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• Post-mine Groundwater t]uality Radian (1981) measured the chemical composition of the Derringer and Enfield Pit overburdens and conducted leach tests to determine the leaching characteristics of these materials.. Radian also conducted batch leaching tests to determine which constituents are likely to be leached from the overburden spoils. The batch tests indicated that manganese, molybdenum and vanadium are species that may potentially leach from overburden at significant concentrations. The batch tests indicated that iron should not significantly leach from the overburden. Concentrations of iron in the post-mine groundwater will probably be significant because the pre-mine conditions are high. Groundwater quality constituent concentrations for some parameters are expected to be higher than pre-mine concentrations for an extended period of time after mining. Sulfate levels in particular can be expected to be higher following mining due to the oxidation of pyrites in the overburden materials. The maximum sulfate concentrations derived from the column leach tests for the weathered and unweathered overburden from the D and E pits varied from 1210 to 2150 mg/l (see Tables 5-4 through 5-7 in Radian, 1981). The higher sulfate levels will be reflected in higher TDS values. The backfill monitoring well maximum sulfate concentrations at Trapper vary, suggesting different water qualities can be anticipated at different locations • The spoil water quality, in general, is better than indicated by the Radian leach tests. The TDS and major constituents from the Cott Seep (mined through in 1988) were less than the maximum observed values from the leach tests. Well GF-5 also exhibits better than the average concentrations from the leach tests. Leach tests commonly over-predict the water quality constituent wncentrations that are expected. The leach tests indicated that several tenths of a mg/I of manganese should be expected in the spoil water. The leach tests also indicated that several hundredths of a mg/I of molybdenum and vanadium should be in the spoil water, while spoil water tested does not contain a significant amount of molybdenum or vanadium. The leach tests seem to be a fairly good indicator of which constituents will be in the spoil water, but their predicted concentrations, in general, are over estimated. The concentrations of water-quality constituents in the springs derived from the spoil aquifers following mining are expected to initially be higher than baseline levels and gradually, over a period of time potentially extending centuries, decline to near baseline values. The sulfate and TDS concentrations in the backfill aquifers are likely related to the amount of pyrite contained in the backfill material. The average percent pyritic sulfur in the sampled Trapper pits varies from a low of 0.1% in the F PiVE. Pyeatt drainage to a high of 0.3°~ in the A PiVJohnson drainage. These values were derived directly from overburden core quality data contained in Volume V-A, Appendix 1, Sections 3 and 4. The average • percent pyritic sulfur content calculated from all core sample values is 0.2°~ . Several processes influence the geochemicel evolution of water quality in backfill aquifers. The primary processes as itlenGfied by the USGS in a study conducted at the Seneca Mine (Water Resources Ravision: 1~'~y 4-238b Approved CT 2 ~ cuUC