Page 405 - Fundamentals of Gas Shale Reservoirs

GROUNDWATER CONTAMINATION 385
of possible water contamination include improper well first independent examination of whether the chemicals uti-
design, inadequate surface casing and substandard or lized during the hydraulic fracturing process pose a threat
improper cementing, improper handling of surface chemi- to local drinking water supplies. DOE’s initial conclusion
cals, improper design/performance of holding ponds, and suggests that hydraulic fracturing does not impact drinking
improper storage and disposal of wastes and produced water. water supplies. Samples from 100 private drinking water
A study of the Marcellus Shale by Duke University pub- wells revealed that arsenic, selenium, strontium, and TDS
lished in June 2013 found that drinking water wells within 1 exceeded the Environmental Protection Agency’s Drinking
km of natural gas fracking wells (horizontal drilling/frac- Water Maximum Contaminant Limit (MCL) in some sam-
turing) were contaminated with stray petroleum gases ples from private water wells located within 3 km of active
including methane, ethane, and propane, with methane con- natural gas wells. Lower levels of arsenic, selenium,
centrations an average of six times higher than those wells strontium, and barium were detected at reference sites
farther away (Jackson et al., 2013). The researchers said outside the Barnett Shale region as well as sites within the
there was no evidence of any chemical contamination from Barnett Shale region located more than 3 km from active
drilling–neither chemicals used for fracking nor from natu- natural gas wells. Methanol and ethanol were also detected
rally occurring brine water that comes along later in the pro- in 29% of samples.
cess. The study states that the two simplest explanations for In July 2013, a study by researchers at the University of
the contamination in drinking water are faulty or inadequate Texas at Arlington, An Evaluation of Water Quality in
steel casings and imperfections in cement sealings. Private Drinking Water Wells Near Natural Gas Extraction
A controversial study conducted by the Energy Institute Sites in the Barnett Shale Formation (Fontenot et al., 2013),
at the University of Texas at Austin, Fact‐based Regulation found elevated levels of arsenic and other heavy metals in
for Environmental Protection in Shale Gas Development, groundwater near natural gas fracking sites in Texas’ Barnett
February 2012, found that many problems attributed to Shale where there are 16,000 active wells. Historical data-
hydraulic fracturing were related to processes common to all bases from the same areas sampled never had these issues
oil and gas drilling operations, such as drilling pipe inade- until the onset of all the fracking.
quately cased in concrete (Groat and Gromshaw, 2012). In March 2013, Resources for the Future, in a paper pub-
Many reports of contamination can be traced to above lished in the Proceedings of the National Academy of
ground spills or other mishandling of wastewater produced Sciences relied upon more than 20,000 surface water quality
from shale drilling and not from hydraulic fracturing. observations taken over 11 years in Pennsylvania to estimate
In July 2013, the U.S. Department of Energy’s National the effects of shale gas development on downstream water
Energy Technology Laboratory (NETL) in Pittsburgh, quality through 2011 (Olmstead et al., 2013). The authors
Pennsylvania, after a year‐long study at a western were unable to find any statistical evidence of water contam-
Pennsylvania drilling site in Washington County, concluded ination due to leaks at the actual well sites. The authors did
that there was no evidence that chemicals used during the find some evidence of pollution downstream from waste-
hydraulic fracturing process have contaminated drinking water treatment facilities in the form of raised chlorine
water aquifers adjacent to the drilling site (NETL, 2013). levels. Fracking was not identified as the cause of the con-
The study found that hydraulic fracturing fluids remained tamination, but the study shows these issues do occur in
thousands of feet below the shallower portions of the aquifer close relation, geographically to natural gas extraction. The
that supply drinking water. results indicated statistically significant water quality
Eight wells in the Marcellus Shale formation were moni- impacts from wastewater sent to treatment plants and runoff
tored seismically and one was injected with four different from well pad development. The study found no systematic
“tracers” at different stages in the hydraulic fracturing pro- statistical evidence of spills or leaks of flowback and pro-
cess. The depth of the injection of the tracers was at approx- duced water from shale gas wells into waterways.
imately 8000 ft below the surface of the well bore. None of Vaughan and Pursell in their 2010 paper summarize the
the tracers were detected in a monitoring zone at a depth of available studies and information on hydraulic fracturing
5000 ft. The study also tracked the maximum extent of the and provide an objective look at the debate. The authors con-
man‐made fractures, and all were at least 6000 ft below the firm that water‐supply contamination from the so‐called
surface of the well bore. Finally, the study also monitored a stray gas occurs more often from failures in well design and
separate series of older gas wells that are about 3000 ft above construction, breaches in spent hydraulic‐fracturing water‐
the Marcellus Shale formation to determine the impacts, if containment ponds, and spills of leftover natural gas liquids
any, of hydraulic fracturing process on these wells. used in drilling. In this respect, waste disposal and safe
Ultimately, the DOE study did not detect the tracers in these materials handling are the biggest challenges to producers.
older gas wells. The authors analyze incidents of contamination cited by
The DOE cautioned that the results of the study are pre- environmental advocates as evidence of contamination
liminary, as the study is ongoing, but that the results are the caused by fracking and conclude that most of those incidents