2013-07-29_HYDROLOGY - M1979191 - Laserfiche WebLink

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Mr. Jared Dains Page 2 of 7 Amended Lafarge Middle Poudre Combined SWSP July 29, 2013 Depletions Three Bells Pit Consumptive use at the Three Bells Pit will consist of evaporation, water used for dust control, and water lost in the mined product. Net evaporative depletions will be unchanged from the 45.55 acre - feet identified in the original SWSP. You have estimated that the amount of water used for dust control purposes at the site will increase from 2 acre -feet to 34 acre -feet. You have indicated that some water use for dust control may occur off -site. Any use of the water for dust control purposes, either at this site or at another location, must be related to gravel mining operations. You anticipate that a total of 420,700 tons of material will be mined at the site during this plan period. The material is mined below the water table in a dewatered state and is not washed; therefore the water retained in the mined product is considered to be 2.0% of the mined material by weight. The amount of water removed in the mined product is estimated to be 6.19 acre -feet for this plan period. The total consumptive use of ground water at the Three Bells Pit is estimated to be 85.75 acre -feet for this plan period. These amounts and uses are consistent with the current well permit for the Three Bells Pit, permit no. 64818 -F. The Alluvial Water Accounting System ( "AWAS ") model was used with the alluvial aquifer boundary condition option to lag depletions to the South Platte River. The following parameters were used in the model for the Three Bells Pit, as reported in the original SWSP: transmissivity (T) = 45,000 gallons per day per foot, distance (X) from the centroid of the surface of the exposed ground water to the river = 1,900 feet, distance (W) from the aquifer boundary through the exposed ground water to the river channel = 4,800 feet, and specific yield (SY) = 0.2. The location of the stream depletion is assumed to be perpendicular to the river. The lagged depletions due to evaporation, dust control, and water removed with the mined product are estimated to total 68.57 acre -feet for this plan period. Kyqer Pit Consumptive use at the Kyger Pit will consist of evaporation and water used to construct a compacted clay liner around the site. Net evaporative depletions will be unchanged from the 22.66 acre - feet identified in the original SWSP. You have estimated that 20 acre -feet of water will be required during this plan period for use in construction of the clay liner. The total consumptive use of ground water at the Kyger Pit is estimated to be 42.66 acre -feet for this plan period. Well permit no. 76210 -F was issued for the Kyger Pit to allow the use of up to 50 acre -feet per year of ground water, in addition to evaporation and dewatering, for dust control, concrete batching, reclamation irrigation, and moisture lost in the mined material. Since use of water for construction of a clay liner is not allowed under the current well permit no. 76210 -F, a new well permit must be obtained that includes this use. The Alluvial Water Accounting System ( "AWAS ") model was used with the alluvial aquifer boundary condition option to lag depletions to the Cache la Poudre River. The following parameters were used in the model for the Kyger Pit, as reported in the original SWSP: transmissivity (T) = 45,000 gallons per day per foot, distance (X) from the centroid of the surface of the exposed ground water to the river = 1,800 feet, distance (W) from the aquifer boundary through the exposed ground water to the river channel = 5,200 feet, and specific yield (SY) = 0.2. The location of the stream depletion is assumed to be perpendicular to the river. The lagged depletions due to evaporation and construction of the clay liner are estimated to total 33.97 acre -feet for this plan period.