Vapor Intrusion refers to what happens when chemical vapors migrate from the soil or groundwater into a home or other building. Many chemicals that move into buildings this way are classed as volatile organic compounds (or VOCs). The term volatile means unstable, which in turn means these chemicals are likely to exist in gas (aka vapor) form. Vapor intrusion has increasingly become more of an issue mainly due to the MassDEP (and EPA) addition of more commonly found constituents benzene, ethylbenzene and naphthalene typically found in petroleum products.
Because they’re gaseous, VOCs can move easily through spaces between soil particles and tend to migrate from high-pressure to low-pressure areas. Since a basement is probably at lower pressure than the soil underneath, these vapors are likely to enter the basement (or other first level) through cracks in the foundation, walls, or floors. Some heating and air conditioning systems will literally pull the gases into the structure. Once they’re inside, natural airflow and ventilation allow the vapors to spread throughout the building. Vapor intrusion can cause indoor air to become polluted and unhealthy.
What are the risks?
The degree of health risk vapor intrusion poses depends on the type of chemical and concentration of the chemical in the home. The most common sources of chemicals that can cause vapor intrusion problems are gas stations and dry cleaners. For example, a nearby gas station might have a leak or spill from an underground storage tank allowing gasoline to release to the soil and possibly groundwater. Short-term exposure to gasoline-related vapors can cause respiratory irritation, nausea, or headaches, and long-term exposure can contribute to long-term effects such as cancer. Vapor intrusion clearly can cause health risks to families. In addition, vapors might pose a liability issue if they intrude into a workplace.
How do I know whether I have vapor intrusion?
There are several ways to test whether toxic chemicals are entering a building: you can collect soil vapor samples in the ground nearby a structure or in the ground right under your foundation; or you may elect to collect indoor air samples. If you learn that a nearby gas station or industry has had a toxic spill or leak, you might call the owners or government officials to request that they test your home for vapor intrusion.
What should I do?
Landlords, property owners, developers, and investors should take vapor intrusion very seriously. They should include Vapor Encroachment Screenings, Vapor Intrusion Testing in their due diligence activities. If tests indicate that chemicals are intruding into your home or commercial structure, there are several actions you could take. You might seal any cracks in your walls or foundation. Or you could have a mitigation and/or remediation system installed.
CSE has certified environmental consultants who conduct Vapor Encroachment Studies according to the guidance of the ASTM E2600-10 ‘Standard Guide for Vapor Encroachment Screening on Property Involved in Real Estate Transactions‘. A Vapor Encroachments Study is a method for evaluating the potential for a vapor intrusion condition.
If the Vapor Encroachment Study determines that a Vapor Intrusion Condition is likely, a Vapor Intrusion Study may be performed. The preferred method for performing a Vapor Intrusion Study involves the collection of soil vapor samples directly adjacent to or beneath the existing structure or the area of a proposed structure. Soil vapor samples collected are compared to prevailing soil vapor screening levels established by the MassDEP, when available. If soil vapor concentrations exceed established screening levels, then a Human Health Risk Assessment may be necessary to determine site specific risks based on many factors including building characteristics. If the Human Health Risk Assessment finds an elevated risk to human health exists, indoor air sampling, mitigation, or remediation may be necessary.