2011-03-07_HYDROLOGY - M1978210 - Laserfiche WebLink

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Ms. Michelle L. Hatcher Page 3 of 6 March 7, 2011 tributary stream system by the "first fill of the gravel pit. The "first fill" is the water that fills an unlined gravel pit and occupies the volume previously occupied by the removed sand and gravel. For the Geisert Pit, the "first fill" was calculated in accordance with the General Guidelines for Substitute Water Supply Plans for Sand and Gravel Pits, based on 150,000 tons of aggregate production multiplied by the percentage gravel matrix (68% assuming a porosity of 32% and a density of the material of 1.69 tons/cubic-yard) and then subtracting the volume of water lost with the mined product (4.4 acre-feet). Based on the above, the water removed by the "first fill" was determined to be 33 acre-feet for 2011. The total consumptive use of ground water at the Geisert Pit (including evaporative and operational losses) is estimated to be 156.3 acre-feet, consisting of 118.9 acre-feet of evaporative loss from 40.6 acres of post-'81 exposed surface area, 4.4 acre-feet of water lost with the mined product (150,000 tons of aggregate), and 33 acre-feet of water removed by the "first fill". The Geisert Pit is located approximately 300 feet from the Cache La Poudre River, therefore depletions were not assumed to have an instantaneous impact on the River. A stream depletion model was used to determine the timing of lagged depletions to the 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 exposed ground water to the river (X) = 300 feet, and the location of the parallel impermeable boundary to the stream (W) = 2,700 feet (based on the USGS Geologic Map of the Boulder-Fort Collins-Greeley Area, Colorado). The total lagged stream depletions from the operation of the Geisert Pit during this plan period are 156.4 acre-. feet. For the purposes of this SWSP, the distance to the exposed ground water surface from the river is accepted; however, should the Applicant seek to renew this SWSP, the Applicant must demonstrate that the depletions were calculated based on the distance to the centroid of the ground water ponds. Replacements The source of replacement water to be used for this plan period is a lease of 156.4 acre- feet of reusable effluent from the City of Greeley's Wastewater Treatment Plant ("WWTP"). Weld County has a perpetual lease with the City of Greeley for the right to use up to 300 acre- feet per year of Greeley's reusable effluent. A copy of the lease agreement with the City of Greeley for 156.4 acre-feet of fully consumable effluent from the WWTP (WDID 0302312) to be used at the Geisert Pit from April 2011 through March 2012 is attached to this letter. Greeley's WWTP discharge point is located approximately two miles downstream of Weld County's Geisert Pit. There are no intervening water rights within this reach, thus the replacement water from the WWTP is sufficient to replace the pit's out-of-priority depletions. The monthly depletions and replacement requirements are found on the attached Table 3. Conditions of Approval I hereby approve the proposed substitute water supply plan in accordance with C.R.S. § 37-90-137(11), subject to the following conditions: 1. This plan shall be valid for the period of April 1, 2011 through March 31, 2012, unless otherwise revoked or modified. If this plan will not be made absolute by a water court action by the plan's expiration date, a renewal request must be submitted to this office with the statutory fee (currently $257) no later than February 15, 2012.