Natural and Anthropogenic Processes Affecting Domestic Groundwater Quality within the Northwestern Appalachian Basin

[Image: see text] Domestic wells serve as the primary drinking-water source for rural residents in the northern Appalachian Basin (NAB), despite a limited understanding of contaminant distributions in groundwater sources. We employ a newly collected dataset of 216 water samples from domestic wells in Ohio and West Virginia and an integrated contaminant-source attribution method to describe water quality in the western NAB and characterize key agents influencing contaminant distributions. Our results reveal arsenic and nitrate concentrations above federal maximum contaminant levels (MCLs) in 6.8 and 1.3% of samples and manganese concentrations above health advisory in 7.3% of samples. Recently recharged groundwaters beneath upland regions appear vulnerable to surface-related impacts, including nitrate pollution from agricultural activities and salinization from road salting and domestic sewage sources. Valley regions serve as terminal discharge points for long-residence-time groundwaters, where mixing with basin brines is possible. Arsenic impairments occurred in alkaline groundwaters with major-ion compositions altered by ion exchange and in low-oxygen metal-rich groundwaters. Mixing with as much as 4–10% of mine discharge-like waters was observed near coal mining operations. Our study provides new insights into key agents of groundwater impairment in an understudied region of the NAB and presents an integrated approach for contaminant-source attribution applicable to other regions of intensive resource extraction.