104
Stray gas has become a “new” groundwater hydrology problem, drawing attention away from “classical” water-soluble contaminants like gasoline, diesel fuel,
and chlorinated solvents. Many hydrologists in the water resource community are
attempting to address stray gas issues, and several groups have recommended that
dedicated groundwater monitoring wells equipped with multilevel samplers to isolate specific flow zones be installed near shale gas wells (e.g. Jackson et al. 2013;
Council of Canadian Academies 2014; Soeder 2018). This has not been carried out
at any significant scale as of this writing, because industry has largely refused to
cooperate with environmental monitoring studies, especially those related to
groundwater. Researchers continue to try to find methods to tag stray gas and trace
it back to a point of origin (Larson et al. 2018).
The single “prospective” groundwater study carried out so far in the United
States has been by Yale University researchers in cooperation with Southwestern
Energy on Marcellus Shale development activity in northeast Pennsylvania (BarthNaftilan et al. 2018). Several groundwater monitoring wells were installed prior to
Marcellus Shale drilling, and monitored through the drilling, fracking, and production process. Some pressure transients and methane fluxes in the groundwater were
seen that could generally be linked to drilling operations, including a rupture in the
production casing that introduced gas to the aquifer until it was repaired. A gradual
increase in groundwater methane concentration was measured on at least one monitoring site near a shale well over an extended time period, but the isotopic signature
of the gas was biogenic in nature, not thermogenic as expected from the Marcellus.
Canadian studies in British Columbia have been using long term soil gas flux
meters to measure methane and CO 2 emissions as these gases migrate through soil
(Forde et al. 2019). Methane fluxes through soils can migrate along preferential
pathways and come to the surface long distances from the wellbore. The Canadian
investigators were even able to inject methane into the unsaturated zone of the soil
to track gas migration and found that changes in barometric pressure greatly influence flow, at least for low-pressure gas migration. These barometric pressure effects
may help explain some of the variability of stray gas migration near well sites.
A site in Canada located at Canadian Forces Base Borden northwest of Toronto
has been used since 1978 for controlled field experiments of groundwater contamination (Cherry et al. 1996). Industrial chemicals were carefully released into the
shallow subsurface and detailed monitoring tracked their movement and fate. A
methane injection experiment was carried out in 2017 at this extremely wellcharacterized site to investigate stray gas migration (Cahill et al. 2017). The methane was injected at two well points in the shallow sand aquifer at Borden and
tracked. Unexpected, strong lateral movement of free gas was observed, along with
dissolved gas dispersion in the direction of gas flow. Hydrochemical impacts from
the methane persisted for over a year after injection. If nothing else, this field experiment clearly demonstrated that stray gas is complicated.
6 Fracking and Water
Stray gas has become a “new” groundwater hydrology problem, drawing attention away from “classical” water-soluble contaminants like gasoline, diesel fuel,
and chlorinated solvents. Many hydrologists in the water resource community are
attempting to address stray gas issues, and several groups have recommended that
dedicated groundwater monitoring wells equipped with multilevel samplers to isolate specific flow zones be installed near shale gas wells (e.g. Jackson et al. 2013;
Council of Canadian Academies 2014; Soeder 2018). This has not been carried out
at any significant scale as of this writing, because industry has largely refused to
cooperate with environmental monitoring studies, especially those related to
groundwater. Researchers continue to try to find methods to tag stray gas and trace
it back to a point of origin (Larson et al. 2018).
The single “prospective” groundwater study carried out so far in the United
States has been by Yale University researchers in cooperation with Southwestern
Energy on Marcellus Shale development activity in northeast Pennsylvania (BarthNaftilan et al. 2018). Several groundwater monitoring wells were installed prior to
Marcellus Shale drilling, and monitored through the drilling, fracking, and production process. Some pressure transients and methane fluxes in the groundwater were
seen that could generally be linked to drilling operations, including a rupture in the
production casing that introduced gas to the aquifer until it was repaired. A gradual
increase in groundwater methane concentration was measured on at least one monitoring site near a shale well over an extended time period, but the isotopic signature
of the gas was biogenic in nature, not thermogenic as expected from the Marcellus.
Canadian studies in British Columbia have been using long term soil gas flux
meters to measure methane and CO 2 emissions as these gases migrate through soil
(Forde et al. 2019). Methane fluxes through soils can migrate along preferential
pathways and come to the surface long distances from the wellbore. The Canadian
investigators were even able to inject methane into the unsaturated zone of the soil
to track gas migration and found that changes in barometric pressure greatly influence flow, at least for low-pressure gas migration. These barometric pressure effects
may help explain some of the variability of stray gas migration near well sites.
A site in Canada located at Canadian Forces Base Borden northwest of Toronto
has been used since 1978 for controlled field experiments of groundwater contamination (Cherry et al. 1996). Industrial chemicals were carefully released into the
shallow subsurface and detailed monitoring tracked their movement and fate. A
methane injection experiment was carried out in 2017 at this extremely wellcharacterized site to investigate stray gas migration (Cahill et al. 2017). The methane was injected at two well points in the shallow sand aquifer at Borden and
tracked. Unexpected, strong lateral movement of free gas was observed, along with
dissolved gas dispersion in the direction of gas flow. Hydrochemical impacts from
the methane persisted for over a year after injection. If nothing else, this field experiment clearly demonstrated that stray gas is complicated.
6 Fracking and Water