SURVEY OF MINING WASTE AT ABANDONED MINE SITES AND POTENTIAL REMEDIATION WITH LIME AND BIOCHAR AMENDMENTS

Acid mine drainage (AMD) is known to have considerable impacts on the surrounding environment, particularly the toxic effects of acidity and toxic metals on living organisms. Developing new cost-effective amendments to minimize acidity and metal leaching is important for mitigating the legacy of historical mining. The central Virginia Gold-Pyrite Belt has numerous abandoned gold and silver mines predating the Civil War whose tailings are actively undergoing AMD in the Lake Anna Watershed. The objectives of this study were to (1) assess elements at former mine sites in the Lake Anna region to determine if the sites are actively undergoing AMD and leaching toxic metals and (2) evaluate the potential efficacy of combined biochar and lime amendments as reclamation strategies for mitigating contamination at these locations. Surficial mine wastes and pine needles were collected from four different mines and adjacent reference sites to characterize the availability of macronutrients (Ca, Mg, K, P), micronutrients (Cu, Zn), toxic elements (As, Cd, Pb), and other pyrite-forming elements (S, Fe). In addition, the pH, organic matter, electrical conductivity, and redox potential were measured. High concentrations of S (avg 1844 mg/kg), Fe (avg 13345 mg/kg), and low soil pH (avg 3.6) were found at the sites suggesting the presence AMD. To follow up, a comparative soil column leaching experiment was conducted to examine the efficacy of increasing application rates of combined lime and biochar additions (0, 0.4, 4, 40 tons/acre) on the immobilization of toxic elements, amelioration of the pH, and restoration of macronutrients. The results from the column experiments show the treatments did not significantly increase the pH nor decrease the toxic metals, but higher application rates minimized Fe and S in leachate. Acid mine drainage in the Lake Anna region presents significant challenges for remediation using cost-effective methods. Despite over a century of environmental exposure, mine tailings continue to leach toxic metals into surrounding ecosystems.