. E-21 Engineering, Inc. Longs Peak Estates Subsidence Investigation Project No. 349 Weld County,Colorado Appendix 1 Figures FOR ST LI d c s I ._ FolColli — ••� �'�,.� 1:3%. W eel , J', love! •Black ollow 1 Mtn: 0L €:. It �; I imniih °r O w _Hurrich � - _J e7Eaton Har ,y fverynce 1.53.1 aleton •MI rMtn I 66e� ly Cer H°H • dle• 'n R dm•�, 2I WI •sort I Luc.rne ,° or, / _ d 1.7 •l 'Barnesvill 0 ar c Bracewell a s rdlmel5 Drake il , �• M Gill nito `edar ax 9 ' J 1 �1► J�� re' er �� 9•�hOH¢ r Y ns l 6641 `l 1 IIPo elf d v.ns� Heights-1 hb 1° He.11 f — •13.33 '•^•r_� •'! � I Camoion I �r El La Sal / J uner •9.' ii1Pd6. r •Blue Mtn • e© ' m J r it see yy _ 1 r-- J _ _ Berth,ud a �' r Pest a _ ° Walk a / 35n tw. 21Fr' vL y fQ° I , • 'latteVtne 1{-µe251 wne0.� o da ' ong o „7�� ``>,O •Table Harney ll lone`�V ' Tarim Fairview Vollma '1 r y •Pwk •Mill• ameztovn I Firestone oPS' UE — •' STUDY ARE kredenck G 4 'K esbur' Z II' 1 9591 33 • .Iae lkg 4 ;g,1 I tiaco�1.� I Fort i6 o. n • Hill in 6 a7�, al►i V• two91 •Crisman 9 ��'en .� r ,II2 Er on11 ' /4m5 2 •'mod ER 'Valm.: cite WallenbergPI I7•�I�j}~!� 68 4/ 67 lVI 66 �•Tomnik 64 — 63 agnolia 1 t yet o0 ��►��/�.1311111L•l l/— outs ille ,5 ac r/ ea 71 I _ I M.rsna r u�' r.r /L:rr Lak V y_ r�ri' 1!� 4 .••y eCroscent Ido do a lake k ' •"'. ats Son Bf••—• • Mender :.'-�l Creek . • Ia " a — t'wce. EI ,I �� rrstDal q1'J H: E ht5 Arood I© `Efly_ h`'•�.� ��41��I� � e in to �� I�Ry�+ erc City I gT — i �"• r/� a I co _ C. den r la a I: MMMnila4 Bennett y u P Wdnln -- oo;W`�Tg'��+�1 iii.;r �I\�d:ids: a o 0 Ma r. �1 !Lr�itiii��lal n u e 'ark, �' _ • Its `2 I4 I.ledale as !r 9 Kittredge Mo rison /• A R A P •Y E-21 Engineering, Inc. Proposed Longs Peak Estates — Project Location Map Weld County, Colorado 400 Corporate Circle, Suite K Golden, Colorado 80401 Figure 1 E-21 Project # 349 February, 2000 E-21 Engineering, Inc. Longs Peak Estates Subsidence Investigation Project No. 349 Weld County,Colorado Appendix 2 Logs of Test Borings And Cross Sections E-21 Engineering, Inc. Exploratory Boring Log Golden, CO 303-277-1548 Boring ID.W-1 Drill Method: Air Rotary with 6 1/2" Bit Grab Sampling Boring Results:Coal Mined/Subs. Start Time: 1505 1-3-01 Total Depth = 115' bgs Boring Location: 4435485 N End Time: 1735 1-4-01 UTM 13 N 0499344 E Proj. Loc.: Weld County, CO. E-21 Project#349 Ground Elev. = 5086.5' MSL Depth to Water= 105 ' bgs 1-4-01 LEGEND: Lost due to borehole collapse -- Boring Co. & Foreman: Precision Water Well, Craig Vigil Bentonite E-21 Geologist: Paul Gottler Bentonite and Cuttings Mix Start And I Comp!. _ End Depth Description Elev. Density Depth Lith. Log LEL O2 0 - 5 ' Orange-brown silt and clay, soft, massive 11 iii i 5 - 11' Grey, silt and clay, soft, massive 5081 @10' s I 11 - 12.5 ' Olive grey silt and clay, soft, massive 5075 2.3 12.5 - 14' Grey, silt and clay, soft, massive 5074 @15' > I 14 - 17' Dark brown, silt and clay, faintly laminated shale 5072 2.1 is 17 -23' Orange-tan silt and clay-shale 5069 @20' i4 I' 'i I — 23-25' Yellow-brown fine sand and silt, hard siltstone/sandstone 5063 2.6 17 I �I 25-28' Grey, silt and clay, soft shale 5061 @25' I 28 - 32' Yellow-brown silt and clay, soft shale 5058 2.2 23 — 32 - 34.5' Dark brown clay, soft shale 5054 @30' as I 34.5 -36' Grey silt, hard siltstone 5052 2.0 28 f 36 -42' Brown, soft, organic-rich, shale 5050 @35' _ 42 -43' Grey silt, hard siltstone 5044 2.1 32 i l 43-49' Brown, silt and clay, soft-shale 5043 @40' 315 l 49 - 51.5 ' Brown, silt and clay, harder shale 5037 2.2 36 li ( I 51.5 -52.5' Brown-grey siltstone 5035 @45' 'I' - — —?.5 - 54' Brown soft, faintly laminated shale, organic-rich 5034 1.9 42- Iii'-' " A -55.5' Black, coal seam (also noted on GeoPhysical Logs (GPL) 5032 @50 I i 55.5 -59 Dark grey-grey clay-shale 5031 2.2 m u, I— 59 - 75' Grey - light grey, very soft clay-shale 5027 @55' 41 a 01 ii . .I .1 l I LOST CIRCULATION AT 75 FT BELOW GRADE 2.4 = s r '' I 0.0 21 85' Black coal returned at 85 ft 5001 @60' s.s Stopped Drilling 1-3-01 at 95 ft bgs. 2.2 . r @65' Sq 105' Circulation Returns at 105 ft bgs, CHANGE TO "BUTTON BIT" 4981 2.2 105 - 106' Grey clay, soft-shale @70' 1- t — 106 - 106.5' Black coal 4980 2.3 kyl 106.5 - 112' Grey-dark grey moderately hard shale @75' ,' • Water entering borehole 2.5 -'r 441 o 112 - 126' Grey silt, hard siltstone 4974 @80' 75 —� t 2.9 it eu - x,7k _: 0.0 21 126 - 143 ' Few cuttings out of hole; Grey, hard shale from logs 4960 @85' T. 4::1:/: 1.4 143 - 151' Brown-dark brown clay-shale 4943 @90' a5 "r : r4:7 0.0 22 1.6 r 151 - 181' Dark brown clay, soft- shale 4935 @95' IIIIMII ' di4 f 181 - 185' Black coal 4905 @85' 1°5 Eri 1.4 �. f" 185 -202' LOST CIRCULATION AT 185 FT BELOW GRADE 4901 @90' ` : : Geophysical Logs show large voids at 193' bgs 1.6 -. r rj 202 -211' Grey, soft shale 4884 @95' „- iglirKg ,11 -215' Yellow brown, hard shale dishcharged from borehole 4875 '.a €sw Total depth of boring 215' below grade surface • , <l It xi Backfilled W-1 With: 8-50# bags of bentonite followed by bentonite cuttings mix to grade c'ta-21AcIive prof\349-Propp Subsidence Evaluatlon1349W-l.lo E-21 Engineering, Inc. Exploratory Boring Log Golden, CO 303-277-1548 Boring ID.W-2 Drill Method: Air Rotary with 6 1/2" Bit Grab Sampling Boring Results:No Mining/Subs. Start Time: 0922 1-3-01 Total Depth =99' bgs Boring Location: 4435374 N End Time: 1112 1-3-01 UTM 13N 0499340 E Proj. Loc.: Weld County, CO. E-21 Proj. # 349 Ground Elev. = 5085.5 ' MSL Depth to Water= Boring Dry on 1-8-01 LEGEND: ,,. Lost due to borehole collapse — Boring Co. & Foreman: Precision Water Well, Craig Vigil Bentonite E-21 Geologist: Paul Gottler I I it Bentonite and Cuttings Mix Start And Ir Comp. End Depth Description Elev. Density Depth Lith. Log LEL O2 0- 15 ' Orange-brown silt and clay, soft, massive 5085 @10' %.+.',A, 2.3 4 . ; 0.0 21.0 15 - 18' Yellow-brown, hard, fine grained sandstone 5070 @15' 6 "` III r I 2.4 18 - 35' Grey-light grey, clay, soft shale bedrock wl orange Fe precip. 5067 @20' - +` I 0.0 21.2 2.7 ill @25' 14 i;i III 35 -38.5' Red-brown, silt, hard, siltstone 5050 2.2 14 38.5 -44' Grey-brown silt and clay interbedded shale and siltstone 5047 @30' 2.1 23 -" @35' r 44 -45' Black coal seam 5041 2.8 Zq III I I II;'ll II 0.0 20.9 @40' 31. hul'IIIl — 45 -47' Grey- light grey, very soft clay-shale 5040 2.0 @45• I 47 -52 ' Red - brown to orange, hard siltstone 5038 2.4 +` 41 eathtIl( 2 - 53' Grey- light grey, very soft, organic-rich shale 5033 @50' 43 2.9 rl,, p` 53 -55' Black coal seam 5032 I I II @55' fl 55 -70' Grey- light grey, very soft clay-shale 5030 2.4 54 s iII il IIIII _ @60' 51 2.1 61 WWII:,,i, ;II @65. e P 70 - 74' Grey-dark grey, organic-rich shale with a few coal laminae 5015 2.2 6c s I I @70' cy5 h;ll I "I 0.0 20.9 2.1 74 -75.5' Black coal soft, "dirty" 5011 a9 75.5 -78' Grey, hard, organic-rich shale 5010 @75' I 0.0 20.9 1.6 81 — 78 - 79' Grey-dark grey moderately hard shale 5007 e4 ti 86 ' 79 - 84' Grey, hard, organic-rich shale 5006 3 i l 0.0 20.9 @80' c° 2.4 95 _ a @85' 84 - 93' Black Coal (Likely mined zone) 5001 1.5 """ (Elevation top of coal = 5,001 ft MSL ; 9.0 ft thickness) @90' tot ---i 0.0 20.9 1.5 — 93 -99' Dark grey-grey shale 4986 @95' 2.4 .." .'' Backfilled W-2 With: 2-50#bags of bentonite followed by bentonite cuttings mix to grade c'.,e.21Acbve pnj1349-Pfopp Subsidence Eveluulion\349W-P.IQO E-21 Engineering, Inc. Exploratory Boring Log Golden, CO 303-277-1548 Boring Boring ID. W-3 Drill Method Air Rotary with 6 1/2" Bit Grab Sampling Boring Results: No Mining/Subs. Start Time: 1245 1-3-01 Total Depth = 110' bgs Boring Location: 4435291 N End Time: 1350 1-3-01 UTM 13 N 0499333 E Proj. Loc.: Weld County, CO. E-21 Project#349 Ground Elev. = 5085.5 ' MSL — Depth to Water= Boring Dry on 1-8-01 LEGEND Bentonite Boring Co.& Foreman: Precision Water Well, Craig Vigil Ilk '; Bentonite and Cuttings Mix E-21 Geologist: Paul Gottler Start And Compl. LEL O2 End Depth Description Depth Density Depth Lith. Lo• 0- 5 ' Orange-brown silt and clay, soft, massive Y„l 1 i 191, 5 - 10' Grey-light grey, clay, soft shale w/orange (Fe?) precipitate 5080 @10' gam, II -- 10 - 16' Yellow-brown, hard, fine grained sandstone/siltstone 2.3 S •,, @15' 41 II 16 -25' Grey-light grey, clay, soft shale 5069 2.1 10 111 0.0 20.9 (Bedrock contains gypsum and iron (?) precipitate) @20' 2.6 16 25 -45' Brown-dark brown, silt and clay, soft-moderately hard, shale 5060 @25' with a few silstone laminae 2.2 I 'a'1 @30' 2.0 25r IIII45 -48' Black coal seam 5040 @35' I 0.0 20.9 - 2.1 ,.. ,I 48 - 50' Dark grey-black, clay, hard shale 5037 @40' JJ 50 - 51' Grey-light grey, clay, soft shale 5035 2.2 s. + I I I _ @45' P 1 - 53' Grey-light grey moderately hard siltstone 5034 1.9 w @50' „a• 'III' I I HidI I 53 —60' Grey-light grey, clay, soft shale 5032 2.2 45 @55' 48 II IIII 60 - 72' Dark grey-black, organic-rich, shale 5025 2.4 S° I II 0.0 20.9 @60' 53 I I 72 - 73' Black coal 5013 2.2 . il 73- 73.5' Dark grey-black,organic-rich,hard shale 5012 @65' •41' I 4'I, !'1''I 73.5 -74.1" Black coal 2.2 Go „; 74.1 - 83' Grey-light grey, clay, soft shale 5011 @70' ,II Organic content increases with depth 2.3 r @75 i 2.5 yi' — 81 - 91' Black coal 5004 @80' 74 NI ! ' " 0.0 20.9 (Likely mined zone of 8.0 ft thickness) 2.9 341 ,... '111 (Elevation top of coal = 5,004 ft MSL) @85' 1.4 11"" 91 -93' Dark grey-black, soft-hard, organic-rich, shale 4994 @90' 83 ' I1 II 1.6 'II 93 -98' Grey, hard, siltstone 4992 @95' 2.5 41 a— d r' 93 98- 100' Grey-light grey, clay, soft shale 4987 0.0 20.9 @100' 98 I 100 - 106' Grey, hard, clay shale 4985 2.6 loo riaj'at , ILL! III -_ 104' @105' Lob 40 — 106 - 110' Grey-light grey, clay, soft shale 4979 2.5 AS" ILO 110' Backfilled W-3 With: 2-50#bags of bentonite followed by bentonite cuttings mix to grade c'1e-21Nclive pmj\348-Propp Subsidence Evaluation\34BW-3log E-21 Engineering, Inc. Exploratory Boring Log Golden, CO 303-277-1548 Boring ID.W-4 Drill Method: Air Rotary with 6 1/2" Bit Grab Sampling Boring Results:Mining/Subs. Start Time: 1456 1-5-01 Total Depth = 102' bgs Boring Loc. 4435213 N — End Time: 1635 1-5-01 UTM 13 N 0499324 E Proj. Loc.: Weld County, CO. E-21 Project#349 Ground Elev. = 5088 ' MSL Depth to Water= Boring Dry on 1-8-01 LEGEND: Lost due to borehole collapse Boring Co. & Foreman: Precision Water Well, Craig Vigil Bentonite E-21 Geologist: Paul Gottler I Bentonite and Cuttings Mix Start And Compl. LEL O2 End Depth Description Elev. Density Depth Lith. Lo. 0-4 ' Brown silt and clay with a little fine sand, soft, massive I 4 -6' Dark borwn, soft shale 5084 @10' 4.g- I IL — 6 - 16' Grey-light grey, clay-soft shale w/orange Fe (?) precipitate. 5082 2.4 t. q @1F 16- 19' Orange-brown, hard siltstone 5072 2.8 ' I 'I I I( 19 - 23' Orange-brown clay and silt, moderately hard shale 5069 @20' 15 2.3 16 , I 23 -29' Grey-grey brown clay, soft shale/claystone 5065 @25' 2.0 29 -31' Grey-light grey hard siltstone 5059 @30' - ms. ii 31 -41' Brown grading to dark brown clay shale 5057 2.4 @351 1 II, 41 -43' Orange-brown, hard siltstone 5047 2.1 @40' 35 I 43 - 52' Grey-grey brown -grades to dark brown clay, soft shale 5045 2.2 38.5 I @45, � 52 - 54' Black coal 5036 2.3 44 'a , I �' @501 47 !Ii ii -- 54 -59' Dark grey-black, organic-rich, hard shale 5034 2.2 @55• sz —J s 3 ' 59 -61' Grey-light grey hard siltstone 5029 2.2 I '' -- 61 -66.5' Dark grey-dark brown, soft shale 5027 @60' ss 1 66.5 -69.5' Grey-light grey hard siltstone 5022 2.0 I II i 69.5 -74' Dark brown- black, organic-rich shale with some coal laminae 5019 @65' ,,, ilIId' 2.2 I I 74 -75' Black coal 5014 @70' 75 -81' Dark grey-grey, soft, shale 5013 1.8 .o " I ulI III @75' «..' 2.3 74 III 75.5 ri IIIIif 81 - 84' Black-dark brown shale 5007 @80' 7! , I 2.3 79 a . 84 -86' Dark grey-grey, hard, siltstone 5004 94 86 - 95' Lose Circulation at 95' (Likely mined zone @ 90' ) 5002 @85' Wood chips, dark brown shale (Elevation top of coal =4,998 ft) 4998 2.0 and other inconsistent debris out discharge pipe I ,I III (Air observed to be venting out of boring C-3, no air at W-3) @90' 13 -r: y, 1.4 a�.r_u`,' I 99 Hard surface encountered at 95 feet; � 94' believed to be bottom of mined zone @95' 2.0 95 - 102' Grey-light grey, clay, moderately hard, shale 4993 @98' 100' 2.3 7717! 102' Backfilled W-4 With: 2-50# bags of bentonite (100 -94' bgs)followed by bentonite cuttings mix to grade c b-21 Active proiv949-Pmpp Subsidence EvalualinnVL9W-4.Lp E-21 Engineering, Inc. Exploratory Boring Log Golden, CO 303-277-1548 Boring ID. C-1 Drill Method: Air Rotary with 6 1/2" Bit Grab Sampling Boring Results:Not Mined/No Subs. Start Time: 0905 1-5-01 Total Depth = 119' bgs Boring Location: 4435422 N End Time: 1020 1-5-01 UTM 13 N 0499377 E Proj. Loc.: Weld County, CO. E-21 Project# 349 Ground Elev. = 5086 ' MSL Depth to Water= Boring Dry on 1-8-01 LEGEND_,.,_ Lost due to borehole collapse — Boring Co.& Foreman: Precision Water Well, Craig Vigil Bentonite E-21 Geologist: Paul Gottler l ft kl Bentonite and Cuttings Mix Start And Comp End Depth Description Depth Density Depth Lith. Log LEL O2 0 -4 ' Brown silt and clay with a little fine sand, soft, massive w7.4l 4 - 9' Grey, soft shale 5082 @10' 4 "'-'I HI 2.1iii 1 — 9 -20' Brown, soft shale with occassional grey silt laminae 5077 @15' 9 2.4 - I . . till @20' .- 20 -22' Grey-light grey, soft shale 5066 2.1 22 -23' Brown, soft-shale 5064 @25' I 23 - 32' Grey-light grey, very soft shale 5063 2.4 zZ - I III _ (caliper to 5.9" at 30 ft depth) @30' t3 32 -43' Brown, moderately soft shale 5054 2.2 •D" @35' l 43-47' Grey-grey brown, moderately soft shale 5043 2.2 32 , III I I l @40' 47 -48.5' Black coal 5039 2.1 l III 48.5 -50' Grey,soft shale 5038 @45' _ - 2.1 0 -52' Dark brown-red brown, moderately hard shale 5036 @50' 43 ' MI ii 1 I 52 -53' Dark grey-black, organic-rich shale 5034 2.5 4? I�II I 53 -55' Black coal 5033 @55' 48.5 • 57- 59.5 Grey-light grey hard shale/siltstone 5029 2.2 S3z III I I I 59.5 -60' Dark brown, moderately hard shale 5027 @60' 5D # VIIIIII III 60- 73' Grey, soft shale 5026 2.2 5,5 _-vs lI L Iii @65' S9S "Pr- 73 - 74' Black coal 5013 @70' +` I iI 74 - 84' Dark grey, soft shale (fractured rock; caliper to 7.9") 5012 2.3 I I 84- 85.5 Dark grey-black, organic-rich shale 5002 @75' x 1 I I III 2.4 ,r !III 85.5-94' Black coal (Likely mined zone) 5000 @80' aid I.I . 0.0 20.6 (Coal thickness =8.5 feet) 2.2 .o Ill Ill I @85' ,:a. I� y�ll 1.4 — 94 -99' Grey, shale, moderately hard layer at 96' depth 4992 @90' 8845 • I I i I Ill 0.0 20.9 99 - 102' Grey, soft shale 4987 @95' 2.6 I I 102 - 104' Brown-light brown, soft shale bedrock 4984 @100' 11 Jill 2.3 omitI I I; 104- 116' Grey, soft-moderately hard shale 4982 @105' 99 ,q i I hi I 2.4 102 112 @110' Loo 2.6 w — 116 - 119' Grey, hard-very hard shale 4970 Nor 118' .► V, 119' Backfilled C-1 With: 2-50# bags of bentonite (118 -112' bgs)followed by bentonite cuttings mix to grade -- c\e-21AIXive p.oj349.Prop.Subsidence Evalua11onls4eC.ilop E-21 Engineering, Inc. Exploratory Boring Log Golden, CO 303-277-1548 Boring ID. C-2 Drill Method: Air Rotary with 6 1/2" Bit Grab Sampling Boring Results:Coal Mined/Subs. Start Time: 1107 1-5-01 Total Depth = 103' bgs Boring Location: 4435324 N End Time: 1222 1-5-01 UTM 13 N 0499380 E Proj. Loc.: Weld County, CO. E-21 Project#349 Ground Elev. = 5090 ' MSL _ Depth to Water= Boring Dry on 1-8-01 LEGEND: ,,,:Lost due to borehole collapse Boring Co. & Foreman: Precision Water Well, Craig Vigil Bentonite E-21 Geologist: Paul Gottler I III I Bentonite and Cuttings Mix Start And Compl. LEL O2 End Depth Description Elev. Density Depth Lith. Lo 0- 8 Brown fine sand, soft, massive @10' — 8 - 10' Brown, soft shale 5082 2.1 „ ' 10 - 12' Grey-light grey, soft shale 5080 1 o y 1 12 - 14' Brown, soft shale 5078 @15' n I 14 - 18' Grey-light grey, soft shale 5076 3.8 14 ' ' P I @20' ..... Ili 18-21' Brown, soft shale 5072 2.2 1g "' I' ' 21 -23' Grey-light grey, soft shale with some gypsum crystals 5069 @25' 21 'a I — 23 -26' Brown shale 5067 2.3 �3 .rS I 26 - 35' Grey, soft shale with orange (Fe?) precipitate 5064 @30' ZG .- i, 2.4 — 35 -38' Brown-grey, shale bedrock with orange (Fe?) precipitate 5055 @35' J I' ! I II 38 - 38.2' Dark brown soft shale 5052 2.5 3S r I" I 38.2 -41.5' Grey, soft shale @40'2.3 38 — I I '.5 -44' Grey, hard, siltstone 5048 @45' 41.5Its I I 44 -46' Brown-red brown, soft shale 2.3 It 44 I�, LI 46- 51' Grey, with brown staining, moderately hard shale 5044 @50' 2.2 51 - 52' Dark grey-black, organic-rich, moderately hard shale 5039 @55' si 53 -55.5' Black coal 5038 3.2 I I i I' 55.5 - 57' Dark grey-black, moderately hard shale 5035 @60' 55'5 I I I!HiI 57 - 58' Grey, soft, shale with gypsum crystals 5033 2.4 58 'I l 58 -65' Grey, soft shale 5032 @65' 11 2.0 65 — IH I I 65 -76' Dark brown shale w/some black shale, and hard siltstone laminae 5025 @70' 1 2.4 a 'I ,IIii,Illil II 76 - 78' As above with hard grey siltstone layer 5014 @75' �,, 2.4 76 lei H ' I 78 -81' LOSE CIRCULATION AT 78 FT BELOW GRADE 5012 @80' Dark grey shale with some black coal discharged 1.9 78 2 I,I 81 -97' LOSE REMAINING CIRCULATION AT 81 FT BELOW GRADE 5009II @85' IIiIIII Geophysical logs as: 2.0 3 I ' ^I ' Density less than 2.0 from 87' - 97 ' below ground surface (bgs) 3 II III, Three arm caliper found borehole expanded at two sites to 7.2 " @90' y Resistivity increase 87 - 97 bgs 1.3 9a I I Natural Gamma increase 88 -96' bgs @95' IIIIII I I I II,I 1.2 102 �• 96 —A7- 102' Dark brown, organic-rich, moderately hard shale 4993 @100' - Drilling on hard surface and circulation returns at 97 ft bgs 1.2 — 102 - 103' Grey, hard-very hard siltstone 4988 102 `, ,1''""1 103 Backfilled C-2 With: 2-50# bags of bentonite(102 -96' bgs)followed by bentonite cuttings mix to grade — cle-PlAUive pcaj34avmyp subsidence EVBivaIlon349Gdiog E-21 Engineering, Inc. Exploratory Boring Log Golden, CO 303-277-1548 Boring ID. C-3 Drill Method: Air Rotary with 6 1/2" Bit Grab Sampling Boring Results: Minining/Subs. — Start Time: 1253 1-5-01 Total Depth = 103' bgs Boring Location: 4435252 N End Time: 1415 1-5-01 UTM 13 N 0499384 E — Proj. Loc.: Weld County, CO. E-21 Project# 349 Ground Elev. = 5089 ' MSL Depth to Water= Boring Dry on 1-8-01 LEGEND: --:.Lost due to borehole collapse _ Boring Co. & Foreman: Precision Water Well, Craig Vigil Bentonite E-21 Geologist: Paul Gottler Bentonite and Cuttings Mix Start And I Comp. LEL O2 End Depth Description Elev. Density Depth Lith. Lo. 0 -2' Brown fine sand, soft, massive a 9!I I 2 -6' Grey-light grey, clay-soft shale, with orange&white precip. 5087 L A lil 6 -7' Brown-dark brown, soft shale 5083 @10' 6 n I — 7 - 7.5' Grey-light grey, soft shale 5082 2.2 8 7.5 - 8' Brown-dark brown, soft shale @15' -- . 8-20' Grey-light grey, soft shale 5081 2.1 it I — !II 20 -25 Grey-light grey, soft shale with gypsum (possible stylolites) 5069 @20' zo ' ° I 2.3 A p,i Al 25 -27.5' Grey, hard, siltstone 5064 @25' 2s d II' 27.5-48' Interbedded brown and grey, shale 5062 2.8 z .s lilt d with orange (Fe?) precipitate and occassional gypsum @30' 2.3 S II I — @35' c mild 48 -49' Dark grey grading to brown, soft shale 5041 2.2 iN ' !uill i,,II 49 - 52' Brown-light brown grading to grey soft shale 5040 @40' li — 2.7si II' I l I J2 - 56' Grey-dark grey, shale 5037 @45' I 56- 58' Dark brown, moderately hard, organic-rich, shale 5033 2.1 48 _ 58 -61' Black coal 5031 @50' 49 2.4 52I "III 61 -65.5' Dark grey-black, organic-rich, shale 5028 @55' 56 1 LI III III I 65.5 -67' Grey, hard, siltstone 5024 2.2 5a .�.,J II�I Ili illll — 67 -71' Grey, soft shale 5022 @60' 1 1.6 71 - 73' Dark grey, soft, shale 5018 @65' 45 noir. i — 73 - 79.5' Dark grey shale with some black shale, and black coal laminae 5016 2.7 Of ,: Ili @70' , I l d 79.5 -80.5 Grey, hard, siltstone 5010 2.3 °4' II _ 80.5 -81' Dark brown, softer, shale 5009 @75' l l 81 - 83' Grey, hard, siltstone 5008 2.2 :. 13 r, 83- 86' Dark brown, grading to dark grey, softer, shale 5006 @80' i9S eo s 86 -87.5' Grey, hard, siltstone 5003 2.6 g I — 87.5 -94' Grey, soft, shale 5002 @85' 86 '. ' 94 - 96' Dark grey- black, organic-rich, shale bedrock 4995 2.1 cos I 96- 105' LOST CIRCULATION AT 96 FT BELOW GRADE @ Coal 4993 @90' ,.,, ill i ' III — Geophysical logs as: 2.2 I Density< 2.0 from 96 to logged depth of 101 ' bgs @95' 94 d II I Three arm caliper found borehole expanded at to 9.4 " at 98 ft 2.2 46 ' II, in , Resistivity increase 97' bgs to total depth logged @100' 3 96 Natural Gamma increase at 96' bgs to total depth logged 0.6 c 405 - 112' Drilling on hard surface at 105 ft, no circulation return 4984 los 102 — Leo r , .. , Backfilled C-3 With: 2-50#bags of bentonite (102-96' bgs) followed by bentonite cuttings mix to grade - .‘e-21Ac1ive proj\349-Propp Subsidence Evalualionl3490-3Iog E-21 Engineering, Inc. Exploratory Boring Log Golden, CO 303-277-1548 Boring ID. C-4 Drill Method: Air Rotary with 6 1/2" Bit Grab Sampling Boring Results:No Mining/Subs. Start Time: 1414 1-8-01 Total Depth = 116' bgs Boring Location: 4435194 N End Time: 1533 1-8-01 UTM 13 N 0499399 E — Proj. Loc.: Weld County, CO. E-21 Project# 349 Ground Elev. = 5092.5 ' MSL Depth to Water= Boring Dry on 1-8-01 LEGEND: Lost due to borehole collapse _ Boring Co. 8, Foreman: Precision Water Well, Craig Vigil Bentonite E-21 Geologist: Paul Gottler Bentonite and Cuttings Mix Start And Ir Comp. LEL O2 End Depth Description Elev. Density Depth Lith. Lo! 0- 3' Brown fine sand and silt, soft, massive 5.4. 4:474 p 3 -4' Red-brown, siltstone, hard 5089 @10' 4 ` 4 - 11' Brown-dark brown, soft shale with Fe (?) precipitate in fractures 5088 2.7 I, _- @15 - q1 11 - 17' Grey-light grey soft shale with gypsum and iron oxidation 5081 2.8 11 9 @20' IIIII — 17 - 20' Brown, clay, soft with black oxide coating 5075 2.7 17 •� 20 -24' Brown clay, soft, out of borehole as spheres-shale 5072 @25' Zo 1" I I.. 24 -29' Grey-grey brown clay, moderately hard shale 5068 @30' 24 — 2.7 ,: i 29- 31' Grey, soft shale 5063 @35' ?? + 1,, I HI 31 -33' Red brown-orange, soft shale, harder with depth 5061 3.0 31 rr -< h6 33 - 35' Grey, very hard, siltstone 5059 @40' 33 ®'jl 35 -38' Brown-grey soft shale with Fe precipitation 5057 2.9 38 I.—I I 38 -41' Grey, shale, moderately hard 5054 @45' ' �. I I III I — --41 -43' Red brown-orange, moderately hard shale, harder with depth 5051 2.9 43 . 'I II, @50' .►`.I' ill„ I 43-46' Grey, clay, soft shale 5049 2.7 46 _. I 46 -52' Dark brown-brown, soft shale 5046 @55' I 2.8 52 I' 11 11 52 - 58' Grey, soft shale 5040 @60' °° III II 2.7 SS I1i1 1 i II II III 58-66' Dark grey, soft shale 5034 @65' M, 2.8 1 66- 71' Dark brown, grading to dark grey, organic-rich soft shale 5024 @70' .. Y 66 w 1! — 71 -73' Dark grey, soft shale 5021 2.9 .ir 1 I I! I 73 -74.5' Grey, hard, shale/siltstone 5019 @75' 71 e, ,., 1, I , 74.5 -78' Grey, soft shale 5018 3.0 75 z! III @80' 745 ri iuli I 78 - 80' Grey, moderately hard- hard shale 5014 2.9 78 :RI I 80 -88' Grey, shale, harder with depth 5012 @85' 80 I 2.6 : II II 88 - 91' Grey, hard, siltstone 5004 @90' too, ,. 91 -93' Dark grey-dark brown, softer, shale, 5001 2.8 8g ' it, I I!I I 93 -94.5' Dark brown, organic-rich, softer shale 4999 91 — 94.5 - 96' Dark grey-dark brown, organic-rich, soft shale 4998 @95' 9q3 96- 97' Black coal 4996 2.6 ? 1 YG l 97 - 100' Grey, soft shale 4995 @100' q7 p!11du I I 108 Agre 100- 102' Black-dark grey, soft, shale 4992 2.6 10o @105' 102, X02 - 112' Black coal 4990 1.7 (Likely mined zone, 10.0 ft thick.) (Elevation top of coal=4,990 ' ) @110' 114 114 - 115' Dark brown, organic-rich, soft shale 4984 1.8 115 - 116 Dark grey- black, soft shale 4983 112 Sr_.,. Backfilled C-4 With: 2-50# bags of bentonite (114 -108' bgs)followed by bentonite cuttings mix tide c'.N-21Anme p,oll349-Pmpp subsidence EvematinnVNsc-4-I0Q E-21 Engineering, Inc. Exploratory Boring Log Golden, CO 303-277-1548 Boring ID. E-1 Drill Method: Air Rotary with 6 1/2" Bit Grab Sampling Borehole Results: Collapse Complete — Start Time: 0918 1-8-01 Total Depth = 105' bgs Boring Location: 4435377 N End Time: 1058 1-8-01 UTM 13 N 0499464 E — Proj. Loc.: Weld County, CO. E-21 Project#349 Ground Elev. = 5088.1 ' MSL Depth to Water= Boring Dry on 1-8-01 LEGEND: Lost due to borehole collapse — Boring Co. & Foreman: Precision Water Well, Craig Vigil Bentonite E-21 Geologist: Paul Gottler I II Bentonite and Cuttings Mix Start And I Comp. _ End Depth Description Elev. Density Depth Lith. Log LEL O2 0 -3' Brown silt and clay, soft, massive 3 3 -5' Brown, fine sand, soft 5085 @10' 5. , "( 5- 10' Brown-dark brown, soft shale with Fe (?) precipitation in vertical and 5083 2.4 horizontal fractures to p 10 - 11' Grey-light grey clay, soft shale 5078 it ii 4 h I 11 - 14' Brown, soft shale @15' i9 a — 14- 16' Grey, soft shale with Fe (?) precipitation in fractures 5074 2.6 1-6 T I 16 - 19' Brown, moderately hard shale 5072 @20' Z1 - II III l 19 - 21' Grey-brown, soft shale 5069 2.2 y, I 21 -25' Brown, moderately hard shale 5067 zs II ' Brown-red brown, hard silstone 5063 25'26 -27' Brown-red brown, hard fine-very fine sandstone 5062 @3.6 27 �s- It 27 - 32' Brown grading to grey, soft clay, shale 5061 @30' 32 'III 2.2 34 ga 32 - 34' Grey, moderately hard shale 5056 @35' 1 34 - 38' Brown, soft shale 5054 2.4 38 — - @40' ail 8-41' Grey soft, with orange/Fe precipitate, shale 5050 2.2 ,. l il @45' 48 it 41 -46' Dark brown-brown, soft shale 5047 2.4 hI @50e Sl 'II m1 II 46 -48' Brown -dark brown, hard shale 5042 3.2 '"' I II;III t 1! @55 - 54 -^- I 48 - 51' Grey-brown, hard, siltstone 5040 2.3 I 51 -57' Grey-dark grey-dark brown, soft shale 5037 @60' "` � Avo, l;l l 2.2 64.5 — CS LL,II 57- 59' Grey-brown, harder, shale 5031 @60' *o 59-64.5' Grey-dark grey, organic-rich soft shale 5029 2.6 — 64.5 -68' Black coal 5024 @65' 75 1 I i 20.9 0.0 68 -70' Dark grey- black, organic-rich, soft shale 5020 1.4 " PL 11IC iII 70 - 75' Grey-dark grey, grades from soft to moderately hard shale 5018 @70' a >, 2.4 83 75 -83' Grey- brown, soft, shale 5013 @75'2. s} 83 - 87' Grey- brown with some dark brown, softer, shale 5005 @80' 88.5 .. — 87 - 88.5' Grey-brown, hard, siltstone 5001 2.0 ! I I 88.5 -95' Dark grey- black, soft shale with pieces of coal still returning 5000 @85' ;' Il GPL Identifies Very Irregular Densities Starting @ 4999' 2.1 e0 96 @90' A— ar GPL Irregular Densities Through Total Borehole Depth 1.8 — 95' LOSE CIRCULATION AT 95 FT BGS 4993 @95' 70$ WI (Former Mined zone) 2.2 — 105' Hard drilling, no return of circulation, grey dust(siltstone?) 4983 @100' 102 out discharge pipe (Hole Collapse, lose bottom 3 ft.) 1.6 `'F"10' Backfilled E-1 With: 2-50#bags of bentonite (102 -96' bgs)followed by bentonite cuttings mix to grade — c\e-21Aclive preA 49 Propp Subsidence Eveluelion\349 E-0.4p E-21 Engineering, Inc. Exploratory Boring Log Golden, CO 303-277-1548 Boring ID. E-2 Drill Method: Air Rotary with 6 1/2" Bit Grab Sampling Borehole Results: Collapse to 78' bgs Start Time: 1139 1-8-01 Total Depth = 105' bgs Boring Location: 4435305 N End Time: 1334 1-8-01 UTM 13 N 0499475 E Proj. Loc.: Weld County, CO. E-21 Project# 349 Ground Elev. = 5096.0' MSL Depth to Water= Boring Dry on 1-8-01 LEGEND Lost due to borehole collapse — Boring Co. & Foreman: Precision Water Well, Craig Vigil Bentonite E-21 Geologist: Paul Gottler Bentonite and Cuttings Mix Start And Compl. End Depth Description Elev. Density Depth Lith. Log LEL O2 0 - 8' Brown silt and clay, soft, massive 5096 - ' I l Ili q'il @10' ' 8 - 15' Grey-light grey clay, soft, shale with Fe oxidation in fractures 5088 2.0 , I i1 @15' & iI 15 - 16' Grey-light grey-brown clay, soft, with black oxidation (?) coating 5081 2.2 7 , l I l 16 - 17' As above with no black coating 5080 @20' 15 ,ifi — 17 -22' Grey, soft shale with some gypsum crystals 5079 2.4 f3 a'_ I Hi I 22 -23' Grey, hard, silstone 5074 I v 23 -24' Grey, soft shale 5073 Ez —_ - 24 -25' Grey, hard, silstone 5072 @25' 1 ' 'III I 25 -25.5' Grey-light grey clay, moderately hard shale 5071 2.4 t8 "" j I I 25.5 - 28' As above, only softer @30' 30 �'', I 2.5 at i ill II 28- 30' Grey, hard, siltstone 5068 @35' y I' 30 - 37' Brown grading to grey, soft shale with some hard siltstone 2.3 31 I J 37 -43' Brown, soft shale, weathered, with Fe in vertical fractures 5059 @40' 1- III II 3.2 3 134 W` 44 1 43 -44' Grey soft shale 5053 @45' I'I -1 44 -51.5' Grey, grey-brown-dark brown soft shale 5052 1.9 @50' 51.5 s9 III Ld 51.5 - 53' Brown, hard, siltstone 5045 2.2 — P I @55' 53-67' Grey-light grey, very soft, shale 5043 4.8 �I III 'I. i 67 -68.5' Brown-grey-dark grey organic-rich, soft shale 5029 @60' I 2.3 ... III 68.5 -72.5' Black coal 5028 @65' Us gm_ 'ITI' @70' 72.5 -74' Grey-dark grey, soft shale with some gypsum crystals 5024 0.6 3% @70' 72s !e"! @c-3 - 74 -78' Grey, hard siltstone 5022 2.2 74 i i ' 4% @75' ?8 Iw I @0-2 78 - 96' LOSE CIRCULATION AT 78 FT BGS (Density erratic to T.D.) 5018 1.6 Ali 1% Coal and grey shale discharged (Collapse from T.D. to 5018') @80' . !PHr, '.I, @E-1 Geophysical logs from 78 -collapsed depth of 88' bgs as : 2.1 7 • @80' Density< 2.0 from 76 to 81 ' below ground surface (bgs) III8% Three arm caliper found borehole expanded to 7.2 "at 81 ft depth @85' n 'I I @c-3 . Resistivity increase 76-77' bgs 2.1 II•-. '► qh 7% Natural Gamma 100-125 CPS through interval (normal shale range) 7 it: • c-2 @90' 96.5 ;. 82 — 96.5' Hard Drilling, no return of circulation 5000 2.4 q9 88 Hole Collapse ��r'"tj, l ° Backfilled E-2 With: 2-50#bags of bentonite (88 -82' bgs)followed by bentonite cuttings mix to grade — c M-3lAUlve goj1349-Pmpp Subsidence Evaluation\349 E-?Lq x oratory oring Log - - ngtneenng, nc. p Golden, CO 303-277-1548 Boring ID. NL-1 JDrill Method Air Rotary with 6 1/2" Bit Grab Sampling Boring Results: No Mining/Subs. Start Time: 1648 1-8-01 Total Depth = 99' bgs Boring Location: 4435574 N 13 N 0499209 E End Time: 1750 1-8-01 UTM J Proj. Loc.: Weld County, CO. E-21 Project#349 Ground Elev. = 5082.0' MSL Depth to Water= Not Evaluated LEGEND: Bentonite JBoring Co. & Foreman: Precision Water Well, Craig Vigil NH Bentonite and Cuttings Mix E-21 Geologist: Paul Gottler Compl.LEL O2 Start And If End Depth Description Elev. Density Depth Lith. Lo! 0 -3' Brown silt and clay, soft, massive 5079 @10' 3 3 - 5' Brown fine sand, soft, massive 5077 35 NI J 3.0 5-8' Grey-brown clay, soft shale g «� 8-22' Brown clay, soft shale 5074 @15' I 3.0 If @20' r 1 I'. 22 -32' Grey, soft shale with some gypsum crystals 5060 2.2 I @25' ' Ill i 32 -33' Grey, harder, shale 5050 2.2 z2. 33 -39' Grey-brown, soft shale 5049 @30' " I II 2.2 1 ill 39 -43' Brown, moderately hard shale 5043 @35' 1 2.4 33 43 -46' Dark grey-dark brown, soft shale 5039 @40' a III 2.3 v II II I 46 -47' Black coal 5036 @45' 37 am,I I i j —a7 - 50' Dark grey-dark brown, soft, shale 5035 1.8 @50' 43 s I I FAI 50- 51.5' Black coal 5032 2.2 4fi ,II"'i II'I�I it 51.5 -54' Grey, grey-brown shale bedrock, soft 5030 @55' 'IS' (Getting dark, working under artificial light source) 2,8 Sisii s l 54-70' Grey shale, hard with some very hard siltstone horizons 5028 @60' 54 IO III' 2.4 fill @65 obeliI 2.4 «. 41I II! "' j 70-74' Dark brown, moderately hard shale 5012 @70' ism I II II, 2.2 , ri IP 74-74.2' Black coal 5008 70 ...___I l!,I,, j 74.2 -76' Grey-dark grey, soft shale @75 76 ,. 'I� !: 1.6 se 76 -78' Dark brown-black, organic-rich, soft shale 5006 so vsII 78- 80' Grey, hard siltstone 5004 @80' i I 3.2 pill' 80- 82.5' Dark grey-black, organic-rich soft shale 5002 91S ii!, I opi1 "' ' `I I i' 82 @85' .4ftII 82.5 -91.5 Black coal (Likely Mined Coal) 4996 1.3 99 '� II (Coal seam thickness=9.0 ft) @90'(Elevation of top of coal =4996' MSL) 1.3 93 .5 -99' Grey shale, soft, getting harder with depth @92.4 99 Backfilled NL-1With: 2-50#bags of bentonite (99 -93' bgs)followed by bentonite cuttings mix to grade — cb-21Acllve prof 349-Propp subsidence Evalualionll49 NL-1.log JOB NAME weld 4jW ,.l-/ 5oLs, cienLa AlJOB NO. E=21 E„n �neL c v.), SNc Pto� CALCULATED BY P. 0 Ther DATE f //of r CHECKED BY DATE SHEET 1 OF 3 a + y h 1- _ ti - 5O40— Silk `alt 1 ri- I ViP! t y.'. - ...... 1 ,c of — ww. WM 0 PS 6 4 at MR IINI MW tit _ s • a r w o_ sh C_Z ter, C-3 • fi O-4 io' e1a5'--a C-1 1 JOB NAME VC/alA Co“otJ 5J5,deoce S JOB NO. F -Zi F.,j,.,ee_e;n1, rv,c R ,. 347 O N CALCULATED BY e C0 ftk! DATE 1/z7I 04 h v CHECKED BY DATE r + t SHEET Z OF 3 �O }}( P tl t L - u..+. IS y yam,. 4. IS ME F NM F Ilia - OS..- rr le S- ,oP, , r ,w . w 3 A. ems- ITOPP 3' .ter r• ei „y.. VIM.. v M all S. wiz .d wis — w�4 W-3 - vir-± Z, M- 125=- • JOB NAME WelA Co....Y/ S.,Ls,cle^ce N JOB NO. E_ 21 Fn5;..ee:;•..) , 2v.,, 349 CALCULATED BY ? Co1-ffr DATE L /27/01 CHECKED BY DATE SHEETS :3 OF 3 j sob 5_______ . 5of ' li 'Id :id "" soce . , are H .. c• - • il5c 5r ... : S 045 "" . :w-- ____ a a SGz4 502 i • v t ' S 3 • a_ JOHN F. ABEL, JR. MINING ENGINEER 310 LOOKOUT VIEW COURT GOLDEN,CO 80401 303-279-4901 FAX 278-8163 JFAS12@Homecorn SUBSIDENCE AND SURFACE STRAIN ANALYSIS LONGS PEAK ESTATES Report to Sergius N. Hanson P.E. , P.G. E-21 Engineering, Inc. 400 Corporate Circle, Suite K Golden, CO 80401 by John F. Abel, Jr. Mining Engineer Colorado P.E . 5642 June 20, 2001 i TABLE OF CONTENTS EXECUTIVE SUMMARY 1 INTRODUCTION 9 SITE CONDITIONS 10 MORRISON MINE 10 CLAYTON MINE 12 GEOLOGIC CONDITIONS 13 EXISTING SURFACE SUBSIDENCE FEATURES 13 SUBSIDENCE PREDICTIONS 18 TROUGH SUBSIDENCE EVALUATION 18 CHIMNEY SUBSIDENCE EVALUATION 27 CONCLUSIONS AND RECOMMENDATIONS 30 31 REFERENCES APPENDIX A: DAMAGE PREDICTIONS WITH RESPECT TO SURFACE STRAINS 35 ii LIST OF PLATES (In pocket) Plate 1 . Longs Peak Estates with underlying and adjacent Morrison Mine workings Plate 2A. Predicted Limit of Subsidence line, 1, 000uE line and less than 1, 000uE area Plate 2B. Predicted maximum pillar failure subsidence strain locations Plate 3 . Morrison Mine map in Longs Peak Estates area Plate 4 . Morrison Mine panel and pillar dimensions Plate 5 . Longs Peak Estates with underlying and adjacent Clayton Mine workings Plate 6. Predicted Limit of Subsidence line, 1, 000uE line, less than 1, 000uE area and subsidence strain locations Plate 7 . Clayton Mine map in Longs Peak Estates area LIST OF TABLES Table 1 . Maximum surface subsidence and strains resulting from failure of mine workings 4 Table 2 . Bank density, swell factor and percent free swell for selected rocks and soils 8 Table Al . Subsidence damage limits, acceptable subsidence damage 35 Table A2 . Tolerance of structures to differential subsidence 36 Table A3 . Subsidence damage description for horizontal strain 37 Table A4 . Polish Ministry for Mining and Power, classification of permissible strain and tilt 39 iii LIST OF FIGURES Figure 1 . Relationship of damage to length of structures and horizontal ground strain 3 Figure 2 . Oblique aerial view of subsidence features 6 Figure 3 . Cumulative percent of chimney collapse height. . 7 Figure 4 . Chimney collapse modes and heights 9 - Figure 5 . Mean diameters of subsidence features 15 Figure 6. Depth of subsidence features 16 Figure 7 . Minimum time interval between mining and 17 subsidence Figure 8 . Trough subsidence nomenclature (adapted from Subsidence Engineers ' Handbook, 1975) 19 Figure 9. Subsidence over super-critical room-and-pillar workings following pillar failure 20 Figure 10 . Graph for predicting maximum slope and strain . . . 23 Figure 11 . Graph for predicting horizontal strain profiles . . 25 Figure 12 . Horizontal deformation of rock mass affected by failing pillar adjacent to collapsed panels . 26 Figure Al . Relationship of damage to length of structures and horizontal ground strain 38 iv Longs Peak Estates Page 1 June 20, 2001 EXECUTIVE SUMMARY Most of the Longs Peak Estates development site overlies abandoned Morrison Mine workings, as shown on Plate 1 . Some of the western part of the site overlies workings of the deeper Clayton Mine . This necessitates an evaluation of worst-case trough and chimney subsidence impacts on the planned development . Trough subsidence can result from the failure of unmined coal pillars left in the mine after either advance mining or after pillar robbing during retreat . The Morrison Mine map indicates unmined coal chain pillars, barrier pillars and irregular blocks of unmined coal which represent a potential long term trough subsidence hazard to surface construction on portions of the site . The Clayton Mine map indicates pillars were left between rooms and development entries abandoned without additional mining. It is necessary to evaluate the location and magnitude of horizontal surface strains that could result from failure . Chimney subsidence can potentially breach the ground surface when roof beds collapse into voids left after retreat mining in the Morrison Mine. The open chain pillar breakthroughs and entry intersections are voids into which the roof beds can collapse, resulting in collapse chimneys up into the overburden. It is necessary to evaluate the location of potential collapse chimneys that might eventually breach the ground surface . The tan shaded areas on Plate 2A indicate less than 1, 000 us (micro-strain) of conservatively predicted horizontal ground surface strains as the result of failure of underlying abandoned Morrison Mine chain and barrier pillars . Tan shaded areas on Plate 6 indicate similar areas of abandoned Clayton Mine pillars . These tan shaded areas should be safe for the planned surface structures because the conservatively predicted less than 1, 000 us horizontal strain magnitude should not damage the planned surface structures . Figure 1 presents the relationship between the length of a structure, horizontal ground strain and struc- tural damage. Appendix A presents tabulations of the structural damage potential for various horizontal strain magnitudes. The white background areas on Plate 2A are underlain by unmined Morrison mine chain pillars, barrier pillars and irregu- lar blocks of coal that could fail, if they are still standing, and subject structures and utility lines at the overlying ground surface to adverse horizontal strains exceeding 1, 000 us. Plate 6 contains three similar white areas with the potential for greater than 1, 000 us on the ground surface if underlying Clayton Mine chain and room pillars fail . Table 1 presents the predicted maximum horizontal surface strains for failure of various unmined coal pillars under and immediately adjacent to the planned Longs Peak Estates site . Plate 2B and Plate 6 indicate by red letters Longs Peak Estates Page 2 June 20, 2001 1, 000 us increments of maximum horizontal ground strain above and along the chain pillars, barrier pillars and unmined blocks of coal, i .e. "A" for maximum strains from 1, 000 to 2, 000 us, "B" for maximum strains from 2, 000 to 3, 000 us, etc. The "A" and "B" corridors are recommended for utilities and streets . Chimney collapse could potentially breach the ground surface at the Longs Peak Estates site. The chimney subsidence hazard is minor and should not prevent development of the Longs Peak Estates site because: 1) There are no existing chimney pits or trenches, such as shown on Figure 2 (Dunrud and Osterwald, 1980) , that should be present if chimney collapse has previously breached the surface in or near the Longs Peak Estates site . The diame- ter (up to 35-ft) and depth (up to 45-ft) of chimney pits, sinkholes, at the surface is not subtle and should be obvious . 2) There is little likelihood that a chimney collapse will breach the surface. Gray, et. al . (1977) cataloged 126 collapse chimneys that breached the ground surface and produced sinkholes above abandoned room and pillar mines in Pennsylvania, West Virginia and Ohio. The statistical plot of their data on Figure 3 indicates that about 10% of the chimneys penetrated through 80 ft of overburden and only one through 200-ft. 3) There is only one type of chimney collapse that can theoretically breach the surface, and only above the Morri- son Mine . Conical chimney collapse could theoretically breach the ground surface through the minimum 82-ft of overburden assuming normal rock or soil bulking (Table 2) and the worst case 30% bulking of British coal measure rocks on Figure 4 . Hynes (1984) unusually low 15% swell could result in chimney collapse to the surface. 4) There are only four 90° Morrison Mine entry intersections and 23 three-way entry and room access intersections that could develop a conical collapse geometry (Piggott and Eynon, 1977) . These intersections are all located in the center of the white corridors shown on Plate 2A, directly above the unmined chain pillars on Plate 1 . The minor chimney collapse hazard can be further reduced by offsetting streets and utility lines from the directly over the chain pillars and locating driveways and individual lot utilities so they cross unmined chain pillars and not breakthroughs . Longs Peak Estates Page 3 June 20, 2001 Figure 1 . Relationship of Damage to Length of Structures and Horizontal Ground Strain 7000 - 6000 © Damage due to extension © Damage due to compression 5000 4000 Strain C E 1 Very v-in. © Severe in. 3000 E © 2000 E Severe E © © Appreciable E C 1000 E Slight O Very Slight © or E C Negligible 0 0 100 200 300 400 500 600 700 (NCB, 1975) Length ( ft. ) subdamg5 I I Longs Peak Estates Page 4 June 20, 2001 Table 1 . Maximum surface subsidence and strains resulting from failure of mine workings Corridors Pillar Minimum Panel Maximum Maximum Distance Noted by Width Panel Extraction Subsidence Horizontal LOS to the Letter (ft) Width (%) (ft) Strain 1, 000u6 Line (ft) (us) (ft) Morrison Mine A 63 593 65 0 .206 1636 49 . 2 A 46 283 65 0. 242 1915 47 . 7 B 35 220 65 0 .283 2245 45 . 1 B 33 500 65 0.293 2322 44 . 3 B 30 298 65 0. 311 2466 44 . 1 B 60 0.286 2268 45. 1 B 28 137 65 0 . 325 2576 42 . 6 B 25 141 65 0. 351 2782 41 . 8 B 24 265 65 0. 361 2863 41 . 4 C 22 142 65 0 . 384 3043 39 . 9 C 20 199 65 0. 421 3337 39. 4 C 16 134 65 0 .486 3853 37 . 7 D 15 380 65 0. 511 4051 37 . 1 D 13 502 65 0 . 573 4539 36 . 3 D 125 60 0. 515 4081 37 . 7 E 10 285 65 0. 711 5636 31. 6 E 279 60 0. 636 5041 34 . 4 Clayton Mine A 30 240 45 0. 522 1679 120 . 3 A 35 300 36 0. 417 1342 187 . 9 B 22 75 40 0 . 271 2344 119 . 2 Avg. 67 135 26 0. 184 818 ! I Longs Peak Estates Page 5 June 20, 2001 Table 1 (Continued) . Maximum surface subsidence and strains resulting from failure of mine workings Corridors noted by "A" potentially subject to horizontal strains from 1, 000 to 2, 000 us Corridors noted by "B" potentially subject to horizontal strains from 2, 000 to 3, 000 us Corridors noted by "C" potentially subject to horizontal strains from 3, 000 to 4, 000 us Corridors noted by "D" potentially subject to horizontal strains from 4, 000 to 5, 000 us Corridors noted by "E" potentially subject to horizontal strains greater than 5, 000 us Abbreviations : LOS - Limit of Subsidence; us - micro-strain (millionths of a ft per ft) Longs Peak Estates Page 6 June 20, 2001 Figure 2 . Oblique aerial view of subsidence features y "t pmt Tr -'; •. - ' - `9 41 M .,,L maw w_ '• Y'' SS,�C� ..+ _ �r +1~ A7 en!" s� N _ `s,�w f ma �� • z ! •,� Ste_ e - �w $, •1 or ire e rr • ve C ! A .,:c: i°Y *` F 7 Y r ,; I. ' it W:4-j C'. t4Y , FIGURE 12.—Oblique aerial view of subsidence features located 1.5-6.5 km north of Beulah,N. Dak.,looking south(October 19761. Pits and troughs occur above elongate rooms in room-and-pillar mine workings in lignitic coal that was mined from -- 1918 to 1952.The overburden averages about 15 m thick and is composed of poorly consolidated daystones,siltstones,and lenticular sandstones overlain by local glacial deposits. The land surface above mine workings is of little use because of subsidence hazards.Wheat farming,the major industry in the area,is hazardous in the old mining areas because the vibra- tions and extra weight of equipment might trigger further collapse. Cultivated areas at right probably overlie areas of unmined coal. (Dunrud&Osterwald, 1980,USGS Prof.Paper 1164) Longs Peak Estates Page 7 June 20, 2001 Figure 3 . Cumulative percent of chimney collapse height (Gray, Bruhn and Turka, 1977) 100 •.• • 90 80 W : > = r 70 J - W C' 4; 60 W '•� re 50 I W : a i > 40 30 V V , 20 :� s 10 •.-� :wry 0 0 50 100 150 200 HEIGHT OF CHIMNEY COLLAPSE (feet) Longs Peak Estates Page 8 June 20, 2001 Table 2 . Bank density, swell factor and percent free swell for selected rocks and soils Rock or Soil Bank Density Swell Factor Free Swell Basalt 185 PCF 0.67 50% Bauxite 119 PCF 0.75 33% Caliche 141 PCF 0.55 82% Carnotite, primary uranium ore 137 PCF 0.74 35% Clay, natural 126 PCF 0.82 22% Coal, anthracite 100 PCF 0.74 35% bituminous 80 PCF 0.74 35% Concrete 120-155 PCF 0.72 40% Conglomerate 153 PCF 0.72-0.63 40-60% Copper ore, altered siliceous 141 PCF 0.74 35% Earth, wet 126 PCF 0.79 27% loam 96 PCF 0.81 23% Granite, quartzite, fresh 163-170 PCF 0.67-0.56 50-80% typical values 0.61 64% Gravel, pit run 135 PCF 0.89 12% Gypsum 198 PCF 0.57 75% Iron ore, high grade hematite 174-237 PCF 0.58-0.55 72-82% limonite 174-237 PCF 0.58 72% magnetite 204 PCF 0.55-0.58 72-82% taconite 192-226 PCF 0.58 72% Limestone 155-163 PCF 0.57-0.60 67-75% typical values 0.59 69% Marble, metamorphic 170 PCF 0.57-0.60 67-75% Montmorillonite, chlorite, kaolin 141 PCF 0.77 30% illite, smektite Pyrite 189 PCF 0.85 18% Sand, dry 100 PCF 0.89 12% damp 120 PCF 0.89 12% wet 130 PCF 0.89 12% Sandstone 153-157 PCF 0.60 67% Shale, mudstone 104 PCF 0.75 33% Siltstone, hard 153-157 PCF 0.57-0.60 67-75% soft 126 PCF 0.82 22% Slate 170-180 PCF 0.77 30% Traprock, basic, igneous 163 PCF 0.67 50% Free swell (%) = change in volume broken as a percent of original bank volume Swell factor = broken density/bank density Adapted from: Caterpillar, Inc., 1987, Caterpillar performance handbook, p 740 and Euclid Road Machinery Co., 1953, Estimating production and costs I i I I I 1 I I 1 I I I I I I I I '71 C H O ' G G 'R ht CO co hi RECTANGULAR COLLAPSE 30 a a 2 �-t'/' C) th Hi h(100) = z Ng• rt __ H %S l7 25 b W ' rt L+I N 2 RANGE OF PERCENT (D CD N'P" `� CO0_ O SWELL FOR Q Z 20.7 COAL MEASURE STRATA n n r0 WEDGE COLLAPSE _i tu 20 s n I I H. T V O c^ v� ODs erved mozlmum height I IG NI \ ' LL LLO 3 of collapse in the mine. I 'L7 cn --J'1 � L _ 2h(ICO) O J 1S ta.t Q' �q I cD T I+—P —*Ia..— N 4 S 2 a <o DC I I O CONICAL COLLAPSE W D ro, v� al a co ho G LO_\._ _ I H K W 6.9 cTQHac< 8.5 a QD Q W 5 4R� CD I. H _ 3h 100) g a OOLl4iesE LIQ h 045 w I G' F4--P—►i I m 0 %S a PERCENT SWELL a V°vo° (100) 0 I0% 20% 30% 40% 50% Vo : ORIGINAL VOLUME OF UNBROKEN STRATA PERCENT SWELL %S Vo = VOLUME OF COLLAPSED ROOF BEDS Graph showing variation in maximum ci Diagram showing notation for calculating height of collapse for different modes maximum height of collapse (H) in of failure and percent swell of rock. M relation to geometry of collapse. N (modified from Piggott& Eynon, 1977) P&Envet O N.) O O H` Longs Peak Estates Page 10 June 20, 2001 INTRODUCTION This report was prepared as requested by Sergius N. Hanson of E-21 Engineering, Inc. to evaluate potential subsidence hazards to the northeast, central and southeast part of the proposed Longs Peak Estates development site resulting from undermining by the Morrison Mine. E-21 Engineering, Inc. provided copies of the final Morrison Mine Map (Wilson and Canis, 1931 through 1966) and the draft subsidence evaluation report for the Longs Peak Estates Site. Plate 1 indicates the relative location of the Longs Peak Estates site in relation to the under- lying and adjacent Morrison Mine workings . The subsidence prediction methods employed included the British National Coal Board' s Subsidence Engineers ' Handbook (1975) for previously subsided longwall panels, Piggott and Eynon' s (1977) method for predicting the maximum chimney collapse height and Abel and Lee' s (1984) method for predicting maximum surface subsidence resulting from pillar failure in room and pillar panels . SITE CONDITIONS The Morrison Mine and Clayton Mine workings that under- lie and are adjacent to the proposed Longs Peak Estates are shown _ - on Plate 1 and 5, respectively. Site conditions involve the mining completed at both mines, the geologic setting and subsi- dence evidence indicated by the 1-ft contour map for the proposed development site. MORRISON MINE In general, the underlying Morrison Mine coal seam increases in depth from 82 to 107-ft from north to south. The coal seam thickness is reported as 8 to 10-ft, whereas the reported mining height was reported as 6 to 8-ft (Turney and Murray-Williams, 1983) . This discrepancy may be the result of leaving top coal for roof stability. It was common to leave one to 2-ft of top coal in the Boulder-Weld coalfield when the immediate roof member was a weak pebble conglomerate. The mine map in the site area, Plate 3 (Wilson & Canis, 1931 through 1966) , shows that the method employed under the site was to advance an initial set of two-entry submains to the north off the West Mains on approxi- mately 650-ft centers until they encountered either the roughly NE-SW fault that cut off the coal seam or dirty, probably unsale- able, coal . The 25-ft wide chain pillars between the main entrys in the north mains were reduced to 20-ft wide between 800-ft and 1300-ft before they anticipated reaching the mining boundary. A second set of submains were driven west on roughly 350-ft centers . The east-west submains outlined roughly 600-ft long by 300-ft wide panels of coal that was room and pillar mined. Longs Peak Estates Page 11 June 20, 2001 The room and pillar method involved driving advancing 25-ft to 30-ft wide rooms on 65-ft to 75-ft centers, temporarily leaving 40-ft to 45-ft wide pillars between the rooms . These pillars were mined, robbed, on the retreat. The mine map indicates that they initially tried to advance the panel rooms completely across the panels before retreating the pillars . Subsequently, they changed to advancing the rooms roughly halfway across the panel from each side and left a narrow barrier pillar in the center of each panel . Pillar robbing results in periodic roof failures . The mine map does not provide any indication of the stump pillars that were left during retreat . Stump pillars are left unmined because conditions deteriorate and continued mining becomes unsafe . When pillar robbing reaches the point where a roof collapse is immanent, a "breaker row" of timber is set across the room before proceeding with pillar robbing. It is never possible to achieve full extraction, as is indicated by the 57% to 65% recovery reported for "conventional" advance and retreat coal mining operations by the U. S . Bureau of Mines IC 8785 (Reese, et. al . , 1978) . The mine map indicates that development entries stopped -- advancing northward between 1938 and 1942 in the Longs Peak Estates site area, when the fault along the northwest side of the Morrison Mine cut off the coal seam. Panel pillar retreat mining from the mine' s fault boundary undoubtedly started shortly after- wards. Surface trough subsidence follows the active retreat pillar robbing and roof collapse line within the panels . Generally, no attempt is made to rob chain pillars in a two-entry system and narrow barrier pillars in room and pillar coal mining because of the difficult access and the high stress in the pillar coal from the overburden arch loads transferred from both adjacent panels . Similarly, robbing narrow barrier pillars are difficult to rob safely during retreat mining because they are even more heavily stressed by the overburden arch loads from the adjacent panel (s) . However, initially stable coal chain and narrow barrier pillars deteriorate over time and may collapse without warning some considerable time after mining. The current topographic contours indicate that some of the chain and barrier pillars have not failed, i . e. crushed, since the mine was closed in 1966. It is therefore necessary to evaluate the potential site subsidence on the basis that the unmined pillars indicated on Plate 1 are still intact and will fail after the surface structures are erected. Longs Peak Estates Page 12 June 20, 2001 CLAYTON MINE Uncertainty is present with respect to some factors required for subsidence prediction for that part of the Longs Peak Estates site overlying the Clayton Mine . The depth of the underlying Clayton Mine coal seam was measured at 202-ft in test boring W-1 . The mine map lists the shaft depth as 314-ft . Turney and Murray- Williams (1983) indicate the depth as 350-ft. Therefore, the shallowest 202-ft depth was utilized because shallower depths produce the most adverse subsidence predictions . The irrigation ditch and the property line running through the site shown on the mine map do not exactly match either the recently surveyed site map or the Morrison Mine map. The maximum east-west discrepancy in the distance between the property line and the easternmost bend in the irrigation ditch is less than 40-ft. The north- south discrepancy appears the be less than 10-ft. This is particularly interesting since the site map and the Morrison Mine map are in agreement and the same engineers prepared both mine maps. The coal seam thickness is reported as 9-ft, whereas no mining height was reported. Therefore, the maximum possible mining height was conservatively used as a worst-case for predic- tion. The mine map in the site area, Plate 7 (Wilson, et. al . , 1920 through 1942) , shows that the method employed by the Clayton Mine was, except under most on the site, was the same used in the overlying Morrison Mine. The chain pillars are, however, typically 30-ft wide by 60-ft long. Most of the mining under the site was not undermined by the Clayton Mine. Plate 5 indicates one underlying panel was retreat mined, two panels advance mined and one area had only development entrys driven and large pillars outlined. Mining extraction in the advance mined areas ranged from 36% to 45% . It is unlikely that pillars the size of the unmined remaining pillars left between panel pillar rooms and the chain pillars along the entrys have failed, but it is a long term possibility. The failure of these pillars was evaluated. The mine map indicates that the Clayton Mine stopped on the north when it encountered the same fault as the overlying Morri- son Mine. However, advance and retreat mining beneath the Longs Peak Estates stopped at the property line. It may be that the coal seam was too thin to profitably mine . The only solid clue provided by the mine map is a notation (36"-c) at the east end of the 54 to 36 entry system, shown on Plate 7 . All eastward mine development stopped when rock was encountered. This is probably the same north-south fault encountered in the Morrison Mine . Longs Peak Estates Page 13 June 20, 2001 GEOLOGIC CONDITIONS The late Cretaceous Boulder-Weld coalfield lies in the Denver formation in the western part of the Denver-Julesburg Basin. The sedimentary beds are generally poorly consolidated claystones, siltstones and sandstones . The coal seams are sub-bituminous . The overburden at the Longs Peak Estates area is described as 80% shale and mudstone and 10% siltstone and sandstone (Hanson & Gottler, 2001) . The Morrison Mine map (Plate 3) shows two faults in the Longs Peak Estates area. The more prominent fault trends roughly northeast-southwest and is the northwest boundary of the Morrison Mine . The smaller fault trends generally north-south, cutting across the northeast property line. The mine map shows that the smaller fault dies out approximately 450-ft into the development site . The mine map further indicates that there was sufficient movement on the smaller north-south fault to offset the 5W and 6W submains approximately 10-ft. A narrow barrier pillar was left along the west side of the smaller fault, apparently for safety. The Clayton Mine map indicates that the same two faults were encountered. However, they are not identified as faults on the Clayton Mine map. In addition, the throw on the north-south - fault is apparently much greater in the Clayton Mine, i .e. suffi- cient to completely cut off the coal seam. The apparent trace of the north-south fault, inferred from three entry penetrations, dies out approximately 1, 000-ft into the development site. If this is the case, the north-south fault has shifted approximately 300-ft further to the east in the southern part of the site, as shown on Plate 7 . EXISTING SURFACE SUBSIDENCE FEATURES The 1-ft surface topographic contours on the Plate 1 site plan indicate trough surface subsidence over most of the mined out panels . The ground surface appears to have subsided approxi- mately two feet over the mined out panels with respect to the lesser subsidence over some of the adjacent unmined chain pillars, barrier pillars and coal blocks. The Plate 1 contours indicate that some of the unmined chain and barrier pillars continue to stand, producing minor overlying linear ridges at the surface . At other surface locations overlying unmined chain and barrier pillars indicate that the pillars have failed, as evidenced by the absence of minor linear ridges interrupting the flat-bottomed troughs . Thorburn and Reid (1977) presented a Scottish case where the progressive failure of multiple pillars in a room and pillar mine caused trough subsidence to develop from 118 to 138 years after Longs Peak Estates Page 14 June 20, 2001 mining ceased. The result was significant damage to overlying residential structures . In this case the 65-ft of overburden was primarily sandstone, differing significantly from the Longs Peak Estates overburden. The subsequent investigation found near- surface bed separations in as yet unaffected adjacent undermined areas . The implication is that the trough subsidence resulting from failure of all unmined pillars must be evaluated and the proposed development adjusted to accommodate the worst-case possibility of future failure of all unmined pillars . Structures must be located over areas with acceptable predicted ground strain. Utility lines and access streets should, wherever possi- ble, be located along corridors with the lowest possible predicted maximum horizontal strains . Utility and road access from the corridors to individual structures should be located in order to minimize potential damage. There are no obvious subsidence pits or trenches exposed anywhere on the ground surface of the proposed development site that are indicative of chimney collapse. Figure 2 shows fifty plus year old subsidence pits and trenches above approximately 50-ft deep room and pillar workings near Beulah, North Dakota. This mine is in contemporaneous coal measures and did not rob pillars on the retreat. Both conical and wedge collapse chimneys can be seen in Figure 2 . The deeper conical collapse pits are in line, apparently where the rooms were turned off from the access entry. The shallower wedge collapse trenches are apparently above individual rooms . Figure 5, from Gray, et.al . (1977) , indicates 2 . 5-ft to 7 . 5-ft modal diameter for subsidence sinkholes (pits) that breached the surface above the room and pillar mines in the Pittsburgh coal seam. Figure 6 indicates that the sinkhole depths below the surface typically ranged from 5-ft to 20-ft . The surface subsidence features demonstrate that robbing panel pillars on the retreat at a depth of approximately 82-ft produces panel wide roof collapse and trough subsidence but prevents chimneys from developing above the panels to the overly- ing ground surface. The absence of identifiable surface subsi- dence pits (sinkholes) above the chain pillar breakthroughs implies, but does not prove, that chimney subsidence will not eventually breach the overlying ground surface . There is no possibility of chimney collapse above the barrier pillars because no void space was ever present in the barrier pillars . Figure 7, also from Gray, et .al . (1977) , indicates that chimney subsidence may breach the ground surface as much as one hundred years after room and pillar mining, provided void space remains in the abandoned mine workings . The implication is that chimney subsidence above the open breakthroughs between adjacent chain pillars must be evaluated as a potential long term hazard I I I I I I i I I I I I I I I I t 60- N-SINKHOLES---..1 - 80 P o r TROUGHS j m ro - 70 u' a pc- 50- z ti m u, w rt • W >, -60 it c gi a m O I- r- 0 w O 40- LEGEND o CD rt Q ALL SITES WHERE MEAN 60 N .o DIAMETER OF SUBSIDENCE tu LI m FEATURE IS KNOWN (163) c o O d ro o SITES WHERE DEPTH OF in 30 - - 40 .o rn c FEATURE AND OVERBURDEN a' ro THICKNESS IS ALSO w o KNOWN (133) - 0 NOTE: MEAN DIAMETER IS AVERAGE OF 30 ° I- o LONG AND SHORT DIAMETERS. y m c 20 - ro O m Z w lI- 20 rr n m in 10 - 10 Cl c c m 0 F771,1 vma — -J — 0 0 0 10 20 30 40 50 60 70 80 150 200 300 1250 1600 Mean Diameter of Subsidence Feature , feet o 0 FIGURE 2.12 MEAN DIAMETERS OF SUBSIDENCE FEATURES (Gray, Bruhn & Turka, 1977) subsbfi Fa I I I i I I I I I I I I I I I I / 1 ro r H 0 4 50 co — I " SINKHOLES ' 1 "m It ON m -60 • w hatx rzi qp_ TROUGHS LEGEND ,S rt c Alt SITES WHERE DEPTH _50 ai m O OF SUBSIDENCE FEATURE 6 c IS KNOWN (IBJ) o o cn ;U SITES WHERE DIAMETER OF u. CA Q 30_ y SUBSIDENCE FEATURE AND -4O w o v ��A OVERBURDEN THICKNESS () CD a IS ALSO KNOWN (133) v l N n N - 30 c ° ro (I7 H a 0 20— m 4 r- a rt.y. G r C /4d //4 % -20 m a E to ezZ % ci .0 0 0 10 20 30 40 50 m Depth of Subsidence Feature, feet o FIGURE 2.13 DEPTHS OF SUBSIDENCE FEATURES (Gray, Bruhn & Turka, 1977) N Subsbe O O I I I I I I txi r H- O 100 \""-�\\ SINKHOLES (76) `Q Nro F- 90- \ (D N \ \ • d 80- \ \ 'HH- m o x 1 SINKHOLES AND TROUGHS, P. rr w La \ , INCLUDING THOSE OF rt mE 70- \ UNSPECIFIED DIMENSIONS u N iZ (/63) Fr N 60 a. `\ t o a) ' r- 1 rt N 50- \ EXAMPLES: c m to a. 60 PERCENT OF THE SINKHOLES a ro 40- , \ DEVELOPED MORE THAN 47 YEARS o AFTER MINING `D f° \ r o 30 \ b. 10 PERCENT OF THE SINKHOLES CD TROUGHS (/3)�\ \ DEVELOPED MORE THAN 78 YEARS O. 20— \ \` AFTER MINING. 5cu _ ≥ \ I"' ; 10 b. \3 .. `� _ \ _ 0) a V 0 I I I 1 I I I I t m y 0 10 20 30 40 50 60 70 80 90 100 b ti m Time Interval , T, years H. a - cD 0 FIGURE 2.I7 MINIMUM TIME INTERVAL BETWEEN MINING AND SUBSIDENCE (D N 0 (Gray, Bruhn & Turka, 1977) 9ubsd4 Longs Peak Estates Page 18 June 20, 2001 and the proposed development adjusted to minimize the potential hazard from the worst-case possibility of future chimney failure to the surface. Locating utility lines and access streets adjacent to, but not directly over unmined chain pillars should minimize the already low possibility of sinkholes developing under utility lines and access streets . SUBSIDENCE PREDICTIONS Horizontal ground surface strains were predicted for the possible failure of unmined Morrison Mine pillars underlying and immediately adjacent to the proposed Longs Peak Estates develop- ment shown on Plate 1 . Horizontal ground surface strains were predicted for the possible failure of the all unmined Clayton Mine pillars underlying and immediately adjacent to the proposed development shown on Plate 1 . The prediction method combined the room and pillar mining method of predicting maximum vertical panel subsidence, developed by Abel and Lee (1984) and the longwall horizontal strain prediction method from the British National Coal Board' s Subsidence Engineers ' Handbook (1975) . Potential chimney subsidence breaching the ground surface over the potentially open Morrison Mine breakthroughs between chain pillars was evaluated assuming sinkholes may develop to the _ - ground surface at these locations. TROUGH SUBSIDENCE EVALUATION The nomenclature used for describing ground surface trough subsidence is shown on Figure 8 . Worst-case trough subsidence predictions were made based on the assumption that the chain pillars, barrier pillars and irregular coal blocks indicated on Plate 1 for the Morrison Mine and Plate 5 for the Clayton Mine are currently standing. It was further assumed that these pillars will fail at some time in the future, after the develop- ment is completed. These assumptions are conservative because the topographic surface contours crossing the Morrison Mine chain and barrier pillars indicate that many have already failed. The maximum trough subsidence resulting from failure of all the pillars in a super-critical room and pillar panel, i .e. panel width equal to or greater than 1 . 4 times the panel depth, was analyzed using field data by Abel and Lee (1984) . Figure 9 presents one of the graphs they developed. At the approximate minimum 82-ft depth the super-critical panel width is 115-ft for the Morrison Mine and at the drilling indicated 202-ft depth of the Clayton Mine the critical panel width is 283-ft. All of the panels resulting from chain, barrier and irregular pillar failure in the Morrison Mine are super-critical . Only one of the panels in the deeper Clayton Mine is super-critical . a � r m F•- 0 kg n G to (D n m m rd 00 m L • w I.J. K tii m H (I) m O Ul ti O t tnG w Fr p Surface and Datum x m 4 • o 1 ,,�_._.._ — J w m \� Smax � / G G 500 _a mi. 1000 %\ $max ��' I /�� O a 1500 \ \,�� 1 �''' ��// / / x 2000 mm h h w Subsidence F Subsidence (s) \ Profiles/ / in 0 up �r«+ / h ro �« m w o 'p +-« n rD r .- w LU �L « rr -F-SubA�ritical� __— ry a m «-Angle of Draw ""`a(A°a g SuperCri!(cal Area w h - Depth a w o m - Mining Thickness ro R ft m a ro hi 4 mm CII b o CA I- I N O 0 Fa Longs Peak Estates Page 20 June 20, 2001 Figure 9 . Subsidence over super-critical room-and-pillar workings following pillar failure. (Modified from Abel & Lee, 1984) Subsidence( /a)=I.39+5.57{L, ("YVA _ r2=C.9i9 Syx=298% • r2=Correlation Coefficient Squared Syx= Standard Error(r based cod ) 30 -t I 25 r C 20 O a' 15 • • LEGEND LmaX = 4.788x10-52J-3-1 . • N 10 • Y = Density (PCF) R = Extraction Ratio • H = Mining Height (ft) 5 W = Pillar Width (ft) D = Depth (ft) • °Jharia 00 t0 2O 3.0 4.0 50 6 0 Lmax(HAV) F� Longs Peak Estates Page 21 June 20, 2001 When a chain pillar, or barrier pillar, between two collapsed panels fails the panel width is the lesser of either the sum of the north-south widths of the two adjacent panels plus the chain or barrier pillar width or the shortest east-west length of the two adjacent panels . For example, the dimensions across the Morrison Mine panel developed by failure of the 25-ft wide chain pillar between 5 West and 6 West entrys is 586-ft north-south (231-ft to the north and 330-ft to the south plus 25-ft for the chain pillar) and 329-ft east-west . These dimen- sions are shown on Plate 4, which presents the pillar widths and panel dimensions digitized from the site mine map (Plate 3) . In the example, the resulting panel minimum width/depth ratio is a very super-critical 4 . 0 . The width of the three sub-critical panels in the Clayton Mine defined by mine openings were conser- vatively assumed to be super-critical . The maximum subsidence resulting from failure of sub-critical panels is reduced by arching across the narrow panel width. The panel width is the distance between solid coal ribs at the sides of the entrys and pillars . For example, the distance of the southwest Clayton Mine panel centered on entrys "5 & 6 South" is 300-ft from the end of the east room to the end the west room. Figure 8 indicates the decrease in maximum subsidence measured over longwall mining panels . This should also be the case for room and pillar panels . _ _ The average Morrison Mine pillar stress (Lmax) equation involves the density of the overburden (150 PCF) , the worst-case depth (82-ft) and the extraction ratio. The panel extraction ratio for the Morrison Mine example was conservatively taken as 0. 65, i . e. 65% of the coal removed by mining. This extraction ratio is highest in the extraction range presented by Reese, et. al . (1978) for the "conventional" full room and pillar retreat mining method observed in use at the Eagle, Washington and Lincoln Mines in the Boulder-Weld Coalfield and Pikeview Mine in the Colorado Springs Coalfield in the 1950s and 1960s and appar- ently employed in the Morrison Mine as indicated by the mine map (Plate 3) . The constant in the equation simply converts the original equation to English units from the published SI units . _ The example calculated average pillar stress is: ', ax = 4 . 788x10-5L 11500(.8625) 10 65) j = 4 . 788x10-5 [ 10233°5° Lax = 1 . 68 Mpa (244 psi ) The shortening of a pillar when it crushes under an applied average stress appears to be a direct function of the applied stress and the height of the pillar and an inverse function of the pillar width. There are numerous exponents applied to the pillar height and width factors by pillar designers . See Abel, 1988 for a discussion of pillar strength design equations. The fit between the field subsidence measurements and the X-axis Longs Peak Estates Page 22 June 20, 2001 input of the field data into the linear subsidence prediction equation appears to be sufficient for reasonable subsidence prediction. The prediction method has been used at three Colorado room and pillar coal mines and checked against the observed subsidence (Pendleton, 1985) . The method appears to be very conservative. In each case the measured subsidence was not more than 63% of the predicted. In the example case, the predicted maximum subsidence over the center of the chain pillar is : L,,,aX (w ) = 1 . 68 (-k ) = 0 . 538 Subsidence (% ) = 1 . 39 + 5 . 57 [Li„a. (w ) ] Subsidence (%) = 1 . 39 + 5. 57 [0 . 538] = 4 . 39% 4 . 39% of 8-ft is 0. 351-ft (4 . 21-in) The maximum downward deflection of the ground surface above a failed pillar will decrease outward from the maximum at the center of the chain pillar to zero at the Limit of Subsidence, a distance related to the angle of draw (the angle from vertical above the chain pillar ribside to the Limit of Subsidence) in the overburden. The data reported by Abel and Lee (1984) indicates the angle of draw increases in shale, claystone and mudstone overburden and decreases in stronger sandstone and limestone overburden. The NCB' s conservative 35 degree angle of draw was used to locate the Limit of Subsidence line in Plate 2A and Plate 2B. _ The NCB correction for subsidence in a virgin (not previ- ously subsided) area, i .e. multiplying predicted maximum subsi- dence by 0 . 9, was conservatively not applied because part of the proposed Morrison Mine development area are underlain by deeper Clayton Mine workings and vice versa. Once the maximum surface subsidence was calculated over a failed chain, barrier or block pillar, the maximum tensile strain (+E) at the ground surface can be calculated using the longwall prediction method from the British National Coal Board' s Subsi- dence Engineers ' Handbook (1975) . Figure 10 is a graph for estimating the maximum slope, tensile (extension) strain and compressive strain values . The maximum tensile microstrain (ye) for greater than 115-ft Morrison Mine super-critical width panels is : +E= 0 . 65( Smax )106 ue Depth/ I E I i i I I I I I I I I r ro r I-'• 0 IC I-1 C CD IV -' m 4•. _ , _ o w [n (11 D rt w rt m 3 SLOPE 7 E O. u? O , c4 ( 4......... 4 W '2 , • / . , - .- _ Icu Q, 4 J / al D w 1f / ,I i I'°-- EXTENSION 1 / - 01 COMPRESSION 1 I 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 Li PANEL WIDTH/PANEL DEPTH 0 5.nT« GRAPH FOR PREDICTING MAXIMUM SLOPE AND STRAIN (NCB, 1975) N 0 N) 0 0 N Longs Peak Estates Page 24 June 20, 2001 and for the Morrison Mine super-critical example case: +E = 0 . 65 ( 2'8:21 ) 106 = 2782 us The location of the 1, 000 us value away from the pillar ribsides was needed in order to draw the 1, 000 us line, shown on Plates 2A and 2B. Figure 11 presents the graph for estimating the distance from Limit of Subsidence line to the 1, 000 us location back toward the failed pillar. In the example case, this distance is calculated as follows : The proportion that 1, 000 us is of the maximum 2782 us tensile strain: 27ez2170802 = 0 . 359E Enter graph on Figure 11 along any horizontal line greater than the "Panel width in terms of depth" line greater that 1 . 4, 2 . 0 is recommended for simplicity. This is possible because the lines on the graph parallel for width/depth ratios greater that 1 . 4, i .e. super-critical . Find the 0 . 359E location on the horizontal line between +0 .2E and +0 . 4E. At the 2 . 0 w/h the 0. 359E value is above approximately 1 . 19 on the "Distance from panel centre in terms of depth" axis (x-axis) and the Limit of Subsidence line is above 1 . 70. The approximate distance from the Limit of Subsidence line to the 1, 000 us line is, therefore: (1 . 70 - 1 . 19) 82 = 41 . 8-ft The 25-ft wide chain pillar example results are shown on Table 1 . In the three sub-critical Clayton Mine panel widths (< 283-ft) it is necessary to use the panel widths measured on Plate 7 to obtain the panel strain factors . Failure of a Morrison Mine chain, barrier and irregular pillar will also develop a zone of horizontal compressive strain in the central part of the white corridors on Plates 2A and 2B. Failure of Clayton Mine chain and room pillars will also develop a zone of horizontal compressive strains toward the central part of the white areas on Plate 6. The maximum compressive surface strain (-E) will be 78 . 5% of the maximum tensile strain (+E) in the case of super-critical the Morrison panel widths . This is not the case for the three sub-critical Clayton Mine panels . 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Sr':• =�si� �i .Z. ��.,�Z) •. -ILL` w•w ii1tw�i.r!'. a Horizontal deformation of rock mass affected by failing pillar adjacent to collapsed panels (modified from Kratzsch, 1983) pl,FaI CD N 0 N 0 0 Fa Longs Peak Estates Page 27 June 20, 2001 The main utility lines and access streets, roughly in the center _ of the white corridors on Plate 2A, Plate 2B (Morrison Mine) and Plate 6 (Clayton Mine) , will be subject to laterally directed compressive strains, possibly as much as the maximum locally predicted compressive strain. The utility lines and access streets to individual lots may be subjected to both the maximum predicted tensile and compressive strains locally predicted where they cross the high strain locations . The strains will be directed longitudinally, in the direction of the individual lot utility lines and driveways . As indicated on Table A4 in Appen- dix A, gas lines to individual lots should be designed with flexible couplings and bedded in loose compressible fill which does not connect directly to individual structures. CHIMNEY SUBSIDENCE EVALUATION Chimney subsidence to the ground surface is possible over unmined Morrison Mine pillars at the Longs Peak Estates develop- ment site . Chimney subsidence is extremely unlikely over Clayton Mine pillars because of its 202-ft depth. Chimney subsidence cannot develop unless the mining height (void space) left after mining is sufficient to accommodate the expansion (swell) of the collapsing overburden. Chimney subsidence cannot develop in the case of barrier pillars because no void space is left after - - retreat mining is complete. Only conical chimney collapse could theoretically breach the ground surface above the Morrison Mine at Longs Peak Estates with roof collapse and breakage if the overburden requires 29%, or less, swell to breach the surface. This can be calculated from the conical collapse equation presented in Figure 4, modified from Piggott and Eynon (1977) , as follows : %S, _ _3h(100) 3(8)100 - 29% H 82 The swell factor of the Clayton Mine overburden would have to be 12%, or less, to breach the surface : $s, _ - 3h(100) 3(8) 100 _ 120 H 202 which only occurs for sand and gravel consolidated by gravity. The overburden rock types in the Morrison and Clayton Mine overburden are shale, mudstone, siltstone and sandstone. Table 2 indicates the typical percent free swell (percent bulking) for sandstone is 67%, shale and mudstone 33%, and soft siltstone 22% . Piggott and Eynon indicate on Figure 4 that 30% is the minimum percent swell for British coal measure rocks . With the unusually low 15% swell reported by Hynes (1984 ) both conical and wedge Longs Peak Estates Page 28 June 20, 2001 chimneys should have collapsed to the surface and sinkhole pits should be present, similar to those on Figure 2 . The site lithology, consisting of 80% shale and mudstone, should not result in chimney subsidence to the surface. Conical collapse chimneys normally develop above entry intersections, where the collapsing roof bed debris can spread unimpeded in four directions . There are only four such inter- - sections under the site, as shown on the Morrison Mine map and none of them are 90° intersections . There are 23 three-way intersections shown on the mine map, which are concentrated at five locations . Wedge type collapse chimneys normally develop above entrys and rooms, i .e. linear excavations between coal pillars . There are seven such locations underlying small areas of the proposed development site. All but one of these locations are on the east side of the site . The other location is in the north-central part of the site in the 6 West entry. Two potential wedge type chimney collapse sites are where pillars between rooms were apparently not retreat mined. These two locations are less than 100-ft wide and 150-ft long and along the southeast site boundary. Two locations are where a narrow pillar parallels one side of a chain pillar. One location is where a large pillar was - left unmined adjacent to one side of a chain pillar. Two locations are where small stump pillars were not robbed during the retreat . Stump pillars are at the entrance to mined out rooms and immediately adjacent to chain pillars . The chimney subsidence hazard is, with the exception of the two small areas where 10-ft wide room pillars were not retreat mined, restricted to above the unmined chain pillars between the two entry submains driven to access the coal panels for advance and retreat extraction. The two-entry submains included break- throughs between individual chain pillars which the mine map indicates were left open after retreat from the panels . The potential for chimney collapse to the ground surface is possible : 1) along the two north-south submains defined by the 5 North/6 North and 7 North/8 North entrys, 2) along the three east-west submains defined by the 1 West/2 West, 3 West/4 West and 5 West/6 West entrys, 3) along the southeast edge of the site above the five apparently unmined room pillars south of the 1 West entry and west of the 4 North entry, Longs Peak Estates Page 29 June 20, 2001 4) along the southeast edge of the site above the three apparently unmined room pillars north of the 2 West entry and west of the 4 North entry. No structures are proposed at these locations because they are in areas where with greater than 1, 000 ue of predicted horizontal strain. The mine map indicates that no openings were driven in the four east-west and one north-south barrier pillars . Therefore, there is no possibility of chimney subsidence developing above the barrier pillars . Longs Peak Estates Page 30 June 20, 2001 CONCLUSIONS AND RECOMMENDATIONS Much of the proposed Longs Peak Estates has already subsided over the retreated room and pillar Morrison Mine panels . However, it is probable that future trough subsidence will occur over and adjacent to unmined chain pillars between the mine' s submains and barrier pillars left between mined out panels when these pillars fail . Minor ridges on the topographic map indicate that some of these pillars may have already failed but the devel- opment design must assume that all the unmined pillars may fail after the proposed development is complete. The magnitude of the maximum potential trough subsidence is less than 0. 75-ft, in most cases less than 0 . 5-ft. However, the resulting maximum horizontal ground surface strains (Table 1) may be as large as 5, 600 us (microstrain) , in most cases less than 3, 400 us. The shallow depth of the Morrison Mine workings, as little as 82-ft, is not sufficient overburden to attenuate the horizontal strains . The predicted maximum horizontal surface strains over deeper (202-ft) Clayton Mine workings are less than 2, 400 us, despite the greater mining height (9-ft versus 8-ft) . Strains greater than 1, 000 us can cause negligible but noticeable adverse effects to residential structures . Plate 2A for the Morrison Mine and Plate 6 for the Clayton Mine, indicate the areas recommended for residential construction and corridors over and adjacent to the chain and barrier pillars suitable only for access streets and flexible utility lines . Natural gas lines crossing higher than 1, 000 ue strain areas must be sufficiently flexible to accommodate the local maximum horizontal strains. It is unlikely, but possible, that chimney collapse will develop to the surface of the proposed Longs Peak Estates devel- opment site. Chimney subsidence that has, or will, develop upward into the overburden will be directly above the open break- throughs left between unmined chain pillars along the Morrison Mine submains . Therefore, the main utility lines and access streets should be located alongside the unmined chain pillars . These are indicated on Plate 1 and in the corridors shown on Plate 2B for the Morrison Mine and Plate 6 for the Clayton Mine . The utility lines and driveways to individual structures should be sited to cross over underlying unmined chain pillars, not open breakthroughs . Longs Peak Estates Page 31 June 20, 2001 REFERENCES Abel, Jr. , J. F. and F.T. Lee, 1984, Lithologic controls on subsidence: Trans . SME/AIME, v 274, p 2028-2034 Abel, Jr. , J. F. , 1988, Soft Rock Pillars : Int' l Jour of Mining and Geol Engrg, v 6, p 215-248 Amuedo and Ivey, 1975, Coal mine subsidence and land use in the Boulder-Weld Coalfield, Boulder and Weld Counties, Colorado: Colorado Geological Survey Environmental Geology Publication No. EG-09 Baker, M. , Jr. , 1974, Architectural measures to minimize subsidence damage : National Technical Information Service PB 242-466 Bell, F.G. , 1975, Site investigations in areas of miming subsidence: Newnes-Butterworths, 168 p Brown, R.W. , S.N. Hanson, and D.R. Ganser, 1992, Subsidence investigation, 80 acre site west of Waneka Reservoir, Boulder County, Colorado: ATEC Associates, Inc. , ATEC Project No. 41-07-92-00022 Colorado Geological Survey, 1989, Mining and surface features : Boulder-Weld Coal Field, (map) Colton, R. B. and R.L. Lowrie, 1973, Map showing mined areas of the Boulder-Weld Coalfield, Colorado: U. S . Geological Survey Miscellaneous Field Studies Map MF-513 Dames and Moore, 1986, Volume I Executive Summary, Boulder County subsidence investigation: prepared for State of Colorado, Geological Survey, Department of Natural Resources, Department of Mined Land Reclamation Dunrud, C.R. and F.W. Osterwald, 1980, Effects of coal mine subsidence in the Sheridan, Wyoming, area: USGS Prof Paper 1164 Gray, R.E . , R.W. Bruhn and R. J. Turka, 1977, Study and analysis of surface subsidence over mined Pittsburgh coalbed: National Technical Information Service PB 261-511, 362 p Hanson, S.N. and P. F. Gottler, 2001, Report of coal-mine subsidence evaluation for Longs Peal Estates Subdivision, Weld County, Colorado: Draft report by E-21 Engineering, Inc. , 31 p Longs Peak Estates Page 32 June 20, 2001 REFERENCES (Continued) Hatton, T. and J.E . Turney, 1984, Annotated bibliography of subsidence studies over abandoned coal mines in Colorado: Colorado Geol Survey Information Series pub IS-22 Hutchings, R. , M. Fajdiga and D. Raisbeck, 1978, The effects of large ground movements resulting from brown coal open cut excavations in the Latrobe Valley, Victoria: in Proc Conference on large ground movements and structures, J.D. Geddes ed, Cardiff, Wales, 1977, p 136-161 Hynes, J.L. , 1984, Tri-towns subsidence investigation, Weld County, Colorado : Colorado Division of Mines, Department of Natural Resources for Colorado Division of Mined Land Reclamation, Inactive Mine Program, Open File Report 87-3 Ivey, J.B. , A.R. Myers, J. Hansen, and R.A. Lindvall, 1974, Subsidence inventory map, Boulder-Weld Coal Field, Boulder and Weld Counties, Colorado: Colorado Geological Survey Map No. 7361-5 Johnson, E. J. and J.W. Himmelreich, 1998, Geologic hazards avoidance or mitigation - A comprehensive guide to state — -- statutes, land use issues, and professional practice in Colorado: Colorado Geological Survey Information Series 47 Kratzsch, H. , 1983, Mining subsidence engineering: Springer-Verlag, 543 p Lee, A. J. , The effect of faulting on mining subsidence: The Mining Engineer, Aug 1966, p 735-745 Lee, F. T . and J. F. Abel, Jr. , 1983, Subsidence from underground mining; Environmental analysis and planning considerations : U.S . Geol . Survey Circular 876, 28 p National Coal Board, (Great Britain) , 1975, Subsidence engineers ' handbook: Mining Dept, London, 111 p Ochab, Z . , 1961, Rules concerning new instructions for the determination of safety pillars in the collieries of Upper Silesian coal fields : Polish Ministry for Mining and Power, Report No. 271 Pendleton, J.A. , 1985, Coal mine subsidence in Colorado, Practical application in a regulatory setting: SME Preprint No. 85-328, 8 p Longs Peak Estates Page 33 June 20, 2001 REFERENCES (Continued) Piggott, R. J. and P. Eynon, 1977, Ground movements from the presence of abandoned mine workings : Proc Conf on Large Ground Movements and Structures, ed J.D. Geddes, J Wiley, p 749-780 Reese, R.G. , B.B. Dash and P.A. Hamilton, 1978, Coal recovery from underground bituminous coal mines in the United States, by mining method: USBM IC 8785, 30 p Schulte, H. F. , 1957, The effects of subsidence on the strata immediately above a working, with different types of packing and in level measures : Proc European Conf on Ground Movement, Leeds, p 188-197, discussion p 198 Thorburn, S . and W.M. Reid, 1977, Incipient failure and demoli- tion of two-storey dwellings due to large ground movements : Proc Conf on Large Ground Movements and Structures, ed J.D. Geddes, J Wiley, p 87-99 Turney, J. E . and L. Murray-Williams, 1983, Colorado front range inactive Colorado mine data and subsidence information, Weld County: Colorado Geological Survey, Department of Natural _ _ Resources, State of Colorado Turney, J.E . , 1984, Subsidence above inactive coal mines, information for the homeowner: Colorado Geological Survey, Special Publication 26 Voight, B. and W. Pariseau, 1970, State of the predictive art in subsidence engineering: Am Soc of Civil Engineers, Jour of Soil Mechanics & Foundation Div, no SM2, p 721-750 Wagner, H. and M.D.G. Salamon, 1973, Strata control techniques in shafts and large excavations : Assoc of Mine Managers of S Africa, v 1972-73, p 123-140 Weld County Assessor' s Office, 2000, Map of 01N68W091 : Weld County Assessor' s Office, 1467-09-1, Map No. 1434, Greeley, Colorado Wilson, G.E. and F.H. Canis, 1931 through 1966, Final Map, Morrison Mine of the Clayton Coal Company, Sections 9 & 16, T. I N. R. 68 W , Weld County, Colorado: Colorado Division of Mines, Department of Natural Resources, File Map No. 123-043300/34-02 . Longs Peak Estates Page 34 June 20, 2001 REFERENCES (Continued) Wilson, G.E. , et . al . , 1920 through 1942, Map of the Clayton Mine, Section 16, T. 1 N. R. 68 W, Weld County, Colorado: Colorado Division of Mines, Department of Natural Resources, File Map No . 120-0432-99/33-01 Yokel, F.Y. , L.A. Salomone and R.M. Chung, 1981, Construction of housing in mine subsidence areas : National Bureau of Standards, Dept of Commerce, Washington D.C. , NBSIR 81-2215, 46 P Appendix A Longs Peak Estates Page 35 June 20, 2001 - APPENDIX A. Table Al . SUBSIDENCE DAMAGE LIMITS ACCEPTABLE SUBSIDENCE DAMAGE Horizontal Vertical Tilt (a) Comments and References Strain (µe) Strain (µe) Tan a minutes) 1000 1000 0. 0010 3 . 43 ' "tolerable level of strain likely to be on the order of"---for high speed shaft hoisting (1) 500-1000 500-1000 High continuous brick walls (2) 1000-2000 1000-2000 One-story brick mill building, wall cracking (2) 1000 1000 Plaster cracking (gypsum) (2) 2500-4000 2500-4000 Reinforced-concrete building frame (2) 3000 3000 Reinforced concrete curtain walls (2) 5000 5000 Steel frame, continuous simple steel frame (2) 0 . 004 13 . 75 ' Tilting of smoke stacks and towers (2) 0 . 010 34 . 37 ' Rolling of trucks stacking goods (2) 0. 003 10 . 32 ' Machine operations : cotton loom (2) 0 . 0002 0. 68 ' Turbo-generator (2) 0. 003 10. 32 ' Crane rails (2) 0. 01 34 . 37 ' Floor drainage to to problems (2) 0. 02 68 . 75' References : (1) Wagner & Salamon, 1973 (2) Voight & Pariseau, 1970 Longs Peak Estates Page 36 June 20, 2001 Table A2 . TOLERANCE OF STRUCTURES TO DIFFERENTIAL SUBSIDENCE (Hutchings, et a1, 1978) DIFFERENTIAL STRUCTURAL SIGNIFICANCE SUBSIDENCE (Strain - %) 0 . 1% Limiting value for high continuous brick walls (1000/16 and brick-clad column frames 0 . 1%-0.2% Single story brick mill building, wall cracking (1000-2000µe) 0. 2%-0 . 4% Limiting value for steel and reinforced concrete (2000-4000µe) frames 0. 7% Structural damage to buildings (7000µe) 0. 8% Slight damage to 2'/2 story brick veneer homes (8000µa) 2% Severe damage to 21/2 story brick veneer (20000/26) Longs Peak Estates Page 37 June 20, 2001 Table A3. SUBSIDENCE DAMAGE DESCRIPTION FOR HORIZONTAL STRAIN (British National Coal Board, 1975) Class of damage Change of length Description of typical damage of structure Very slight Up to 0.1 ft Hair cracks in plaster. Perhaps isolated or negligible slight fracture in the building, not visible on outside. Example: 50-ft long building extended 50 u - in./in. Slight 0.1 ft-0.2 ft Several slight fractures showing inside the building. Doors and windows may stick slightly. Repairs to decoration Example: 110-ft long building probably necessary. extended 1,600 u - in./in. Appreciable 0.2 ft-0.4 ft Slight fractures showing on outside of building (or one main fracture). Doors and windows sticking ; service pipes Example: 90 ft long building may fracture. extended 3,700 u - in./in. Severe 0.4 ft-0.6 ft Service pipes disrupted. Open fractures requiring rebonding and allowing weather into the structure. Window and door frames distorted; floors sloping noticeably. Some loss of bearing in If beams. If compressive damage, overlapping of roof joints and lifting of brickwork with open horizontal Example: 220 ft long apartment fractures. house under compression 2,300 u - in./in. Very severe More than 0.6 ft As above, but worse, and requiring partial or complete rebuilding. Roof and floor beams lose bearing and walls lean badly and need shoring up. Windows broken with distortion. Severe slopes on floors. If compressive damage, severe buckling and bulging of the roofs and Example: 180 ft long apartment walls. house with extension of 6,000 u - in./in. Longs Peak Estates Page 38 June 20, 2001 Figure Al . Relationship of Damage to Length of Structures and Horizontal Ground Strain 7000 6000 OO © Damage due to extension © Damage due to compression 5000 4000 — - Strain C 4 Very v—in. E Severe in. 3000 E C © 2000 E Severe E © C Appreciable © 1000 C E Slight O Very Slight © C -^ or Negligible 0 0 100 200 300 400 500 600 700 (NCB, 1975) Length ( ft. ) Subdam95 Longs Peak Estates Page 39 June 20, 2001 Table A4 . POLISH MINISTRY FOR MINING AND POWER CLASSIFICATION OF PERMISSIBLE STRAIN AND TILT (Ochab, 1961) PERMISSIBLE TYPE OF STRUCTURE OR SERVICE HORIZONTAL TILT STRAIN (MIN) 0 .2% 8 . 5 Gas mains which require particular protection (2000 µe) against the danger of a gas explosion if damaged, also items such as water tanks and industrial installations recognized as being especially important or particularly susceptible to damage with regard to life and safety 0 . 4% 17 Industrial reinforced concrete buildings of (4000 ye) monolithic construction or with gantry cranes, churches with domes and other big buildings for public use such as hospitals, theaters, etc, river beds and water reservoirs, provided the hydro-geological opinion is that the character of the ground does not require any increase or - - decrease of safety conditions, main railway lines and railway stations with a quantity of technical equipment, tunnels and arched bridges, _ main water pipes, also large residential buildings with a length of more than 20 m 0 . 6% 34 Main streets, railway tracks and small railway (6000 µe) stations, girder bridges, industrial buildings of brick, steel and timber construction without cranes and which are not too susceptible to ground movements, cooling towers, high chimney stacks, water towers, churches with beam construction roofs, residential buildings with a length of 10 to 20 m, residential buildings more than 20 m long, but of a specially protected construction, main sewers and airfields 0 . 9% 51 . 5 Large sports stadiums, residential buildings up (9000 µe) 10 m long, residential buildings 10 to 20 m long of a specially protected construction and other items of small importance Hello