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Home My WebLink About20111686.tiff f• MbTETRA TECH July 8, 2011 . 1' -8 II: 2 ' Mr. Peter S. Hays Environmental Protection Specialist _. -.• . -w—' Division of Reclamation, Mining and Safety 1313 Sherman Street, Room 215 Denver, CO 80203 RE: Response to Iverson Mine(M-2011-001)Third Adequacy Review Comments Dear Peter: We received your Third Adequacy Review comments dated June 28, 2011 regarding the Iverson Mine (M-2011-001). Following is a listing of each of your comments followed by our responses. 6.4.4 Exhibit D—Mininq Plan 1. In response to Question#16 from the April 1, 2011 adequacy letter, Tetra Tech conducted a site visit to reevaluate the impact flow of the Cache la Poudre River may have on the Iverson Mine. As a result, the mining limits were revised to a 200 foot set back from the top of bank where the pit side of the river is adjacent to the erosive side of the river and a 100 foot set back from the top of bank where the pit side of the river is adjacent to the depositional side of the river. The revised mining offsets from the Cache la Poudre River are acceptable to the Division, however the Applicant must indicate on the Mining Plan Map where the 100/200 foot offset transition points begin and end. We have added setback dimension lines to Exhibit C, the Mining Plan Map, to show where the 100 foot setback and transitions to a 200 foot setback. Attached is a revised version of Exhibit C (Attachment 1). 6.4.5 Exhibit E— Reclamation Plan 2. The revised Reclamation Plan received on June 6, 2011 did not include the Applicant's commitment to eradicate the Russian Olives at the site upon commencement of operations from the April 29, 2011 adequacy letter from Tetra Tech. Please revise Exhibit E to indicate the previous commitment by the Applicant. We apologize for this oversight; the version of Exhibit E submitted on June Ern was an update to the original version of Exhibit E rather than the April 29, 2011 version of Exhibit E. Lafarge does still commit to eradicating the Russian Olives upon commencement of operations. We deleted the statement regarding Russian Olives from the attached version of Exhibit E(Attachment 2) so that it matches the April 29`h version of Exhibit E which you found to be acceptable. 3. Tetra Tech recommended inflow and outflow spillways be installed in conjunction with site reclamation to control the matter in which high river flows impact the site. The installation of the spillways during reclamation is acceptable to the Division as long as the proposed sequence of mining and reclamation progressing from the southeast corner, center, north end and southwest corner is followed. If the sequence is altered and the southwest portion is not mined last, the spillway structures must be installed after the southern portions of the site have been mined and reclaimed. Lafarge commits to mining the site in the sequence described in Exhibit E so that the southwest portion is mined last. 1900 5.Siunse. Street.S ute Tel 353. 7 7/1 ,1P Fax 303727 2011-1686 l°L 711$/I' llEt TETRA TECH Page 2 of 3 Mr. Peter S. Hays July 8, 2011 4. The Applicant states the spillways are in accordance with the best practices of the Urban Drainage and Flood Control District guidelines. Please provide additional information pertaining to the design and construction of the inflow and outflow structures. At minimum, please include the following information: a. Justification for the spillway locations b. Spillway invert elevations c. Cross-section details (both lateral and longitudinal) d. Design parameters The design parameters should include the expected flood flow elevations and peak flows, frequency of the expected flood flows, the expected water elevation in the lake if the spillways are designed to control the lake surface elevation. Additionally, a copy of the Weld County Drainage Report(draft or final version)would be helpful in the Division's evaluation of the spillway design. The spillway locations are placed in such a way that would allow river water currents to enter and leave the pond in a manner that follows the natural flow of the river. The Army Corps of Engineers conducted a general investigation study of the Cache La Poudre River at Greeley, CO. According to the hydrologic analysis prepared for this study, a flow greater than 1600 cfs would overtop the Cache La Poudre River bank and flow onto the Iverson Mine property. 1600 cfs is slightly greater than the 2-year peak flow of the river. The spillways for the reclamation pond are designed to convey one third of the stream flow of the river, or 533 cfs. UDFCD guidelines do not set any flow rate requirements for spillways. The length criteria set forth in UDFCD guidelines require very large spillways relative to the final storage capacity of the reclaimed mine. Calculations for the spillways show that the inflow fills the reclaimed mine in approximately 1.2 hours, reducing the pressure on the riverside banks due to varying water surface elevations on either side of the bank. Because the pond will be unlined, the water surface elevation of the pond will change seasonally with the groundwater elevation. However, the water surface elevation shall not exceed the crest elevation of the outflow spillway of 4679.1 ft. Cross-sections and plans are presented in Attachment 3. These plans are conceptual at this time and may change in the future due to regulatory requirements and County review. As requested, a copy of the most current version of the Drainage Report is provided as Attachment 4. 6.5 Geotechnical Stability Exhibit 5. The Applicant's revised slope stability analysis with stockpile and tower surcharge loads of 1,100 and 3,000 pounds per square foot respectively was duplicated for verification by the Division using Galena. No potential failure surfaces with lower safety factors than the Applicant's identified critical slop circle were located. The safety factor produced by Galena is slightly higher than that produced by the Applicant's model. The accuracy of the Applicant's analysis is confirmed. A copy of the Galena cross-section is attached for reference. Noted; thank you for a copy of the Galena cross-section. We understand that the current Decision Date for this application is July 25, 2011. Please notify us as soon as possible or no later than July 18, 2011 if you need more time to complete your review of this application and determine that the items have all been satisfactorily addressed so that you can issue the permit. If you need more time, we will request a Decision Date extension. TETRA TECH Page 3 of 3 IN Mr. Peter S. Hays July 8, 2011 Thank you for your consideration. Sincerely, TETRA TECH 411teh- C4471&- Pamela Franch Hora, AICP Senior Planner Attachment 1: Exhibit C Attachment 2: Exhibit E Attachment 3: Exhibits A, B-1 and B-2 Attachment 4: Iverson Mine Drainage Report cc: Anne Johnson, Lafarge West, Inc. 1900 S.Sunset Street.Suite i-F.Longmont CO 80501 Tel 303 772 5282 Fax 303.772.7039 www,tetratech_com LARGE MAPS ARE LOCATED IN ORIGINAL FILE ATTACHMENT 2 a EXHIBIT E Reclamation Plan Design Intent The Iverson property will be reclaimed as an unlined, open water pond surrounded by uplands. Native and adaptive plantings and ground covers will be used to restore and enhance all areas disturbed by mining activities. The most appropriate primary post-mining land use designation for the site is wildlife habitat given the fact that a majority of the property will be covered by the open water pond. However, this designation is for purposes of the DRMS application only and the property is not designated by any other agency as wildlife habitat. Therefore, following reclamation and release of the property by the DRMS, the land use of the property could be changed by the land owner according to the land use regulations of Weld County. This Iverson Mine reclamation plan was developed based on the following considerations: • A thorough evaluation of the environmental resources and existing conditions on and adjacent to the property, particularly the Cache la Poudre River riparian corridor along the west, north and east sides of the property; • The context of the property relative to existing and planned land uses in the area; • The volume, depth and configuration of the mineral resource; • The landowners' plans for the property; and • The rules and policies of the Colorado Division of Minerals and Geology and other applicable local, State and Federal agencies. • The open water pond, which will be created upon reclamation of the Iverson property, may provide some wildlife habitat due to its proximity to the river corridor. Post-Mining Land Use Following the mining of the Iverson property, the land will be reclaimed with an open water pond surrounded by upland. All areas reclaimed as upland will be re-vegetated with a native seed mix, as recommended by the Soil Conservation Service (recommended seed mixes below). This use is compatible with the surrounding land uses. Lafarge will concurrently reclaim mine walls where mining has been completed. Reclamation, including re-grading and seeding, will be completed within two to five years following the completion of mining or filling operations. The mining and reclamation will leave no high walls on the property. No acid forming or toxic materials will be used or encountered in the mining. There will be no auger holes, adits, or shafts left on the site. Topsoiling Topsoils in the proposed mine areas are Aquolls and Aquents, Ascalon loam, Dacono clay loam, Nunn loam, and Otero sandy loam. All suitable soil material will be salvaged for topsoil replacement. The topsoil will be segregated and stored separately from the overburden material as required by Rule 3.1.9(1). Upon reclamation of the site, all upland areas will be reclaimed with at least six inches of topsoil. Iverson Mine DRMS 112 Reclamation Permit Application Page El of E4 Soil amendments are not expected to be required due to the nature of the soils. However, topsoil samples will be subjected to agricultural testing prior to reclamation to assess fertilizer requirements. The Soil Conservation Services (SCS) will be contacted periodically throughout reclamation for soil tests. SCS soil fertilizer recommendations, if any, will be followed. Reclamation Measures—Material Handling Site reclamation measures are illustrated on Exhibit F. The Iverson property will be reclaimed as an open water pond surrounded by upland. The pond will be an un-sealed groundwater pond. All mine walls will be re-graded with overburden material. If needed, portions of the deposit not mined may be used to supplement the overburden. Slopes both above and below the post-mine high water level will all be 3H:1 V or flatter. Topsoil will be spread over the surface of the re-graded slopes in all areas above the post-mining pond level; all topsoil-covered surfaces will be revegetated with the appropriate seed mix. Topsoil replaced in upland areas will be at a depth of at least six inches. Scrapers and a dozer will be used to place the backfilled overburden and topsoil. Using the scrapers and dozer to layer the lifts at a maximum 3H:1 V slope ensures a stable configuration. Site grading will be performed to create stable topography and will be consistent with post-closure land uses. Reclamation costs and quantities are summarized in Exhibit L. Water Overburden and mine materials will be inert and impacts to local surface water or groundwater quality are not anticipated to occur as a result of mining activities. Lafarge West, Inc. will comply with all applicable Colorado water laws and all applicable Federal and State water quality laws and regulations and appropriate storm water management and erosion control to protect the river and existing riparian vegetation. Wildlife The Iverson property is adjacent to the Cache la Poudre River corridor which provides wildlife habitat to a variety of species (see Exhibit H for details). All mining will be setback 100-200 feet from the bank of the river to be outside of the riparian corridor to minimize any potential impacts on wildlife within the riparian corridor. Revegetation Following topsoil replacement, reseeding will be performed according to SCS recommended practices. Based on SCS guidance for other local projects having similar surficial soils, the following revegetation procedures are anticipated: • Grass seed will typically be planted in unfrozen soil between October 1 and April 30. • Grass seed will be planted with a grass drill, or where necessary, with a broadcast seeder. • The proposed seed mix and application rates in pounds of pure live seed per acre are described on the following pages. • Weed control practices will be implemented as required. Iverson Mine DRMS 112 Reclamation Permit Application Page E2 of E4 The above procedures may be modified as conditions dictate. If a significant invasion of noxious weeds occurs, the area will be mowed periodically for control. Weeds will be mowed before they go to seed during the first growing season. Mechanical control will be used as a first priority. Chemical methods will be used only if no other alternative produces acceptable results. Marsh and aquatic plants are expected to establish themselves along the shoreline of the post- mining pond. The species of plants anticipated to establish themselves naturally along the pond shoreline include cattails, willows, cottonwoods, and bulrushes. The existing riparian areas along the Cache la Poudre River would function as a seed bank for the pond area. These plants should minimize shore erosion potential. The following are the proposed seed mixtures to be used on site where appropriate. However, availability may dictate the need for variety substitution. Seed Mix for Upland Areas of PLSt Common Name Scientific Name Variety Nlix Application Rate(Ibs/ac} Western Wheatgrass Agropyron smithii Arriba 17.0% 2.55 Sideoats Grama Bouteloua curtipendia Butte 17.5% 2.63 Mountain Brome Bromus marginatus Bromar 17.0 % 2.55 Prairie Sandreed Calamovilfa longifolia Goshen 1.0% .15 Switchgrass Panicum virgatum Pathfinder 7.0% 1.05 Alkali Sacaton Sporobolus airoides 1.0% .15 Needle and Thread Stipa comata 13.0% 1.95 Northern Sweetvetch Hedysarum boreale Timp. 10.0% 1.50 Rocky Mountain Penstemon Penstemon strictus Bandera 5.0% .75 Scarlet Globemallow Sphaeralcea coccinea ARS2936 3.0% .45 Prairie Wildrose Rosa Arkansans 8.5% 1.28 Total lbs/ac 100% 15.01 Pure Live Seed pounds per acre; rates shown are for drill seeding; double rates for broadcast seeding. Iverson Mine DRIVE ll2 Reclamation Permit Application Page E3 of EA Seed Mix for Transitional Zone/Water's Edge Common N a meScientific Sine °o of � "��riefY Application Western Wheatgrass Agropyron smithii Arriba 10.6% 1.59 Side Oats Grama Bouteloua curtipendia Butte 9.2% 1.38 Canada wildrye Elymus canadensis Mandan 18.1% 2.72 Streambank Wheatgrass Elymus lanceolatus ssp. Sodar 9.8% psammophilus 1.47 Switchgrass Panicum virgatum Pathfinder 53% .86 Sand dropseed Sporobolus cryptandrus 0.2% 0.03 Scarlet Globemallow Sphaeralcea coccinea ARS2936 3.8% 0.57 American vetch Vica americana 42.6% 6.39 Total lbs/ac 100% 15.01 Pure Live Seed pounds per acre; rates shown are for drill seeding; double rates for broadcast seeding. 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LdI Ld IL Y I Z o O O d o N - N w i o Cq O w p 8; a o s 1 tL Z J U_ H K W a to o >- N J J u co u w' C - LT Q .11 o m 1 1' I 5 co 0 V O 0 < ' o O = E LL- M < w V A G v < W € „° g ' tz o I ° ,No I H o_ _o 0 F„ W yo uail r3 oox 0 o 00 7 o$ 0 Lo" rc 7 - 0 33 L in=V o 2 1 1 wo ry 0.00 rl am _ _ oI o O ' _,. ,-05�-1._+b S5 b 0G o m m r 0 L0 r m m m (O to e e e e e e Elevation • u w 0 0 o C t gra\Al'NNVIN OMO Ea CIA Aga a 1191HX3 NOV913Sl00MONINIVASIIBIHX3\S3ll'133HS\OVO\Z000l-1 ISEESELULSEZId-Aid ZO'Sir LLOi ATTACHMENT 4 U • • • • • • FINAL DRAINAGE REPORT FOR IVERSON MINE • • WELD COUNTY, COLORADO • • • • Prepared for: Lafarge West, Inc. • 11409 Business Park Circle, Suite 200 • Longmont, CO 80504 • • Prepared by: • • TETRA TECH • 1900 South Sunset, Suite 1-F • Longmont, Colorado 80501 • Tetra Tech Job No. 133-23511-10002 • • • February 2011 • • • • TETRA TECH • • • • • • S • • . TETRA TECH • • • • February 1,2011 Mr. Clay Kimmi • Weld County-Public Works Department • 1111 H Street . Greeley,CO 80631 Re: Final Drainage Report for Iverson Mine . Tetra Tech Job No. 133-23511.10002 • Dear Mr. Kimmi: . On behalf of Lafarge West, Inc.,we are submitting this Final Drainage Report for Iverson Mine. . The enclosed report provides information on the site's historic drainage patterns, and evaluates the site's mining and reclamation drainage patterns. If there are any questions or comments concerning this report,please feel free to contact us. Sincerely, . TETRA TECH / , I a l Karlie M. M . , E.I.T.,CFM • Design • y ne•r Jere, r .n,P.E., CFM Projec En a. er Enclosures • . P:\235111133-23511-10002\Delivcrables\Drainage Report\Drainagc Reportdoc • • • TETRA TECH • • • ENGINEER'S CERTIFICATION • • • I hereby certify that this Final Drainage Report for Iverson Mine was prepared under my direct . supervision in accordance with the provisions of the Weld County Storm Design Criteria and the Urban Storm Drainage Criteria Manual, Volumes 1, 2 and 3, and was designed to comply with the provisions thereof. st,.. .....Ce VO P• Ey BST•Fi /�� li •' • i1►.; 3 !I • Jeffre . !' License' Profes ion'i _• , urt\\C? ` State of Colorado No. OP • TABLE OF CONTENTS • Page • 1.0 INTRODUCTION 1 • 2.0 INTENT 1 • 3.0 HISTORIC SITE TOPOGRAPHY AND DRAINAGE CHARACTERISTICS 1 • 4.0 ANALYSIS CRITERIA 2 5.0 EXISTING DRAINAGE CHARACTERISTICS 3 6.0 MINING DRAINAGE CHARACTERISTICS 3 7.0 RECLAIMED DRAINAGE CHARACTERISTICS 4 8.0 SAFETY HAZARDS 5 • 9.0 CONCLUSION 5 List of Appendices . Appendix A Vicinity Map Appendix B Site Properties Appendix C Adjacent Ownership Map . Appendix D Historic Drainage Analysis Appendix E Mining Drainage Analysis Appendix F Reclamation Drainage Analysis List of Tables Table 9.1 —Storm Drainage Comparison List of Drawings . Historic Drainage Plan Appendix D Mining Drainage Plan Appendix E Reclamation Drainage Plan Appendix F I 1.0 INTRODUCTION The proposed Iverson Mine site is located in the Section 34, Township 6 North, Range 66 • West of the 6th Principal Meridian, Weld County, State of Colorado. The site is bounded to • the north, west and east by the Cache la Poudre River and to the south by the Poudre Trail • and rural residential/agricultural land. The site is located approximately 0.3 miles north of the City of Greeley and contains 83.06 acres,more or less. The property contains a significant • commercial deposit of aggregate along the Cache la Poudre River. There are several existing • gravel mine operations in the project vicinity. The Iverson Mine is under review by the . Colorado Division of Reclamation, Mining and Safety (DRMS), (File Number M-2011-001). A vicinity map is presented in Appendix A. • • 2.0 INTENT • The purpose of this report is to provide an evaluation of the exiting, mining and reclamation • conditions for the Iverson Mine property. The contents of this report are prepared in • accordance with Weld County Storm Design Criteria and the Urban Storm Drainage Criteria Manual, Volumes 1, 2 and 3. This report examines the existing topography, existing, mining . and reclamation stormwater runoff through the site and describes the existing and proposed site features. It is intended to show that the site development will not increase runoff to • adjacent property owners. 3.0 HISTORIC SITE TOPOGRAPHY AND DRAINAGE CHARACTERISTICS • Figure 1 is a vicinity map showing the site and surrounding area. The area of disturbance will . encompass approximately 64.3 acres of the site, with 45.1 acres of the site to be mined. The remaining unmined acres will be used for overburden and topsoil stockpiles, an internal road and conveyor access. The irregularly shaped parcel is relatively flat and low lying in the • greater floodplain of the Cache la Poudre River. There are no significant areas of concentrated flow. . • The site is owned by Tim and Jeanne Iverson and will be mined by Lafarge West under • license. For the names of all property owners and those within 200 feet of the Iverson Mine Property boundary see the Adjacent Ownership Map presented in Appendix C. • • According to the United States Department of Agriculture Soil Conservation Service Web • Soil Survey of Weld County, Colorado the site soils belong to Hydraulic Soil Groups B, C and D. Gravelly substratum, Ascalon loam, Dacono clay loam,Nunn loam, and Otero sandy • loam are the soil types on the site. Please refer to the Soil Map provided in Appendix B for • the soil type reference. • Portions of the site are within a Zone A3 floodplain according to the Federal Emergency • Management Agency (FEMA) Flood Insurance Rate Map (FIRM) Community-Panel No. • 080266-0609-C, dated September 28, 1992. The Corps of Engineers completed a Flood • Insurance Study in October 2003 for the Cache la Poudre River in the vicinity of the Iverson site. This study is currently under review by FEMA but has not yet become the effective • study. For the purposes of this Flood Hazard Development Permit, the 100-year floodplain • and floodway boundaries of this pending study will be adopted as the best available • - 1 - • Final Drainage Report Iverson Mine February 2011 • Pd2351 I\133-23511-I 0002'Dclivcrables\Drainage Report\Drainage Report.doc • • information. For flood plain information refer to the Flood Hazard Development application • dated February, 2011,prepared by Tetra Tech. • 4.0 ANALYSIS CRITERIA Design Criteria and Constraints • This report was prepared in compliance with the Urban Storm Drainage Criteria Manual . (USDCM). The Criteria was followed in accordance with the Weld County Code and the . Weld County Storm Drainage Criteria Addendum to the Urban Storm Drainage Criteria Manuals Volumes 1, 2 and 3. Based on these criteria, a 100-year storm was used as the • major storm in the drainage analysis. • The constraints related to mining and reclamation of the Iverson Mine site deal primarily with mining setbacks from property boundaries, wetlands, river banks, and existing gas/oil • wells and appurtenances. During mining phases, temporary topsoil and overburden stockpiles will be constructed adjacent to the mined areas. These temporary stockpiles will be located outside of the floodway boundaries and oriented parallel to the direction of overbank flow. • Upon completion of the reclamation phase of the project, all temporary stockpiles will be removed and final grading within the limits of the 100-year floodplain will be to an elevation • at or below pre-mining grades. • Hydrologic Criteria • Since all basins were less than 160 acres in area, the Rational Method was used in stormwater runoff calculations. Runoff coefficients (C), applied in the Rational Method, were weighted • based on the historic and existing land use, and on the types of soils on the site. The site • rainfall depth information was obtained using the information provided in the City of Greeley • Storm Drainage Design Criteria and Construction Specification Document. The 5-year and 100-year 1-hour storms have magnitudes of 1.49 inches and 2.78 inches,respectively. The • percent imperviousness was determined for the anticipated land use from Table RO-3 of the • Urban Drainage and Flood Control District Drainage Criteria Manual(UDFCDM). The • runoff coefficients were then taken from Table RO-5 of the UDFCDMbased on the soil map average. Historic runoff coefficients are C5 = 0.128, and C100=0.442 for basin H-1 and C5 = • 0.112, and C100= 0.409 for basin H-2. Historic flow calculations are presented in Appendix • D. Please refer to Historic Drainage Plan presented in Appendix D. • Hydraulic Criteria • • During the mining phases of this project,direct precipitation on the mined areas and runoff • from minor on-site basins will be captured in the mining areas. A dewatering trench and dewatering pump will be utilized to remove this captured runoff from the mining areas. If • necessary, discharge permits will be obtained for each of these dewatering discharge points to • allow discharge to the natural drainage ways. The runoff from the site is significantly reduced after reclamation is completed as compared with the existing conditions. The reclaimed pond will capture and attenuate surface runoff • that historically flowed across the parcels. Existing natural drainage ways will remain • - 2 - • Final Drainage Report Iverson Mine February 2011 • P:\23511\133-23511-10002\Deliverables\Dramagc Report\Drainage Report.doc • S • • • • undisturbed. For reclamation, there are no proposed hydraulic components such as • conveyance channels, rundown channels, culverts, grade control structures, or detention outlets. The pond will be constructed with an emergency spillway to maintain the normal • pool elevation. • 10 EXISTING DRAINAGE CHARACTERISTICS • The existing drainage conditions at the Iverson Mine site are presented in the Historic • Drainage Plan presented in Appendix D. The site was delineated into two basins, H-1 and H- . 2 and was analyzed with two design points, DPI and DP2. DPI is meant to represent a majority of the site at one point along the Cache la Poudre River. In reality, existing • conditions do not collect at one point on the river. Site topography drains continuously along • the south bank of the river. The peak runoff results for the 100-year storm events are . discussed below. The following is a more detailed description of each existing drainage basin. Calculations are presented in Appendix D. • • Design Point I Basin H-1 contains approximately 81.38 acres of undeveloped, agricultural land and • therefore has an imperviousness of 2 percent. Basin H-1 has an average slope of 0.6 percent • and storm water drains from southwest to northeast as overland flow and returns to the Cache • la Poudre River as such. Based on the runoff equation in the USDCM, the runoff coefficient was calculated to be 0.442 for the 100-year storm. A time of concentration of 111 minutes • would result in a 100-year rainfall intensity of 1.83 inches per hour. Applying the rational • method produced a peak runoff of 65.79 cfs. • Design Point 2 • Basin H-2 contains approximately 23.43 acres of undeveloped, agricultural land and • therefore has an imperviousness of 2 percent. Basin H-2 has an average slope of 0.9 percent. • Storm water drains from the southwest to northeast and sheetflows off the property to the east to wetlands adjacent to the Cache la Poudre River. Based on the runoff equation in the USDCM,the runoff coefficient was calculated to be 0.409 for the 100-year storm. A time of • concentration of 83 minutes would result in a 100-year rainfall intensity of 2.24 inches per • hour. Applying the rational method produced a peak runoff of 21.50 cfs. • 6.0 MINING DRAINAGE CHARACTERISTICS • Mining for the Iverson Mine site will occur in one phase. Mining operations either will not • change or will significantly reduce the drainage area and historical runoff leaving the site • from each historical basin. The mining phase will incorporate the use of temporary topsoil • and overburden stockpiles around the perimeter of the mining area. A conveyor will be used . to move mined materials to the processing plant. Lafarge anticipates mining and reclaiming the site in approximately 4-5 years; however, the rate of mining and overall life of the mine is dependent upon demand and market conditions. • Design Point / • Basin M-1 has an area of 29.15 acres of undeveloped, agricultural land and therefore has an • imperviousness of 2 percent and will drain to design point DPI. No mining activities are • proposed for this basin and therefore the imperviousness will remain 2 percent. Based on the • - 3 - • Final Drainage Report Iverson Mine February 2011 . P:\23511\133 3511-10002\Dcliverables\Drainage Report\Drainage Report.doc • . runoff equation in the USDCM, the runoff coefficient was calculated to be 0.454 for the 100- year storm. A time of concentration of 44 minutes would result in a 100-year rainfall intensity of 3.45 inches per hour. Applying the rational method produced a peak runoff of 45.70 cfs. Basin M-1 will drain as it did historically and travel by overland flow until it . reaches the Cache la Poudre River. During mining conditions, runoff to design point 1 will be . reduced from historical conditions from 65.79 cfs to 45.70 cfs. The drainage area contributing to flow leaving the site reduces from the historical condition of 81.38 acres to a mining condition of 29.15 acres. Design Point 2 Basin M-2 has an area of 8.44 acres and will drain to design point DP2. No mining activities are proposed for this basin and therefore the imperviousness will remain 2 percent. The . runoff coefficient was calculated to be 0.473 for the 100-year storm. A time of concentration . of 81 minutes would result in a 100-year rainfall intensity of 2.29 inches per hour. Applying the rational method produced a peak runoff of 9.13 cfs. Basin M-2 will sheetflow across the property and off the site to the east. During mining conditions, runoff to design point 2 will . be reduced from historical conditions from 21.50 cfs to 9.13 cfs. The drainage area . contributing to flow leaving the site reduces from the historical condition of 23.43 acres to a mining condition of 8.44 acres. Basin M-3 has an area of 67.22 acres and is completely captured within the gravel mine. Water collected in the mine will be collected into a drainage swale system and conveyed to the Cache la Poudre River at one of two discharge points. Please refer to the Mining Drainage Plan and calculations presented in Appendix E. 7.0 RECLAIMED DRAINAGE CHARACTERISTICS . Site reclamation either will not change or will significantly reduce the drainage area and . historical runoff leaving the site from each historical basin. Upon completion of the gravel mining, the site will be reclaimed as an open water pond and upland areas as shown in the Reclamation Drainage Plan presented in Appendix F. Design Point / The reclaimed site will have three drainage basins. Basin R-1 contains approximately 31.31 acres and will follow historic drainage patterns and sheetflow off the property and into the . Cache la Poudre River. Basin R-1 contains undeveloped, agricultural land and therefore has . an imperviousness of 2 percent. Based on the runoff equation in the USDCM, the runoff coefficient was calculated to be 0.456 for the 100-year storm. A time of concentration of 44 minutes would result in a 100-year rainfall intensity of 3.46 inches per hour. Applying the . rational method produced a peak runoff of 49.40 cfs. Basin R-1 returns to the Cache la Poudre River as overland flow at DPI. Reclaimed conditions will reduce the runoff to design . point 1 from historical conditions from 65.79 cfs to 49.40 cfs. The drainage area contributing to flow leaving the site reduces from the historical condition of 81.38 acres to a reclaimed condition of 31.31 acres. 0 - 4 - II Final Drainage Report Iverson Mine February 2011 . P:'23511\I 33-23511-10002\Dcliverables\Drainage Report\Drainage Report doe U S . Design Point 2 • Basin R-2 contains approximately 23.42 acres and will follow historic drainage patterns and sheetflow off the property to the east and into wetlands adjacent to the Cache la Poudre River. Basin R-2 contains undeveloped, agricultural land and therefore has an imperviousness of 2 percent. The runoff coefficient was calculated to be 0.409 for the 100- e year storm. A time of concentration of 83 minutes would results in a 100-year rainfall intensity of 2.24 inches per hour. Applying the rational method produced a peak runoff of 21.49 cfs. Reclaimed conditions for this basin will return to historic conditions and will not increase the runoff, or area, flowing to design point 2. Basin R-3 is 50.08 acres and will consist entirely of the reclamation pond. The proposed pond has a surface area of 36.8 acres and an available storage volume for storm water capture of 115 acre-feet above the normal pool. The unlined pond is assumed to have a minimum of . approximately 3 feet of freeboard above natural high water level before overtopping could occur. . The surface hydrology associated with the reclaimed condition will not adversely impact the . adjacent properties. Final grading will result in contours that either match or are below pre- mining contours. Surface runoff from the majority of the site will flow directly into the unlined pond and upland areas. 8.0 SAFETY HAZARDS The drainage structures proposed for this project have minimal associated safety hazards. . Safety concerns for the mining operation have been addressed in the permit applications to . the State. . 9.0 CONCLUSION This report was prepared in compliance with the Weld County Code and the Weld County Storm Drainage Criteria Addendum to the Urban Storm Drainage Criteria Manuals Volumes . 1, 2 and 3. The proposed Iverson Mine development will reduce the runoff from the site due to the capture of runoff within the mining area. Upon completion of the mining project, the . screening/overburden stockpile berms will be removed and used for reclamation of the unlined open water pond and upland areas. For existing conditions, the sum of all drainage basin areas is 104.81 acres. Direct . precipitation on the reclaimed unlined pond and the sum of the basin area that would be . captured by the unlined pond is 50.08 acres. The reclaimed site will reduce the contributing drainage area to approximately 48 percent of the historic area without increasing the imperviousness of the contributing drainage area. - 5 - . Final Drainage Report Iverson Mine February 2011 P.23511\133-2351 I-I 0002rDeIiverablcs\Drainage Report\Drainage Report.doc OP • • Table 9.1 —Storm Drainage Comparison • Design Point Existing Conditions Mining Conditions Reclaimed Conditions Q100(cfs) Qioa(cfs) Q100 (efs) • 1 65.79 45.70 49.40 . 2 21.50 9.13 21.49 Total 87.29 54.83 70.89 . A copy of the Historic Drainage Plan,Mining Drainage Plan, and Reclamation Drainage Plan, and the drainage calculations follows for your review. • - 6 - • Final Drainage Report Iverson Mine February 2011 0 P.`235I I\133-23511-10002\Deliverables\Drainage Report\Drainage Report.doc 5 4. 4. APPENDIX A +• VICINITY MAP • AP • • SP • 40, • 115, 41, • • • • 111, • • • • • • • Copyright: Tetra Tech • a • • tr 1 • 9 10 11 12 \ 9- \\\8r 1WJ ZO �J. w COUNTY RD 70 • Igp co n o O O •• z o 17 16 \ a 15 143 18 7 16 K C -< j\ \�\ 2 —`STATE HWY 392• a STATE H 392 •--1 1 \ / \ i• >- ) 20 21 r 22 1 23 24 • 24 19 20 L 21 • _ IVERSON • _ � , MINE SITE • O 29 0 28 27 x 6 29 28 co cn • a =COUNTY F D 64 _H_r4 � �, _ O ST r OO fA p r. ME LA FOVEAE RIVER t ! ! : ttL Q� 3536ra 6T v'� t', � � \ 5 T6N • W x ate v\ tth "� • Nf. '-' 10TH . H-IWY 34 , • $ ,� �� CITY OF GREELEY V\ �� o � rV � � tiy < ` 1J , m s e- 2' RST v \ t o • m © • a � �\ • 0 3000' 6000' ii. E % • m 1 37TH ST. 0 \ • a SCALE: 1"=6000' /J • EN,1 Project No.: 133-23511-10002 • Elj TETRA TECH Date: 02-01-11 • = IVERSON MINE SITE Designed By: MM • ' www.tetratech.com VICINITY MAP FIGURE • r _ 1900 S.Sunset Street,Ste.1-F • ri'sLongmont Colorado 80501 PHONE'(303)772-5282 FAX (303)772-7039 LAFARGE WEST, INC. H • • Copyright: Tetra Tech • a ID i r O t APPENDIX B 0 S • SITE PROPERTIES 0 O 0 0 0 0 r 9 0 0 II 0 r 0 0 S 0 II I S I I I I I r 0 I I I I _ N414•410••••••••be�f'a,w- a- sr. II i • -�-- - milr 39 SMIls 0 ......, tr. .... .......... _ . ____........ . ., , n..„....,., _ . , _ , . . _ . . I / !__� 111 is _�Smem I r ., mow.\. - �'M4.r!IllW _ r I � 1. l ' , • -' L 0 ts, as "i( 1 0 r. I. \I\ ., r+ �` 1 > d • e % . 1 a , !! �`' 4 $ /1 f I ii: i ar., v / 111 ; i • . 4.: 1 I • x ' ia , / r ._.. _ . � .., • ! 1 �1• !• _ . .. T • At 1 y d� i H .• . \! r1 • " f� 'e � y. ,• . le T...... __ x_ r , 1 t 11 • ! 1 / ifiller. i ; .- • , : 9 .. ., C.1 V41 ic .- / i _...... ,....- tir . 7. • \',/ • �_ ,� - , fi H - - - -4° 1t U 1. I cc T4.. _____/ 1 :. i ‘7,4v /Ai\ ,,,,,„,; j -, J • . ,, lb • a. , .. . . • ..„ , ....... ..„ `g • °, ,, s. --. ,•• • . • .. . ,,,,, xa'ak Nrrs a: / 1 _ - 4 p � ~ ! N• • (.0 r'" r � � y 11 l -J• Lii . ". ‘�' . . :- ^`mac- ,� ' II---.., ', Y. • l - ar O 0 • N O O O ! 0 250' 500' in 0 M • r SCALE: 1 "=500' • co • 2 LAFARGE WEST, INC. Project No.: 133-23511-10002 • 1.O 0 TETRA TECH IVERSON MINE Date: 1-31-11 N Designed By: JAB N • eNi www.tetratech.com FIGURE 0 ! 1900 S. SUNSET STREET,STE 1-F SOIL MAP 2 LONGMONT, COLORADO 80501 / N ` PHONE: (303) 772-5282 FAX: (303)772-7039 ill ` Bar Measures 1 inch 0 0 0 0 S N % a O o C O • co 0 -(15co o ° � E 2 = 9 0 ® co t \ 2 % r co -oco co O b / o ( / E q / � � / \ / 3 § \ % % / m r a o _o / \ % -0 \ x E co ? q m q ® / / — c 5" § / $ / O OM . fE < = a § / / k k % 3 O U - O QN � > 7 ° \ • 'k k E 3 2 m o co a c ® o Ce 4 2fD k O)El a \ § § / k o • C r \ E co j U. al a• • _ = 2 / ' / - -C / 4- k / / \ / \ \ E \ 7 Es -c8 Q P \ / a ! \ ° % \ a / / ® _ D c •/ 0 Q b \ 2 2 m \ \ .N o 2 o / / \ cn ) � E oo f r ° o c C a w � f < 0 k 2 2 a / / % ≥ ° ' fo \ E / / \ aco � •E t R . / \ ? - CO _ .00 « co / _ ka _ co ci_ ( 9 ° - ° / a § co O o ' e / a) / r ) 0 0 2 0 E ° ? \ VCD / E ca()) E / 2 H E E m s U H a m m 0 Hof ± 0 O U) • / a T. 2 O Z v .E O u \ \ ° ] U 2 75 a § • d a) • .K a to f \ % Co / • co_ ! ® Z ) a § - k » cn S W { \ » \ \ g Co \ W a ± @ / ] O CL 2 § - / = m - 2 . 5 C 7,1) \ i « \ CO 2 O / O / \U. \ 0 cp \ $ cc \ \ 2 \ — Ct e \ a e . 2 co t | ❑ i ❑ / 0 t § t . / S § 2i lm } « ■ 0 0 I • S • 0 . 0 0 0 . 0 0 S U • • Hydrologic Soil Group—Weld County,Colorado,Southern Part • • Hydrologic Soil Group • • • Hydrologic Soil Group—Summary by Map Unit—Weld County,Colorado,Southern Part • Map unit symbol I Map unit name Rating I Acres in AOI I Percent of AOI • '..3 Aquolls and Aquents,gravelly ',D 209.2 59.8% • substratum • 8 Ascalon loam,0 to 1 percent slopes 0 23.6 6.7% 10 Bankard s sandy loam,0 to 3 percent A 8.9 2.6% . slopes • 13 Cascajo slopes gravelly sandy loam,5 to 20 A 23.7 6.8%per• 21 Dacono clay loam,0 to 1 percent '..B if 8.0 2.3%1 • _. slopes. • 39 Nunn loam,0 to 1 percent slopes C 26.4 7.5%'.. • 51 Otero sandy loam, 1 to 3 percent B 23.6 6.7% slopes • 85 Water 26.3 7.5% • Totals for Area of Interest 349.7 100.0% • • • • • • • • • • • • • • • • • USDA Natural Resources Web Soil Survey 1/20/2011 • a Conservation Service National Cooperative Soil Survey Page 3 of 5 ID • DRAINAGE CRITERIA MANUAL(V. 1) RUNOFF • 2.4 Time of Concentration • One of the basic assumptions underlying the Rational Method is that runoff is a function of the average 111 rainfall rate during the time required for water to flow from the most remote part of the drainage area under consideration to the design point. However, in practice,the time of concentration can be an • empirical value that results in reasonable and acceptable peak flow calculations. The time of • concentration relationships recommended in this Manual are based in part on the rainfall-runoff data collected in the Denver metropolitan area and are designed to work with the runoff coefficients also • recommended in this Manual. As a result, these recommendations need to be used with a great deal of • caution whenever working in areas that may differ significantly from the climate or topography found in • the Denver region. • For urban areas,the time of concentration, re, consists of an initial time or overland flow time, r,, plus the • travel time,t,, in the storm sewer, paved gutter, roadside drainage ditch,or drainage channel. For non- • urban areas,the time of concentration consists of an overland flow time, r,, plus the time of travel in a • defined form, such as a swale, channel, or drainageway. The travel portion, r,, of the time of • concentration can be estimated from the hydraulic properties of the storm sewer, gutter, swale,ditch, or • drainageway. Initial time, on the other hand,will vary with surface slope, depression storage, surface cover,antecedent rainfall, and infiltration capacity of the soil, as well as distance of surface flow. The • time of concentration is represented by Equation RO-2 for both urban and non-urban areas: • • lc. =t; +t (RO-2) • in which: • • r�=time of concentration(minutes) • r,=initial or overland flow time(minutes) t,=travel time in the ditch,channel, gutter, storm sewer, etc_ (minutes) • • 2.4.1 Initial Flow Time • The initial or overland flow time, t,, may be calculated using equation RO-3: • t 0.395(1.1-C5)- . _ (RO-3) • . s°.33 • in which: • r,=initial or overland flow time(minutes) • C5= runoff coefficient for 5-year frequency(from Table RO-5) • • • • 2007-01 RO-5 Urban Drainage and Flood Control District • i • • RUNOFF DRAINAGE CRITERIA MANUAL (V. 1) L=length of overland flow(500 ft maximum for non-urban land uses, 300 ft maximum for urban land uses) • S= average basin slope (ft/ft) Equation RO-3 is adequate for distances up to 500 feet. Note that, in some urban watersheds, the • overland flow time may be very small because flows quickly channelize. • 2.4.2 Overland Travel Time • For catchments with overland and channelized flow, the time of concentration needs to be considered in combination with the overland travel time, r,, which is calculated using the hydraulic properties of the • swale,ditch, or channel. For preliminary work,the overland travel time, r,, can be estimated with the help • of Figure RO-1 or the following equation(Guo 1999): • V CoS,,," (RO-4) • • in which: V= velocity (ft/sec) • Cv=conveyance coefficient(from Table RO-2) • S,,,=watercourse slope (ft/ft) • Table RO-2—Conveyance Coefficient, C,, • Type of Land Surface Conveyance Coefficient, C, • Heavy meadow 2.5 Tillage/field 5 • Short pasture and lawns 7 Nearly bare ground 10 • Grassed waterway 15 • Paved areas and shallow paved swales 20 t • The time of concentration, lc, is then the sum of the initial flow time, r,,and the travel time, r,, as per • Equation RO-2. • 2.4.3 First Design Point Time of Concentration in Urban Catchments • Using this procedure,the time of concentration at the first design point(i.e., initial flow time, r,)in an • urbanized catchment should not exceed the time of concentration calculated using Equation RO-5. • t` = + 10 (RO-5) • ]80• in which: • re= maximum time of concentration at the first design point in an urban watershed (minutes) • • • RO-6 2007-01 Urban Drainage and Flood Control District • • • • • DRAINAGE CRITERIA MANUAL(V. 1) RUNOFF • Table RO-3--Recommended Percentage Imperviousness Values Land Use or Percentage • Surface Characteristics Imperviousness . Business: Commercial areas 95 • Neighborhood areas 85 • Residential: • Single-family • Multi-unit(detached) 60 • Multi-unit(attached) 75 Half-acre lot or larger• * Apartments 80 • Industrial: • Light areas 80 • Heavy areas 90 • Parks,cemeteries 5 Playgrounds 10 . Schools 50 • Railroad yard areas 15 • Undeveloped Areas: • Historic flow analysis 2 • Greenbelts, agricultural 2 . Off-site flow analysis 45 (when land use not defined) • Streets: • Paved 100 • Gravel (packed) 40 • • Drive and walks 90 Roofs 90 . Lawns, sandy soil 0 Lawns, clayey soil 0 • * See Figures RO-3 through RO-5 for percentage imperviousness. • CA = KA + .31i3 —1.4412 + 1.1351—0.12)for CA ≥0, otherwise CA =0 (RO-6) CCD =KcD + (0.858/3 - 0.786i2 +0.774i+0.04) (RO-7) • (( l • CB _-_(C A + C(D)/2 • • • 2007-01 RO-9 Urban Drainage and Flood Control District 5 • • • • • • • • • • 1.04 1.49 1.76 2.51 2.78 • The IDF curves were developed by distributing the one-hour point rainfall values using the • factors obtained from the NOAA Atlas as presented below. • • � __ L • • s Duration(minutes) 5 10 15 30 • • Ratio to 1-hour Depth 0.29 0.45 0.57 0.79 • The point values were then converted to intensities and plotted on Figure 3-1. 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TIME IN MINUTES • I • Of � Colorado INTENSITY-DURATION-FREQUENCY CURVES •• reeley PUBLIC WORKS DEPARTMENT FIGURE 3-1 • (3t�lRaor 3ethotuidTlR STORMWATER MANAGEMENT DIVISION , SCALE:FITS ,q, Nomi Avow mr,caws tout REVISED AUG 1996 0 • • • • • • • • • • APPENDIX C • •• ADJACENT OWNERSHIP MAP • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • is. r BONNIE J.BEEBE, • VERA A.SMOTHERMAN TRUST AND JEANNE B.CREECH TRUST I. `` ROBERT HENRY BROWN AND BETTY DEE DAVEE RAY B.AND _ ' • CAROLE:ALE TENNY ON • j .....lb • _ft.. GREAT wFS ER"N"—... r LAFARGE • �/ ' tee. T ` Ns RAl(wAV OFCOLo>,,�( WEST, INC • RAY B.AND \\ I / I CAROLE DALE • TENNYSON ` ` / I ROBERT HENRY BROWN AND • I BETTY DEE DAVEE • s \ i L ` t IVERSON MINE • • 1 USR BOUNDARY ` I _ CITY OF w cc • w ` _-.-.� GREELEY • 1 0 1 1 �� • / i w ` - 1 • oo z 1. BONNIE J.BEEBE, • w r, VERA A.SMOTHERMAN TRUST I I V T AND JEANNE B.CREECH TRUST I MINING LIMITS • z t I / WELD • U.1 / COUNTY cli ‘ II / _ __,_„__,„,- • m 1 �� 1 1 w j LOWELL THREE LLC AND • 3 - - - - - -- -- -- LOWELL FOUR -' - x n • a ♦ LOWELL FOUR • o I"i^�..-,- _ _ ,�� LLQ AND JOSEPH D.AND i LOWELL THREE KORTNEY L.NELSON • MARY C.STEVENS LC !/ 05 I // DOUGLAS K. KREYKES AND co• M / JEANNIE L LEONARD N 0 2� 50 500 7 JEREMIAH J AND • N —�� JENNIFER C MONGAN I SCALE:1"=500' I = • LAFARGE WEST,INC. Project No.: 133-23511-• 10002 m • TETRA TECH IVERSON MINE Date: 1.31-11 F o t. Designed By: JAB • _ www.tetratech.corn IVERSON MINE FIGURE a • N 1sooS.suNSETSTREET,STE1-F ADJACENT OWNERSHIP MAP 3 v ry LONG-5262 COLORADO-7039 1 \ PHONE.(303)772-5282 FAX(303)712-7039 r• yiiir_I Bar Measures 1 inch • I I I I I I r I • ✓ APPENDIX D • • • HISTORIC RUNOFF CALCULATIONS • • I I I I I I • I I I • • • • • • I • • • • • • • • • • • • U s S S • FINAL DRAINAGE REPORT • IVERSON MINE . WELD COUNTY, COLORADO HISTORIC DRAINAGE ANALYSIS Historic stormwater runoff was evaluated using two drainage basins for the site. The 5-year storm event was used for minor runoff calculations and the 100-year storm event was used for major runoff calculations. The drainage basins were less than 160 acres; therefore, the Rational Method was used for stormwater runoff calculations. Historic flows were calculated for 2, 5, 10 and 100-year storms. Please refer to the Historic Drainage Plan located in the back pocket of this report for basin delineation. . Design Storms: Minor Storm: 5-year event . Major Storm: 100-year event f Runoff Quantities: The historic basin was less than 160 acres; therefore, design storm runoff rates were calculated using the Rational Method. Runoff Coefficients: The percent imperviousness was determined for the anticipated land use from Table RO-3 of the Urban Drainage and Flood Control District Drainage Criteria Manual. The runoff coefficients were O then taken from the Urban Storm Drainage Criteria Manual. Soil Conditions: Gravelly substratum, Ascalon loam, Dacono clay loam,Nunn loam, and Otero sandy loam are the soil types on the site. The site soils belong to Hydraulic Soil Groups B, C and D. Overland Flow Length: Flow length, L, was considered to be the furthest distance from the know discharge point to the upstream end of the basin. Time of Concentration: The time of concentration for the historic basin was calculated using . equation RO-2. A maximum distance of 500 feet was used for the initial or overland flow time. Calculations and Urban Storm Drainage References are included in this section of the report. Rainfall Intensities: Rainfall intensity values were calculated using equation . I= 28.5*P] taken from the Urban Storm Drainage Criteria (10+Tc)°.786 Manual. Historic flows are included in this section of Appendix D. IP • • • • 2 } g2. „ w o • 3 . • O• ` N Lei m h M L v o W N - O — Cl • r— .c • e W • • _E A. w • F- S. n m E 1. v . _ V M • F £ 4C • o 0, • . N } V O L }' W CI C o O V O N 6p 1- C. •m o_• o o n 0 o N o F co U y c • C °e z o a L 2 J' n N E C } e . YcC d _ r�l p o d O' I. • ID NO v e a ti s O. • e 0 c 3 CZ o o co a. • d c • = e O o K O 0 t — N N c • O. n E • e o o • a v z I: c r N • o o = v y • d co z to • ` __ W T A O c o tt! • CO F , - F O_ a O L� yeo u) y aa • O w O Y. No > y �n a U >. O '0 O . u Q x N e r, o o ry o Um o • C Q3. U — O C Nci, J• — i Q • i m = T a N CC F F O-5 M• 9, C • N Ill • a L • • • • • • • • • • • • • APPENDIX E • • MINING RUNOFF CALCULATIONS • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • OP • FINAL DRAINAGE REPORT . IVERSON MINE . WELD COUNTY, COLORADO MINING DRAINAGE ANALYSIS The overall stormwater runoff for the mining development was evaluated using three drainage basins. Developed runoff rates for the 2-year, 5-year, 10-year and 100-year storm events were calculated using the Rational Method. Calculated flows were used in the onsite drainage facility evaluation. Please refer to the Mining Drainage Plan located in the back pocket of this report for basin delineation. Design Storms: Minor Storm: 5 - year events Major Storm: 100 - year event Runoff Quantities: Developed basins were less than 160 acres; therefore, design storm runoff rates were calculated using the Rational Method. Runoff Coefficients: Percent imperviousness was determined for the anticipated land use from Table RO-3 of the Urban Drainage and Flood Control District Drainage Criteria Manual. The runoff coefficients were then taken from the Urban Storm Drainage Criteria Manual. . Soil Conditions: Gravelly substratum, Ascalon loam, Dacono clay loam, Nunn loam, and Otero sandy loam are the soil types on the site. The site soils belong to Hydraulic Soil Groups B, C and D. . Overland Flow Length: Flow length, L, was considered to be the furthest distance from the know discharge point to the upstream end of the basin. Time of Concentration: The time of concentration for the historic basin was calculated using equation RO-2. A maximum distance of 500 feet was used for the initial or overland flow time. Calculations and Urban Storm Drainage References are included in this section of the report. . Rainfall Intensities: Rainfall intensity values were calculated using equation 28.5*P1 Pl I= se taken from the Urban Storm Drainage Criteria O (10+Tc) Manual. Calculations of the mining runoff rates are included in this section of Appendix E. OP • • O careens 0 N 0 N a e • o s L N aN . m ain t" - d' s . ' .ORNO _, 0 en N N 0 C 0 L 0 0 C . 4. .52 .-.. ,0 E Sc v w c .,0 P a F EMMM . 00 .0 b N h N • a - >= 0. a> eo vvv 0 �"' a C d 0 0 O o i v0 ,-; a y = e m U 9 `e o e . t a"n000 0 'n _ it c . / o U e _. .. 0 t G c. e. . . . ; '� '� a o, O O o O ii e . .?. .. E. 88. x L -' N N - O ill E 7 . D U U t . o on v m E H m ,o N C . o0 - C m to Q n . 1 a 6 m p O .o 0 o O P N CO ,-0 -- r .l. H _O d d O 6 y t - o 55 E . 0 N y ^. 4• N U c r N . U Q N b .n O O' O O U o N Co . U ce• m o m e rim g ap,Ci v, ¢y U . 4• m G G N T a ^ T ; N 04 m fi m e 6 g ` 4 o • • • • • • • • • • • APPENDIX F • • • RECLAMATION RUNOFF CALCULATIONS • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • S • FINAL DRAINAGE REPORT • IVERSON MINE • WELD COUNTY,COLORADO • • RECLAMATION DRAINAGE ANALYSIS • The overall stormwater runoff for the reclaimed site was evaluated using three drainage basins. • Reclaimed runoff rates for the 2-year, 5-year, 10-year and 100-year storm events were calculated • using the Rational Method. Calculated flows were used in the onsite drainage facility evaluation. • Please refer to the Reclamation Drainage Plan located in the back pocket of this report for basin • delineation. • Design Storms: Minor Storm: 5 - year events • Major Storm: 100 - year event • Runoff Quantities: Developed basins were less than 160 acres; therefore, design storm • runoff rates were calculated using the Rational Method. • • Runoff Coefficients: Percent imperviousness was determined for the anticipated land use from Table RO-3 of the Urban Drainage and Flood Control District • Drainage Criteria Manual. The runoff coefficients were then taken • from the Urban Storm Drainage Criteria Manual. • Soil Conditions: Gravelly substratum, Ascalon loam, Dacono clay loam, Nunn loam, and Otero sandy loam are the soil types on the site. The site soils • belong to Hydraulic Soil Groups B, C and D. • Overland Flow Length: Flow length, L, was considered to be the furthest distance from the know discharge point to the upstream end of the basin. • Time of Concentration: The time of concentration for the historic basin was calculated using • equation RO-2. A maximum distance of 500 feet was used for the • initial or overland flow time. Calculations and Urban Storm Drainage References are included in this section of the report. • • Rainfall Intensities: Rainfall intensity values were calculated using equation • 28.5*Pl I= 0 786 taken from the Urban Storm Drainage Criteria • (10+Tc) • Manual. • Calculations of the reclaimed runoff rates are included in this section of Appendix F. 9 0 4} • 44N apart - o • } � r � • m � t`: M2 .C • `o aro O Cl Cl M r _ C Y • 71 O } GC O W 0 wF` 'E 'c m a • c a. Co ..q £ ip F O • .c e c n M N • F E 'er — n M a • o O C .0 ° in N N • O a • co }` ms. }` o0 C! O O n t •;": v 6 O N C V O O O q O O N • g C O 9 `a O p c z • i e 0 N v Ce • d j > Cn _ C5,1 E o >-• v y C o O o oe '^ — c a. • y o e U p = L • o e o 0 o ; 'c •_ - n o 0 0 J • e • c e 0 0 0 N E r Oj C O • E • o v o N •4 N 7 o o ec F ry • r N --t- • o • u em m y a d o • T O ,c1-- m W O M V 0 Ll r m F — N F O p 6 O O • Q u cn C.2 Q • 1 N © N r- V N • Q N O b V 0 0 0 C irq O o O = O • _ CC aC CC a — tc 4, N M p a -.). ^ a>, (J • G m K CC C N � a, re oN F F F M • C _ a e a 00 C • N 1 • • • Hello