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24 Grassy Valley hydrologic conditions <br />Surface water flow data <br />Flow data for Grassy Valley have been collected periodically since early 1997 and are <br />presented in Table 4.1 and Figure 4.2. The flow rate is variable throughout the year with <br />the highest flows occurring in spring and summer (the highest average monthly flow of <br />143 gpm occurs in June), and low to zero flows in winter. The average annual flow at <br />GV-03 is approximately 40 gpm. Table 4.1 presents available flow rate data and also an <br />estimate of average monthly values based on available data. <br />Surface water chemistry data <br />The period of record, water quality statistics and field parameter data summaries for the <br />three stations have been compiled and are provided in Tables C1 through C3 <br />(Attachment C), respectively. Average major ion chemistries measured at surface water <br />monitoring locations in Grassy Valley are presented in Figure 4.3. As shown in this <br />figure, surface water samples from upstream station, GV-01, are generally characterized <br />as sodium sulfate-bicarbonate waters. Samples from GV-02 are generally calcium <br />sulfate-bicarbonate water, and samples from GV-03 are calcium-sodium sulfate waters. <br />These data suggest that the surface water is increasing in the proportions of calcium and <br />sulfate in the downstream direction. Average field pH values for GV-01, GV-02 and GV- <br />03 were near-neutral, ranging from 6.5 to 7.3 su. Historical tailings and tailings ponds <br />are located in the drainage between GV-01 and GV-02. Sulfate concentrations generally <br />increased in the downstream direction from 42 mg/L at GV-01 to 565 and 422 mg/L at <br />GV-02 and GV-03, respectively. <br />4.3.3 Shallow groundwater <br />In 2001, a series of piezometers/probe holes were installed in the upper portion of <br />Grassy Valley northwest of the Cameron Railroad Grade to investigate the nature of the <br />shallow alluvial materials in this area. Boring logs for these probe holes indicate that the <br />alluvial material contains significant amounts of clay from argillic alteration of the <br />underlying bedrock. Only about half of the probe holes encountered water or damp <br />alluvium. Free water was noted in a few holes within thin sections of coarse sand to <br />gravel between dry, stiff clay. It was generally concluded that the high clay content of <br />portions of the alluvial materials and altered/weathered bedrock is responsible for <br />perched water table conditions and the development of riparian areas in upper Grassy <br />Valley. The clay material likely also inhibits the flow of shallow alluvial groundwater. <br />Flow in the alluvial material is controlled by the highly variable composition of the <br />alluvium which ranges from gravelly to very-fine grained material with high clay content. <br />Some of the higher permeability areas do not appear to be laterally continuous and are <br />likely isolated by low permeability clay zones. An additional 12 piezometers were <br />installed in the Grassy Valley riparian areas in 2006 to assess the shallow saturated <br />conditions. These piezometers were less than 5 feet in depth and were completed with <br />slotted PVC pipe. These piezometers are monitored during the growing season. <br /> <br />2736 <br />Cripple Creek & Victor Gold Mining Company <br />Water Management Consultants <br />