CHARACTERIZATION OF STREAM WATERS IN THE VICINITY OF THE UNDEVELOPED COLES HILL URANIUM DEPOSIT, PITTSYLVANIA COUNTY, VIRGINIA

The two ore bodies at Coles Hill in Pittsylvania County, Virginia, represent the largest undeveloped uranium deposit in the United States. This site presents a unique opportunity to conduct baseline characterization prior to the development of a proposed uranium mine in a temperate climate. A pre-operational baseline study provides data which enable both the monitoring of environmental impacts during proposed mining and the establishment of post-mining remediation goals. At the Coles Hill site, a study area was defined that encompasses sampling points in streams both upgradient and downgradient of the potential mine workings, mill, and tailings storage facilities as well as sites in surrounding watersheds that are outside of the footprint expected to be affected by mining.

Monthly sampling is ongoing within the study area, and temporal changes have been observed in flow and composition. To date, results show that waters are slightly acidic to circum-neutral (pH 5.0 – 7.6) with low specific conductance (8 – 89 µS/cm) and trace metal and radionuclide concentrations below regulatory guidelines. Dominant dissolved constituents include Ca (1.62 – 9.39 mg/L) and bicarbonate (alkalinity 6.2 – 49.3 mg/L as CaCO₃). Dissolved organic carbon ranges from 1.57 – 17.2 mg/L. Also of particular interest at this site are U (<0.1 – 0.95 µg/L), Pb (<0.05 – 0.73 µg/L), V (<0.5 – 2.3 µg/L), Ra-226 (<0.2 – 0.265 pCi/L), and Th-230 (<0.05 – 0.312 pCi/L). Uranium concentrations above 0.1 µg/L detection occur in small drainages downhill and to the east of the ore bodies; these sites also yield the highest Pb and V concentrations.

To date, although element concentrations in surface water samples are, on average, lower in the Piedmont crystalline region northwest and generally upstream of the deposit than in the Triassic basin sediments to the southeast of the deposit, the difference is not statistically significant. Additional statistical tests will be used to compare upstream and background sampling sites with locations downstream of the deposit to assess the impact of the undeveloped deposit on surface water quality. Data will ultimately be integrated with those from soils, groundwater, and other media to develop a mass transport model for the deposit.