2014-02-20_HYDROLOGY - M1984094 - Laserfiche WebLink

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Gloria Z Pit SWSP February 18, 2014 Page 2 of 5 The water that will be used to replace these depletions is 1 acre -foot of water leased from the Headwater Authority of the South Platte ( "HASP "). Depletions Depletions from the Gloria Z Pit will result from evaporation of exposed groundwater and operational losses resulting from mining activity. Currently there are three ponds on the site described as; the plant settling pond (18,000 square feet), the plant infiltration pond (32,230 square feet) and the mining pit (6,000 square feet). The plant settling pond is where tailings from the sluice flow after processing, the plant infiltration pond receives water overflow from the plant settling pond to allow water infiltration back into the local ground water regime, and the mine pit is the groundwater pond where the mining of material occurs. The settling and infiltration ponds are not constructed to expose groundwater. Evaporation from each pond was calculated using a gross annual evaporation of 35 inches from the exposed water surface, with a credit of 9.15 inches for effective precipitation, based on average annual precipitation of 13.07 inches for the Fairplay S Park Rd weather station (COOP ID 052816). 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, January and February based on the average monthly temperatures of 31.2° F for December, 32.0° F for January and 30.4° F for February. Temperature data were obtained from the Fairplay S Park Rd weather station for the time period of 2002 through 2012. 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 ground water surface area that may occur during the assumed ice covered period (December through February) for any time that the pit is not completely covered by ice. Net evaporative losses at the site were estimated to equal 0.85 acre -feet for the settling pond, 1.55 acre -feet for the infiltration pond, and 0.29 acre -feet for the mining pit during this plan period. Operational losses associated with mining activities will include water removed with the mined product and water used for dust control. Depletions resulting from the "first fill' of the pit were replaced in 2013. The site will be wet mined but will be continuously backfilled during mining, maintaining the exposed surface area of the pit at 6,000 square feet. The Applicant has estimated that 20,000 tons of mined material will leave the site in 2014. The material is mined below the water table; therefore the water retained in the mined product is considered to be 4.0% of the mined material by weight. This results in a consumptive use of 0.59 acre -feet. The Applicant has estimated an annual dust control requirement of 0.39 acre -feet. Additional depletions will also result due to evaporation from mined material being stockpiled on site (prior to being used to backfill the mining pit), water used in the trommel, water used in the sluice, and water used for dust control in the crushing and screening of gravel. Evaporative losses for the stockpiles, trammel, and sluice were calculated based on their respective surface area. The evaporation calculations for the trammel and sluice take into consideration that the plant is operated only 7 hours per day, and are doubled to account for the turbulence of flow and provide a conservative estimate of consumptive use. The amount of water sprayed for dust control during crushing and screening of gravel was estimated at a typical ratio of 3.97 gallons per ton. The Applicant has estimated these processing depletions to total 0.35 acre -feet for this plan period. Total consumptive use during this SWSP period is projected to be 4.01 acre -feet. The monthly ground water depletions were lagged from the pit using the Alluvial Water Accounting System (AWAS) program developed by the Integrated Decision Support (IDS) Group at Colorado State University with the following parameters, which were, developed by DWR staff based on a review of the site: • Distance from the gravel pit centroid to the river (X) = 300 feet