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3. Exhibit C(Pre-Mining and Mine Plan Map) depicts the location of the topsoil piles along the <br />top of the mining limits on the south side of Phase I and the north, south and east sides of <br />Phase II. Please inform the Division how the topsoil piles will be protected from the mining <br />operation where slopes will be mined to neaz-vertical. If the pit is to be mined to a depth of <br />25 feet at a O.Sh:ly slope, the topsoil piles may become unstable and slope failure may occur <br />if an adequate buffer distance is not established. The applicant has the following options: <br />• Demonstrate that topsoil piles will be stable under the proposed mining conditions using <br />a stability slope analysis (according to the map, the topsoil pile is on the top edge of the <br />mining limits), <br />• Maintain a set back distance at 2 times the depth of the pit (in this case a 20' deep pit <br />would need a 40' setback distance) and revise the maps to reflect this buffer, <br />• Revise the mining and reclamation plan to include sloping, benching or terracing and <br />including a slope stability analysis, or <br />• Relocate the topsoil pile to a more stable location, and revise the maps accordingly. <br />Rule 6.4.7 Exhibit G- Water Information <br />The Division of Minerals and Geology (DMG) staff has reviewed the Duckworth Pit <br />Groundwater Study for the LaFazge West, Inc. site, M-2003-091 completed by Applegate Group, <br />Inc. in March 2004. The Division has the following comments related to the report. <br />4. The groundwater hydrology report prepared by the Applegate Group identified three wells <br />registered with the Office of the State Engineer (OSE) that maybe impacted as a result of the <br />mining operation. The wells were identified within %x mile of the pit, and are depicted on <br />Figure 1. The well to the south appeazs to be closerthan %x mile and possibly as close as 500 <br />feet. Lafazge will need to accurately locate all wells, including wells that may not be <br />permitted with the OSE. <br />The Introduction of the Groundwater study indicates that the site will be dry mined. The <br />report states that water will be dischazged into the Smith & Emmons Ditch or Idaho Creek <br />and ultimately to the St. Vrain River or the water will be discharged into an existing lake <br />north of the site. The applicant must obtain permission from the ditch company to discharge <br />water into the ditch. The Smith & Emmons ditch is an unlined ditch and may be prone to <br />erosion if the dischazge rates exceed the carrying capacity of the ditch. The applicant should <br />submit documentation to the Division for review as to the proposed maximum dischazge rate <br />into the ditch and specifications as to how much water the ditch can carry without <br />experiencing erosion. <br />6. The report contains recent monitoring well groundwater measurements, but although a map <br />contained in the report depicts observation locations, the report does not contain a map that <br />identifies the location of each of the monitoring wells. The Applicant should submit a map <br />i~ ita th~afinnc of ihP mnnitnn_____n~welle fnr the Tliviginn tn~ra,~;P~s~ _ _ <br />7. The report states, "The results of the modeling also show that a practical mitigation <br />alternative would be to dischazge the water from the dewatering operation into the adjacent <br />