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32 Grassy Valley hydrologic conditions <br />Average monthly pan evaporation data used in the model are presented in Table 2.4. A <br />correction factor of 80 percent was applied to pan evaporation data to estimate the <br />evaporation rate from in the riparian areas in Grassy Valley. <br />There are no ET data for the Grassy Valley area, however ET rates in Grassy Valley are <br />considered to be high for the following reasons: <br />• There is a thick layer of alluvium and organic matter over Grassy Valley, some of <br />which has high porosity and can store a significant volume of water. The clay within <br />the alluvium reduces infiltration to deeper alluvium or towards Grassy Creek. <br />Therefore, there is significant shallow water available for evaporation. <br />• The high water storage capacity of the alluvium in the Grassy Creek drainage has <br />allowed significant growth of vegetation -both grasses and trees, which consume <br />and transpire significant quantities of water. <br />ET was used as a calibration parameter in the simulation of current conditions. The ET rates <br />estimated during calibration of the base case model are presented in Table 4.3. These data <br />represent average ET from existing vegetation which include' grasses (lower slopes) and <br />trees (upper slopes). <br />Table 4.3 Average monthly ET values used in the base case water balance <br /> Estimated monthly <br /> ET (in) <br />Jan 0.0 <br />Feb 0.0 <br />Mar 0.4 <br />Apr 1.7 <br />May 2.5 <br />Jun 3.3 <br />Jul 3.2 <br />Aug 2.7 <br />Sep 1.1 <br />Oct 0.0 <br />Nov 0.0 <br />Dec 0.0 <br />Total 15.0 <br />Runoff <br />There is no evidence of surface runoff from the Grassy Valley hill slopes with the exceptions <br />of Grassy Creek and one small side drainage overlying granite on the north side of the <br />Grassy Valley drainage. Thus the majority of precipitation falling on Grassy Valley either <br />evaporates/evapotranspires/sublimates or infiltrates into alluvium and bedrock. <br />During mining, runoff from reclaimed portions of the ECOSA will be diverted to Grassy <br />Creek; runoff from unreclaimed portions of the ECOSA is not expected, as described in the <br />conceptual .model for mining conditions. However, to be conservative, the modeling <br />assumes no runoff from the ECOSA during the mining period. During the post-mining period, <br />runoff from the revegetated ECOSA is expected. The HELP model (United States <br />2736 <br />Cripple Creek & Victor Gold Mining Company <br />Water Management Consultan[s <br />