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Uc(,s -\Q sus Q'rJt)P, (?6c?_0,,; C5 ./ <br />WWE r <br />r C&fs PI T rWr Water Engineers, Inc. m ct 1 ??? S? <br />-ght 1666 N. Main Avenue, Suite C www.wrightwater.com <br />Durango, Colorado 81301 e-mail:pfoster@wrightwater.com <br />(970) 259-7411 TEL <br />(970) 259-8758 FAX <br />March 22, 2011 <br />Via E-Mail: jeff.deatherage@state.co.us <br />Jeff Deatherage, P.E. <br />Colorado Division of Water Resources <br />1313 Sherman St., Room 818 <br />Denver, CO 80203 <br />Re: DRMS Water Supply Requirement for Bonding Determination for United Companies' <br />Colona Gravel Operation <br />Dear Jeff, <br />Wright Water Engineers, Inc. (WWE), on behalf of Oldcastle Southwest Group, Inc, d/b/a United <br />Companies (United), is happy to provide you with this memo outlining the current water supply <br />requirements at the Colona gravel operation. It is our understanding that the Division of <br />Reclamation, Mining, and Safety (DRMS) has required a plan for replacement supplies in the <br />event that operations should cease at a given gravel mine. The following sections of this memo <br />detail the mining operation at the Colona Pit and the associated water depletions if operations <br />were to cease. <br />CURRENT OPERATION <br />United is using a wet mining technique at Colona which does not require dewatering of the pit, <br />thus if operations cease the water surface area should not change. Based on a review of a 2009 <br />aerial photo and conversations with United the current exposed groundwater surface area is 4.4 <br />acres (see Figure 1). <br />WATER DEPLETIONS <br />If mining operations were to cease, depletions at the Colona Pit would occur as a result of only <br />evaporation from the exposed groundwater surface. <br />In months that the average monthly temperature has historically been less than 32 degrees <br />Fahrenheit, we assumed the pit will be iced over and no evaporation will occur (Table 1, Column <br />7). After accounting for ice, the net unit evaporation at the Colona Pit is calculated at 2.55 feet <br />per year (Table 1, Column 8). Multiplying the unit evaporation by the exposed water surface <br />area gives an annual depletion of 11.24 AF of water (Table 1, Column 9). <br />DENVER GLENWOOD SPRINGS <br />(303) 480-1700 TEL (303) 480-1020 FAX (970) 945-7755 TEL (970) 945-9210 FAX <br />