94
The consensus view of a large group of North American hydrologists is that the
most significant contamination risks from shale gas and tight oil development are
stray gas migration in aquifers, and the potential for contamination of both groundwater and surface water from the chemical additives used for drilling, completion,
and hydraulic fracturing (Soeder 2018). The flowback and produced water from the
wells also contain these chemicals, along with other compounds from the geologic
formation, including high levels of TDS, dissolved metals, radionuclides, and
organics (e.g. Orem et al. 2014; Renock et al. 2016). A third potential risk is leachate from solid materials like black shale drill cuttings left on the surface that may
also be a source of water contamination (Phan et al. 2015). Chemical contamination
is thought to largely occur on the surface, rather than migrating upward from below.
This places surface water bodies like streams and lakes at risk, and if the chemicals
infiltrate into the ground and reach the water table, groundwater can be at risk also.
Water quality assessment often has the same problem as air pollution in distinguishing contaminants introduced by fracking from contaminants contributed by
everything else. Many of the chemical substances added to or recovered from shale
wells have also entered groundwater from a variety of other sources. A long legacy
of conventional oil and gas development and other industrial activities on many of
the landscapes that are now hosting shale plays has contributed a host of background water contaminants that are difficult to separate by source. The assessments
can be complicated by the natural seepage of brine upward toward the surface at
some locations, often accompanied by methane (Warner et al. 2012; Harkness
et al. 2017).
Specific water quality indicators that would positively identify water contamination from a shale gas or tight oil well would be extremely useful, but so far none
have been fully developed. Most people use an assemblage that includes high TDS,
along with the presence of chloride, bromide, barium, strontium, and radium in the
water (Brantley et al. 2014). This provides a clue, but it is far from definitive (road
salt, for example, can supply many of these). Researchers have shown that certain
strontium isotope ratios are indicative of produced water from the Marcellus Shale
(Chapman et al. 2012). The application of this technique is complicated, expensive,
and thus not used very often.
Several overarching documents have attempted to summarize the large number
of publications addressing various aspects of water quality impacts from fracking,
including reviews by the U.S. Environmental Protection Agency (USEPA 2016) and
the Health Effects Institute (HEI 2019). These reports note that many studies have
focused on monitoring surface water and groundwater contamination, while others
have investigated the natural breakdown paths of spilled chemicals through reactive
transport modeling. A few investigations have combined both.
Contaminants associated with shale gas and tight oil development that have been
measured in groundwater, surface water, and produced water include inorganic
chemicals, organic compounds, endocrine disruptors, and radioactive elements such
as radium. A subset of studies also investigated the capture and residence times of
chemicals in stream sediments, and the rates at which these may slowly introduce
contaminants into surface waters for a time after a spill. Water quality investigations
6 Fracking and Water
The consensus view of a large group of North American hydrologists is that the
most significant contamination risks from shale gas and tight oil development are
stray gas migration in aquifers, and the potential for contamination of both groundwater and surface water from the chemical additives used for drilling, completion,
and hydraulic fracturing (Soeder 2018). The flowback and produced water from the
wells also contain these chemicals, along with other compounds from the geologic
formation, including high levels of TDS, dissolved metals, radionuclides, and
organics (e.g. Orem et al. 2014; Renock et al. 2016). A third potential risk is leachate from solid materials like black shale drill cuttings left on the surface that may
also be a source of water contamination (Phan et al. 2015). Chemical contamination
is thought to largely occur on the surface, rather than migrating upward from below.
This places surface water bodies like streams and lakes at risk, and if the chemicals
infiltrate into the ground and reach the water table, groundwater can be at risk also.
Water quality assessment often has the same problem as air pollution in distinguishing contaminants introduced by fracking from contaminants contributed by
everything else. Many of the chemical substances added to or recovered from shale
wells have also entered groundwater from a variety of other sources. A long legacy
of conventional oil and gas development and other industrial activities on many of
the landscapes that are now hosting shale plays has contributed a host of background water contaminants that are difficult to separate by source. The assessments
can be complicated by the natural seepage of brine upward toward the surface at
some locations, often accompanied by methane (Warner et al. 2012; Harkness
et al. 2017).
Specific water quality indicators that would positively identify water contamination from a shale gas or tight oil well would be extremely useful, but so far none
have been fully developed. Most people use an assemblage that includes high TDS,
along with the presence of chloride, bromide, barium, strontium, and radium in the
water (Brantley et al. 2014). This provides a clue, but it is far from definitive (road
salt, for example, can supply many of these). Researchers have shown that certain
strontium isotope ratios are indicative of produced water from the Marcellus Shale
(Chapman et al. 2012). The application of this technique is complicated, expensive,
and thus not used very often.
Several overarching documents have attempted to summarize the large number
of publications addressing various aspects of water quality impacts from fracking,
including reviews by the U.S. Environmental Protection Agency (USEPA 2016) and
the Health Effects Institute (HEI 2019). These reports note that many studies have
focused on monitoring surface water and groundwater contamination, while others
have investigated the natural breakdown paths of spilled chemicals through reactive
transport modeling. A few investigations have combined both.
Contaminants associated with shale gas and tight oil development that have been
measured in groundwater, surface water, and produced water include inorganic
chemicals, organic compounds, endocrine disruptors, and radioactive elements such
as radium. A subset of studies also investigated the capture and residence times of
chemicals in stream sediments, and the rates at which these may slowly introduce
contaminants into surface waters for a time after a spill. Water quality investigations
6 Fracking and Water