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Monitoring of metals at stream locations downstream of mining on Grassy and Cow Camp Creeks suggest that lead, zinc, selenium, copper and cadmium occasionally exceed stream standards at the Seneca II Mine. However, the frequency and duration of these exceedences do not preclude beneficial uses, primarily agriculture, water supply, recreation and aquatic habitat, for which the water is used downstream. Increased Total Dissolved Solids Loading An increase in salinity, as represented by TDS concentrations, is the major impact caused by the mining of Seneca II Mine. The disturbance of sedimentary rocks during the mining and reclamation process exposes more surface area for the solution of minerals and increases the amount of solute available for transport to surface streams. An increase in TDS concentration of approximately 1000 mg/1 between upstream and downstream stations on Grassy Creek has been observed at Seneca II Mine. An effect of this magnitude has been apparent throughout the monitoring period, 1981 to 1985. This upstream to downstream increase is attributable to mining. An increase in TDS from 600 mg/1 prior to mining in the Cow Camp Creek Drainage to 1900 mg/1 has been observed in monitoring data collected in the Fish Creek basin. The operator has suggested stabilization of the TDS concentration will occur at this level in Cow Camp and Bond Creeks based on conditions observed in the Grassy Creek drainage during the course of mining. However, this prediction is based upon the quality of water which discharges from the Wadge Impoundment, a structure which may be left after mining is completed. It is thought that water which discharges from tfiis large impoundment will be of significantly better quality than direct discharge from the spoil aquifer. A stabilization at this level has been suggested by the operator as the extent of increase to be expected in Fish Creek, based on conditions observed Grassy Creek during the course of continued mining operations. A prediction of TDS loading which could be expected to occur in both the Fish Creek and Grassy Creek basins during the months of June through September has been developed by the operator and included in the statement of probable hydrologic consequences. Mean monthly flow and maximum observed TDS concentrations from monitoring of spoils aquifer wells were used in the analysis. Predicted TDS concentrations for downstream locations on both Fish and Grassy Creeks were calculated using the mass-balance approach. Results of the analysis indicate that a maximum TDS of 2341 mg/1 would occur during September at a location below the mine on Grassy Creek. A corresponding flow of 0.84 cfs would result. Results of the analysis on Fish Creek predict a cumulative effect from the Cow Camp and Bond Creek drainages to result in an instream TDS concentration of 607 mg/1 in Fish Creek below the mine during the month of July. This conclusion was based on assumed discharge of 0.2 cfs with a TDS concentration _pl _