OXIDATIVE EXHAUSTION: ASSESSING THE TIME FRAME FOR THE CESSATION OF ACID MINE DRAINAGE PRODUCTION WITHIN TWO APPALACHIAN WATERSHEDS

Water resources across Ohio and Appalachia are degraded by contamination from legacy coal mining operations, primarily as a result of acid mine drainage (AMD) which has severe, long lasting impacts on water quality and stream ecology in affected watersheds. The reactions that generate AMD via the oxidation of pyrite in abandoned mines will continue until the biogeochemical endpoint known as “oxidative exhaustion”. The time frame for when oxidative exhaustion might occur is not well constrained which has major implications for reclamation projects that must be kept active and maintained to prevent ecological impact. Discharge from two deep mines in Ohio in the Huff Run (HR) and Yellow Creek (YC) watersheds, have been sampled (bi)weekly to measure AMD output (discharge, pH, DO, and metal loading) and seasonal variability. AMD from YC has a higher acid and metal loading compared to HR, which is consistent with historic data; AMD output from both sites has also decreased over twenty years. Both sites exhibit seasonal changes in AMD output, however, concentration-discharge (Q) behavior is dependent on local hydro(geo)logical and geochemical factors; with higher Q, the HR discharge is more acidic (i.e. higher weathering rates) whereas the YC discharge is less acidic (i.e. dilution). Comparison to historic data indicates that discharge from the mines may reach background metal and acid loadings within a few decades (HR) or centuries (YC). Ongoing work aims to characterize the mineralogy and geochemistry of the coal shales to better estimate the amount of pyrite remaining that could contribute to future AMD production. Developing a framework for cost-effective and targeted treatment that accounts for local variability is critically needed. Knowing if these costs are likely to continue for decades, centuries, or even longer is required for planning future treatment plans as inadequate reclamation project support would result in recontamination and ecological impairment.