Last month, the State of Washington issued an update to their Vapor Intrusion Guidance. This update is to the Draft Guidance for Evaluating Vapor Intrusion in Washington State: Investigation and Remedial Action (2021). This guidance also incorporates the Updated July 2022 Cleanup Levels and Risk Calculation (CLARC) tables as an amendment to the Model Toxics Control Act (MTCA) Regulation.
For our purposes as consultants who work on behalf of property owners, operators, and managers, the meaningful portion of the guidance is divided into four main parts (There are seven chapters in the guidance; however, we are going to focus on the four main parts that apply to us). These four main parts are:
- Preliminary Assessments;
- Tier 1 Evaluations;
- Tier 2 Evaluations; and
- Mitigations & Cleanup Actions.
Like most investigations we conduct, this is a scientific iterative process. The Preliminary Assessment portion in practice will be covered in a Phase I Environmental Site Assessment (ESA) or for more complex sites, an ASTM E2600-15 vapor encroachment screening. If a threat to indoor air is identified the investigation will proceed to a Tier 1 Evaluation.
The Tier 1 Evaluation will be performed during a Phase II ESA conducted for soil vapor and /or groundwater comparing data collected to the CLARC Data Tables. If a threat to indoor air is identified the investigation will proceed to a Tier 2 Evaluation.
The Tier 2 Evaluation will consist of sub-slab or crawl space soil vapor sampling and indoor air sampling. If a threat to indoor air is confirmed the project will proceed to mitigations and Cleanup Actions.
The guidance proceeds to present information on Mitigations and Cleanup Actions as well as public outreach and other concerns; however, for the purpose of this blog post, we will stop with the investigation phase. Contact us if you have further comments or concerns.