2018-02-14_HYDROLOGY - M2000082 - Laserfiche WebLink

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East 8th Street SWSP February 12, 2018 Plan ID 4701 Page 2 of 6 plan for the pit is to create a lined storage reservoir for the City of Greeley. Depletions The exposed surface area at this site is expected to total 11.5 acres during this plan period, consisting of the west cell, settling ponds, and dewatering trenches in the east cell. Net evaporative loss was determined to be 2.93 feet per exposed acre, as approved in previous SWSPs. This value was calculated using a gross annual evaporation of 45 inches from the exposed water surface, with a credit of 9.9 inches for effective precipitation, based on average annual precipitation of 14.14 inches for the Greeley UNC weather station. Net evaporative losses at the site are therefore estimated to total 33.64 acre-feet for the 11.5 acres exposed during this plan period. The Applicant anticipates mining 250,000 tons of aggregate during this plan period. The material will be mined below the ground water table in a dewatered state and not 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 3.68 acre-feet. The Applicant projects using 0.50 acre-feet of water per year from the pit for dust control purposes. All water used for dust control purposes is assumed to be 100% consumed. The total consumptive use of ground water at the East 8th Street Pit (including evaporative and operational losses) is estimated to be 37.82 acre-feet for this plan period. The east cell will be continuously dewatered during this SWSP period, and all such water will be discharged to the Cache la Poudre River. As long as the pit is continuously dewatered and all water is discharged to the Cache la Poudre River, the accretions to the stream system should be sufficient to replace the lagged dewatering depletions. All site dewatering must be accounted for in a method satisfactory to the division engineer and water commissioner. Adequate measuring devices may be required in order to adequately account for the dewatering. After cessation of dewatering the west cell in July 2016, the cell filled to a depth of approximately 4 feet with a surface area of 7 acres, for a total fill volume of 28 acre-feet. You have assumed that the refilling occurred evenly over the three-month period of August, and September, and October 2016. The lagged depletions associated with the temporary refilling of the west cell, including lagged depletions from evaporation off the increased surface area of the cell, will be replaced under this SWSP. The IDS Alluvial Water Accounting System (AWAS) analytical stream depletion model, which uses the Glover method, was used to calculate the lagged depletions to the Cache la Poudre River. The following parameters were used in the model: transmissivity (T) = 120,000 gallons per day per foot, specific yield (SY) = 0.2, the distance from the river to the edge of the alluvium = 11,000 feet, and the distance from the centroid of the exposed surface water areas to the river = 600 feet. The total lagged depletions were determined to be 34.92 acre-feet for this plan period. This amount includes lagged depletions resulting from past consumptive use at the site that are projected to impact the river during this plan period, including those from the refilling of the west cell in 2016. The attached Table 1 shows the monthly breakdown of evaporative, operational, and lagged depletions. Replacements Pursuant to a mining lease agreement between Laser and the City of Greeley ("Greeley"), of colo Office of the State Engineer 1313 Sherman Street, Room 821, Denver,CO 80203 P 303.866.3581 www.water.state.co.us + * 1870