2013-03-28_HYDROLOGY - M1977151 - Laserfiche WebLink

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Mr. Jared Dains, E.I. Page 2 of 8 March 27, 2013 after that date. The Water Court effectively held that Senate Bill 120 of 1989, as amended in Senate Bill 93 -260, exempted all pre -1981 exposed ground water regardless of whether open mining operations continued or were reactivated on or after January 1, 1981. Accordingly, for the 72.0 acres of ground water currently exposed at the Greeley Pit, replacement of evaporative depletions is only required from the 31.8 acres exposed after December 31, 1980. The area exposed prior to January 1, 1981 is shown on the attached Figure 1, dated July 13, 2010. The exception to the requirement to replace evaporative depletions for the pre -1981 area is tied to the 5.7 -acre pond, the 21.2 -acre pond, and the 13.3 acres of the 40 -acre pond identified on Figure 1, dated July 13, 2010, and may not be applied to other areas of ground water exposure within the gravel pit permit boundary. The current exposed area and the additional 0.3 acres to be exposed during this plan period is shown on the attached Figure 2. Net evaporative depletions were calculated using a gross annual evaporation of 45 inches from the exposed water surface, with a credit of 9.81 inches for effective precipitation. Based on monthly average temperatures reported for the Greeley UNC weather station, ice cover was assumed for the months of December and January, therefore no evaporative consumptive use was charged for those months. However, for the purposes of this SWSP, the Applicant shall replace the net evaporative depletions from the exposed ground water surface area that may occur during the assumed ice cover period (December and January) for any time that the pit is not completely covered by ice. The net depletion of ground water due to evaporation from the surface area of the Greeley Pit exposed after December 31, 1980 was calculated to be 88.31 acre -feet during the approval period of this plan, as shown on the attached Table 1. The Applicant has estimated that 1.00 acre -foot of water will be used for dust control purposes from March to October of each year. The Applicant anticipates mining 20,400 tons of material during the approval period of this plan period. The material is mined below the water table and is not washed; therefore the water retained in the mined product is considered to be 4.0% of the mined material by weight. The water removed in the mined product is estimated to be 0.60 acre -feet for the approval period of this plan. This plan also accounts for water removed from the tributary stream system by the "intermittent fill" of the gravel pit. The "intermittent fill" is the water that fills an unlined gravel pit and occupies the volume previously occupied by the removed material. For the Greeley Pit, the "intermittent fill" was calculated in accordance with the General Guidelines for Substitute Water Supply Plans for Sand and Gravel Pits, using a specific weight of 125 pounds per cubic foot and a porosity of 45 %. Based on the above, the water removed by the "intermittent fill" was determined to be 3.52 acre -feet for the approval period of this plan. The total consumptive use of ground water at the Greeley Pit (including evaporative and operational losses) is estimated to be 93.43 acre -feet for the approval period of this plan. A stream depletion model using the Glover infinite aquifer condition was used to calculate the lagged depletions to the Cache La Poudre River. The following parameters were used in the model: aquifer transmissivity (T) = 120,000 gallons per day per foot, specific yield (SY) = 0.2, and the distance from the centroid of the 40 -acre pond to the Cache La Poudre River = 1,120 feet. The total lagged depletions that will hit the river during the approval period of this plan period are 90.90 acre -feet.