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• Little Grassy Creek alluvium. This is probably a reflection of Che dilution of this cater <br />through mixing with undisturbed, upper Grassy Creek alluvial water. <br />In the Cou Camp Creek (tributary of Fish Creek) alluvium, water quality is measured at two <br />cells. Welt 46-A has a MgCa504HC03 type cater with water quality notably different from <br />other alluvial eater in the Seneca Mine area. This well exhibited a high TDS <br />concentration prior to mining in the vicinity (2,068 mg/l in November 7982). High TDS <br />values are also exhibited in the alluvium upstream of this cell at Spring ifs (14,200 mg/l <br />in September, 1985). Apparently, eater quality in this alluvium is affected by a high <br />concentration of naturally occurring salts that are further conceniraced by <br />evapotranspiration. Mine runoff and spoil spring discharge has caused TDS values at,Well <br />46•A to increase further, up to October 77, 7986 (with a TDS of 3,498 mg/t), after which <br />TDS values have steadily decreased with a May 18, 7990 TDS value of 2,436 mg/l. This is <br />in spite of the fact that TDS values upstream at the 004 pond have increased steadily <br />since 1982 (ui th a TDS of 3,250 mg/l on May 3, 1990). The decrease in TDS at Well 46-A may <br />possibly be due to the 004 pond diversion ditch which enters Cow Camp Creek between the <br />D04 pond and the eel 1. This ditch carries runoff from undisturbed land and a currently <br />• unused haul road to the west of the 004 pond. When the haul road corridor was new, <br />recently disturbed land may have contributed to increases in TDS values in the ditch <br />water. As vegetation esiablished itself, the TDS values in the ditch could probably have <br />decreased. The drainage basin for this ditch has also decreased due to mining activities. <br />The second well in the Cou Camp Creek alluvium, Nell 69-A, was completed in the summer of <br />1988. It is located approximately one and one-half miles downstream of Well 46-A. The <br />water samples at this well displayed a CaMg-S04 type water. The average TDS values for <br />this well in 7990 were 38 percent higher than Well 46-A. This is most likely a result of <br />the high amount of salts in the soils of Tuentymi le Park (see later discussion of the <br />Twentymile Park and Fish Creek surface water systems). <br />Nell 68-A, completed in the Bond Creek alluvium, was also completed in the summer of 1988. <br />It is located approximately two miles downstream of the 008 pond. The eater samples at <br />this well displayed a Cang-S04 type water. TDS values were 46 percent higher than <br />observed at Nell 69-A on Cou Camp Creek (3404 mg/l average, 1990), and were significantly <br />higher then measured at NPDES DOS (1074 mg/l evera9 e, 1990). Local alluvial geochemistry <br />most likely accounts for this difference. <br />7 <br />