103
The actual cause of the damage remains unknown. The ground was frozen solid
with little snow cover and no one claims to have witnessed the event.
Baseline data from drinking water supply wells has been used in three classic
and mutually contradictory studies of stray gas in groundwater. Duke University
claimed to have found that methane concentrations in northeastern Pennsylvania
groundwater increase with decreasing distance from a shale well (Osborn et al.
2011). GSI Environmental and Cabot Oil & Gas analyzed a larger number of samples from the same general area and concluded that the methane content of groundwater was related to topography (lowest in highlands, highest in valleys), not the
location of gas wells (Molofsky et al. 2013). A third study by Syracuse University
and Chesapeake Energy used a massive database of water well baseline data from
the same region and found no statistical correlation between proximity to shale gas
wells and methane in groundwater (Siegel et al. 2015).
In a related study, Yan et al. (2017) looked at inorganic dissolved solids in
groundwater samples from this same region, including Ca, Na, Mn, Fe, Cl, and SO 4 .
Groundwater near shale gas wells located in valleys was significantly higher in
these constituents than valley groundwater farther from wells, and groundwater
from upland areas had lower dissolved solids than valley samples. The authors speculate that valleys experience a greater mixing of shallow and deep groundwater,
possibly triggered by the shale gas development process. However, earlier studies
by Warner et al. (2012) concluded that the higher salt content in valley groundwater
was a natural occurrence, as was the higher methane content. The number of samples matters–too many may dilute any contamination signal from a gas well and
make it hard to distinguish these events from background (Brantley et al. 2014). The
possible links between groundwater quality and proximity to fracked shale wells are
complicated, confusing, and remain unsettled.
Substantial amounts of baseline water quality data from drinking water supply
wells are available thanks to the shale boom. Just because these measurements exist,
however, it does not mean that they are necessarily useful for stray gas migration
studies. Part of the problem is that the data are collected pre-drilling, so if any gas
migration occurs after the well is drilled and fracked, it won’t be measured. In fact,
the study by Siegel et al. (2015) recognized this issue and used a massive amount of
data from more than 11,000 wells to have a high enough sample density for at least
some of the “pre-drilling” analyses to provide “post-drilling” data from other nearby
shale wells that had already been fracked.
A second data concern for stray gas and other water quality investigations using
drinking water wells is that because these wells are pumped, and are often uncased
through the aquifer they might draw in contaminants from anywhere that could
never be linked to a fracked well. These open-hole completions randomly mix water
from the different aquifer flow zones inside the borehole, making it extremely challenging if not impossible to trace flowpaths for stray gas or other contaminants.
However, the thousands of domestic water wells near shale gas and tight oil development sites that are being sampled routinely by the drilling companies for legal
protection are pretty much the only option available for data.
6.1 Water Quality and Stray Gas
The actual cause of the damage remains unknown. The ground was frozen solid
with little snow cover and no one claims to have witnessed the event.
Baseline data from drinking water supply wells has been used in three classic
and mutually contradictory studies of stray gas in groundwater. Duke University
claimed to have found that methane concentrations in northeastern Pennsylvania
groundwater increase with decreasing distance from a shale well (Osborn et al.
2011). GSI Environmental and Cabot Oil & Gas analyzed a larger number of samples from the same general area and concluded that the methane content of groundwater was related to topography (lowest in highlands, highest in valleys), not the
location of gas wells (Molofsky et al. 2013). A third study by Syracuse University
and Chesapeake Energy used a massive database of water well baseline data from
the same region and found no statistical correlation between proximity to shale gas
wells and methane in groundwater (Siegel et al. 2015).
In a related study, Yan et al. (2017) looked at inorganic dissolved solids in
groundwater samples from this same region, including Ca, Na, Mn, Fe, Cl, and SO 4 .
Groundwater near shale gas wells located in valleys was significantly higher in
these constituents than valley groundwater farther from wells, and groundwater
from upland areas had lower dissolved solids than valley samples. The authors speculate that valleys experience a greater mixing of shallow and deep groundwater,
possibly triggered by the shale gas development process. However, earlier studies
by Warner et al. (2012) concluded that the higher salt content in valley groundwater
was a natural occurrence, as was the higher methane content. The number of samples matters–too many may dilute any contamination signal from a gas well and
make it hard to distinguish these events from background (Brantley et al. 2014). The
possible links between groundwater quality and proximity to fracked shale wells are
complicated, confusing, and remain unsettled.
Substantial amounts of baseline water quality data from drinking water supply
wells are available thanks to the shale boom. Just because these measurements exist,
however, it does not mean that they are necessarily useful for stray gas migration
studies. Part of the problem is that the data are collected pre-drilling, so if any gas
migration occurs after the well is drilled and fracked, it won’t be measured. In fact,
the study by Siegel et al. (2015) recognized this issue and used a massive amount of
data from more than 11,000 wells to have a high enough sample density for at least
some of the “pre-drilling” analyses to provide “post-drilling” data from other nearby
shale wells that had already been fracked.
A second data concern for stray gas and other water quality investigations using
drinking water wells is that because these wells are pumped, and are often uncased
through the aquifer they might draw in contaminants from anywhere that could
never be linked to a fracked well. These open-hole completions randomly mix water
from the different aquifer flow zones inside the borehole, making it extremely challenging if not impossible to trace flowpaths for stray gas or other contaminants.
However, the thousands of domestic water wells near shale gas and tight oil development sites that are being sampled routinely by the drilling companies for legal
protection are pretty much the only option available for data.
6.1 Water Quality and Stray Gas