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Logan Wash Mine TR No. 8 <br />The water chemistry of Outfall 001 water reflects a water of sodium sulfate type. The average <br />total dissolved solids (TDS) concentration is 2,280 milligrams per liter (mg /1). Average <br />concentrations of other primary constituents include calcium (87 mg /L), bicarbonate (272 mg /L), <br />chloride (37 mg /L), magnesium (97 mg /L), potassium (86 mg /L), sodium (424 mg /L), and <br />sulfate (1,255 mg /L). The average pH of the water is 8.03 s.u. <br />4.3 Vicinity Groundwater <br />Table 2 presents a statistical summary of water chemistry constituents for the LW -001 mine <br />water along with analytical data for groundwater samples recently collected at wells LWCW -IA <br />and LW -22. These wells are screened within the alluvial aquifer in the immediate vicinity of <br />Logan Wash Mine. Well LWCW -IA is considered the downgradient compliance well and is <br />located in Dry Gulch a few hundred feet downslope of the toe of the Lower Dump. Well LW -22 <br />is an older alluvial well that is located near the Logan Wash drainage channel approximately 2 <br />miles downstream of the mine site. <br />Table 2 shows that the LW -001 mine water is generally similar to alluvial groundwater in the <br />vicinity of the mine. Like the LW -001 water, the LWCW -IA and LW -22 groundwater is of <br />sodium sulfate type. In addition, the LWCW -IA and LW -22 groundwater both exceed the <br />proposed compliance limits for arsenic and boron specified in the LW -001 permit. These <br />findings support the position that the LW -001 mine water would be better regulated as <br />groundwater and not as discharge to a surface water feature. Furthermore, because of their <br />similar chemistry, co- mingling of discharged LW -001 mine water with ambient alluvial <br />groundwater is not expected to result in any degradation of the local groundwater resource. <br />Table 3 presents other groundwater data collected in the mine vicinity that were compiled by <br />Hester 1983) to evaluate the potential effects of modified in situ retorting on groundwater <br />chemistry. Hester compiled groundwater chemistry data from 9 alluvial wells, 12 deep bedrock <br />wells (200 to 1,400 ft deep), 15 bedrock wells near the retorts, and 2 springs. Bedrock at the <br />mine refers to the Parachute Creek Member of the Green River Formation, the formation in <br />which the mine was constructed. Due to the large number of wells and multiple sample events, <br />Hester only reported summary statistics for individual chemical constituents. Table 3 highlights <br />the constituents that are common to both Tables 1 and 2. <br />Water quality data for mine water originating in the Research Mine is shown in Table 4. The data <br />are sparse, and the lack of cation analysis results prohibits characterizing the water type. Overall. <br />the TDS concentration is lower and water appears to be of better quality than the LW -001 mine <br />water. <br />5.0 Waste Dump Stability <br />Constant infiltration of water on the waste -rock dump may be a concern for potential slope <br />stability issues. Increased pore water pressure can weaken rock shear strength and facilitate <br />gravitational movement of a rock mass. <br />Western Water & Land, Inc. 4 <br />