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The alluvial aquifer system, which includes alluvial bodies in the Fish Creek <br />Drainage (including Bond and Cow Camp Creeks) and the Grassy Creek Drainage, <br />will be impacted by mining activities. <br />During mining, surface runoff from the disturbed areas is contained in sediment <br />ponds prior to discharging from the s~'e. Historically, [he sediment ponds at the <br />Seneca II Mine discharge regulazly throughout the year to the associated drainages <br />(Grassy Creek, Bond Creek, Cow Camp Creek). These drainages, at various times <br />of the yeaz, recharge the associated alluvial/colluvial aquifers with the sediment <br />pond discharge. These sediment pond discharges are typically higher in dissolved <br />constituents than the naturally occurring runoff from the undisturbed site. As the <br />alluvial/colluvial water quality closely mirrors the quality of the stream, a <br />degradation (i.e. increase in TDS) is observable in alluvial monitoring wells <br />down-gradient of the mine site. In portions of Little Grassy Creek drainage in <br />contact with previously disturbed lands, TDS increase over baseline conditions is <br />observable. This is due to the addition of spoils water, which has been discharged <br />from backfilled portions of the mine site, to the alluvial system. <br />This general trend can be seen in water quality analyses from alluvial wells in Grassy <br />Creek and Little Grassy Creek. The water in these alluvial systems is down-gradient <br />of spoils and are probably receiving a contribution from spoils water containing high <br />levels of dissolved solids. Jn general, water from these sites has shown an overall <br />trend toward increasing TDS. Because the systems receive water from other <br />sources, the relative amounts of high-TDS spoils water and relatively "clean" water <br />vary with other factors, so the trend c` increasing salt content is not clearly defined. <br />One exception to the non-linear trend is the water from the alluvial well GWS6-A <br />which displays a smooth trend of increasing dissolved solids. Possibly this well <br />samples a zone receiving a relatively constant supply of spoil water and thus shows <br />TDS concentration increasing linearly with time. <br />Wells in the alluvium of the two east-draining creeks show that high-TDS water <br />from mining activity has not yet migrated very far beneath those creekbeds. The <br />wellsite neazest the disturbed area, S46-A on Cow Camp Creek just downstream of <br />Pond 004, displayed a decrease in TDS concentration from 1987 to 1991 and has <br />increased since then. The well downgradient of that, S69-A, has recently displayed a <br />trend of decreasing TDS. Possibly the water being sampled currently at S69-A is <br />that which passed through the upstream site several years ago. Using that <br />hypothesis, the travel time for groundwater within the Cow Camp Creek alluvium is <br />lower than calculated below. <br />32 <br />