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Ms. Erica Crosby, Division of Minerals and Geology <br />March 31, 2005 <br />Page 8 <br />site. Please explain how Hall•Irwin will be in compliance with Colorado Water Laws and <br />regulations governing injury to existing water rights. In accordance with Rule 6.4.7(2)(b), <br />the Division requests that the applicant identify and characterize the aquifer to be mined in <br />or through. The Division also requests that the applicant define or predict the cone of <br />depression expected for any areas to be dewatered and dry mined during the life of the <br />operation. The cone of depression assessment should define, at a minimum, the horizontal <br />and vertical extent of drawdown expected. If during the assessment, the applicant <br />determines that a drawdown will occur offsite that may impact a current groundwater user, <br />the applicant should explain any mitigation measures to be implemented and trigger points <br />that would put mitigation measures into effect. <br />We are working on a groundwater model for this property, we will forward it to the Division shortly. <br />32. Hall-Irwin provided the names and address of well owners within 600 feet of the permit area. <br />The well permit numbers do not correlate with the well map located in the application. <br />Please provide the name and location of all wells in the surrounding area that may be <br />impacted by the proposed mining operation (please note that this may be further than 600 <br />feet as indicated in the application). <br />We have printed a larger version of the well map so you can see that the permit numbers correlate <br />with the well map. This information will be included in the groundwater model. <br />33. It appears that the ParkerlDersham site is within the 100-year floodplain of the South Platte <br />River. Please provide the Flood elevations(s) to be expected under a "worst case" flooding <br />scenario and specific mitigation measures that will be implemented to minimize the <br />potential for any offsite impacts. Legible copies of fhe Flood Insurance Rate Maps ("FIRM") <br />through the mine reach would facilitate the Division's review. <br />BRAD <br />34. Please explain how water from dewatering of the ParkerlDersham site will be managed to <br />protect against pollution of surface of groundwater both during and after the mining <br />operation (Rule 6.4.7(2)(c)). <br />ANDY <br />35. Hall-Irwin proposes to discharge mine water and sediment generated from localized <br />stormwater runoff into the ponds already existing at the previously permitted Baseline <br />Resources pit (M-1997-058J. Please further describe how the water will be routed towards <br />the Baseline ponds and provide designs of the predicted flow and structures that will be <br />used to facilitate this runoff. In addition, the operator will be required to revise the mining <br />and reclamation permit of the Baseline pit to account for this additional runoff. <br />Hall-Irwin will install nuisance flow and minor storm flow drainage channels around the perimeter of <br />the site to mitigate offsite runoff. A design flow of 20 cf:r was used to simulate nuisance flows and <br />design storm drainage channels. The drainage channels will be approximately 2.5 to 3 feet deep <br />with 2.5H to 1V sides slopes with a 1.5 foot bottom width. They will be constructed at the existing <br />land slope of 0.5%. Wattles and straw bales will be pla~;ed in the ditches acting as grade control <br />and sediment mitigation structures. These flows will be: routed to a central discharge point as <br />