COAL MINING WASTE AS SOURCE OF HEAVY METALS IN SURFACE- AND GROUND-WATER

Most of the research addressing environmental problems associated with coal mining focuses on the disposal of ash and scrubber sludge, products of coal combustion and slurry produced at coal prep-plants. Little attention is directed at valley-fills composed of overburden rocks topping coal seams removed during strip-mining. Typically, valley-fills consist of sandstone, bituminous shale and upper seams of coal, often with high pyrite content. In a Programmatic Environmental Impact Statement of 2005, the US EPA concluded that mountaintop mines and valley-fills directly alter stream ecosystems in five principal ways:

1. Springs and ephemeral, intermittent and perennial streams are permanently lost with the removal of the mountain and from burial under fill,
2. concentrations of major chemical ions are persistently elevated downstream,
3. degraded water quality reaches levels that are acutely lethal to organisms in standard aquatic toxicity tests,
4. selenium concentrations are elevated, reaching concentrations that have caused toxic effects in fish and birds, and
5. macroinvertebrate and fish communities are consistently degraded.

However, the US EPA has not addressed specifically the impact of valley-fills on downstream ground-water quality.

We analyzed ground-water sampled from residential water wells and surface water downstream from several valley-fills in Southern West Virginia. We found that the concentration of various heavy metals declines exponentially with respect to downstream distance from the valley-fill. The pattern of exponential decline apparently reflects the metal sorption process in the alluvial clays. Yet, we found that the concentration of Lead and Arsenic exceeds US EPA MCL Primary Drinking Water Standards in a number of residential water wells closest to the valley-fill. Also, the concentration of Aluminum often exceed WHO drinking water standards. Moreover, the concentrations of Iron and Manganese, while declining exponentially in terms of downstream distance from the valley-fill, their concentrations grossly exceed US EPA MCL Secondary Drinking Water Standards in almost all the samples. In conclusion, we postulate that the concentration of heavy metals downstream from a valley-fill depends on the amount of alluvial clays in the valley profile and on their sorption capacity.