Effect on sediment yield and water quality of a nonrehabilitated surface mine in north-central Wyoming

Sediment and chemical quality of water data were collected from two adjacent drainage basins in northern Wyoming to compare hydrologic differences between an undisturbed basin and a surface-mined, virtually unrehabilitated basin. Rate of sediment accumulation in a pond in the basin that was surface mined for coal and left unrehabilitated was over 11 times greater than in a pond in the adjacent unmined basin. The additional sediment came primarily from barren high walls and roughly graded spoils. No sediment was yielded from ungraded spoil rows that drained to closed depressions. Most sediment yielded from the two basins was trapped in the two ponds. The chemical composition of materials from slopes, channels, and pond bottoms of the two basins were similar; however, concentrations of dissolved and suspended matter in waters of the two ponds were different. Low concentrations of dissolved chemical constituents in the pond water below the unmined basin suggest surface runoff as the source. Higher concentrations of dissolved chemical constituents , notably calcium, magnesium, and sulfate, in pond water below the mined area suggest ground-water discharge as the source. Sediment yield was a better indicator of the effects of disturbance on mined areas than chemical quality of water. (Woodard-USGS)