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Vapor Intrusion

Chemicals used in commercial activities – such as dry cleaning chemicals, chemical degreasers and petroleum products like gasoline – are known as volatile organic compounds (VOCs). Spilled VOCs and those disposed of down sewers sometimes can leak into soil and groundwater and if they become a gas or vapor, can potentially enter buildings. This process is known as vapor intrusion which has been linked to some short- and long-term health effects.

This webpage contains general information about vapor intrusion for property owners, tenants and the general public.

Vapor Intrusion Videos


Vapor Intrusion Resources

Summa cannister
Summa canisters are often used to collect a vapor sample for laboratory analysis.

What is Vapor Intrusion (RR-892) [PDF] - Certain chemicals that get spilled or discharged into the ground emit gases, or vapors, that can move through the soil. These vapors may enter a house or building through cracks, holes, drains and other small openings in a basement floor, wall or foundation slab. This is called vapor intrusion. It is similar to how radon, a naturally occurring gas, enters a house or building.

Why Test for Vapor Intrusion? (RR-953) [PDF] or ¿Por Qué Probar la Intrusión de Vapor? (RR-953a: Spanish version) [PDF] - If a nearby property is contaminated, it is possible that chemical gases, or vapors, are moving through the soil and could be entering your house or building. Sampling and testing determines whether or not these soil gases are present in your indoor air.

What to Expect During Vapor Intrusion Sampling (RR-954) [PDF] - The collection of soil gas samples is performed by environmental professionals. It involves drilling one or more small holes into a basement floor or foundation, extracting soil gas from under the building into an airtight container, and then sending the soil gas sample to a specialized laboratory for testing and analysis. Samples of indoor air may also be collected and sent to the lab.

Understanding Chemical Vapor Intrusion Testing Results (RR-977) [PDF] - If vapor samples were taken from underneath your house or building, and possibly indoors as well, these samples have been tested by a certified laboratory and results were reported. The DNR uses these test results to determine if people in the building are being exposed to chemical vapors coming from nearby contaminated soil or groundwater, and to decide what, if any, action is needed to prevent this exposure.

Mitigation: Protection from Vapor Intrusion (RR-094) [PDF] or Mitigación: Protección Contra La Intrusión De Vapor (RR-094a: Spanish version) [PDF] - When test results show contaminant vapors are present in the air below a building, these vapors can get into the indoor air and present a health risk. Options are available to prevent these contaminant vapors from getting indoors, called vapor mitigation. This document explains the basics of mitigation and clarifies roles and responsibilities for maintenance.

Who Should I Contact About Vapor Intrusion Investigations? (RR-934) [PDF] - This document defines the responsibilities of the Department of Health Services/Division of Public Health (DHS/DPH), local health departments and DNR staff in assessing and mitigating human health risk at vapor intrusion sites.

Environmental Contamination & Your Real Estate (RR-973) [PDF] - When soil or groundwater contamination is discovered in a rural or urban area, one of the questions that homeowners may raise is whether such information will impact the market value of their property and if so, to what extent.

Maintenance Requirements

The manometer measures suction created by the vapor mitigation system fan. The uneven levels of the liquid indicate the system fan is running, but cannot be used exclusively to determine the effectiveness of the system.

Vapor mitigation on your property

If the vapor mitigation was required as part of an environmental cleanup under ch. 292, Wis. Stats.,  the continued operation and maintenance of vapor mitigation can be made a continuing obligation for a property ( ch. 726, Wis. Adm. Code), and the current property owner must comply with these requirements ( ch. 727, Wis. Adm. Code).

If operation and maintenance of a mitigation system is a continuing obligation on a property, the specific requirements should be included in a letter issued from the DNR, and instructions for care and inspection of the system should be summarized in the maintenance plan. Both the letter and the maintenance plan should be available at the property.

Who can help?

Vapor mitigation systems are similar or equivalent to radon mitigation systems. The Wisconsin Department of Health Services (DHS) maintains a list of radon mitigation contractors that have passed national proficiency standards: Radon Mitigation: Wisconsin Certified Radon Mitigation Contractors [exit DNR]. If help is needed with repairs or replacement of a mitigation system, the DNR strongly suggests work be performed by contractors who have been certified by the National Radon Proficiency Program (NRPP).

Copies of DNR letter or maintenance plan

Electronic copies can be downloaded from Wisconsin's Remediation and Redevelopment Database (BRRTS on the Web). BRRTS on the Web (BOTW) is a database organized by BRRTS activity number, which is assigned to the property that was the source of the contamination. (Note: Your address may be the same or different than the address listed in BOTW, depending on if the property was the original source or an offsite affected property). The DNR letter that summarizes the continuing obligations (requirements) and maintenance plan for a property are found in within the closure or registry packet.

How to use BOTW to find the maintenance plan and DNR continuing obligations letter for a property

  • Go to Wisconsin's Remediation and Redevelopment Database
  • If you know the BRRTS activity number for the site that was the source of the contamination:
    • Click on the link for BRRTS on the Web
    • Enter the number into activity number search field
  • If you don’t know the BRRTS activity number:
    • Click on the link for RR Sites Map
    • Use the zoom tools or search for address tool to find your property
    • Search for a BRRTS site on or near your property boundaries*.
    • Using the identify tool click on the point to get more information, including the BRRTS activity number
    • Click on the link to the listing on BRRTS on the Web

      *Note: If your property does not include a BRRTS site, it is likely you are an offsite affected property and you will need to find the BRRTS site located near your property on the map. If there are multiple BRRTS sites surrounding your property, you may need to review several BRRTS activity numbers to find the closure packet that has your maintenance plan.

  • Find a link to a PDF of the registry or closure packet posted on BRRTS on the Web after closure.
  • Search through the packet to find the maintenance plan for your property.
  • Print out the pages containing a copy of your maintenance plan.

Questions? See a list of DNR contacts on the right side of this page.


Health information

The DNR partners with the Wisconsin Department of Health Services (DHS) and local health departments regarding short-term (acute) and long-term (chronic) risks to human health, as well as determining appropriate immediate and interim actions (e.g., ventilation, mitigation) at affected sites. DHS and local health departments assist the DNR, responsible parties and environmental consultants with health risk communications, including supportive literature.

Additional health-related information is available on the Vapor Intrusion Resources for Environmental Professionals webpage under the "Health" tab.