A Comprehensive Analysis of Groundwater Quality in the Barnett Shale Region Page: 3
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Environmental Science & Technology
The potential effects of unconventional oil and gas (UOG) drilling activities on
groundwater quality have led to much concern despite a relative lack of scientific data.
Recently, investigations in the Marcellus and Barnett shale formations in Pennsylvania and
Texas found elevated levels of dissolved methane' 2 and heavy metals in private water wells
located near unconventional drilling sites. A number of extraction processes are utilized during
unconventional shale exploration including directional drilling, shale acidization, and hydraulic
fracturing, in which large quantities of water, proppants, and chemical additives are used to
extract sequestered hydrocarbons. Additives used during hydraulic fracturing include
viscosifiers, descaling agents, anti-corrosive compounds, lubricants, pH stabilizers, and other
solvents that could be harmful if introduced into the environment.4 Instances of chemical
contamination can result from casing failures, which happen in approximately 3% of new gas
well operations,4 although recent findings indicate failure rates closer to 12% within the first
year of operation.5 Recent research has shown that hydraulic fracturing could potentially alter
contaminant pathways to aquifers via increased advective transport and/or flow through
existing fractures widened by UOG activities.6'7 Additionally, surface sources such as
mishandled waste fluid and produced waters or spills of UOG fluids during stimulation or
completion of wells may contaminate groundwater, and shallow water wells may be
vulnerable to such contamination. 8
One of the more active regions for UOG drilling is in north-central Texas where the
Barnett shale formation supports approximately 20,000 UOG wells. This region includes a
portion of the Dallas-Fort Worth metropolitan area and outlying areas, and groundwater is
potentially vulnerable to contamination from various urban and rural sources. The Trinity and
Woodbine aquifers overlying the Barnett shale formation have historically been described as
good quality with low levels of heavy metals such as arsenic, selenium, strontium, and barium
ACS Paragon Pi us Environment
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Hildenbrand, Zacariah Louis; Carlton Jr., Doug D.; Fontenot, Brian; Meik, Jesse M.; Walton, Jayme; Taylor, Josh et al. A Comprehensive Analysis of Groundwater Quality in the Barnett Shale Region, article, June 16, 2015; Washington, DC. (digital.library.unt.edu/ark:/67531/metadc849992/m1/4/: accessed December 14, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT College of Arts and Sciences.