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16 <br />Schwartzwalder Mine -Hydrologic Evaluation of Mine Closure and Reclamation <br />Table 7. Seasonal Distribution of Average Flows in Ralston Creek <br />Measured at Nine Stations Near the Schwartzwalder Mine, October 1998 -September 1999 <br />Season Months Flow Rate cfs <br />Fall Sept-Oct-Nov 5.50 <br />Winter Dec-Jan-Feb <br />^ 3.76 <br />_ <br />Spring <br />Summer Mar-A r-Ma <br />June-Jul -Au 19.02 <br />11.14 <br />Flow rates in Ralston Creek have been affected by several project-related activities: <br />• Sumps. Four sumps were operated in the alluvium and fill adjacent to Ralston Creek. The sumps were <br />designed to limit direct seepage of uranium-impacted water from the alluvium into the creek by <br />collecting water from engineered French drains. The source of uranium in the alluvial sump water was <br />not entirely known, although leaching from treatment pond sediments that were covered by <br />construction of the ore sorter may be one potential source (Section 10.2). Water collected from the <br />sumps was sent through the water treatment plant, and discharged into Ralston Creek at station SW- <br />DIS001. As a result, the net affect of the sumps on flow rates in the creek was negligible. <br />• Water Treatment Plant. Until May 2002, flow rates in Ralston Creek were also affected by mine water <br />which was pumped from the lower levels, treated, and discharged from the water treatment plant. Mine <br />water pumping rates averaged about 200 gpm from 1995 to 1999 (Section 5.2.1). This contribution <br />increased the net flow rate in Ralston Creek, although the increase was insufficient to be detected <br />within the precision of the stream flow monitoring program. The change in flow from the treatment <br />plant was not distinguishable in the flow rates measured in Ralston Creek. <br />Since pumping from the mine ceased in May 2000, and the mine sumps and water treatment plant were <br />taken offline in June 2002, flows in Ralston Creek are no longer affected by pumping from bedrock or <br />alluvium and return flow to surface water at the site. <br />4. GROUNDWATER <br />Groundwater occurs in two primary zones: bedrock and alluvium. Bedrock in the project area consists of <br />amphibolite-grade metamorphic rocks. Alluvium is largely confined to stream deposits of limited thickness <br />and extent along Ralston Creek, as shown in Figure 4. <br />4.1 Groundwater in Bedrock <br />Bedrock consists of three main lithologic units: <br />1) Lime-silicate-hornblende gneiss (LSHG); <br />2) Mica schist (MS); and <br />3) Garnet-biotite gneiss and quartzite rock of the Schwartz Trend. <br />The LSHG and MS rock types comprise the majority of the rock mass at the site. Bedrock north of the <br />mine is composed of lime-silicate-hornblende gneiss. Bedrock south of the mine is predominantly mica <br />schist. Uranium ore was hosted by Schwartz Trend rocks which form a thin band of brittle garnet-biotite <br />gneiss and quartzite along the near vertical contact between the more extensive LSHG and MS units. A <br />geologic map of the mine area is presented in Figure 3. <br />Pegmatite intrusive rocks comprise a fourth lithologic unit in the area, but represent a very small portion of <br />the total rock mass. The pegmatites were significant to the mine's hydrology, however, in that they yielded <br />large volumes of water to underground workings when initially drilled. <br />Whetstone Associates <br />4109B.071116 <br />