Environmental Functions of Alluvial Soils in Coal Mining Regions of Eastern Pennsylvania.

Alluvial soils form as a function of periodic deposition of sediment from watershed sources. In areas of extensive industrial mining these soils can store large quantities of eroded mine tailings and associated pollutants. In eastern Pennsylvania, mining for anthracite coal has caused extensive environmental degradation to both water and land resources of the region. We have begun to quantify the impacts of coal mining on floodplain landscapes along the North Branch Susquehanna River (NBSR), which is impacted by acid mine drainage and sediment contributions from large mine spoil banks. Our research goals are to quantify the spatial extent of coal contaminated alluvial soils along the NBSR, evaluate contaminant metal concentrations in these soils, and test for the presence of sulfidic materials capable of forming acid sulfate conditions. Soil data were collected from forested fluvial landforms in the NBSR basin including topographically low-lying river islands (n = 4) and alluvial deltaic deposits at the mouth of large tributary streams (n = 4). Our preliminary data suggest that there are many floodplain landscapes that may be contaminated with coal overwash (>2000 ha) within the greater Susquehanna River basin and metal concentrations in these deposits are typically greater than regional background levels. Alluvial soil horizons had concentrations of Pb ranging from 23-127 mg/kg and As between 9-38 mg/kg. Coal contaminated soils also had high total sulfur concentrations (range 874-14797 mg/kg). Aerobic incubation experiments showed pH drops ranging from 5.17-6.62 initially to 4.30-6.10 after 16 weeks. These results indicate that reworked alluvial coal deposits contain elevated trace metals, but do not classify as sulfidic materials, possibly due to sulfide oxidation since initial deposition over the past century.