124-4 How are abandoned oil and gas wells impacting groundwater quality in the Appalachian Basin?

Session: Fixing the Silent Leak: Identifying, Quantifying, Prioritizing, and Mitigating the Environmental and Health Impacts of Legacy Oil and Gas Drilling in North America

Presenting Author:

Samuel Shaheen

Authors:

Shaheen, Samuel¹, Lloyd, Max², Roden, Eric³, Brantley, Susan L.⁴

(1) Earth & Environmental Sciences, University of Minnesota, Minneapolis, MN, USA; Geosciences, Penn State University, University Park, PA, USA, (2) Geosciences, Penn State University, University Park, PA, USA, (3) Geoscience, University of Wisconsin, Middleton, WI, USA, (4) Geosciences, Penn State University, University Park, PA, USA; Earth and Environmental Systems Institute, Penn State University, University Park, PA, USA,

Abstract:

The groundwater impacts of orphaned and abandoned oil and gas wells are one of the least well-understood environmental impacts of these legacy wells. In this study, we investigated how the loss of well integrity over long timescales can deleteriously affect the quality of groundwater in Pennsylvania (U.S.A.), home to some of the oldest oil and gas wells in the world. To investigate the migration pathways of fluids leaking from legacy oil and gas wells as well as the biogeochemical processes that ensue when leaked fluids contact shallow aquifers, we extensively characterized the geochemistry and microbiology of groundwater across 18 impacted sites. Geochemical ratios and strontium isotopes indicate a loss of well integrity at shallow depths, with the majority of groundwaters discharging via abandoned wellbores derived from shallow aquifers rather than deep basin brines. While all sites were associated with high concentrations of dissolved methane, methane isotopes and microbial assemblages indicated that leakage from legacy wells can promote both microbial consumption and production of methane. As a result, the oxidation of methane by microorganisms under anaerobic conditions can promote the mobilization of toxic metals, and under low-sulfate conditions, can alter methane isotopes in a non-traditional manner, complicating the attribution of dissolved gas sources. Our results indicate the primary mechanisms through which legacy oil and gas wells are impacting groundwater are a.) direct migration of hydrocarbons into shallow groundwater via abandoned wellbores and b.) secondary production of methane and mobilization of toxic trace species such as arsenic following hydrocarbon migration.

Geological Society of America Abstracts with Programs. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-9783

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