GROUNDWATER CONTAMINATION FROM HYDRAULIC FRACTURING - HOW WILL WE KNOW?

Concern over groundwater contamination from hydraulic fracturing (HF) activities is of keen interest to both environmental professionals and the public. Recent investigations at locations such as Pavillion, WY and Dimock, PA have made national headlines. Currently the USEPA is undertaking 7 studies (both prospective and retrospective) to evaluate links between HF and groundwater contamination. It remains unclear that specific instances of groundwater contamination have been linked directly to HF.

Defining even potential links between HF and groundwater contamination can be difficult: Use of HF in unconventional gas reserves involves both subsurface and surface operations, and theoretical releases to groundwater may occur at different depths and times. The relative sparseness of subsurface data and expense of investigation limits the ability to test potential migration pathways, or know at which point releases could have occurred.

EPA's recent Pavillion study points out some of these challenges. The Pavillion gas field shares the Wind River Formation with a regional aquifer. Vertical migration of methane generated shallow gas deposits (some at depths equivalent to EPA’s sampling locations), but no site-specific baseline or background data was available to evaluate methane detections in residential wells assumed impacted by HF. Major ion water quality in the regional aquifer is variable, but samples collected from residential wells with taste and odor complaints were insufficient to document changes in groundwater chemistry. Other potentially HF-related materials detected (BTEX compounds, glycols, elevated pH, Cl and K) have multiple anthropogenic and natural sources, including sources within the USEPA’s monitoring wells. Furthermore, shallow contamination associated with surface activities is known, and provides complications for evaluating migration pathways, particularly when groundwater flowpaths may be shortcut by leaky well casings or (unknown) abandoned wells, and regional hydraulic gradients are downward.

Proposed solutions to the problem have included routine sampling for very large (expensive) suites of compounds in baseline samples and the use of unique tracers in HF fluids.