ELECTRICAL RESISTIVITY IMAGING OF PREFERENTIAL SUBSURFACE FLOWPATHS TO MONITOR PASSIVE ACID MINE DRAINAGE SITE CONTAMINANTS

The Critical Zone represents the surficial and shallow layer of rock, air, water and soil where most interactions between living organisms and the Earth occur. Acid mine drainage (AMD) resulting from coal extraction can influence both biological and geochemical processes across this zone. Conservative estimates suggest that more than 300 million gallons of AMD are released daily, making this acidic solution of water and contaminants a common issue in areas with legacy or current coal extraction. Electrical resistivity imaging (ERI) provides a rapid and minimally invasive method to identify and monitor contaminant pathways from AMD remediation systems in the subsurface of the Critical Zone. The technique yields resistivity data that can be inverted to determine a nearly spatially continuous electrical conductivity distribution within the subsurface. Since elevated concentrations of heavy metals can directly influence soil conductivity, ERI data can be used to trace flow pathways or unknown mine conduits that transport heavy metals through the subsurface near acid mine drainage sources. This study aims to examine preferential contaminant migration through substrate pores, fractures, and shallow mine workings in the near subsurface surrounding AMD sites in eastern Ohio and western Pennsylvania. We utilize time lapse ERI measures during different hydrologic conditions to better understand the variability of preferential flow pathways in relation to changes in state and discharge within the remediation systems. In addition, we employ a suite of direct measures to geochemically constrain the geophysics of the resistivity profiles, including flow, discharge and conductivity data from the remediation systems, as well as Inductively Coupled Plasma Optical Emission Spectrometry (ICPOES) bulk chemistry data from stream and transect water samples. Through these combined methods, we can provide insight into the ability of engineered systems to contain and isolate metals in passive acid mine drainage treatment systems.