Checked against published sources on September 9, 2026.
MassDEP still lists its October 2016 Vapor Intrusion Guidance: Site Assessment, Mitigation and Closure, Policy WSC-16-435, as its current guidance. No newer replacement was identified in its current guidance library. Later publications address related issues, including TCE toxicity and ambient air guidelines, but should not be described as a new edition of the vapor intrusion guidance. MassDEP guidance library
Core purpose
The guidance helps environmental professionals investigate vapor intrusion, protect building occupants, and support site closure under Massachusetts’ contaminated-site cleanup framework. It connects technical assessment and mitigation practices with requirements under the Massachusetts Contingency Plan, or MCP. EPA’s account of the release confirms that it incorporates updated science, professional practice, and the June 2014 MCP amendments. EPA release summary
Key framework elements
The guidance follows three connected tasks:
- Assess: Build a conceptual site model linking contamination, migration routes, buildings, and occupants. Evaluate multiple lines of evidence.
- Mitigate: Reduce exposure and verify that protective measures work.
- Close: Demonstrate that the response supports closure and maintain any necessary protective measures.
Indoor air threshold values support assessment; they do not independently establish site closure. MassDEP guidance, Sections 2–4
What are the latest published levels?
Selected indoor air threshold values from the currently listed guidance are below. All concentrations are in micrograms per cubic metre (µg/m³).
| Chemical | Residential | Commercial/industrial |
|---|---|---|
| Benzene | 2.3 | 11 |
| Trichloroethylene (TCE) | 0.4 | 1.8 |
| Tetrachloroethylene (PCE) | 1.4 | 4.1 |
| Vinyl chloride | 0.27 | 1.3 |
| Naphthalene | 0.6 | 2.7 |
| Toluene | 54 | 4,400 |
These are selected screening thresholds, published in the October 2016 edition. No newer replacement tables were identified. Appendix I contains the full indoor air tables; Appendix II addresses sub-slab soil gas screening. Use the correct medium and occupancy category. MassDEP guidance, Appendices I–II
TCE also has separate urgent-response levels
Massachusetts publishes the following TCE Imminent Hazard values:
| Exposed population | Residential indoor air | Workplace indoor air |
|---|---|---|
| Women early in pregnancy | 6 µg/m³ | 24 µg/m³ |
| Everyone else | 20 µg/m³ | 80 µg/m³ |
These address short-term exposure concerns. Exceedances require notification and immediate actions to address the source and reduce exposure. They serve a different purpose from the screening thresholds above. Massachusetts TCE indoor air information
When were updates made, and what changed?
Three dates matter:
- October 2016 — current vapor intrusion guidance. The final document incorporated more recent science and practice and aligned assessment, mitigation, and closure guidance with the June 2014 MCP amendments. This was a broader technical and regulatory update, rather than simply a new concentration table. EPA release summary
- January 7, 2025 — TCE scientific review. MassDEP’s Office of Research and Standards recommended retaining the existing method for calculating TCE Imminent Hazard concentrations, based on potential fetal heart malformations. The review did not recommend relaxing that approach. MassDEP also issued a response letter dated February 19, 2025. MassDEP technical memorandum, response letter
- September 2024 — separate ambient air guidelines. MassDEP updated its Allowable Ambient Limits and Threshold Effect Exposure Limits using newer toxicity information and added 141 chemicals. These values primarily support air permitting, although they also inform health evaluations. This publication is separate from the vapor intrusion threshold tables. MassDEP ambient air guidelines
Applying standards in ESdat
ESdat has recently compiled updated standards across North America, Europe, and Australia. These updates allow users to apply current guideline values, automate compliance monitoring, and incorporate the latest standards into reporting and decision-making workflows in ESdat.
Its standards library supports comparisons with laboratory and field results, guideline-exceedance alerts, and site-specific limits. For Massachusetts projects, record the selected guideline, edition, units, and exposure setting alongside each comparison. ESdat environmental standards
Key takeaways
- The current listed vapor intrusion guidance remains the October 2016 edition.
- Match each value to its purpose: screening, exposure evaluation, or urgent response.
- The 2025 TCE review recommended retaining the existing Imminent Hazard approach.
- Record source dates so newer related publications are applied correctly.
Glossary
- Vapor intrusion: Movement of subsurface chemical vapors into buildings.
- MCP: Massachusetts Contingency Plan, the state’s contaminated-site cleanup regulations.
- Conceptual site model: An explanation of contamination sources, migration routes, and potential exposure.
- Sub-slab soil gas: Gas beneath a building’s floor slab.
- µg/m³: Micrograms of a substance per cubic metre of air.
FAQs
Does exceeding an indoor air threshold prove vapor intrusion?
No. Thresholds are one line of evidence; the investigation must establish the source and pathway. MassDEP guidance, Section 2.2
Did MassDEP introduce new TCE Imminent Hazard levels in 2025?
The January 2025 review recommended retaining the existing calculation approach. MassDEP TCE memorandum
Can ESdat accommodate project-specific limits?
Yes. Users can add their own standards or site limits and compare results against them. ESdat standards library
Recommended reading for Massachusetts DEP Vapor Intrusion
Major Updates to the Massachusetts Contingency Plan: What Environmental Professionals Need to Know
What are the Massachusetts Contingency Plan (MCP) Numerical Standards?
What are Massachusetts MCP Standards for?
Massachusetts MCP Standards
What are US environmental standards?
Environmental Standards Databases Explained
