2012-04-26_HYDROLOGY - M2001085 - Laserfiche WebLink

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Mr. Craig Lis GSL Sand and Gravel SWSP March 22, 2012 Page 2of5 ground water exposed at the site was calculated to be 33.85 acre -feet for the period of this SWSP. In November 2011, the Applicant estimated that a total of 0.11 acre -feet of water was used for dust suppression and 0.49 acre -feet of water was removed with the mined product as the result of 33,000 tons of aggregate production. The material was in a dewatered state and not washed and therefore was assumed to have a ground water moisture content of 2% by weight. Dewatering operations in November 2011 caused the diversion of 19.73 acre -feet of ground water. With the cessation of dewatering, the pit filled with ground water. The applicant modeled this effect on the ground water basin by prorating the number of days of filling in each month compared to the estimated volume when the surface area of the pit is 15 acres to determine the monthly volume of ground water diverted. It was determined the pit filled with 188.94 acre -feet of ground water. The total consumptive use from the mining operation during this approval period is 250.77 acre -feet which includes evaporation, operational losses, and ground water diverted out of priority to fill the pit. 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: transmissivity (T) = 63,000 gallons per day per foot, distance (X) from the surface of the exposed ground water to the river = 2,295 feet, distance (W) from the aquifer boundary through the exposed ground water to the river channel = 3,836 feet, and specific yield (SY) = 0.2. The location of the stream depletion is assumed to be perpendicular to the river. Evaporative and operational losses were considered back to January 1, 2009 because depletions during this time period may still be impacting the river. The site has been continuously dewatered since July 2009. Dewatering occurred at an approximate rate of 26.90 acre -feet per month up till November 2011. During dewatering, water was returned to the South Platte River at the same rate as dewatering occurs, but resulted in delayed depletions to the stream system. Approximately half (13.45 acre -feet per month) of the water removed during dewatering is placed in the Henderson Ski Lake (aka Zigan Pit 2, DRMS M- 1982 -174, WDID 0203313), with the remainder placed in the South Platte River. Evaporation from Henderson Ski Lake is included in the Zigan Augmentation plan decreed in water court case no. 82CW393. Accretions to the Henderson Ski Lake were lagged using the following parameters: transmissivity (T) = 61,600 gallons per day per foot, distance (X) from the Ski Lake to the river = 1,808 feet, distance (W) from the aquifer boundary through the Ski Lake to the river channel = 5,300 feet, and specific yield (SY) = 0.2. The net effect to the river as a result of dewatering is shown in the attached Table 3. Replacements The replacement source for this plan period is fully consumable Fulton Ditch (WDID 0200808) water leased from the City of Brighton ( "Brighton "). The fully consumable water will be released to the South Platte River from Brighton's Midland augmentation station (located at North 21 Street and Midland Street) or Brighton's 124 Avenue (WDID 0203324) or Ken Mitchell Lake (WDID 0203361) storage facilities. The proposed replacement schedule is provided in Table 4. A copy of this lease agreement dated March 21, 2012 is attached. Long Term Depletions The final reclamation plan for DRMS Mining Permit No M- 2001 -085 had been to create a water storage reservoir through the installation of a slurry wall. The slurry wall was constructed