EVALUATION OF WATER QUALITY CONDITIONS IN COAL MINE BACKFILL IN THE POWDER RIVER BASIN OF WYOMING

In the Powder River Basin of Wyoming, water quality monitoring data were evaluated for a number of wells completed in mine backfill, which have sufficiently recharged for evaluation of mining impacts on water quality. Based on the data reviewed to date, the backfill water quality is usually similar to baseline water quality in the Wyodak-Anderson coal aquifer and Wasatch overburden. However, as the backfill materials recharge, the trends in the concentrations of specific constituents (in particular, total dissolved solids and sulfate) may reflect site- specific conditions, including: proximity to recharge sources (e.g., clinker, unmined coal, and coal fenders between mines); changes in mining activities (e.g., temporary cessation of mining); and local conditions (e.g., leakage from impoundments). In some situations, constituent concentrations increase over time, while in others, constituent concentrations are relatively constant or are decreasing.