Ohio EPA Significantly Revises Vapor Intrusion Guidance – July 2019


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Ohio EPA Significantly Revises Vapor Intrusion Guidance – July 2019

By: George Colvin, CPG, CHMM

On June 26, 2019, Ohio EPA released a draft final version of its updated “Sample Collection and Evaluation of Vapor Intrusion to Indoor Air for Remedial Response and Voluntary Action Programs Guidance Document” (Ohio EPA VI Guidance or Guidance). Comments were requested by no later than July 15, 2019.  Cox-Colvin & Associates commented on the document and we hope others in the regulated community did as well. 

The Ohio EPA VI Guidance was first released in 2010.  The Ohio EPA VI Guidance was developed for sites under the oversight of 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).  This is the second update to the 2010 Guidance. In May 2016, Ohio EPA rescinded Chapters 10 (data evaluation) and 11 (modeling the VI pathway using the Johnson and Ettinger [J&E] model). Ohio EPA considered Chapters 10 and 11 out of date and no longer appropriate for projects seeking cleanup under any of the DERR programs.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 2019 draft final Ohio EPA VI Guidance has been significantly expanded and, in many ways, improved. I can appreciate the difficulty and effort that went into the rewrite, given the continued rapid evolution in the science of vapor intrusion and in the underlying human health toxicity factors for which there seems to be little consensus. 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 in the August 2016 Ohio EPA “Recommendations Regarding Response Action Levels and Timeframes for Common Contaminants of Concern at Vapor Intrusion Sites in Ohio.”   The August 2016 Ohio EPA established response actions and timeframes for concentrations of common chemicals (TCE and others) encountered during VI investigations when receptors are present.  When EPA updated the risk assessment for trichloroethene (TCE) in 2011, they based the non-carcinogenic Hazard Index on a controversial study that ties TCE to fetal heart defects.  This lowered the acceptable maximum concentration of TCE in indoor air for many programs, but more importantly, it raised the issue of exposure duration.  Most TCE screening levels were previously tied to cancer, which is generally associated with years or decades of exposure.  Non-carcinogenic effects from chemical exposure can take place more rapidly, and in the case of TCE, fetal heart defects could potentially result from exposure periods of weeks or days.  Incorporation of the August 2016 response action guidelines is primarily by reference as the actual response action levels (concentrations) are not included in the draft final Ohio EPA VI Guidance. 
  • The Guidance seems to reflect a welcome and fundamental shift in the significance of subslab sampling, with greater emphasis on the use of sub-slab data, and less emphasis on groundwater, bulk soil, and exterior soil gas data. Historically, investigations have typically started with soil sampling and then progressed to groundwater sampling and finally vapor intrusion sampling. Increasingly, sub-slab sampling is seen as a more appropriate first step in environmental assessment that is often easier and quicker to perform than soil sampling.
  • The Guidance now includes an entirely new Section addressing 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 petroleum VI sites with relatively small petroleum releases than for chlorinated solvent sites.
  • The Guidance now includes the following critical statements related to the evaluation of VI data.  “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, I 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, for the first time, addresses the vast difference in concentration between OSHA permissible exposure limits and VI defined acceptable indoor air concentrations for commercial/industrial receptors. For example, the Ohio EPA commercial/industrial indoor air standard for TCE associated with VI is 8.8 µg/m3,while the comparable OSHA PEL, also for a 40 hour a week exposure, is over 500,000 µg/m3.  The Guidance also 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 an all new Remedy section organized largely around the concept of risk level and time frame, including imminent, acute, chronic, and unknown.
  • Included in the Remedy section 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 (to a limited degree), as Section 13, the seldom discussed, but 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 field standard operating procedures, Ohio EPA’s field data collection forms, comparison of tubing type to vapor absorption, and soil gas analytical methods and reporting limit ranges.  

Finally, regarding the ever-present use of guidance as regulation issue, Section 2 states the Ohio EPA VI Guidance document

“… is a guidance document and does not impose any requirements or obligations on the regulated community.  Other technically equivalent sampling and engineering procedures exists and those investigating vapor intrusion may use other technically sound approaches.”

This is simply not true.  Like it or not, the Guidance does impose requirements or obligations, on the regulated community investigating and/or remediating the VI pathway.  To their credit, Ohio EPA does consider and allow technically equivalent sampling and engineering procedures to be used.  However, it is typically not the sampling and engineering procedures that are problematic in the same way as the critical policy issues such as attenuation factors, acceptable risk levels, sampling/seasonal frequency, separation distance, etc. from which Ohio EPA will typically not deviate.  The good news here is that the values utilized in the Guidance are generally consistent with federal and most state requirements.

Published in the July 2019 Cox-Colvin & Associates Newsletter: Focus on the Environment


George H. Colvin is a hydrogeologist with over 30 years of consulting experience. Much of his experience has focused on RCRA Corrective Action, RCRA closure, and groundwater investigation, monitoring, and cleanup. He holds a BS in Geology from Ohio University and MS in geology and hydrology from Vanderbilt University. He is a Certified Professional Geologist with the American Institute of Professional Geologists, a registered geologist in Kentucky, Pennsylvania, and Tennessee, and a Certified Hazardous Materials Manager.