2015-05-01_HYDROLOGY - M2008006 - Laserfiche WebLink

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Mr. Todd Williams, P.E. April 24, 2015 ID h Page 2 of 6 the entire month of April 2015 with 0 acres exposed for the remainder of the plan period (May 2015 through March 2016). Evaporative depletions were calculated rusing a gross annual evaporation of 40 inches distributed as 3.60 inches during the month of April, with a credit of 1.03 inches for effective precipitation (based on an average April precipitation for the Windsor weather station). For the total of 7.0 acres of ground water exposed at this site, net evaporation is equal to 1.50 acre -feet (see attached Table 1). The Applicant plans to remove from the site 15,000 tons of sand and gravel removed from the pit in April and May 2015 and stockpiled at the site. The material is 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 0.22 acre -feet of ground water lost with the mined material. The Applicant has proposed to use a portion of the approximately 5.6 acre -feet of ground water contained within the lined area for dust control purposes at the site, and to pump the remaining water back to the Poudre River. For the purposes of this SWSP, you have assumed that the entire_ 5.6 acre -feet of water remaining in the pit will be consumed for dust control purposes during April 2015., Please note that while the previous SWSP allowed for up to 4.00 acre -feet of water to be pumped from the SerFer Pit for dust control purposes, no water from the SerFer Pit has previously been used for dust control purposes. Total operational consumptive use at the site during this plan period is projected to equal 5.82 acre -feet (see attached Table 2). Total evaporative and operational consumptive use at the site during this plan period is projected to equal 7.32 acre -feet (see attached Table 3). Past dewatering operations at the SerFer Pit occurred between May 2012 and December 2014. The lagged depletions to be replaced during this plan period due to past dewatering equal 33.6 acre - feet. The Alluvial Water Accounting System (AWAS) stream depletion model developed by the Integrated Decision Support Group was used to determine the lagged depletions from the SerFer Pit to the Cache La Poudre River from past and projected evaporation and operational losses at the site. The following parameters were used in the model: • Distance from the gravel pit centroid to the river (X) = 600 ft • Alluvial aquifer width (W) = 4,300 ft • Specific yield (S) = 0.2 • Transmissivity (T) = 45,000 (gpd /ft) Lagged stream depletions are estimated to total 41.15 acre -feet during this plan period, as shown on the attached Table 8. Over 95% of the lagged depletions due to past mining and dewatering operations at the SerFer Pit will have accrued to the river by the end of March 2016. You have chosen to wrap all remaining lagged depletions into this plan period (April 1, 2015 - March 31, 2016) for replacement. The total amount of depletions to be replaced under this SWSP will therefore equal 51.84 acre -feet. Provided that the clay liner for the site receives approval from the SEO, no depletions associated with the SerFer Pit will remain after the conclusion of this plan period and no subsequent SWSP will be required for this site. Replacements . The source of replacement water for this plan is excess recharge credit from the Applicant's Timnath- Connell Pit SWSP (WDID 0302526). The Applicant has available a total of 164.42 acre -feet of excess recharge credit during this plan period, of which a total of 52.32 acre -feet will be dedicated