PADEP’s New Soil Vapor Screening Values Are Helpful (At Some Sites)
2022 brought a new headache to the Act 2 process in Pennsylvania – the need to evaluate possible Mercury vapor intrusion to buildings.
The Problem
One of the requirements of Act 2 has always been that the vapor intrusion pathway to buildings must be evaluated for substances of vapor intrusion concern. But this had previously been reserved for organic compounds in soil or groundwater — not for metals. In 2022, because of its volatility, Mercury was added to the list of regulated substances needing a vapor intrusion assessment as part of PADEP’s Act 2 approval process. And mercury is sometimes detected at concentrations exceeding Act 2 Statewide Health Standards in “historic fill” in urban areas.
The Dilemma
Unfortunately, the mercury vapor assessment process proved to be challenging, as the PADEP had not yet published screening values to perform the evaluation. Also, US EPA Regional Screening Levels are not directly applicable in many instances. And pursuing the Site Specific Standard for Mercury in soil instead of the Statewide Health Standard can add another big layer of unexpected complexity.
A Partial Solution
The process gained some clarity in October 2022, when the PADEP issued vapor intrusion screening values for indoor air, sub-slab, and near source soil gas samples that can be applied within the Act 2 program. These new screening values begin to solve the problem, as they provide a more concrete method for evaluating possible vapor intrusion to onsite and offsite buildings. But you still need to collect soil gas samples to use those screening levels, as screening values are still not yet available for soil or groundwater.
Options:
For sites where mercury vapor is identified as a potential concern, and relief of cleanup liability is desired for mercury in soil, two primary options exist:
- Mitigate the vapor intrusion pathway – This option typically involves the use of a vapor barrier and/or sub-slab depressurization system. If not already included in the cleanup plan for your site, the addition of these systems to a building can prove to be an unnecessary expense for sites where mercury exists at low levels or in a form that does not produce appreciable vapors.
- Collect soil gas samples to evaluate the vapor intrusion pathway – This option involves the collection of air samples from the subsurface, beneath a building slab, or inside a building to compare to the newly published mercury vapor intrusion screening values. This may provide options that eliminate the need to install potentially costly vapor mitigation systems. While there may be some additional time and cost for this testing, it may be well worth it if it avoids the time and cost needed for installation of a DEP-approved vapor mitigation system.
Evaluation of the threat of vapor intrusion due to mercury is continuing to evolve. Brickhouse has been working with PADEP on several remediation projects involving the issue and continues to find creative ways to ensure the safety of building occupants, avoid significant unnecessary expenses, and work within the regulatory structure to provide liability protections for property owners and land developers.
For more information, or to discuss various options for your property, please contact us at (610) 692-5770 to talk with Steve Huxta or one of our other vapor intrusion experts.
