2010-06-04_HYDROLOGY - M1985218 - Laserfiche WebLink

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Richard T. Raines May 25, 2010 DEPLETIONS Page 2 During this plan year, the site excavations may expose a maximum total of 16.7 acres of ground water. You have also performed a depletion analysis based upon the net replacement obligation and the aquifer characteristics to show the lagged depletion schedule to the Arkansas River, as presented in your Table 3. The total lagged depletions for this plan year are estimated to be 57.57 acre-feet (54.83 from the Active Pit and 1.73 from the Unused Wash Pond). During the April 1, 2010 through March 31, 2011 plan year, the site excavations will not expose any additional ground water. You have submitted an analysis that shows the calculated evaporation, effective precipitation, and resultant net replacement obligation in the same tables above. You have also performed a depletion analysis based upon the net replacement obligation and the aquifer characteristics to show the lagged depletion schedule to the Arkansas River, as presented in your above referenced Table 3. The total lagged depletions for this plan year are estimated to be 56.57 acre-feet, and there is an additional 1 acre-foot depletion from Well Permit No. 66042-F (1405128). Transit losses from the Twin Lakes Reservoir to the Rich Pit were calculated to be 8.35 acre-feet, bringing the total replacement water to 65.92 acre-feet. No mining or dewatering will take place during these plan years unless an amendment to this plan is approved. Your analysis shows that 25.99 acre-feet of depletions from the Active Pit will accrue to the river after the expiration date of this plan. The analysis for the unused wash pond from prior years' submittals shows that about 1.46 acre-feet of post plan depletions will accrue to the river from this pond. Therefore, the total combined post plan depletions are approximately 27.45 acre-feet. Stream depletion analyses for both the Active Pit area and the Unused Wash Pond (attached) used the Stream Depletion Factors of 7.3 days for the Active Pit and 120 days for the Unused Wash Pond, obtained from the USGS Publication 72-192 "Stream Depletion Factors, Arkansas River Valley, Southeastern Colorado". REPLACEMENTS The source of replacement water is the Lower Arkansas Valley Water Conservancy District, and a 5-year lease agreement has been submitted as verification to this office. The terms of the lease are 93 shares of Twin Lakes water per year, commencing April 1, 2010. You have considered transit losses of 10% from Twin Lakes Reservoir to Pueblo Reservoir and 0.25 percent per mile for 18 miles to the Rich Pit. The total transit loss is 9.5 acre-feet. You estimate that these 93 shares will provide in excess of 70.68 acre-feet per year of replacement water and will therefore be sufficient to replace depletions associated with the Rich Pit and transit losses, which total 65.91 acre-feet. A new lease agreement must be provided for any renewal of this SWSP in the coming years. The source of renewable long-term replacement water sufficient to cover evaporative depletions has not been secured for this plan. Lafarge West, Inc. is negotiating with the City of Aurora and Aurora has filed amendments to Case Nos. 99CW169 and 99CW170 to include the Rich Pit for water storage. Aurora has also included the Rich Pit in Case No. 05CW105 as an upstream point of exchange. You state that if Aurora purchases this site, then Aurora will provide the long-term commitment of water supply from its Arkansas Basin water rights. Aurora intends to construct a slurry wall liner and use the pit as a reservoir.