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Heidi Frey <br />February 4, 2011 <br />Page 2 <br />PREVIOUS SWSP APPROVAL <br />The June 30, 2010 SWSP approval letter required that an augmentation station be constructed on the <br />Lester-Attebery Ditch. In May, 2010, a 2-foot weir was installed to measure deliveries from the Lester- <br />Attebery Ditch into the Grisenti Pit Phase 1 pond. A Sutron SDR continuous recorder was included in <br />the installation to record the deliveries to the pit. Additionally, the Lester-Attebery Ditch was cleaned <br />out and re-graded in places in order to reduce backup in the ditch. Finally, in September 2010, a <br />Sutron SDR continuous recorder was installed in the flume on east side of Highway 115 which records <br />the total diversions through the ditch (not including wasteway water). It is our understanding that the <br />Water Commissioner is now satisfied with the measuring devices on the ditch. <br />DEPLETIONS <br />The depletions at the Grisenti Pit include water removed in the mined material, water used for dust <br />control, and evaporation from 19 acres of exposed ground water. The projected water requirements are <br />summarized in Table 1. Transit Mix will continue to mine within their Phase 2 pit. Mining has <br />temporarily ceased and is projected to resume in May of this year for several months. However, in <br />order to conservatively project the depletions, we have projected full production of 260,000 tons for <br />the duration of this SWSP request. Using the recommended moisture content of four percent by <br />weight, direct water losses from mining production will deplete a maximum of about 7.65 ac-ft per <br />year. <br />Pumping for dust control is assumed to be 100% consumptive. Dust control water is measured through <br />a totalizing flow meter and projected to be no more than 5 ac-ft per year. The projected dust control <br />was determined based upon maximum historical dust control pumping. <br />The total exposed ground water area at the Grisenti Pit is 19.37 acres. This total consists of a 15.62 <br />acre pond in Phase 1 which is being used as the settling pond, a 1.25 acre fresh water supply pond in <br />Phase 2 which is used for washing and dust suppression, and a 2.5 acre pond in Phase 2 which only <br />exists when mining ceases and the dewatering pump is shut off. When Phase 2 mining resumes, the pit <br />will be dewatered, and the exposed ground water area will decrease. For this SWSP, we have shown <br />depletions caused by the full 19.37 acres of exposed ground water area thru July, 2011 and an <br />additional 5.7 acres from August, 2011 forward in order to be conservative. The increased surface area <br />accounts for the maximum projected increase in Phase 2 exposed ground water once mining ceases <br />again. We will account for the actual exposed area during the SWSP. According to the NOAA <br />Evaporation Atlas, the area has an average gross evaporation rate of 45.4 inches per year. This annual <br />rate was distributed monthly based upon the State's SB-120 guidelines in order to determine the <br />monthly evaporation rates (see Table 1). Climate data from the Canon City weather station was <br />tabulated for the period from 1950 through 2003, and an average precipitation rate of 12.7 inches per <br />year was determined. Based upon the State's guidelines, gross evaporation was reduced by an effective <br />precipitation credit equal to 70 percent of the total precipitation, resulting in a net evaporative loss at <br />the site equal to approximately 3.0 ac-ft per acre per year (ft/yr). As shown in Table 1, the net <br />evaporative loss is conservatively projected to be approximately 65.66 ac-ft in 2011 and 76.08 ac-ft in <br />2012.