Cleanup of Chlorides in Soils at Natural Gas Well Sites

November 13, 2011
As described in our previous posting, CEC recently learned that the Pennsylvania Department of Environmental Protection (PADEP) will soon be issuing draft guidance that standardizes the regulatory requirements for reporting, remediating, and restoring areas impacted by spills or releases from oil and gas (O&G) well operations. That guidance specifies that the remediation of specific types of releases will be referred to the Bureau of Environmental Cleanup and Brownfields (BECB) for oversight of remedial activities which will be performed in accordance with the provisions of the Pennsylvania Land Recycling Program, commonly known as Act 2. Among the other provisions of Act 2, it requires that a site be remediated using one of three standards available in Act 2: Background Standard; Statewide Health Standard; or Site-Specific Standard. One parameter that must often be addressed after releases at natural gas well sites is chloride. Act 2 does not have a Media Specific Concentration (MSC) established for chlorides in soils for use in achieving the Statewide Health Standard, which could preclude the use of that cleanup standard. The lack of an established regulatory standard for chlorides in soil to guide remedial activities is also a potential concern in surrounding states.
The term “chloride” does not refer to any specific compound but is a category of substances that are either present in the deep groundwater encountered during well drilling to reach the Marcellus Shale, or are added to drilling muds or hydrofracturing fluids to facilitate development of a gas well.  The most common chlorides of interest include sodium chloride, calcium chloride, magnesium chloride, ammonium chloride, potassium chloride, and barium chloride. Act 2 established a MSC of 250 mg/l for chlorides in groundwater based on the Secondary Maximum Concentration Level (SMCL) promulgated by the United States Environmental Protection Agency (EPA). However, as stated earlier in this blog, Pennsylvania does not have a MSC for chlorides in soil. Both PADEP and industry personnel have requested guidance on how to address chlorides in soils.  As a result, PADEP is considering proposing the use of a Site-Specific Standard for chlorides in soil that would address both the potential soil-to-groundwater pathway and the ecological pathway that could impact species and habitats of concern.
The soil-to-groundwater pathway could be evaluated by submitting samples of impacted soil to a laboratory for analysis using the Synthetic Precipitation Leaching Procedure (SPLP).  Soils with a SPLP-leachable chloride concentration less than the groundwater MSC of 250 mg/l would be considered as having achieved attainment with the soil-to-groundwater MSC.  Additionally, potential surface water impacts to seeps/springs and stormwater runoff would be evaluated using the water quality standard (WQS) of 250 mg/l.  The potential for using soil to groundwater leachability calculations to derive cleanup standards for chlorides and other soluble constituents such as sulfate and bromide may also be considered since methods for performing these calculations have already been established under Act 2.
Under the existing Act 2 process, an evaluation of the ecological risk must be performed to address potential species and habitats of concern, but the evaluation does not have to consider impacts to common plant species.  PADEP is considering implementing additional requirements in an attempt to prevent the development of a Site-Specific Standard that would be considered to be protective of the species and habitats of concern specified in the Act 2 regulations while allowing residual chloride concentrations to remain in the soil that would negatively impact vegetation on the property.  These additional requirements would include an assessment of the chloride tolerance of the vegetation present at a site to develop a Site-Specific Standard.  This site-specific vegetation chloride tolerance approach could result in a large variation of chloride cleanup criteria from site to site.  For example, some agricultural crops can tolerate total chloride concentrations in soils of up to 1,500 mg/kg while more sensitive species cannot tolerate total chloride concentrations in soils at concentrations in the range of 500 to 800 mg/kg.  Proper selection and application of soil amendments can reduce the amount of chlorides and other ions (particularly sodium) in the soil that are potentially deleterious to plants, thereby reducing the potential toxicity due to residual chloride concentrations.
If you have questions on how the spill and release guidance might apply to your operations, please contact Bo Valli, P.G., ( or Tom Maher, P.G., ( at 800-365-2324.

About the Author

Thomas L. Maher, Jr., P.G.

Tom Maher Jr., P.G., is a Vice President and serves as CEC's corporate Environmental Engineering and Sciences Practice Lead. His areas of expertise are in leading site investigation and remediation projects and in performing environmental permitting, Phase I and II environmental site assessments, and compliance support for industrial facilities.

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