An evaluation of geochemical parameters of the overburden and the water quality associated with strip mining of the Sewanee seam in the southern coalfield of East Tennessee

Water samples were collected twice a month from April 1976 to July 1977 from two strip mines in the southern Cumberland Plateau in Tennessee. Rock samples from two highwall sections, and a roadcut within the same stratigraphic intervals were also collected.

The water samples were collected from four specific sites at each mine: a raw drainage sample, a "treated" sample which was the mine effluent, an upstream sample above the mining activity which was a control point, and a downstream sample below the confluence of the mine effluent and main stream. The water samples were analyzed for the following water quality parameters: pH, Ca, Mg, Fe, Mn, total dissolved solids, total suspended solids, S0₄, and a number of trace metals including Co, Cu, Cr, Pb, Ni, Zn, and Cd. Rock samples were chemically analyzed for Ca, Fe, Mn, Cr, Cu, Ni, Zn, Co, Pb and Cd. An acid/neutralization potential was also determined for the rock samples.

The results of the water quality analyses showed that on the average Ca, Fe, Mn, Mg, TSS, TDS, acidity and S0₄ concentrations all increased in waters downstream from the mines as a result of mining disturbance. . However, concentrations fluctuated on the basis of stream flow and rainfall. Increases in stream flow were generally related to decreases in metal concentrations and visa versa. There was also a marked difference in the character of water analyzed from the two mines.

Analyzing the trace metals in the rock units showed that the coals and organic rich siltstones generally contained the highest metal concentrations; the sandstone and sandy siltstones contained the lowest metal concentrations. The organic rich units and coals also had the highest acid potential, while the sandy units had the lowest.

The difference in water quality at the two mines may be equated with the difference in metal concentrations and acid potentials in the highwalls at the two mines. Rocks from the mine with the poorer water quality also had the highest acid potentials and metal values.

An evaluation is made of the treatment facilities set up at each mine. At one mine a limestone barrier at the edge of a settling pond was used while at the other mine a mechanical device which discharged NaOH into the effluent was used. This latter treatment facility was very effective in reducing metal concentrations by raising the pH, but was little used during the course of the study. The limestone barrier yielded only minimum improvement in water quality.