Source water vulnerability to elevated total dissolved solids within a mixed-use Appalachian River basin

Abstract

The upper Monongahela River basin in West Virginia represents a watershed wherein historic land use activities, including coal mining, conventional oil and gas development, and residential and urban development have contributed to elevated total dissolved solids (TDS) concentrations within surface and source waters with widespread exceedance of the 500 mg/L secondary drinking water standard for TDS. Our research was designed to characterize spatial variability in and sources of elevated and assess vulnerability of surface and source waters to additional TDS sources and loading. We compiled 3439 unique water quality sampling records throughout the study area over a ten-year period and applied boosted regression tree (BRT) analysis to model log[x]-transformed TDS as a function of landscape attributes across the 885 sampled NHD catchments. We predicted (i.e., elevated TDS and reduced dilution capacity) and observed (i.e., increased variability in TDS and temporary exceedances of 500 mg/L) elevated vulnerability of source waters, with vulnerability being largely driven by a few dominant contributors of TDS throughout the stream network. Notably, seven 12-digit hydrologic unit code (HUC) inflows to the Monongahela River and its vulnerable tributaries were predicted to require a combined 6,664,879 m3 of water (i.e., chemical footprint) to dilute TDS concentrations below 500 mg/L from July through September. Our results provide insights into how the mixed land uses containing extractive industries can impact water quality and demonstrates the importance of both spatial and temporal processes in controlling vulnerability of source waters to water pollution.