2011-02-25_REPORT - C1980005 - Laserfiche WebLink

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during the July visit. This reduction in flow is due to stream channel infiltration and evapotranspiration. The TDS plot indicates a decreasing trend. - Surface Water Site SW-S2-11 (SSF11). This site monitors Fish Creek upstream of its confluence of Cow Camp Creek. It is required to be monitored May through July on a monthly basis, but only if either Sites 10 or 12 are flowing (for this year, May and June only). However, field parameters and flow estimates may sometimes be provided voluntarily when not required. This site is upstream of Seneca II Mine discharges. The TDS plot indicates a decreasing trend. - Surface Water Site SW-S2-13 (SSF13). This site monitors Fish Creek downstream of its confluences with Cow Camp Creek and Bond Creek. It is monitored at the same frequency as Site 11. The increase in TDS values, from Site 11 to Site 13, was from 330 to 430 mg/1 (30% increase) in May, and 310 to 330 mg/1 (6% increase) in June. This site displays a decreasing TDS trend. On Page 7-247 of the Seneca II Mine Probable Hydrologic Consequences (PHC), predictions were made for the TDS increases to be observed on Fish Creek during the months of June and July due to discharges from the Seneca II Mine. In June, an increase from 421 to 497 mg/1 (18%) is predicted between SSF11 and SSF13. In July, an increase from 533 to 607 mg/1 (13%) is predicted between SSF11 and SSF13. As stated in the previous paragraph, a 6% increase was observed in June. It appears that the Seneca II Mine has little impact on Fish Creek. Water discharged from the mine is lost to stock ponds, evapotranspiration, and the alluvium as it flows through Twentymile Park. Dissolved solids from mine discharges are diluted during the snowmelt runoff in March and April (prior to the irrigation season) by high stream flows with relatively low TDS concentrations. The natural conditions in Twentymile Park appear to have a much greater impact on the water quality of Fish Creek. • 9