The spoil resulting from contour surface mining of coal in the mountainous of New River Basin of Tennessee was examined to determine its extent of saturation and water quality associated with this saturated zone. Two well study sites were established on the mining spoil in two small watersheds of the upper New River Basin. At each a set of permanent wells running in a line from the bench to the toe of the spoil was installed and periodically monitored for groundwater elevations and water quality. The extent and quality of the spoil saturated zone throughout each watershed was examined with a series of temporary, hand-driven observation wells. The spoil bank investigation covered a period of six years between 1975 and 1981 and was part of a larger comprehensive study in the New River Area examining environmental changes associated with the surface mining of coal. Principle support for this work came from the United States Department of Energy and its predecessor, the Energy Research and Development Administration.
Several large hydrologic and groundwater quality data bases were developed and are summarized with descriptive statistics. Spatial and temporal variations in the data are examined as well as chemical relationships between water quality constituents. Storage volumes and mineral constituent masses mobilized within the mining spoil are quantified. This information and surface hydrologic and water quality data from the larger comprehensive study are used to assess the impact of the surface mining spoil on low flow hydrology in the two study watersheds.
The contour surface mining spoils examined are a heterogeneous, apparently anisotropic, predominately clay material interspersed with weathering fragments of sandstone and shale of various size. They are generally saturated along their lower boundary. The size of this saturated zone, however, is known to vary as a function of surface conditions. The spoil material represents an acid soil.
Concentrations of dissolved mineral constituents found in the saturated zone are moderated compared to spoils of acid drainage areas in the East and those containing glacial deposits in the Midwest. Overall pH is acidic with a median value of 6.3 Calcium and magnesium are the major cations; bicarbonate the major anion. Acid reducing conditions were found to be associated. Constituent concentrations show negative correlation with redox potential and positive associations with alkalinity and sulfate. An attempt was made to quantify the contribution of aluminosilicate minerals to calcium, magnesium and alkalinity found in spoil subsurface waters. The results were inconclusive; however, indirect evidence suggests this contribution is small compared to the dissolution of carbonate materials.
The contour surface mining spoil was shown to store a substantial volume of water and mobilized mineral constituent mass and to have a significant impact on the low flow hydrology of mining disturbed basins. The degree of saturation within the spoils examined was found to be increasing with time, apparently independent of short term annual trends in rainfall. This raises the question as to the long-term stability of these embankments.
Constituent concentrations in the spoil subsurface water are significantly elevated above those found in the shallow, undisturbed groundwater system of the watersheds examined. However, heavy metal concentrations in the spoil drainage are low. Except for isolated point sources of acid mine drainage, this water appears suitable for livestock, irrigation, and, with conventional treatment technology, water supply purposes. No overall, long term decreasing trend in subsurface constituent concentrations, suggestive of recovery, were observed in the spoil quality data. However, short-term variations with hydrologic condition in the spoil are noted
