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Schwartzwalder Mine -Hydrologic Evaluation of Mine Closure and Reclamation 94 <br />7.2 Alluvial Water Quality <br />Water quality data are available for 9 monitoring wells completed in alluvium adjacent to Ralston Creek <br />(Figure 2). Six of the wells (MWO, MWO1, MW02, MW04, MW06, and MW07) were sampled and <br />analyzed for uranium, radium, and field parameters (temperature, pH, and conductivity) for approximately <br />9 years, prior to the start of the 1998 - 1999 baseline hydrologic study. Three additional wells (MW9, <br />MWSR, and MW00) were constructed in the alluvium in 1999 as part of the mine closure baseline <br />hydrology study. These wells have been routinely monitored to the present, and several are slated for <br />abandonment (in accordance with Colorado water well regulations) as part of mine closure. <br />Water quality for the alluvial monitoring wells is provided in Table 29. The water is acalcium-bicarbonate <br />to calcium-sulfate-bicarbonate type water, with low dissolved solids and near neutral pH. TDS averages <br />170 mg/L in upgradient well MW00, and increases to about 340 mg/L in the vicinity of the mine. Trace <br />metals are below detection in alluvial groundwater, with the exception of molybdenum and uranium. <br />The observed fluctuations in uranium concentrations in alluvial monitoring wells (Figure 38) may have <br />resulted from surface disturbance related to reclamation activities. A trend of increasing concentrations in <br />alluvial groundwater related to mine refilling is not apparent because (1) concentration trends do not <br />coincide with mine refill trends (Section 5.2.3), (2) the highest concentrations in alluvial groundwater were <br />observed in 2002 - 2003 when water levels in the mine were 400 - 600 feet below the creek level, and (3) <br />groundwater in the mine and in the alluvium have distinct geochemical signatures. Nor are seasonal trends <br />observed in surface water apparent in the alluvial groundwater. Surface water in Ralston Creek exhibits <br />low concentrations during spring (high flow) months and higher concentrations during winter (low flow) <br />months. Although more water flows through the alluvium in the spring, the higher water levels may <br />liberate oxidized salts from above the normal water level in the alluvium and fill. <br />The point of compliance well drilled near the property boundary (MW8) was intended to monitor water <br />quality in the alluvium as it exits the site. However, monitoring well MW8 is always dry and has never <br />been sampled. As described in Section 4.2.1 and shown in Figure 4, the alluvium pinches out at the eastern <br />edge of Section 25, near the property boundary, where a natural constriction in the valley occurs. Bedrock <br />is exposed along the width of the valley floor and groundwater previously flowing in the alluvium is forced <br />to the surface where it enters Ralston Creek. The point of compliance for groundwater in the alluvium is <br />surface water station SW-BPL (below the property line). <br />4109B.071116 Whetstone Associates <br />