Citation:

Pinto, P., S. Al-Abed, C. Holder, R. Warner, J. McKernan, S. Fulton, AND E. Somerville. Assessing the Impact of Removing Select Materials from Coal Mine Overburden, Central Appalachia Region, USA. Robert Kleinmann (ed.), Mine Water and the Environment. Springer-Verlag, BERLIN-HEIDELBERG, Germany, 37(1):31-41, (2018).

Impact/Purpose:

The objective of this study was to evaluate the leachate EC of overburden materials in a column test that was intended to simulate surface coal mining conditions and its correlation with cations, anions, pH, and alkalinity in two scenarios: 'Modified' and 'Unmodified'. For the unmodified scenario, all overburden strata were included in the leaching tests, while the modified scenario excluded the 15% of the overburden strata (by mass) with the highest conductivities, as measured in the screening-level assessment. The 15% criterion was based on the authors' professional judgment that this would be a reasonable overburden quantity to be selectively identified and isolated in a typical surface coal mining operation.

Description:

The exposure of readily soluble components of overburden materials from surface coal mining to air and water results in mineral oxidation and carbonate mineral dissolution, thus increasing coal mine water conductivity. A conductivity benchmark of 300 µS/cm for mine water discharges in the Appalachian region has been suggested to protect aquatic life and the environment. A USGS screening-level leach test was applied to individual strata from three cores collected from a surface mine site in the central Appalachian region to generate preliminary conductivity rankings, which were used to classify strata for two disposal scenarios: (1) unmodified scenario, which included all extracted strata and (2) modified scenario, which excluded 15% (by mass) of the overburden materials with the highest conductivities. We evaluated overburden leaching conductivity using EPA Method 1627 in 18 dry-wet cycles, generating conductivities of 1020-1150 µS/cm for the unmodified scenario and 624-979 µS/cm for the modified scenario. Hence, overburden segregation was successful in reducing the leachate conductivity, but did not reach the proposed benchmark. The leachate was dominated by sulfate in the first four cycles and by bicarbonates in cycles 5-18 in columns with higher sulfur content, while bicarbonates were dominant throughout experiments with overburden having lower sulfur content. The use of conductivity rankings, isolation of potentially problematic overburden strata, and appropriate materials management could reduce conductivity in central Appalachian streams and other surface mining areas.

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