Vapor intrusion occurs when there is a migration of vapor-forming chemicals from any subsurface source into an overlying building. The vapors can enter buildings through cracks in basements and foundations, or through conduits and other openings. Examples of vapor-forming chemicals that are hazardous to human health include methane (from landfills), tetrachloroethene (PCE) and trichloroethene (TCE) from dry cleaners, benzene (from petroleum products), and radon.
Since 2000, research has shown that exposure to toxic vapors has much greater health risks than previously known. Long term exposure to even very low concentrations can result in cancer. In response, the federal and state governments have lowered the safe exposure limits, and regulators have recently updated guidance for assessing vapor intrusion.
EPA published new guidance for assessing vapor intrusion in June 2015. (OSWER Technical Guide for Assessing and Mitigating the Vapor Intrusion Pathway from Subsurface Vapor Sources to Indoor Air; OSWER Pub 9200.2-154). The document provides guidance on conducting investigations, including collecting samples; interpreting risk assessments; and mitigating vapor intrusion.
Washington State subsequently updated their guidance for vapor intrusion in February 2016 (Washington State Department of Ecology, Guidance for Evaluating Soil Vapor Intrusion in Washington State: Investigation and Remedial Action, Pub 09-09-047). This document describes Tier I Screening assessments and Tier II sampling assessments.
Hawaii published their VI guidance in 2014 (Technical Guidance Manual for the Implementation of the Hawai’i State Contingency Plan, Section 7: Soil Vapor and Indoor Air Sampling Guidance). This document provides good information on different types of sampling equipment, with photos.
The state of Oregon is using vapor intrusion guidance published in 2010 (Guidance for Assessing and Remediating Vapor Intrusion in Buildings). The guidance describes how to perform risk-based evaluations, and the state periodically publishes updated risk-based concentrations for chemicals.
In the state of Minnesota, vapor intrusion concerns have significantly affected the real estate market. Starting in 2017, if a building is suspected of having contaminated soil below or around it, the state has asked the owners to test for vapors and fix vapor problems before the property can be sold. This can significantly add to the costs of property transfers and delay sales or even scare off buyers.
Here in the Pacific Northwest, the states are not requiring soil vapor testing, although near landfills methane vapor testing is often required. Also, areas with known radon often require vapor mitigation systems. But your environmental consultant should be considering vapor intrusion risks during Phase I Environmental Site Assessments, and might recommend soil vapor tests during Phase II investigations. Vapor intrusion is complicated – vapors move more easily than soil or groundwater contamination. It takes careful evaluation and interpretation of the guidance and test results to help property owners and purchasers make knowledgeable decisions.
Questions? Contact Anne Conrad, (425) 775-4682