Date of Award
Spring 2024
Document Type
Dissertation
Degree Name
Doctor of Philosophy (PhD)
Department
Forestry and Environmental Studies
First Advisor
Saiers, James
Abstract
The Northwestern Appalachian Basin (NAB) encompasses a region of more than 100,000 square kilometers across parts of Ohio, Pennsylvania, and West Virginia and is home to a population of nearly 700,000 rural residents who rely on private groundwater wells as their sole source of drinking water. Rural communities in the NAB are often under-resourced and the cost of treatment or replacement of private water supplies may be prohibitive to many, leaving residents susceptible to health impacts associated with groundwater contamination and shifts in water availability under a changing climate. While vital to the rural communities of the NAB, groundwater withdrawals from the shallow bedrock aquifers of the NAB are small (445 Mgal/day) and provide less economic benefit than the billions of gallons of water produced daily within the major aquifer systems of the United States. As a result, few studies have sought to discern factors influencing groundwater quality and availability in the NAB, despite the importance of groundwater supplies to rural populations. This dissertation focuses on elucidating the main geophysical and anthropogenic factors influencing groundwater quality and availability in the shallow bedrock aquifer systems of the NAB. Data collected as part of Chapter 2 of this dissertation addresses previous knowledge gaps in the NAB, including the extent of inorganic water quality impairments in private groundwater supplies and key agents of contamination. Through the implementation of a unique combination of geochemical modeling, hierarchical cluster analysis (HCA), and geospatial analyses, Chapter 2 of this work further advances methods for contaminant source attribution and the rapid characterization of factors influencing groundwater quality. Topographic position is identified as an important predictor of inorganic water quality, with water wells positioned in upslope recharge zones susceptible to contamination from surface activities, including road salting and agricultural runoff. Water wells situated in valley regions primarily intercept longer groundwater flow paths that may exhibit pH and redox conditions favoring the mobilization of arsenic from aquifer materials. Finally, private wells collocated with coal mining activities are found to have groundwater chemistries consistent with a small degree of mixing with coal mine drainage-like waters, suggesting ongoing impacts from mining activities on water resources. Expanding upon this initial work, Chapter 3 describes for the first time the distribution of per- and poly-fluorinated substances (PFAS) in private water supplies in West Virginia. Topographic setting, major ion composition, and PFAS carbon-chain length are identified as important predictors of PFAS concentrations in private water supplies, likely reflecting both the susceptibility of recharge zones within the NAB to contamination from surface activities and the combined effects of adsorption and hydrodynamic diffusion within the aquifer. Proximity to sites with registered National Pollutant Discharge Elimination System (NPDES) permits, active UOG operations, and the density of surrounding COG wells were identified as additional predictors of PFAS concentrations, indicating potential impacts from industrial activities, including oil and gas development, in the region. In Chapter 4, shifts in recharge and groundwater availability in response to changes in temperature and precipitation predicted by three global circulation models (GCMs) and two shared socio-economic pathways (SSPs) are assessed using a 3-D numerical groundwater flow model constructed in the open-source finite difference groundwater flow model, Modflow. Groundwater flow simulations determined that water wells completed above, and below semi-confining units exhibit different responses to changes in climate. Water wells completed within the unconfined portion of the aquifer respond to shifts in recharge on shorter timescales and with larger magnitude fluctuations in groundwater levels (x̃ = 2.04 m annually and x̃ = 0.20 to 0.40 m monthly), while water wells completed within semi-confined aquifers are less temporally sensitive to shifts in recharge and exhibit smaller annual fluctuations in groundwater levels (x̃ = 0.1 m annually and x̃ = 0.012 to 0.027 m monthly). Groundwater levels are found to increase over the next century in the upper unconfined aquifers, with slight seasonal shifts in the timing of maximum and minimum groundwater levels in response to predicted changes in precipitation and temperature. Decreasing trends in groundwater levels that were observed in the semi-confined aquifers of the model domain throughout the historic period (183 mm/year) are balanced by increasing recharge by the end of the century, with declining groundwater levels either stabilizing or decreasing at lower rates (45 to 52 mm/year). Throughout this work, the impacts of anthropogenic activities and natural processes on groundwater supplies and the rural populations that depend on them are evaluated. Inorganic water quality is found to be generally good with 10% of private water wells exhibiting concentrations of at least one constituent above maximum contaminant levels (MCLs) set by the U.S. Environmental Protection Agency (EPA). Total targeted PFAS concentrations in private wells ranged between non-detect and 36.8 ng/L but were notably higher in private wells situated in upslope recharge zones. This is consistent with findings in Chapter 2 that topographic setting is an important control on the susceptibility of private water wells to contamination from surface activities. Private water wells situated in valley regions were found to primarily intercept deeper more-evolved groundwater flow paths that exhibit lower targeted PFAS concentrations, but higher concentrations of geogenic arsenic on average. Mixing with as much as 4-10% of coal mine drainage-like waters was identified in private wells in proximity to coal mining operations, while a higher probability of observing elevated PFAS concentrations was identified in proximity to locations with either an active NPDES permit, a high density of COG wells, or an active UOG. Regardless of topographic position, groundwater wells terminating above a semi-confining underclay layer are found to be more temporally sensitive to shifts in recharge predicted by GCMs, while water wells within semi-confined aquifers are slower to recover groundwater levels following declines, suggesting that the presence of an overlying semi-confining unit is a better predictor of future behavior in response to climate change than topography alone. Together this work advances understandings of private groundwater quality and availability in the NAB, a region where the health and well-being of rural populations are vulnerable to mineral-resource extraction and growing pressures of anthropogenic climate change. By expanding our knowledge of private water quality and key agents of groundwater impairment, this work aids human health and regulatory agencies in the development of community health initiatives, such as drinking water testing and aquifer protection programs, that are vital to the health of rural populations. Brackets on groundwater responses to projected climate scenarios from this work also provide critical information to researchers and public officials for the development of climate adaptation and mitigation strategies. Finally, this work advances methods for contaminant source attribution and provides additional tools for researchers seeking to evaluate controls on groundwater quality in other regions with intensive anthropogenic pressures.
Recommended Citation
Siegel, Helen Grace, "Investigation of Natural and Anthropogenic Factors Influencing Groundwater Quality and Availability in the Northwestern Appalachian Basin" (2024). Yale Graduate School of Arts and Sciences Dissertations. 1483.
https://elischolar.library.yale.edu/gsas_dissertations/1483
