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Ms. Michelle L. Hatcher Page 2 <br />August 24, 2010 <br />The total consumptive use of ground water at the Geisert Pit (including evaporative and <br />operational losses) is estimated to be 158.3 acre-feet. You have provided a monthly breakdown of the <br />annual depletions totaling 118.9 acre-feet of evaporative loss from 40.6 acres of exposed surface area, <br />2.00 acre-feet of water used and consumed for dust control, 4.4 acre-feet of water lost with the mined <br />product (150,000 tons of aggregate), and 33 acre-feet of water removed by the "first fill". The average <br />precipitation from the Greeley UNC weather station for the years 1967 to 2005 was used to determine the <br />consumptive use from evaporation. The average precipitation for this time period is 14.1 inches. No <br />phreatophyte credit has been applied to this plan. <br />According to the "General Guidelines for Substitute Water Supply Plans for Sand and Gravel Pits", <br />water consumption by the mining operation will also include water removed from the tributary stream <br />system by the "first fill" of the gravel pit. The "first fill" is the water that fills the gravel pit and occupies the <br />volume previously occupied by the removed sand and gravel. For the Geisert Pit, the "first fill" was <br />estimated based on 150,000 tons of aggregate production for 2010 multiplied by the percentage gravel <br />matrix (68% assuming a porosity of 32% and a density of the material of 1.69 tons/cubic-yard) and then <br />subtracting the volume of water lost with the mined product. Based on the above, the water removed by <br />the "first fill" was determined to be 33 acre-feet for 2010. <br />A stream depletion model was used to determine the lagged depletions to the Cache La Poudre <br />River. 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 of the exposed ground water to the river = 300 feet, and the <br />location of the parallel impermeable boundary was estimated to be 2,700 feet from the stream (based on <br />the USGS Geologic Map of the Boulder-Fort Collins-Greeley Area, Colorado). The total lagged stream <br />depletions from the operation of the Geisert Pit during this plan period are 158.1 acre-feet. <br />Replacements <br />The source of replacement water to be used for this plan is a lease of 158.1 acre-feet of reusable <br />effluent from the City of Greeley. Weld County has a perpetual lease with the City of Greeley for the right <br />to use up to 300 acre-feet per year of the Greeley's reusable effluent. A copy of the lease agreement with <br />the City of Greeley for 158.1 acre-feet of fully consumable effluent from Greeley's Wastewater Treatment <br />Plant ("WWTP")(WDID 0302312) to be used at the Geisert Pit was submitted to this office on May 28, <br />2010 and is attached to this letter. Greeley's WWTP discharge point is located approximately two miles <br />downstream of Weld County's Geisert Pit. There are no intervening water rights within this reach, thus the <br />replacement water from the WWTP is sufficient to replace the pit's out-of-priority depletions The monthly <br />depletions and replacement requirements are found on the attached Table I. <br />Conditions of Approval <br />I hereby approve the proposed substitute water supply plan in accordance with C.R.S. § 37-90- <br />137(11), subject to the following conditions: <br />1. This plan shall be valid for the period of April 1, 2010 through March 31, 2011, unless otherwise <br />revoked or modified. If this plan will not be made absolute by a water court action by the plan's <br />expiration date, a renewal request must be submitted to this office with the statutory fee (currently <br />$257) no later than February 15, 2011.