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times as much pyritic sulfur in the Seneca II overburden and 2.4 times as much sulfate • sulfur in the Seneca II-W overburden. The total sulfur concentrations in the tr+o overburdens are almost comparable. There are no noticeable high trace element concentrations in either mine's overburden. As was mentioned earlier, the pH at Seneca II-W is not expected to drop below seven, thus there is no potential for mobilizing significant concentrations of trace elements in the Seneca II-W spoil aquifer. Of note, mean weighted concentrations of boron, iron, and manganese were twice as high in the Seneca II-W overburden. The mean weighted copper and mercury concentrations at Seneca II-W are 10 times and 1.4 times as great, respectively, as those in the Seneca II overburden. All other trace elements are comparable or below the concentrations measured in the Seneca 11 overburden. Ta61e 17-10 summarizes the aforementioned statements concerning major ion and trace element concentrations in the Seneca II and II-W overburden. Tab 6, Geology, should be referred to for additional discussions regarding overburden characteristics and chemistry. Controls on Spoil and Downgradient Water Quality. The resultant chemistry and water quality of the Seneca II-W spoil aquifer will be a function of several processes: 1) the • dissolution of mineral species present in the spoil; 2) dissociation of the dissolved compounds; 3) oxidation; 4) reactions with atmospheric C02; and 5) cation exchange processes. Several mineral species have been identified by x-ray diffraction analyses performed by the USGS on spoil samples and core samples of the Wadge overburden. The principal rock minerals identified were plagioclase feldspar (NaA1Si308-CaA75i308), calcite (CaC03), dolomite (CaMg(C03)2), quartz (5102), ankerite (CaFe(C03 )2 ), potash feldspar (KA75i30g), pyrite (Fe52), sideri to (FeC03), and gypsum (CaSO4.2M20), Powder x-ray diffraction analyses were also performed to determine clay mineral species present and their relative proportions. Clay minerals identified were illite, which is a general term used to refer to both trioctahedral and dioctahedral micas and can be described by the formulas for muscovite and bioti to (KA72(A1513010)(OH)2-N(Mg,Fe)3(A15i3070)(OH)2), kaol finite (A125i205(OH)4), chlorite (Mg,Fe)3(Si ,AI)4010(OH)2.(Mg,Fe)3(OH)6, and mixed layered illite/sonectites. The smecti to clay mineral present is most likely montmorillonite, which has the general formula ((A1,Mg)8(5i4 10)3(OH)10.12H2 8a sed on a knowledge of the mineral and clay mineral species present, the more probable • chemical reactions can be formulated. Atmospheric CO will mix with the spoils water 2 28