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The Northwest Impoundment discharged oil and grease at 214 mg/1 on May <br />08, 1991. The excess oil and grease was generated when the truck pond, which <br />drains to the Northwest Impoundment, was dredged. Subsequent samples taken <br />May 23, June 1, June 10,. and June 19, 1991 showed oil and grease concentrates <br />below allowable limits. <br />Pond 004 discharges were beyond acceptable pH values on June 15, 1987 and <br />June 22, 1987. An algae bloom in the pond resulted in pH values of 9.03 and <br />9.04, respectively. No pH problems have been observed in the pond since then. <br />Increased Total Dissolved Solids Loading <br />An increase in salinity, as represented by TDS concentrations, is the major <br />surface water impact caused by the Seneca II Mine. The disturbance of <br />sedimentary rocks during the mining and reclamation process exposes more <br />surface area for the solution of minerals and increases the amount of solute <br />available for transport to surface streams. <br />An increase in TDS concentration of approximately 1500 mg/1 between upstream <br />and downstream stations on Grassy Creek has been observed at the Seneca II <br />Mine. An effect of this magnitude has been apparent throughout the monitoring <br />period, 1981 to 1991. This upstream to downstream increase is likely <br />attributable to mining. <br />An increase in TDS from 600 mg/1 prior to mining in the Cow Camp Creek <br />Drainage to 3000 mg/1 has been observed in monitoring data collected from 1981 <br />to 1991. TDS in Bond Creek has risen from 550 mg/1 in 1987 to 1350 mg/1 in <br />1991. The operator has suggested that TDS levels in Bond Creek and Cow Camp <br />Creek will stabilize after mining activities cease, as has been observed in <br />the portion of the Grassy Creek drainage where mining has ceased. <br />A prediction of TDS loading which could be expected to occur in both the <br />Fish Creek and Grassy Creek basins during the months of June through September <br />has been developed by the operator and included in the statement of probable <br />hydrologic consequences. Mean monthly flow and maximum observed TDS <br />concentrations from monitoring of spoils aquifer wells were used in the <br />analysis. Predicted TDS concentrations for downstream locations on both <br />Fish and Grassy Creeks were calculated using the mass-balance approach. <br />Results of the analysis indicate that a maximum TDS of 2341 mg/1 would occur <br />~_ during September at a location below the mine on Grassy Creek. A <br />corresponding flow of 0.84 cfs would result. <br />Results of the analysis on Fish Creek predict a cumulative effect from the <br />Cow Camp and Bond Creek drainages to result in an instream TDS concentration <br />of 607 mg/1 in Fish Creek below the mine during the month of July. This <br />conclusion was based on assumed discharge of 0.2 cfs with a TDS concentration <br />of 2245 mg/1 from both Cow Camp Creek and Bond Creek. During August and <br />September no flow in the tributaries is expected to reach Fish Creek as <br />surface flow. <br />-24- <br />