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Vapor Intrusion Resources for Local Governments

Certain chemicals that are spilled or discharged into the environment can emit gases, or vapors, that move through the soil. Contaminated vapors may enter a house or building through cracks, holes, drains and other small openings in a basement floor, wall or foundation slab – even with new construction. This is called vapor intrusion. It is similar to how radon, a naturally occurring gas, enters a house or building.

Contaminated vapors, which may be odorless and colorless, can accumulate and become a potential health risk. When vapor intrusion occurs, the local government and health department may be a valuable resource to the affected individuals and community.  

Understanding how vapor can migrate is important when local governments are starting to plan for utility work, building and occupancy permits, re-zoning, and development. The DNR recommends communicating with DNR staff early in the development planning process, so that DNR may provide relevant information regarding the NR 700 process and timeline, which may help keep developments on time and at cost.

The DNR does not have the authority to regulate building occupancy. Building occupancy is typically regulated by local authorities in the city or county where the building is located. Local health departments may also assist in situations involving indoor air quality.

  • What is Vapor Intrusion? - The U.S. Environmental Protection Agency (EPA) website on vapor intrusion includes additional information and resources.
An infographic showing that common sources of contamination can be underground petroleum storage tanks and spilled chlorinated solvents from old dry cleaning facilities. These chemicals are known as volatile organic compounds or VOCs. VOCs leach into the soil or cause a groundwater plume. When VOCs evaporate into vapors, they can enter building through cracks in the floor or wall, spaces near utility lines, or gaps in the foundation – this is called vapor intrusion. The vapors can travel through the building through air vents or other open spaces.
Vapors can enter a building from many sources and locations.

Awareness is the first line of defense against vapor intrusion.

BRRTS On The Web (BOTW) is a searchable directory which provides users with a comprehensive online database of contaminated properties and other activities in Wisconsin. BOTW contains many search criteria, including the ability to search by substances such as trichloroethylene (TCE), perchloroethylene (PCE or PERC), chlorinated solvents, and volatile organic compounds (VOCs).  BOTW only contains information on open and closed activities, it does not contain information about contaminated sites that have not yet been identified.

RR Sites Map (RRSM) is a web-based mapping system that provides locations of and information about contaminated properties and other related activities.

Blueprint with solid fill

The Vapor Intrusion Prevention & Partnership Toolkit provides resources on how to proactively protect the health of your community by preventing exposure to Vapor Intrusion.


Hazardous substance discharges and environmental pollution from industrial facilities, businesses with solvent dip tanks or parts washers, historical dry cleaners, leaking underground storage tanks and other chemical spills may be sources of contaminated vapors that result in vapor intrusion.

The proximity of a property to a contaminated site or facility may put owners and occupants at risk. Properties nearby or adjacent to a contaminated site may be at particular risk for vapor intrusion and health risks; however, in some cases it is possible for contamination to travel far from the source property. The DNR and environmental consultants use specified criteria to determine if sampling is recommended to assess vapor intrusion risk. Contact regional DNR vapor intrusion staff or the site-specific project manager for more information.


Protection of public health and successful mitigation, remediation and redevelopment of properties with vapor intrusion is dependent on a full understanding of the degree and extent of contamination and may require completing a site investigation.

Site investigations and cleanup procedures can be complex, time-consuming and costly. It is important to select a qualified environmental consultant to perform the tasks required to thoroughly investigate, assess the potential for vapor intrusion and clean up contamination.

A competent and experienced consultant can also help you explore redevelopment options for your property and ensure that you have information about possible financial assistance. More information can be found on selecting an environmental consultant.


Mitigation is used to interrupt and prevent vapor from entering indoor air. Sometimes, immediate actions are needed to protect human health.

Immediate Actions

Immediate actions to mitigate vapor intrusion may include:

  • Increased building ventilation
  • Minimization of exposure
  • Portable air treatment units
  • Temporarily modifying the heating, ventilation and air conditioning (HVAC) system
  • Appropriate emergency actions where there is an imminent threat to public health, safety, welfare or the environment. Note: The DNR does not have the authority to regulate building occupancy. Building occupancy is typically regulated by local authorities in the city or county where the building is located; local government may require relocation of residents.

Long-term Mitigation

Many options exist for long-term mitigation of vapor intrusion, including:

  • Sealing building openings
  • Installing vapor barriers
  • Installing a vapor intrusion mitigation system that will be maintained properly

The DNR strongly recommends using National Radon Proficiency Program (NRPP)-certified mitigators with experience in chemical vapor intrusion and/or mitigators with national certification for radon and chemical vapor intrusion who follow American Association of Radon Scientist and Technologists (AARST) / Indoor Environments Association or American National Standards Institute (ANSI) standards.

Vapor Intrusion Prevention

Work with environmental consultants to proactively plan projects that ensure building systems and components are designed, installed, tested, operated and maintained according to vapor intrusion mitigation best practices. When planning construction projects, local governments can also plan for utility work, building and occupancy permits, re-zoning, and development with vapor intrusion in mind.


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 related to vapor intrusion, and DNR partners may make recommendations on 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. 

DHS factsheet specific to the health concerns of trichloroethylene (TCE) in the air of buildings where the chemical may have unexpectedly traveled (e.g., residences, schools, daycares, businesses that do not use TCE):

DHS two-page fact sheet specific to the health concerns of TCE when used as a chemical in the workplace:

For more information about vapor intrusion and health, visit the DHS website or view their vapor intrusion fact sheet:

Additional technical publications regarding vapor intrusion are available on the Vapor Intrusion Resources For Environmental Professionals webpage.


For more information, contact DNR's vapor intrusion experts.