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Since the mine will encounter water 4 feet below the surface of excavation, and permanent lakes <br />will be left as part of the reclamation plan, consumptive use totals are calculated below. A well <br />permit has been applied for with the Division of Water Resources. The well permit will cover pit <br />pumping as well as all consumptive uses for the operation. During the mining stage of the <br />project, consumptive uses will be limited to the evaporation from the sediment pond, road <br />watering, plant water sprays, and gravel retention. After mining, the consumptive use will be <br />lake evaporation. All consumptive uses are shown below: <br />After Mining and Reclamation <br />1) The permanent lakes will total approximately 23 acres in size, which may fluctuate <br />depending upon the groundwater level. Total average water surface is expected to be 22.9 <br />acres. Since the lake bottoms and sides are always saturated due to the level of alluvial <br />water, no losses will occur due to infiltration. Losses will occur due to evaporation at the <br />water surface. With an approximate annual evaporation of 40" annually (Colorado <br />Annual Evaporation Chart NOAA Tech Report NWS33), this results in a consumptive <br />use of 76.3 acre-feet annually using an area of 22.9 acres. <br />During <br />1) During mine operation, consumptive use will occur as result of mining the gravel <br />exposing it to air before it run through the crushing/screening operation and trucked off <br />site. Based on Colorado Division of Water Resources guidelines, groundwater depletions <br />are equivalent to the volume mined below the water table. The use will be based on <br />average annual tonnage for the project of 125,000 tons per year. Therefore, this <br />consumptive use will be 44.27 acre-feet perms. This use will only occur for the years <br />during which mining occurs. It is far below the level of evaporation from the lake <br />surface, therefore it does not count in the worst case calculations. <br />2) Evaporation will occur as a result of pumping water into the sediment pond and exposing <br />this water to the surface. Most of the water will seep back into the ground, but the surface <br />area of the pond will add approximately 0.4 acres. Using the rate calculated of 3.11 acre- <br />feet per acre, this results in a use of 1.24 acre-feet per year. <br />3) Consumptive use for road dust control will be minor since the access road will be <br />primarily maintained with magnesium chloride and/or water as needed. Under very dry <br />Gehrman Pit October 09 G-3