In the previous installments in this series on acquiring former dry cleaner properties (What’s the Big Deal About Dry Cleaners?, December 2019 and Potentially Contaminated, Perfect Location, Now What?, January 2020), a prospective buyer of a property learns why dry cleaner sites raise a red flag, how to go about investigating through a Phase I and sub-slab and indoor air sampling, and how to understand what those investigations tell you. For this fictional property, our buyer has discovered that the property evidences vapor intrusion gas from PCE, but he decides that he must have this property location for his next commercial enterprise. This installment discusses the next step in learning more about the health risk at the site and where that knowledge may lead.

(Editor’s note: The processes described herein have been greatly accelerated and simplified for purposes of readability. The investigative process and determination of risk levels and  resolutions take much longer in reality and in this case, were negotiated with the seller of the property.)

            EPA has suggested that a multiple-line-of-evidence approach be used to understand the risk to a human receptor from such a site. Our buyer has already completed vapor intrusion and indoor air sampling and discovered that health risk is unacceptable from a former PCE release at the old dry cleaner property. The buyer’s consultant correctly advises that some intrusive soil sampling (Phase II) is needed to find the source of the vapor intrusion and then use that information to determine what remedy is recommended for the property. This data helps tell the buyer where the contamination is located, the strength of the contamination source, whether ground water is involved, and how/where it may be moving at the site. It is usual that this intrusive sampling step is repeated until the site problem has been fully delineated. Once this investigation data is in hand, the consultant can recommend a remedial decision.

            For this installment, the intrusive investigation indicates where the source area for the PCE is located, allowing for an excavation of a small area where the PCE materials had been used in the former dry cleaner. With the contaminant source removed, the consultant additionally recommended the installation of a vapor mitigation system under the floor of the small building, also known as a sub-slab depressurization system. This ensures that remaining PCE gases in the soil would be removed and exhausted, thereby ensuring no unacceptable human exposure levels within the building.

            After allowing the mitigation system to operate for a few weeks, additional sub-slab and indoor air samples were taken to confirm the expected benefit of limited human risk from vapor intrusion.  Our buyer learns that the confirmation samples indicate that risk levels are now well below EPA’s action levels for indoor air and sub-slab soil gas for a commercial site.  Since ground water was not encountered during the soil boring investigations, this was not a pathway for any human exposure.       

          

            The next installment in this series will consider a site with greater contamination and a more complex remedial process. All of these scenarios are based upon actual CTI project experience.