Ohio EPA Issues Final Vapor Intrusion Guidance

By: Craig Cox and Laurie Chilcote

Published in the March 2020 Focus on the Environment Newsletter

Cox-Colvin & Associates personnel routinely provide vapor intrusion (VI) training to regulators, attorneys, environmental professionals, and the regulated community; and have helped in the development of VI guidance within the US and throughout Latin America and Europe.  As a result, we have had the opportunity to review a large number of VI guidance documents over the years.

On March 10, 2020, Ohio EPA released a final version of its updated “Sample Collection and Evaluation of Vapor Intrusion to Indoor Air for Remedial Response and Voluntary Action Programs” (Ohio EPA VI Guidance or Guidance).  In our opinion, Ohio EPA, with input from a variety of experienced stakeholders, have crafted a very comprehensive yet flexible approach to the assessment and mitigation of VI sites within Ohio.  Even though the Guidance is by nature Ohio-centric, the approaches, processes, and documentation presented in the document could be helpful to anyone conducting VI assessments.

The Ohio EPA VI Guidance, initially released in 2010, was developed for sites under the oversight of the Comprehensive Environmental Response, Compensation, and Liability Act of 1980 (CERCLA), the Resource Conservation and Recovery Act (RCRA), and the Voluntary Action Program (VAP), carried out under the supervision of Ohio EPA Division of Environmental Response and Revitalization (DERR).  The 2020 Version is the second update. In May 2016, Ohio EPA rescinded Chapters 10 (data evaluation) and 11 (modeling the VI pathway using the Johnson and Ettinger [J&E] model). Ohio EPA considered Chapters 10 and 11 out of date and no longer appropriate for projects seeking cleanup under any of the DERR programs.

The 2020 Guidance has been significantly expanded and improved in many ways. We can appreciate the difficulty and effort that went into the rewrite, given the continued rapid evolution in the science of VI and in the underlying human health toxicity factors for which there seems to be little consensus.

The general approach to sites is similar to other modern guidance documents for VI: understand the history of volatile compound uses and/or releases at your site, develop a robust conceptual site model (including preferential pathway analysis), base decisions on multiple lines evidence (sampling of various environmental media), compare results to applicable standards and mitigate as necessary.

Provided below are some of the more significant changes to the Guidance.

  • The Guidance incorporates Ohio EPA’s somewhat controversial imminent hazard indoor air action levels published by Ohio EPA in the August 2016 as a standalone document titled “Recommendations Regarding Response Action Levels and Timeframes for Common Contaminants of Concern at Vapor Intrusion Sites in Ohio.”   In the 2016 document, Ohio EPA established response actions and timeframes for common chemicals (TCE and others) encountered during VI investigations when receptors are present.  The response actions, tied to specific indoor air and/or sub-slab soil gas concentrations, include removal of occupants until a remedy can be put in place.  If you are a VI practitioner, you need to be aware of these limits and have a frank discussion with your client about potential actions that may be advised following the receipt of the analytical results.
  • Collecting environmental samples to support multiple lines of evidence is a common theme in the guidance.  The 202 guidance incorporate a welcomed and fundamental shift in the significance of sub-slab sampling, placing greater emphasis on the use of sub-slab data, and less emphasis on groundwater, bulk soil, and exterior soil gas data.  It is encouraging to see that Ohio EPA has included significant warnings against using bulk soil samples.  We have reviewed many assessments that have incorrectly concluded that VI pathway was incomplete based on the results of bulk soil samples.  The most important message we provide during VI training is that if you want to understand VI, you must collect soil gas samples.
  • The Guidance includes a section devoted to VI from petroleum releases, based in part on the 2015 US EPA Technical Guide for Addressing Vapor Intrusion at Leaking Underground Storage Tank Sites.  Once released, petroleum hydrocarbons behave differently in the environment and are generally less toxic and less mobile than chlorinated solvents.  Because of the effectiveness and speed of aerobic biodegradation in biologically active soils, Ohio EPA recommends, consistent with US EPA and ITRC Guidance, reduced lateral and vertical investigation distances at relatively small petroleum releases compared to chlorinated solvent sites.
  • The Guidance includes the following critical statements related to the evaluation of VI data in Ohio.  “For Ohio EPA DERR RP (remedial program) sites, when considering concentrations measured in sub-slab, soil gas, or ground water, the VISLs should be applied corresponding to an excess lifetime cancer risk (ELCR) of 1E-5 and a hazard quotient (HQ) of 1.  If the measured concentrations in the sampled media are less than the appropriate VISLs set at an ELCR of 1E-05 and a HQ of 1 for the appropriate exposure scenario, Ohio EPA DERR considers the pathway to be ‘incomplete’ and additional investigation or risk estimation of this pathway is not warranted.”  Although Ohio EPA DERR has consistently utilized an ELCR of 1E-5 and a HQ of 1 in VI work, we believe this is the first time this has been clearly stated in the guidance.  A similar comment is included for Ohio VAP sites which includes reference to the VAP-required multiple chemical adjustment.
  • The Guidance presents Ohio EPA’s position on the Ohio EPA/OSHA jurisdiction issue when it comes to indoor air contamination derived from vapor intrusion.  You may or may not agree with the position, but at least it’s out in the open.
  • The Guidance includes a section devoted to remedies (Section 13) organized largely around the concept of risk level and time frame, including imminent, acute, chronic, and unknown.  Included in Section 13 are discussions of monitoring requirements for engineering controls (mapping of the depressurization field and indoor air sampling) and post-mitigation sampling (pressure and/or indoor air sampling to demonstrate system effectiveness through seasonal variation).
  • The Guidance covers, as Section 14, the critically important topic of long-term management and exit strategies at VI sites where mitigation measures are installed.
  • Included as appendices to the Guidance are special considerations for evaluating residential properties, a VI conceptual site model checklist, Ohio EPA’s standard operating procedures and field data collection forms, comparison of tubing type to vapor absorption, and soil gas analytical methods and reporting limit ranges.

Although the Guidance is very comprehensive, we do suggest that practitioners may want to keep a few things in mind going forward.

  • The Guidance suggests that you limit the COC for indoor air to those compounds detected in sub-slab soil gas so that you can more easily eliminate the compounds associated with indoor sources.  We believe this is a bit too conservative.  Sanitary sewers are probably the most important preferential pathway and as such, you should expand the indoor COC list a bit to include compounds such as chloroform, carbon disulfide, bromoform, and tetrahydrofuran.  If these compounds are detected in indoor air, the VI issue may be related to poor plumbing connections, which can be easily and inexpensively resolved.  Without this data, you may end up installing a more expensive sub-slab system and still have a VI issue.
  • The Guidance is silent to PFAS and PFOS.  These compounds may become risk drivers for indoor air in the future.
  • US EPA is placing a renewed emphasis on how to predict the most opportune time to collect an indoor air sample.  Expect new guidance on using surrogates such as sub-slab differential pressure reading, indoor radon concentration, outdoor temperature, and barometric pressure to predict timing of air sampling.
  • Continuous vapor monitoring over a brief period (2 weeks or less) can help sort out the complexities and temporal variability of COC concentrations in indoor air.  The Guidance is silent on this as an approach; however, we are confident if you proposed it for your site, Ohio EPA would not resist its use.

Craig Cox is a principal and co-founder of Cox-Colvin & Associates, Inc., and holds degrees in geology and mineralogy from the Ohio State University and hydrogeology from the Colorado School of Mines. Mr. Cox has over 30 years of experience managing large environmental project implemented under CERCLA and state voluntary action programs. Mr. Cox is the inventor of the Vapor Pin® and has developed a variety of software products including Data Inspector, an internet-enabled environmental database application. Mr. Cox is a Certified Professional Geologist (CPG) with AIPG and is a Certified Professional (CP) under Ohio EPA’s Voluntary Action Program. Laurie Chilcote currently serves as Office Manager and Director of Sales & Marketing for Cox-Colvin & Associates, Inc, and is a Director and Vice President of Vapor Pin Enterprises, Inc. At Cox-Colvin, Ms. Chilcote is responsible for management and presentation of analytical data including the transfer of electronic analytical results from various resources. In addition, she is a managing Director and Vice President of Vapor Pin Enterprises and Vapor Pin Brazil, where she provides managerial and technical oversight on all marketing and sales for the Vapor Pin® both within the USA and Internationally. Laurie’s role includes educating the environmental community on Vapor Pin® technology, implementation, and quality control by making presentations to environmental firms, regulatory agencies and developers throughout the USA and Internationally.