2011-10-17_HYDROLOGY - M1980136 - Laserfiche WebLink

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Eagle Pit SWSP October 5, 2011 Depletions Page 2of8 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. In accordance with approach nos. 1 and 3, you have indicated that a bond has been obtained for $694,934 through the Division of Reclamation, Mining, and Safety ( "DRMS ") to assure that depletions from groundwater evaporation do not occur in the unforeseen event, or events that would lead to the abandonment of the gravel pit. The anticipated net depletions for this SWSP are 29.24 acre -feet per year. This SWSP anticipates that a total of 3.5 acres of water surface will be exposed at the site in the dewatering trenches around the mined area. You have provided a monthly breakdown of the annual depletions made up of 9.41 acre -feet of net evaporative Toss, 3.83 acre -feet of water lost with the mined product (which represents 130,000 tons of mined product), 16.00 acre -feet of water used for dust control, and 0.01 acre -feet used for domestic purposes. The attached Table 1 depicts the projected consumptive use including evaporative losses and operational losses. A stream depletion model was developed for the Eagle Pit and the effects of the delayed impacts are found on the attached Table 2. The aquifer characteristics used in the model are: transmissivity (T) = 100,000 gallons per day per foot, specific yield (SY) = 0.2, the distance from the stream to the centroid of the dewatering trench = 1,000 feet, and the location of the parallel impermeable boundary was estimated to be 1,300 feet from the stream. The total lagged depletions from evaporation and operational uses are anticipated to equal 29.01 acre -feet for the period of July 1, 2011 through June 30, 2012 and 29.24 acre -feet for the period of July 1, 2012 through June 30, 2013. In consolidated Case Nos. 81 CW94 and 81 CW291, water for industrial purposes is to be supplied by the C -1 Well (well permit no. 38079 -F). Annual diversions from the C -1 Well for industrial purposes were estimated to be 21.5 acre -feet (17.2 acre - feet to be diverted during the historical irrigation season and 4.3 acre -feet would be diverted outside of the historical irrigation season) and annual depletions for industrial purposes were estimated to be 10.8 acre -feet (9.3 acre -feet to occur during the historical irrigation season and 1.5 acre -feet to occur outside of the historical irrigation season). This SWSP will replace industrial depletions in excess of the water supplied by the C -1 Well (up to a maximum annual depletion amount supplied by the C -1 Well of 10.8 acre - feet). Assuming the maximum depletion amount of 10.8 acre - feet/year is supplied by the C -1 Well, the remaining depletions that will be replaced under this SWSP are 18.2 acre -feet (29.01 AF —10.8 AF) during the period of July 1, 2011 through June 30, 2012 and 18.44 acre -feet (29.24 AF — 10.8 AF) for the period of July 1, 2012 through June 30, 2013. The dewatering depletions at the Eagle Pit were calculated to have reached a steady -state condition. Therefore no depletions or excess credits need to be accounted for in this SWSP.