Spatial Convergence in Major Dissolved Ion Concentrations and Implications of Headwater Mining for Downstream Water Quality.

Spatial patterns in major dissolved solute concentrations were examined to better understand impact of surface coal mining in headwaters on downstream water chemistry. Sixty sites were sampled seasonally from 2012 to 2014 in an eastern Kentucky watershed. Watershed areas (WA) ranged from 1.6 to 400.5 km2 and were mostly forested (58%-95%), but some drained as much as 31% surface mining. Measures of total dissolved solutes and most component ions were positively correlated with mining. Analytes showed strong convergent spatial patterns with high variability in headwaters (<15 km2 WA) that stabilized downstream (WA > 75 km2), indicating hydrologic mixing primarily controls downstream values. Mean headwater solute concentrations were a good predictor of downstream values, with % differences ranging from 0.55% (Na+) to 28.78% (Mg2+). In a mined scenario where all headwaters had impacts, downstream solute concentrations roughly doubled. Alternatively, if mining impacts to headwaters were minimized, downstream solute concentrations better approximated the 300 µS/cm conductivity criterion deemed protective of aquatic life. Temporal variability also had convergent spatial patterns and mined streams were less variable due to unnaturally stable hydrology. The highly conserved nature of dissolved solutes from mining activities and lack of viable treatment options suggest forested, unmined watersheds would provide dilution that would be protective of downstream aquatic life.

Assessing the Impact of Removing Select Materials from Coal Mine Overburden, Central Appalachia Region, USA.

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: (i) Unmodified Scenario, which included all extracted strata and (ii) 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 1,020-1,150 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 lower sulfur content in overburden. 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.