2013-01-03_HYDROLOGY - M2011054 - Laserfiche WebLink

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Mr. Peter Foster, P.E. December 24, 2012 DeBeque Pit (M2011 -054) SWSP Page 2 Depletions Gross annual evaporation at the gravel pit location is estimated to be 47.0 inches per year and the monthly distribution is as depicted on the attached Table 1. Net evaporation is defined as gross evaporation less the consumptive use of water by vegetation that naturally occurred at the site prior to construction of the pit. The historical consumptive use was assumed to be equal to the effective precipitation, which was estimated based on the data from the Palisade weather station. The net evaporation for the exposed water surface is 40.01 inches per year, with a monthly distribution as shown on the attached Table 1 and using the estimated exposed water surface area of 0.78 acres, the total annual stream depletion resulting from the exposure of groundwater is estimated to be 2.47 acre - feet. Computation of evaporation under this SWSP was reduced during the ice covered period. You have assumed the ice covered period will occur during the months of December and January based on average monthly temperatures less than 32 °F taken from the Palisade weather station over the period of record 1911 -2012. However, for the purpose of this SWSP, the Applicant shall replace the net evaporation depletions from the exposed ground water surface area that may occur during the assumed ice covered period (the months of December and January) for any time that the pit is not completely covered by ice. Computation of the net evaporation during any time that the pit is not completely covered by ice shall be determined as the pro -rata amount of the monthly gross evaporation rate distribution amount identified in the State Engineer's General Guidelines for Substitute Supply Plans for Sand and Gravel Pits, subtracting the pro -rata amount of the effective precipitation for that period. The anticipated net depletions for this plan are 12.65 acre -feet for the period of August 1, 2012 through July 31, 2013 and 13.39 acre -feet for the period of August 1, 2013 through July 31, 2014 for up to 0.78 acres of water surface exposed in the dewatering trenches and dewatering sump (Figure 2). You have provided a monthly breakdown of the annual depletions made up of 2.47 acre -feet per year of evaporative loss for the first two years of operation, 7.98 acre -feet per year of water used and consumed for dust control for the first two years of operation, 2.21 acre -feet of water lost with the mined product (which represents 75,000 tons of mined product) for the first year of operation and 2.94 acre -feet of water lost with the mined product (which represents 100,000 tons of mined product) for the second year of operation. The Glover analysis was used to determine the lagged depletions to the Colorado River. The aquifer characteristics used in the model are based on the lagging parameters decreed for the nearby DeBeque Pit (M81 -058) in Case No. 2005CW76 and they are: transmissivity (T) = 50,880 gallons per day per foot and specific yield (SY) = 0.2. Because there is an existing lake between the mining area and the river you measured the distance from the centroid of the exposed ground water to the edge of the existing lake and from the edge of the existing lake to the river, which was determined to be =906 feet. The lagged stream depletions for the period of this SWSP are estimated at 12.65 acre -feet for the period of August 1, 2012 through July 31, 2013 and 13.39 acre -feet for the period of August 1, 2013 through July 31, 2014 (Table 2). The pit must be continuously dewatered until such time as the pit can be filled by ground water infiltration during a free river period, or an amendment to the SWSP must be requested and approved to include additional replacement water to offset the volume of water required to fill the pit during the call period. You indicated that the pit will be continuously dewatered at a rate of 500 GPM. However, if the