The process for addressing vapor intrusion (VI) continues to evolve and recently updated guidance in New York State could have potentially significant impacts to various stakeholders.
Just over 10 years ago, the New York State Department of Health (NYSDOH) issued the Guidance for Evaluating Soil Vapor Intrusion (available here), which is used throughout New York to investigate and mitigate sites for vapor intrusion. (Image source: USEPA)
Based on reviews of toxicity data, risk assessments, and soil VI data collected in New York over the past decade, the NYSDOH issued an update to their Soil Vapor/Indoor Air Decision Matrices (available here) in May 2017. These Decision Matrices are used to compare indoor air concentrations of select chlorinated volatile organic compounds (CVOCs) to sub-slab vapor concentrations to determine the NYSDOH’s recommended action with regards to VI mitigation. The range of concentrations in each Decision Matrix is based on a number of factors such as human health risk, background concentrations in air, attenuation factors, and the NYSDOH guidelines for volatile chemicals in air.
In general, the updates have resulted in more comprehensive and stringent recommendations. The CVOC methylene chloride was added as a parameter to be used for evaluating VI and a new Decision Matrix was developed for vinyl chloride alone.
A comparison of the former and current matrices indicates the limits of sub-slab vapor and indoor air concentrations have become more restrictive and lower concentrations of CVOCs are now resulting in mitigation as the recommended action. For example, the upper limit of sub-slab vapor concentrations in which mitigation is recommended regardless of indoor air concentrations was greatly reduced for TCE, carbon tetrachloride, cis-1,2-DCE, 1,1-DCE, and vinyl chloride. The following table summarizes these new guidelines (concentrations are in micrograms per cubic meter (µg/m3):
In addition, notes to each matrix now stipulate lower reporting limits and that mitigation might be recommended when the results of multiple contaminants indicate monitoring is recommended.
TRC will continue to track state and federal guidance, as well as policy and statutes to keep our clients abreast of important changes as the approach to VI investigation and mitigation evolves.