Seasonal variability in the hydrogeochemical behavior and metal fluxes of acid mine drainage: Implications for long-term output and treatment

Abstract

The timeframe for when water quality impairment from acid mine drainage (AMD) from abandoned coal mines might end is often poorly constrained. The response of AMD composition to changes in discharge can provide insight into how mines store and release water and solutes. This work aimed to determine seasonal variability, hydrogeochemical behavior, and metal fluxes from two abandoned coal mines in Appalachian Ohio that represent end-member hydrologic conditions within the Huff Run (HR, groundwater-fed) and Yellow Creek (YC, surface water-fed) watersheds, by: (1) monitoring AMD output to establish seasonal variability; (2) comparing current output to publicly available historical data; and (3) linking metal loadings in the AMD from each mine to characteristics of the coal and abandoned mine works. The HR AMD was dominated by chemostasis ("pipe-full"), whereas the YC AMD was dominated by dilution ("not pipe-full"). For HR, the combination of continuously flooded mineworks recharged primarily by groundwater combined with the presence of fine-grained, diffusely disseminated pyrite in the host rock results in slower AMD production, although shorter timeframe for water quality impairment (decades) given current conditions. In contrast, the faster pace of YC AMD depletion is likely due to the combination of pseudokarstic flow conditions fed by surface water with large, seasonal pulses of dissolved metals from the weathering of coarse-grained aggregates of pyrite but a longer timeframe for AMD impairment to cease (decades to centuries). These results highlight the importance of establishing how the combination of local and regional conditions influence the timeframe for on-going AMD production.

Keywords: Acid mine drainage; Concentration-discharge; Hydrogeochemistry; Metals; Pyrite.