RECONNAISSANCE MONITORING OF ACID MINE DRAINAGE FROM AN INCOMPLETELY REMEDIATED SITE AT ORE KNOB, NORTH CAROLINA

The Ore Knob deposit in Ashe County, North Carolina is one of numerous volcanogenic massive sulfide deposits in the Appalachian Mountains. Mining began in the 1850’s and continued sporadically until the underground workings and mine tailings were abandoned in 1962. Since then, acid mine drainage (AMD) from the pyrite and pyrrhotite-rich tailings have affected creeks that drain into the South Fork of the New River, which has been designated as both a National Wild and Scenic and an American Heritage River. Spot checks of water quality by the Army Corps of Engineers (ACOE) indicate that a limited attempt at remediation in the early 1990’s has resulted in no apparent long-term improvement, but there has been no systematic monitoring. A second, more extentsive, remediation project is now in the final planning stages.

The two creeks that drain from the mine site, Big and Little Peak Creek, were sampled periodically over nine and three month periods, respectively, to provide baseline data for gauging the success of the new project. Instream measurements of pH and conductivity and water samples were gathered from three sites (tailings drainage and upstream and downstream from the stream/tailings drainage confluence). In addition, samples from the South Fork of the New River upstream and downstream of the Big Peak Creek confluence were also obtained.

The direct tailings drainage has values (pH 3.0, conductivity 665 µS, Fe 35 mg/l, SO4 350mg/l) at the low end for reported AMD, indicating that the initial remediation may have been more effective than initially thought. Dissolved Fe and SO4 values rapidly decrease downstream, likely due to dilution and microbial activity, but pH remains significantly abnormal (4.6). Mixing of this creek with the South Fork of the New River results in a lowering of the river pH by nearly a full unit (7.1 to 6.2) despite over an order magnitude difference in discharge. The ACOE project is expected to return the drainage to an approximately normal state for the first time in over 40 years.