Towards Quantifying the Likelihood of Water Resource Impacts from Unconventional Gas Development

Abstract

Gas production from unconventional reservoirs has led to widespread environmental concerns. Despite several excellent reviews of various potential impacts to water resources from unconventional gas production, no study has systematically and quantitatively assessed the potential for these impacts to occur. We use empirical evidence and numerical and analytical models to quantify the likelihood of surface water and groundwater contamination, and shallow aquifer depletion from unconventional gas developments. These likelihoods are not intended to be exact. They provide a starting point for comparing the probabilities of adverse impacts between types of water resources and pathways. This analysis provides much needed insight into what are "probable" rather than simply "possible" impacts. The results suggest that the most likely water resource impacts are surface water and groundwater contamination from spills at the well pad, which can be as high as 1 in 10 and 1 in 100 for each gas well, respectively. For wells that are hydraulically fractured, the likelihood of contamination due to inter-aquifer leakage is 1 in 10 or lower (dependent on the separation distance between the production formation and the aquifer). For gas-bearing formations that were initially over-pressurized, the potential for contamination from inter-aquifer leakage after production ceases could be as high as 1 in 400 where the separation between gas formation and shallow aquifer is 500 m, but will be much lower for greater separation distances (more characteristic of shale gas).

Evaluating Domestic Well Vulnerability to Contamination From Unconventional Oil and Gas Development Sites

“…The method also complements geochemical fingerprinting techniques (e.g., McIntosh et al, 2019) as an additional line of evidence in retrospective studies. Moreover, coupling the receptor‐based vulnerability analysis with hazard assessment models (e.g., Rozell & Reaven, 2012; Shanafield et al, 2019) is a necessary step towards a more holistic understanding of the groundwater contamination risks posed by UD.…”

“…Groundwater contamination risks from surface spills of drilling fluids, frac fluids, and produced water at well pads have received less attention from the modeling community despite evidence that this pathway constitutes the most likely source of drinking water impairment (Shanafield et al, 2019). The traditional approach for investigating the fate of spilled contaminants has been to simulate forward transport from known source locations, assuming the composition, volume, and temporal input history related to the spill are also known.…”

Groundwater sources for the Mataranka Springs (Northern Territory, Australia)

“…The potential for hydraulic fracturing to increase the vertical connectivity between water resources and deeper geological formations is a key concern of the public relative to unconventional gas resources development in Beetaloo Sub-basin 32 and elsewhere 33 , 34 . Demonstrating the presence of a deeper groundwater source at the springs (and for the CLA in general 24 ) is a key requirement for pre-development baseline assessments for unconventional gas resources 35 – 37 .…”

Groundwaters in Northeastern Pennsylvania near intense hydraulic fracturing activities exhibit few organic chemical impacts

“…First, the model only accounts for contamination at the well pads, excluding accidents such as roadside spills during uid and waste View Article Online transportation. Nevertheless, spills at well pads are probable sources of HDHF-associated water contamination 59 and the groundwater physics is illustrative nonetheless. Second, this groundwater model does not account for contaminant transport in surface waters (e.g., streams or rivers) that may have orders of magnitude more rapid transport velocities.…”