2018-11-07_HYDROLOGY - M1982131 - Laserfiche WebLink

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Bucklen Pit SWSP November 7, 2018 Plan ID 3183 Page 2 of 9 sand and gravel, regardless of whether mining continued after December 31, 1980. This office has previously recognized 5.27 acres of the 17.65-acre pond as having been exposed prior to January 1, 1981. The location of the pre-81 area is permanently tied to the location depicted in Figure 2 and may not be re-allocated to other areas of ground water exposure within the gravel pit boundaries. Any pre-81 area that is backfilled will lose the pre-81 exemption should it be excavated in the future. Additionally the backfilling of the pre-81 area shall not create a credit to be used elsewhere. 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 an average annual precipitation of 14.02 inches. Computation of evaporation under this plan was reduced during the ice covered period. You have assumed the ice covered period to occur during the months of December and January based on the average monthly temperatures of 29.4°F for December, and 28.6°F for January. Temperature and precipitation data were obtained from the Greeley UNC weather station (053553) for the time period of 1967 through 2005. The ice covered periods may be used to reduce the amount of evaporative losses that need to be replaced; however, for the purpose of this SWSP, the Applicant shall replace the net evaporation depletions from the exposed groundwater surface area that may occur during the assumed ice covered period (December through 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 net depletion of ground water due to evaporation from the 12.54 acres exposed after December 31, 1980 is projected to total 34.60 acre-feet during this plan period, as shown on the attached Table 1. Operational losses associated with mining activities will include water removed with the mined product and water used for dust control. Up to 50,000 tons of material is projected to be mined during this plan period. The material will be mined below the groundwater table in a dewatered state and will not be washed; therefore the water retained in the mined product is considered to be 2.0% of the mined material by weight. This results in a groundwater loss of 0.74 acre-feet. The Applicant has estimated that 2,000 gallons of water per day will be used for dust control purposes during the months of March through October. Water used for dust control purposes is assumed to be 100% consumed. The amount of water lost to dust control during this plan period is therefore estimated to be 1.50 acre-feet. The estimated monthly depletions due to operational losses are shown on the attached Table 2. The total projected operational consumptive use for this plan period is 2.24 acre-feet. According to information previously provided to this office, dewatering commenced in Amendment Area A in the summer of 1998 and is not projected to cease until 2021. Dewatering occurs through the use of two pumps, with one pump usually running continuously, and two pumps running in high water events. The water is pumped into two settling ponds north of Amendment Area A and immediately adjacent to the Cache la Poudre River, where it is allowed to seep and discharge into the river. Prior to November 2012, the volume of water pumped for dewatering was not included in the accounting submitted to this office or otherwise tracked. Subsequent SWSP approvals have required monthly volumes of dewatering discharge into the settling ponds to be recorded. However, these volumes do not need to be analyzed for depletions to the river as tong as pumping remains relatively constant month to month. Dewatering operations that are constant and continuous will eventually reach a steady state condition where the accretions to the river generated by dewatering are equal to the depletions to the river generated by dewatering. Given the long