Potential Impacts of Shale Gas Development on Inorganic Groundwater Chemistry: Implications for Environmental Baseline Assessment in Shallow Aquifers

Abstract

The potential contamination of shallow groundwater with inorganic constituents is a major environmental concern associated with shale gas extraction through hydraulic fracturing. However, the impact of shale gas development on groundwater quality is a highly controversial issue. The only way to reliably assess whether groundwater quality has been impacted by shale gas development is to collect pre-development baseline data against which subsequent changes in groundwater quality can be compared. The objective of this paper is to provide a conceptual and methodological framework for establishing a baseline of inorganic groundwater quality in shale gas areas, which is becoming standard practice as a prerequisite for evaluating shale gas development impacts on shallow aquifers. For this purpose, this paper first reviews the potential sources of inorganic contaminants in shallow groundwater from shale gas areas. Then, it reviews the previous baseline studies of groundwater geochemistry in shale gas areas, showing that a comprehensive baseline assessment includes documenting the natural sources of salinity, potential geogenic contamination, and potential anthropogenic influences from legacy contamination and surface land use activities that are not related to shale gas development. Based on this knowledge, best practices are identified in terms of baseline sampling, selection of inorganic baseline parameters, and definition of threshold levels.

Regional Scale Assessment of Shallow Groundwater Vulnerability to Contamination from Unconventional Hydrocarbon Extraction

“…The assessment of groundwater vulnerability to contamination can facilitate groundwater quality-monitoring efforts, identifying locales where UOG-derived contaminants are likely to be detected, should they be released through spills or leaks in the shallow subsurface. ,,,, Such information is crucial given that groundwater quality data are not routinely collected in rural areas where UOG development tends to be most intense, especially in the absence of adequate resources and regulatory monitoring requirements …”

“…7,13,80,90,91 Such information is crucial given that groundwater quality data are not routinely collected in rural areas where UOG development tends to be most intense, especially in the absence of adequate resources and regulatory monitoring requirements. 92 The term "vulnerability" has also been applied in the context of environmental justice concerns arising from disproportionate exposure of certain demographic groups to undesirable UOG impacts. 93−95 In this case, socioeconomic characteristics of populations living nearer to UOG are compared to those of populations living farther away.…”

Investigation of the Enrichment and Accumulation of Normal Pressure Shale Gas in Anchang Syncline Outside of Sichuan Basin

“…Anchang area is a typical synclinal structure with normal pressure out of Sichuan basin, and shale gas migration firstly occurs in the process of accumulation. The lateral migration of shale gas from the generation stratum to the shallow buried stratum is influenced by the tectonic uplift, denudation, as well as groundwater activities (Hammond et al, 2020;Bondu et al, 2021). The difference of burial depth and pore fluid pressure in different parts of Anchang syncline may reflect the difference of shale gas lateral migration.…”

Importance of Multicomponent Mass Transfer on the Dissolution of Trapped Gas: A Focus on Geo-Energy Applications in the Shallow Subsurface

“…32 Biological activity and soil respiration can consume oxygen and produce CO 2 . 33,34 Dissolved gases may also be derived from deeper geological sources, such as magmatic sources, gas reservoirs, or deep mantle sources which may migrate upward 35,36 Despite their abundance in aquifer systems, background dissolved gases are often neglected in groundwater monitoring programs 4,37 and multicomponent effects have been neglected in dissolved gas concentration analysis 38 and numerical models. 8,39 The presence of trapped gas below the water table has long been understood to impact the transport of dissolved gases in the subsurface but has not been included in studies of natural gas migration from leaking wells.…”