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Home My WebLink About20093064.tiffRESOLUTION RE: APPROVE AGREEMENT TO MINE WITHIN 200 FEET OF PERMANENT MANMADE STRUCTURES AND AUTHORIZE CHAIR TO SIGN - LAFARGE WEST, INC. WHEREAS, the Board of County Commissioners of Weld County, Colorado, pursuant to Colorado statute and the Weld County Home Rule Charter, is vested with the authority of administering the affairs of Weld County, Colorado, and WHEREAS, the Board has been presented with an Agreement to Mine within 200 Feet of Permanent Manmade Structures between the County of Weld, State of Colorado, by and through the Board of County Commissioners of Weld County, and Lafarge West, Inc., for property described below, commencing upon full execution, with terms and conditions being as stated in said agreement, and E1/2 SE1/4 of Section 25, Township 6 North, Range 67 West; the W1/2 SW1/4 of Section 30, Township 6 North, Range 66 West; the NE1/4 of Section 36, Township 6 North Range 67; and the NW1/4 of Section 31, Township 6 North, Range 66 West of the 6th P.M., Weld County, Colorado WHEREAS, after review, the Board deems it advisable to approve said agreement, a copy of which is attached hereto and incorporated herein by reference. NOW, THEREFORE, BE IT RESOLVED by the Board of County Commissioners of Weld County, Colorado, that the Agreement to Mine within 200 Feet of Permanent Manmade Structures between the County of Weld, State of Colorado, by and through the Board of County Commissioners of Weld County, and Lafarge West, Inc., be, and hereby is, approved, with the following sentence added to the end of the last paragraph of page one of the agreement: "Any replacement or compensation must provide for the restoration of said structure to its condition immediately prior to the damage taking place." BE IT FURTHER RESOLVED by the Board that the Chair be, and hereby is, authorized to sign said agreement. 2009-3064 BC0040 APPROVE AGREEMENT TO MINE WITHIN 200 FEET OF PERMANENT MANMADE STRUCTURES AND AUTHORIZE CHAIR TO SIGN - LAFARGE WEST, INC. PAGE 2 The above and foregoing Resolution was, on motion duly made and seconded, adopted by the following vote on the 23rd day of November, A.D., 2009. ATTEST: Weld County Clerk to the Bo BY: AP ounty Attorney David E Date of signature: I") tqlcci BOARD OF COUNTY COMMISSIONERS EL4 COON Y, COLORADO am F. Garcia, Chair „O.. ou gIaa demacljer, Pro-Tem s4R EXCUSED ,/_ B-arkaca Kirkmeyer/ Long \/ 2009-3064 BC0040 Sea n P. Conway AGREEMENT TO MINE WITHIN 200 FEET 156 OF PERMANENT MANMADE STRUCTURES THIS AGREEMENT, entered into by and between Lafarge West, Inc., hereinafter called "Lafarge", whose address is 10170 Church Ranch Way, Suite 200, Westminster, CO 80021, and: Weld County, Colorado, P.O. Box 758, 915 10t Street, Greeley, CO 80632 Hereinafter referred to as the "Structure Owner". The Colorado Mined Land Reclamation Act requires that landowners adjacent to a proposed mining operation be informed about the mine and the reclamation. Further, the Act provides protection for structures that are within 200 feet of a mining operation. Lafarge submitted an application to the State of Colorado Division of Reclamation, Mining and Safety for a 112 Reclamation Operation Permit and an application to Weld County for a Use by Special Review Permit for sand and gravel mining located within the east %2 of the southeast '/ of Section 25, T6N, R67W; the west 1/2 of the southwest Y of Section 30, T6N, R66W; the northeast 'A of Section 36, T6N, R67W; and the NW % of Section 31, T6N, R66W of the 6`h P.M., Weld County, Colorado. The Structure Owner owns a permanent manmade structure or structures within 200 feet of the land affected by the mining and reclamation operations. The description of the structure(s) is as follows: Concrete bike path (Poudre River Trail) Lafarge must attempt to obtain permission from Structure Owner in order to conduct operations closer than 200 feet to the structures owned by the Structure Owner. In addition, Lafarge must commit to repairing, replacing, or compensating Structure Owner for any damage that might be caused to its structure(s) by the mining operation of Lafarge at this site. By this agreement, Structure Owner consents to Lafarge conducting mining operations up to a 50 foot setback from Structure Owner's structure(s). Lafarge commits that, if its operation causes damages to Structure Owner's structure(s) within 200 feet of said operations, Lafarge will repair or replace such structure(s) or compensate Structure Owner for the value of said structure(s). 111111111111111111111111 III 111111111111 III 11111 IIII 1111 3667156 12/28/2009 11:36A Weld County, CO 1 of 2 R 0.00 D 0.00 Steve Moreno Clerk & Recorder Page 1 of 2 Song -.Og Structure Owner Signature 1 111111 11111 111111 111111 III 111110 11111 III 11111 IIII IIII November as Chair The parties hereto acknowledge and agree to the above -stated items. AGREED: Lafarge West, Inc. By: Anne Johnson Land Manager State of Colorado nn ) ss. County of 12x,, -eca R The foregoing instrument was acknowledged before me this ( 3-4)_ day of o C`F ^'n \,,o2 2 , 200 ``j , by Anne Johnson as Land Manager for Lafarge West, My Commis on Expires: (; C FZ, C�• v I cp-c) \) ) _Lk s2 Notary Public Structure Owner Date: 11/23/2009 State of Colorado ) ) ss. County of Weld The foregoing instrument was acknowledged before me this 23rd day of ,20 09 ,by William F. Garcia of Board of Weld County Commissioners• My Commission Expires: 'V�jDyoyc'V L Notary Publi Ri JU] 029',Documents,Adjacent Swcture\Snucture (Truer Agreements Poudre River Tra MY COMMISSION DPW& 0440 2011 Page 2 of 2 Agreement to Mine Within 200 Feet of Permanent Manmade Structures T,afarge West, Inc./Poudre River Trail Corridor, Inc. 3667156 12/28/2009 1136A Weld County, CO 2 of 2 R 0.00 D 0.00 Steve Moreno Clerk & Recorder pco9 -.3D6 t$ • VECCHI & ASSOCIATES, LLC URBAN PLANNING & DESIGN P O. Box 75 Longmont, Co 80502-1175 Phone 303-774-0173 Fax 303-774-0173 VecchlAssociates©comcastnet November 16, 2009 Mr. Bruce Barker Weld County Commissioners do County Attorney P.O. Box 758 Greeley, CO 80632 NOV18700g WELD COUNTY ATTORNEY'S OFFICE RE: Manmade structures within 200' of the PARSONS MINE located within portions of Section 25 and Section 36, T6N, R 67W of the 6`h P.M.; and Section 30 and Section 31, T6N, R 66W, of the 6th P.M., County of Weld, State of Colorado, Colorado Division of Reclamation, Mining & Safety, Regular 112 Operation Permit M-2009-082 and Weld County Use by Special Review Permit 1657. Dear Bruce: Lafarge West Inc. (Lafarge) has applied for a Regular 112 Operation Permit with the Colorado Division of Reclamation, Mining, and Safety (DRMS) to mine sand and gravel as referenced above. We are notifying you because you have been identified as owning a manmade structure within 200' of the amended permitted area for the Parsons mining site. Deere & Ault Consultants, Inc. performed a Stability Analysis of the site to determine appropriate setbacks from permanent man made structures within 200' of the mining area. The attached Stability Report and map identify the structures and appropriate setbacks. Please contact us immediately if you have an interest in a permanent man made structure within 200' that is not identified on the attached list. Lafarge will maintain minimum setbacks as identified in the attached report. While mining following these minimum setbacks should not pose a hazard to nearby structures, we are enclosing an Agreement that states that we will fully repair, or we will provide full compensation for, any damage caused by the mining operation to a permanent man-made structure that you own within 200 feet of the affected land. Please execute, notarize and return one original of the agreement, which has already been executed by Lafarge, to Jennifer E. Vecchi at the address below, or if you have any questions or comments please contact me by that date. The agreement will then be recorded and a copy of the recorded, fully executed document returned to you. If we do not hear from you by December 11, 2009 your agreement with the setbacks as outlined in the attached report will be assumed. I Page 2 of 2 Mr. Bruce Barker November 16, 2009 Jennifer E. Vecchi Vecchi & Associates, LLC P.O. Box 1175 Longmont, Colorado 80502-1175 Phone: 303-774-0173 Fax: 303-774-0173 Email: vecchiassociates@a,comcast.net Thank you for your attention to this matter. Sincerely, VECVHI & ASSOCIATES, fer E. Vecchi, AICP Principal Attachments: Structures Agreements (two signed originals) Structures Map Stability Analysis Parsons Project Overall Mining Plan Map Overall Reclamation Plan Map cc: Anne Best Johnson Jim King E: V&AlafargeParsonsStmcturesAgreementsCorrespondencePoudreRiver Trail_Weld CountyCERTIFIEDLetter I I-16-09 STABILITY ANALYSIS PARSONS PROJECT Prepared for: LAFARGE WEST 1800 North Taft Hill Road Fort Collins, Colorado 80521 December 2007 Revised April 2008 Revised October 2009 DEERE & AULT CONSULTANTS, INC. 600 South Airport Road, Suite A-205 Longmont, CO 80503 (303) 651-1468 • Fax (303) 651-1469 STABILITY EXHIBIT General A slope stability analysis was performed for the Parsons Mine located in Weld County, Colorado. The purpose of this analysis was to investigate appropriate mining-highwall setback distances from man made structures. Below we present a brief background and the results of our findings. Background The site is located east of the city limits of Windsor, Colorado. Weld County Road (WCR) 641/2 forms the northern boundary. WCR 25 bisects the site. The Cache La Poudre River flows through and adjacent to the southern portion of the site. The proposed gravel mine is to be mined with a highwall slope inclination of approximately 0.5:1 (horizontal to vertical). After mining, a final reclamation slope of 4:1 or flatter will be constructed using on -site overburden soils. Analysis Our stability analysis involved generating a computer model of limit equilibrium analysis using the Slope/W computer program. In addition to the mining highwall, long-term stability of the reclaimed slope was also evaluated. The stratigraphy, encountered during the March 2002 to April 2007, site investigations was used to develop the model. Sandy clay layers are typically encountered in the alluvial sand and gravel stratum. These layers are colloquially known as "mud lenses." No significant mud lenses were encountered during the investigation of this site. Therefore, mud lenses were not incorporated in the slope stability model. A worst case cross section was used to evaluate the set back distances for each phase during mining. The worst case of these was used for the long term reclaimed slope. A description of each cross section is presented below. The soil information used for our analysis came from six test pits and 45 borings. The various exploration locations used in our analysis are shown on Figure 1 and the information gained the soil explorations is summarized on Table 1 below. Copies of the exploration logs are attached. Table 1: Parsons Mine Borings Boring Name Depth (feet below ground surface) of Unit Encountered Estimated Depth to groundwater during drilling(feet) Silt and Clay Sand and Gravel Bedrock MW -1 0 to 9 9 to 14 14 9 MW -2 0 to 14 14 to 28 28 14 MW -3 0 to 4 4 to 29 29 14 MW -4 0to4 4to11 11 4 MW -5 0 to 14 14 to 28 28 9 MW -6 0 to 9 9 to 24 24 9 MW -7 0 to 9 and 11 to 14 9to11 14 9 MW -8 O to 5 5 to 17 17 9 MW -9 0 to 4 4 to l4 14 9 MW -10 0to4 4to14 14 4 MW -11 0to4 4to 15.5 15.5 9 MW -I2 0to4 4to13 13 9 MW -13 0 to 9 9 to 18 18 9 MW -14 0 to 4.5 4.5 to 14 14 9 ET02-TP0I 0 to 10 10 to 18 N/A IS ET02-TP02 0 to 12 12 to 18 N/A 13 ET02-TP03 0 to 10 10 to 18 N/A 10 to II ET02-TP04 0 to 3 3 to 9 N/A 4 ET02-TP05 0 to 2 2 to 11 N/A 5 ET02-TP06 0 to 11 11 to 18 N/A 12 to 13 ET02-BH01 0 to 10 10 to 25 25 15 ET02-BH02 0 to 1.5 1.5 to 7 7 N/A ET02-BH03 0 to 5 5 to 11 11 <5 ET02-BH04 0 to 11 11 to 26.5 26.5 N/A ET02-BH05 0 to 13.5 13.5 to 31.5 31.5 N/A ET02-BH06 0 to 11 11 to 28 28 N/A ET02-BH07 0 to 11 II to 27 27 N/A LI03-BH01 0 to 10 and 24 to 29 10 to 24 29 N/A L103-BH02 0 to 10 10 to 26 26 N/A PA04-BH01 0 to 5 5 to 13 13 N/A PA04-BH02 0 to 6 6 to 14 14 N/A PA04-BH03 0 to 5.5 5.5 to 16 16 N/A PA04-B1104 0 to 5.5 5.5 to 13 13 N/A PA04-BH05 0 to 4.5 4.5 to 15 15 N/A PA04-BH06 0 to 4.5 4.5 to 12 12 N/A PA04-BH07 0 to 5.5 5.5 to 9 9 N/A PA04-BH08 0 to 4 4 to 14 14 N/A PA04-B1109 0 to 4.5 4.5 to 15 15 N/A PA04-BH10 0 to 5 5 to 11 11 N/A PA04-BH I 1 0 to 4.5 4.5 to 14 14 N/A NO.1 0 to 6.5 6.5 to 29.5 29.5 12.5 NO.2 0 to 3 3 to 30.5 30.5 17 NO.3 0 to 2 2 to 27.5 27.5 17 NO.4 0 to 1.5 1.5 to 24.5 24.5 17.5 NO.5 0 to 0.5 0.5 to 12 12 Dry NO.6 0to4 4to9 9 4 NO.7 0 to 10 10 to 27 27 15 NO.8 Otoll l l 11 to 31 31 18 NO.9 0 to 8 8 to 25 25 18 NO.10 0 to l 1 11 to 25 25 18 NO.11 0to7 7to31 31 18 Parsons Mine DRMS 112 Permit Page SE2 of SE8 Individual Cross Sections Phase IA The bedrock in this phase dips slightly northward. Therefore a worst case scenario is represented by the north mining highwall of this phase. The soil profile analyzed was based on a conglomeration of soil information from exploration locations ET02-BH06, ET02-TP03, ET02-BH05, No.1, No.2 and MW -3. The model analyzed; a soil overburden that was 9 feet thick, a sand and gravel layer that was 21 feet thick, and a total pit depth of 30 feet. The highest groundwater monitored in the area was in MW -3 approximately 10 feet below the ground surface. A soil screening berm was placed north of the pit. Flood irrigation, north of WCR 64%, was simulated by raising the piezometric surface, under the road and in the borrow ditch just south of the existing road, above the highest monitored surface to the ground surface. The road is planned to be widened. The widening will result in the ditch being relocated southward. Phase lB The deepest depth to bedrock near a structure occurs near the northwest portion of the mining cell. The soil profile analyzed was based on a conglomeration of soil information from exploration locations ET02-BH01, ET02-TP05, No.9, No.10 and MW -1. The model analyzed; a soil overburden that was 9 feet thick, a sand and gravel layer that was 19 feet thick, and a total pit depth of 28 feet. The highest groundwater monitored in the area was in MW -1 approximately 10 feet below the ground surface. An overburden stockpile was placed northwest of the pit. No flood irrigation is near this mining cell; therefore the piezometric surface was based on the site monitoring. Phase IC The deepest depth to bedrock near a structure occurs near the northwest portion of the mining cell. The soil profile analyzed was based on a conglomeration of soil information from exploration locations PA04-BH07, No.5 and MW -13. The model analyzed; a soil overburden that was 6 feet thick, a sand and gravel layer that was 14 feet thick, and a total pit depth of 20 feet. The highest groundwater monitored in the area was in MW -1 approximately 9 feet below the ground surface. An overburden stockpile was placed northwest of the pit. No flood irrigation is near this mining cell; therefore the piezometric surface was based on the site monitoring. Parsons Mine DRMS 112 Permit Page SE3 of SE8 Phase 2 Eastside The depth to bedrock in this area is greatest in the middle of the mining cell. Therefore a worst case scenario is represented by the middle of the east mining highwall of this phase. The soil profile analyzed was based on a conglomeration of soil information from exploration locations LI03-BH01, ET02-TP06, No.3, No.9 and MW -4. The model analyzed; a soil overburden that was 8 feet thick, a sand and gravel layer that was 21 feet thick, and a total pit depth of 29 feet. The highest groundwater monitored in the area was in MW -4 at an approximate elevation of 4731. An overburden stockpile was placed east of the pit. No flood irrigation is near this mining cell; therefore the piezometric surface was based on the site monitoring. Phase 2 Westside Due to the presence of flood irrigation to the west of this mining phase a second cross section was analyzed on the west side. The depth to bedrock in this area is greatest in the middle of the mining cell. Therefore a worst case scenario is represented by the middle of the west mining highwall of this phase. The soil profile analyzed was based on a conglomeration of soil information from exploration locations LI03-BH02 and MW -6. The model analyzed; a soil overburden that was 10 feet thick, a sand and gravel layer that was 16 feet thick, and a total pit depth of 26 feet. The highest groundwater monitored in the area was in MW -6 approximately 9 feet below the ground surface. Flood irrigation, west of the mining cell, was simulated by raising the piezometric surface, at the fenceline (40 -feet from the mining highwall), above the highest monitored surface to the ground surface. Phase 3 The depth to bedrock in this area is greatest near the southern portion of the mining cell. Therefore a worst case scenario is represented near the southern portion of the mining highwall of this phase. The soil profile analyzed was based on a conglomeration of soil information from exploration locations PA04-BH02 and MW -14. The model analyzed; a soil overburden that was 6 feet thick, a sand and gravel layer that was 9 feet thick, and a total pit depth of 15 feet. The highest groundwater monitored in the area was in MW -14 approximately 9 feet below the ground surface. No stockpiles are currently planned to be next to this mining cell. No flood irrigation is near this mining cell; therefore the piezometric surface was based on the site monitoring. Phase 4A The depth to bedrock in this area is greatest near the western portion of the mining cell. Therefore a worst case scenario is represented near the western portion of the mining highwall of this phase. The soil profile analyzed was based on a conglomeration of soil information from exploration locations PA04-BH01 and PA04-BH1 I. The model analyzed; a soil overburden that was 5 feet thick, a sand and gravel layer that was 8 feet thick, and a total pit depth of 13 feet. The highest groundwater monitored in the area was in MW -7 approximately 8 feet below the ground surface. An overburden stockpile was placed west of the pit. No flood irrigation is near this mining cell; therefore the piezometric surface was based on the site monitoring. Parsons Mine DRMS 112 Permit Page SE4 of SE8 Phase 4B The depth to bedrock in this area is greatest near the western portion of the mining cell. Therefore a worst case scenario is represented near the western portion of the mining highwall of this phase. The soil profile analyzed was based on a conglomeration of soil information from exploration locations PA04-BH02, PA04-BH09 and PA04-BH11. The model analyzed; a soil overburden that was 5 feet thick, a sand and gravel layer that was 10 feet thick, and a total pit depth of 15 feet. The highest groundwater monitored in the area was in MW -8 approximately 8 feet below the ground surface. No stockpiles are currently planned to be next to this mining cell. No flood irrigation is near this mining cell; therefore the piezometric surface was based on the site monitoring. Phase 4C The depth to bedrock in this area is greatest near the eastern portion of the mining cell. Therefore a worst case scenario is represented near the eastern portion of the mining highwall of this phase. The soil profile analyzed was based on a conglomeration of soil information from exploration locations PA04- BHIO, PA04-BH11, MW -7 and MW -12. The model analyzed; a soil overburden that was 5 feet thick, a sand and gravel layer that was 8 feet thick, and a total pit depth of 13 feet. The highest groundwater monitored in the area was in MW -7 approximately 8 feet below the ground surface. An overburden stockpile was placed east of the pit. No flood irrigation is near this mining cell; therefore the piezometric surface was based on the site monitoring. Phase 5A The depth to bedrock in this area is greatest near the western portion of the mining cell. Therefore a worst case scenario is represented near the western portion of the mining highwall of this phase. The soil profile analyzed was based on a conglomeration of soil information from exploration locations MW -9 and MW -10. The model analyzed; a soil overburden that was 4 feet thick, a sand and gravel layer that was 10 feet thick, and a total pit depth of 14 feet. The highest groundwater monitored in the area was in MW -10 approximately 8 feet below the ground surface. No stockpiles are currently planned to be next to this mining cell. No flood irrigation is near this mining cell; therefore the piezometric surface was based on the site monitoring. Parsons Mine DRMS 112 Permit Page SE5 of SE8 Phase 5B The depth to bedrock in this area is greatest near the southeastern portion of the mining cell. Therefore a worst case scenario is represented near the southeastern portion of the mining highwall of this phase. The soil profile analyzed was based on a conglomeration of soil information from exploration locations MW -9 and MW -10. The model analyzed; a soil overburden that was 4 feet thick, a sand and gravel layer that was 10 feet thick, and a total pit depth of 14 feet. The highest groundwater monitored in the area was in MW -9 approximately 8 feet below the ground surface. An overburden stockpile was placed southeast of this mining cell. Flood irrigation, south of the mining cell, was simulated by raising the piezometric surface, at the fenceline (70 -feet from the mining highwall), above the highest monitored surface to the ground surface. Phase 5C The depth to bedrock in this area is greatest near the southern portion of the mining cell. Therefore a worst case scenario is represented near the southern portion of the mining highwall of this phase. The soil profile analyzed was based on a conglomeration of soil information from exploration locations PA04-BH10, MW -9 and MW -I0. The model analyzed; a soil overburden that was 4 feet thick, a sand and gravel layer that was 5 feet thick, and a total pit depth of 9 feet. The highest groundwater monitored in the area was in MW -9 approximately 8 feet below the ground surface. An overburden stockpile was placed south of this mining cell. No flood irrigation is near this mining cell; therefore the piezometric surface was based on the site monitoring. Longterm This stability run uses the lithology of Phase 1A. The soil profile analyzed was based on a conglomeration of soil information from exploration locations ET02-BH06, ET02-TP03, ET02-BH05, No.1, No.2 and MW -3. The model analyzed; a soil overburden that was 9 feet thick, a sand and gravel layer that was 21 feet thick, and a total pit depth of 30 feet. The highest groundwater monitored in the area was in MW -3 approximately 10 feet below the ground surface. Flood irrigation, north of WCR 64'/, was simulated by raising the piezometric surface, under the road and in the borrow ditch just south of the existing road, above the highest monitored surface to the ground surface. The road is planned to be widened. The widening will result in the ditch being relocated southward. Parsons Mine DRMS 112 Permit Page SE6 of SE8 DRMS Analysis, Highwall Setback to Property Line The Division of Reclamation Mining and Safety (DRMS) requires that gravel pit highwalls within 200 feet of significant manmade permanent structures (such as utilities) be investigated for slope stability. Furthermore, the DRMS requires that the gravel mine highwalls be modeled as vertical unless it can be demonstrated that the slope angle of the highwall will be controlled during mining. Additionally, the DRMS requires that the analysis be performed using the DRMS parameters for sites where laboratory testing is absent. These parameters are given below on Table 2: Table 2: DRMS Model Parameters Soil Type Effective Friction Angle O' (degrees) Effective Cohesion c' (psi) Saturated Unit Weight 2ca, (P4i) Overburden 28 50 114 Gravel 35 0 130 Weathered Bedrock 14 0 124 Bedrock 28 100 124 The parameters for weathered bedrock are much more conservative than those typically encountered in the project area and, it is our opinion, that they are not representative of conditions at the site. We analyzed a vertical highwall section for each phase. The depth to bedrock varied from 7 to 31 feet across the project site. The vertical section corresponds to a steep highwall mining scenario where the highwall inclination is approximately 0.5:1. Table 3 below summarizes the results of our analysis. The analysis was performed using the DRMS parameters shown in Table 2. The factor of safety required by the DRMS for temporary mine slopes and reservoir embankments are provided for comparison. Output graphics for each of the analyses are attached. Table 3: Highwall Setback DRMS Analysis Resul Model Setback Distance (feet) Calculated FS Eery f Safety Required Factor of Safety Phase IA 46 1.00 1.0 Phase 1B 39 1.01 1.0 Phase 1C 30 1.04 1.0 Phase 2 Eastside 35 1.03 1.0 Phase 2 Westside 37 1.03 1.0 Phase 3 25 1.11 1.0 Phase 4A 25 1.10 1.0 Phase 4B 25 1.11 1.0 Phase 4C 25 1.16 1.0 Phase 5A 25 1.21 1.0 Phase 5B 25 1.08 1.0 Phase 5C 25 1.25 1.0 Longterm Case 25 1.68 N/A The setback distance in Table 2 is calculated from the crest of the mine highwall to the potential failure surface intersection with the existing ground. Parsons Mine DRMS 112 Permit Page SE7 of SE8 Inflow and Outflow Structures In order to mine within 400 feet of the Cache la Poudre River, the Division of Reclamation Mining and Safety (DRMS) requires the construction of engineered inflow and outflow structures. A single inflow/outflow structure will be required for each of the following mining phases: IC, 3, 4B, 4C, 5A, 5B, and 5C. Each inflow/outflow structure will be a native grass -lined trapezoidal channel excavated to a depth of two feet with 4:1 (horizontal:vertical) side slopes. Because flow can be bi-directional, these channels are to be constructed with no longitudinal slope. Each channel is approximately 200 feet in length with the exception of the channel for Phase 4B which is approximately 300 feet in length. The bottom width of the trapezoidal channel will vary from 20 to 100 feet depending on the size of the phase. Phases IC, 3, 5A, and 5C require a bottom width of 20 feet while Phases 4B and 5B require a bottom width of 50 feet and Phase 4C requires a bottom width of 100 feet. The rate of inflow from the river will vary as the river stage rises above the invert of the inflow/outflow structure based on HEC- RAS modeling of the inflow/outflow structures. For the 200 -ft channel with a bottom width of 20 feet, the inflow would be 30 cfs, 60 cfs, and 120 cfs at river stages of 1.0 feet, 1.5 feet, and 2.0 feet above the channel invert, respectively. The 200 -ft channel with a bottom width of 50 feet would convey inflows of 60 cfs, 140 cfs, and 270 cfs at similar stages of 1.0 feet, 1.5 feet, and 2.0 feet, respectively. For the 300 -ft channel with a bottom width of 50 feet, these inflows would decrease slightly to 50 cfs, 120 cfs, and 220 cfs at similar stages of 1.0 feet, 1.5 feet, and 2.0 feet, respectively. The inflow through the 200 - ft channel with a bottom width of 100 feet would be 120 cfs, 280 cfs, and 510 cfs at stages of 1.0 feet, 1.5 feet, and 2.0 feet respectively. At these inflow rates, the cells will fill from the normal water line to the invert of the inflow/outflow channel in approximately 5 to 14 hours at a river stage of 1.0 foot above the channel invert. Fill time decreases to 3 to 6 hours with the stage at 1.5 feet above the channel invert and further decreases to Ito 3 hours at 2.0 feet above the channel invert. Based on the 2003 floodplain study of the Cache la Poudre River by the Corps of Engineers, these inflow/outflow channels will convey flood flows into the cells more frequent that a 10 -year event and possibly more frequent than a 5 -year event. Inflows to the mined cells will be conveyed through the grass -lined channels at non -erosive velocities less than 5 feet per second. In the vicinity of the mined cell, higher velocities would be expected as the inflow runs down the 4:1 side slope of the reclaimed cell. Slope protection such as a turf reinforcement mat or an articulating concrete block revetment is recommended to protect the rundown portion of these reclaimed slopes. Final design of this slope protection will be prepared prior to construction. 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