Groundwater in Pavillion, WY contaminated by hydraulic fracturing through multiple subsurface pathways
Posted December 9, 2011
The Environmental Protection Agency (EPA) released a draft report of its investigation of groundwater contamination near Pavillion, WY. It appears likely that groundwater in Pavillion was contaminated by the hydraulic fracturing process itself, rather than by surface spills or leaks of chemicals. EPA determined that hydraulic fracturing chemicals and methane could have reached groundwater by migrating through the annular space of poorly constructed wells, through subsurface formations due to lack of a lithologic barrier (a.k.a. confining zone), or through fractures generated or enlarged by hydraulic fracturing.
NRDC has advocated that wells that will be hydraulically fractured be located in a geologically suitable location such that a suitable confining zone is present, any potential contamination pathways – including improperly constructed or abandoned wells – must be identified and remediated, and properly constructed wells, baseline testing, and site characterization are crucial to preventing contamination of USDWs. EPA’s findings from Pavillion underscore the need for these critical protections.
The principle findings of the study are:
- Water samples taken from two EPA monitoring wells had anomalously high pH values (highly alkaline). Chemical analyses and modeling indicated this elevation in pH could have been caused by small additions of potassium hydroxide (KOH). Potassium hydroxide was a constituent of two hydraulic fracturing chemicals used in oil and gas wells in the area.
- Groundwater from the Wind River formation in the two EPA monitoring wells had inorganic geochemical compositions distinct from both shallow groundwater and the typical geochemical composition of Wind River formation water. Both wells had elevated potassium levels and one well had elevated chloride levels. The compositions of both samples were out of equilibrium with regional trends. Potassium and chloride were constituents of multiple hydraulic fracturing chemicals used in oil and gas wells in the area.
- A number of synthetic organic chemicals were detected in samples from both monitoring wells, including isopropanol, diethylene glycol, and triethylene glycol. Each of these was a constituent of one or more hydraulic fracturing chemicals used in oil and gas wells in the area. In addition, tert-butyl alcohol (TBA), which is a known break-down product of chemicals used in hydraulic fracturing, was detected in one well. Although Material Safety Data Sheets (MSDS) did not indicate that those chemicals were used in the area, EPA noted that MSDS, “do not contain proprietary information and the chemical ingredients of many additives” and that TBA would not be expected to occur naturally in groundwater.
- Petroleum hydrocarbons including BTEX, trimethylbenzenes, and naphthalene were detected in one monitoring well and diesel range organics (DRO) and gasoline range organics (GRO) were detected in both wells. Each of these was a constituent of one of more hydraulic fracturing chemicals used in oil and gas wells in the area.
- Reviews of well completion reports for oil and gas wells showed that in some cases surface casing did not extend below the deepest domestic wells, production casing was not fully cemented to surface, there were multiple instances of poor cement bonding behind production casing, and hydraulic fracturing occurred in or near zones with inadequate cement.
- This area lacks a suitable confining zone to separate formations that are hydraulically fractured from groundwater.
- While some migration of gas into groundwater would be expected above gas fields such as Pavillion, isotopic chemical evidence, methane concentrations, well construction practices, and the timing of citizen complaints relative to the timing of hydraulic fracturing indicate that gas migration has been enhanced by natural gas production activities.
EPA considered multiple alternative explanations for the presence of each of the contaminants but in each case concluded that hydraulic fracturing chemicals were the most likely source.
These findings led EPA to reach two important conclusions:
- Groundwater near Pavillion, WY has been contaminated by chemicals used in hydraulic fracturing, and;
- Those chemicals most likely reached groundwater through subsurface pathways.
The report is still in draft form and will undergo peer review and public comment before being finalized. These are important steps in validating EPA’s research and findings. If EPA’s conclusions are confirmed through this process, there can no longer be a question as to the serious threat that hydraulic fracturing can pose to our drinking water. As EPA stated, “Ground water contamination with constituents such as those found at Pavillion is typically infeasible or too expensive to remediate or restore.”
While the environmental risks from an industrial activity like oil and gas production can never be completely eliminated, adopting best practices can help to reduce those risks. When oil and gas companies choose not to adopt best practices voluntarily, they must be required by regulation. As noted by my colleague Amy Mall, federal regulation of hydraulic fracturing under the Safe Drinking Water Act is imperative to ensuring that groundwater everywhere is protected.