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East 8th Street Pit SWSP Page 2 of 5 <br />October 29, 2015 <br />end of October. Net evaporative loss was determined to be 2.93 feet per exposed acre, as approved <br />in previous SWSPs. This value was calculated using a gross annual evaporation of 45 inches from the <br />exposed water surface, with a credit of 9.9 inches for effective precipitation, based on average <br />annual precipitation of 14.14 inches for the Greeley UNC weather station. Net evaporative losses at <br />the site are therefore estimated to total 10.71 acre-feet for this plan period. <br />The Applicant anticipates mining 500,000 tons of aggregate during this plan period. The <br />material will be mined below the ground water table in a dewatered state and not washed; therefore <br />the water retained in the mined product is considered to be 2.0% of the mined material by weight. <br />This results in a groundwater loss of 7.36 acre-feet. <br />The Applicant projects using 1.38 acre-feet of water per year from the pit for dust control <br />purposes. <br />Once dewatering at the west cell ceases, the delayed depletions to the stream system, <br />including water removed from the tributary stream system by the "first fill" of the cell, must be <br />replaced. The "first fill" is defined as the water that fills an unlined gravel pit and occupies the <br />volume previously occupied by the removed sand and gravel. For the purposes of this SWSP, you <br />have proposed to replace a conservative refill volume of 560 acre-feet after dewatering at the site <br />ceases, based on a surface area of 14 acres, a pit depth of 50 feet, and a depth to ground water of <br />10 feet. You have assumed that the refilling will occur evenly over the three-month period of <br />August, September, and October 2016. Although dewatering of the west cell will cease, dewatering <br />of the east cell is anticipated to commence concurrently or shortly thereafter. Once dewatering of <br />the east cell commences, it will be continuously dewatered during this SWSP period, and all such <br />water will be discharged to the Cache la Poudre River. As long as the pit is continuously dewatered <br />and all water is discharged to the Cache la Poudre River, the accretions to the stream system from <br />dewatering of the east cell should be sufficient to replace the lagged dewatering depletions from the <br />east and west cells. Should there be a delay between the cessation of dewatering at the west <br />cell and the commencement of dewatering at the east cell, all lagged dewatering depletions <br />impacting the stream during that time period are required to be replaced under this SWSP. The <br />Applicant must notify the water commissioner both when dewatering ceases at the west cell and <br />when dewatering commences at the east cell. All site dewatering must be accounted for in a <br />method satisfactory to the division engineer and water commissioner. Adequate measuring devices <br />may be required in order to adequately account for the dewatering. <br />The total consumptive use of ground water at the East 8th Street Pit (including evaporative <br />and operational losses) is estimated to be 579.44 acre-feet for this plan period. <br />The IDS Alluvial Water Accounting System (AWAS) analytical stream depletion model, which <br />uses the Glover method, was used to calculate the lagged depletions to the Cache la Poudre River. <br />The following parameters were used in the model: transmissivity (T) = 120,000 gallons per day per <br />foot, specific yield (SY) = 0.2, the distance from the river to the edge of the alluvium = 11,000 feet, <br />and the distance from the centroid of the exposed surface water areas to the river = 600 feet. The <br />total lagged depletions were determined to be 450.59 acre-feet for this plan period. This amount <br />includes lagged depletions resulting from past consumptive use at the site that are projected to <br />impact the river during this plan period. <br />The attached Table 1 shows the monthly breakdown of evaporative, operational, and lagged <br />depletions. <br />Replacements <br />Pursuant to a mining lease agreement between Laser and the City of Greeley ("Greeley"), <br />Greeley will provide the required augmentation water for the East 8th Street Pit. A copy of the <br />