2011-04-19_HYDROLOGY - M1997058 - Laserfiche WebLink

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Mr. Andy Rodriguez, P.E. Page 2 of 6 April 18, 2011 and the Mineral Rules and Regulations for the protection of water resources. The April 30, 2010 letter from DRMS requires that you provide information to DRMS to demonstrate you can replace long term injurious stream depletions that result from mining related exposure of ground water. The DRMS letter identifies four approaches to satisfy this requirement. In accordance with approach nos. 1 and 3, you have obtained a bond for $1,013,500 through DRMS for lining or backfilling of the exposed ground water. Depletions Currently 7.6 acres of ground water surface is exposed at the Baseline Resource pit (WDID 0203017), composed of 7.18 acres in the settling ponds and 0.42 acres in dewatering trenches. Net evaporative depletions were calculated using a gross annual evaporation of 45.5 inches from the exposed water surface, with a credit of 10.19 inches for effective precipitation. The net depletion of ground water due to evaporation from the 7.6 acres of ground water exposed at the site was calculated to be 22.38 acre-feet. Approximately 92,000 cubic yards of concrete will be batched onsite using the well with permit no. 66961-F at a depletion of 40 gallons per cubic yard, resulting in 11.29 acre-feet per year consumed in batching. As previously stated, 1.66 acre-feet of water from this well will also be used for dust suppression at the Baseline Resource site. The total consumptive use of ground water associated with the Baseline Resource pit is estimated to be 35.33 acre-feet, consisting of 22.38 acre-feet of evaporation loss from 7.6 acres of exposed surface area, 1.66 acre-feet for on-site dust control, and 11.29 acre-feet used for concrete batching, as shown in the attached Table 1. The depletions from the mining operation were lagged to the stream using the SDF method. The construction of the slung wall affects the timing of the lagged impacts on the South Platte River. The applicant previously prepared a numeric model to account for this affect. According to the model, the SDF for the Batch Plant production well (concrete production and dust suppression) was estimated to be 176 days and the SDF for the evaporation loss and water lost in product was estimated to be 205 days. Replacements The proposed sources of replacement water for this plan are fully consumable effluent leased from the City of Aurora and nontributary ground water pumped from an existing Laramie- Fox Hills aquifer well. The applicant has entered into a long term lease agreement with the City of Aurora ("Aurora") whereby Aurora will deliver up to 49 acre-feet of fully consumable water to the South Platte River at the confluence of the South Platte River & Sand Creek, just north of Metro Wastewater Treatment Plant. The confluence is located approximately 20 miles upstream of the Baseline Resource Pit. A 0.25 percent per mile transit loss for November through March (5.0 percent overall loss) and a 0.5 percent per mile transit loss for April through October (10.0 percent overall loss) has been accounted for in the replacement schedule. In addition to replacing 20.00 acre-feet of depletions resulting from this mining operation, the City of Aurora effluent will also be used by the Applicant to replace 5.65 acre-feet of depletions resulting from operations at the Parker-Dersham Resource site in accordance with the C.R.S. 37-90-137(11) SWSP approved for Hall-Irwin and 22.74 acre-feet of depletions