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2.04.7 Hydrology Description <br />PR -02 <br />Alluvial groundwater is recharged by stream flow in the upper reaches of <br />the drainages where there is more likely to be a separation between the <br />channel bottom and the underlying alluvial water table. Recharge of the <br />groundwater is greatest during precipitation events or snow melt runoff <br />when the stage of the creeks increase and more water is able to infiltrate. <br />A lesser amount of recharge may occur from bedrock formations and from <br />irrigation return flows south of the mine. In the lower reaches of the <br />drainages generally south of the mine, the alluvial groundwater may <br />discharge to the creeks because of shallow water table conditions. This is <br />evidenced by natural sub -irrigated vegetation, such as cottonwoods and <br />tamarisk, within valley bottoms. <br />Baseline water quality data for shallow groundwater at the mine is <br />available from three monitoring wells, GWA , GW -9, and GW -3. GWA is <br />an up gradient well, GW -9 is located south of the office complex and GW - <br />3 is located east of the bridge leading to the reclaimed Munger Canyon <br />Mine. <br />Baseline information, for the three alluvial monitoring wells is provided in <br />Tables 4.2ii. Tables 4.2i and 4.2ii. Table 4.2i is a summary of the data <br />presented in Table 4.2ii. <br />The quality of alluvial groundwater in the upper reaches of the major <br />drainages in the area is generally better than in the lower reaches of the <br />drainages. The progressive increase in ion concentrations in groundwater <br />is due to ion dissolution and ion exchange from the changing nature of <br />bedrock underlying the alluvium (Coffin et al. 1971). The principal ions in <br />the alluvial groundwater are calcium, magnesium, sodium and <br />bicarbonate. <br />Both surface and groundwater analysis exhibit high total dissolved solids <br />and can be characterized as sulfate bicarbonate waters. Analysis for the <br />period December 1977 to April 1979, shown in Tables 4.2-1 through 4.2- <br />5, indicated that groundwater in the alluvium is a sodium sulfate type <br />containing dissolved solids ranging from 1,000 to 6,000 mg/I. These data <br />suggest an increase in both dissolved solids concentration and sodium <br />sulfate in the downstream direction. Groundwater quality as shown in the <br />above noted tables was established from sampling six alluvial wells as <br />2.04-17 <br />03/13 <br />