St. Paul: University Ave. and Pascal St. area vapor site

The MPCA is investigating the presence of trichloroethylene (TCE) and perchloroethylene (PCE, also called “perc” or tetrachloroethylene) in the soil and groundwater in a mixed commercial/residential area in St. Paul. The site is east of North Pascal Street and north of University Avenue West.

This site has been added to the MPCA's State Superfund Permanent List of Priorities (PLP). This means that the agency has access to additional funding to perform work at the site.

Initial investigations were associated with the Kline Auto World (KAW) property located at the northwest corner of the intersection of University Avenue and Pascal Street. The property was enrolled in the MPCA Voluntary Investigation and Cleanup (VIC) Program during its redevelopment. Testing of groundwater and soil vapor on the KAW property identified TCE and PCE contamination.

The PCE and TCE contamination is believed to have been released by either historical or ongoing commercial operations at certain properties along University Avenue. The map below outlines the area of concern.

The MPCA became involved to determine the extent of the groundwater and soil vapor contamination beyond the KAW property boundary, to determine and characterize the source or sources of the contamination, and conduct remediation. MPCA investigations have identified elevated concentrations of TCE and PCE in soil vapor at several properties between Pascal Street and Albert Street and along both Sherburne and University avenues. The investigation’s initial focus has been on identifying homes that may be at risk of vapor intrusion of the chemicals TCE and PCE from soil vapor. The MPCA is installing vapor mitigation systems at residential properties where TCE and PCE soil vapor concentrations are found to be above levels of concern.

The issue: Vapor intrusion

TCE- and PCE-contaminated soil vapors can rise through the soil and migrate through basement and foundation cracks into homes and other buildings, where they could be inhaled by people. This is known as “vapor intrusion.” If vapor intrusion is occurring, it is likely that TCE and PCE vapors are higher in basements than on upper floors.

If a person breathes in low levels of contaminants in indoor air for a long time, there is an increased chance that the person’s health could be affected. The risk to health depends on several factors, such as how much and what kind of contamination is present and how long a person has breathed it. The MPCA wants to identify vapor intrusion and take steps to reduce or eliminate it where possible.

The MPCA has information about vapor intrusion and information about understanding vapor intrusion test results. The Minnesota Department of Health (MDH) has a Vapor Intrusion webpage, information about health concerns associated with TCE in air, and information about health concerns associated with PCE in air.

One way to prevent vapor intrusion in a home is to install a vapor mitigation system, which is designed and operates like a home radon mitigation system. The vapor mitigation system creates a slight depressurization beneath the building floor slab with a low-wattage fan installed in PVC piping that exhausts above the roof line. Measurements collected before and after installation of the mitigation system are used to verify that the system is functioning properly. A vapor mitigation system can prevent intrusion of both chemical vapors and radon vapors.

Next steps

The MPCA continues to seek access to residential and commercial properties in areas of potential concern to sample soil vapor to determine whether TCE and/or PCE present in the soil vapor could make its way inside, creating exposure for occupants. The MPCA needs the cooperation of property owners to compete this work.

The MPCA and its contractors will do the testing and install vapor mitigation systems at affected properties.

Drinking water: No effects

The properties at this site are on public water supply that is not affected by the groundwater contamination at the site. St. Paul’s municipal water system currently meets all federal and state drinking water requirements.


The map shows the extent of the current MPCA investigation and the status of mitigation efforts at buildings in the study area.

Map of vapor intrusion site at University and Pascal in St. Paul


Time period Activity
February - December 2011 Kline Auto World (KAW), located on northwest corner of University Avenue and Pascal Street, removes petroleum storage tanks, hoists, and buildings and conducts sampling prior to redevelopment. KAW reports finding PCE in soil and TCE in groundwater to the MPCA. KAW enrolls site in MPCA Brownfields Program.
January - December 2012 KAW identifies elevated levels of TCE and PCE in groundwater and soil vapor on its property and on both east and west sides of Pascal Street. Soil vapor investigations identify potential vapor concerns on the eastern and northeastern portions of the KAW property.
January – December 2013 KAW collects additional groundwater and soil vapor data beyond its site boundaries and confirms concentrations are higher east and southeast of its property along Pascal Street. These contaminant patterns and the northerly groundwater flow direction suggest the presence of a possible offsite source for the higher concentrations of TCE and PCE on the eastern edge of the KAW property. The former Midway Plaza site, south of University Avenue, where PCE impacts to the groundwater from a dry cleaner were monitored and partially cleaned up in the mid- to late1990s, is considered a possible source of the contamination identified during the KAW investigation.
January – May 2014 The MPCA Site Assessment Program agrees to investigate the contamination not originating from the KAW property while KAW continues as a cooperative party in the MPCA VIC Program. MPCA Site Assessment (SA) Program investigates and identifies TCE and PCE groundwater and soil vapor contamination along Sherburne Ave east of Pascal Street almost to Albert Street. Several residential properties along Sherburne Ave are considered to have vapor intrusion concerns due to their proximity to elevated TCE and PCE soil vapor concentrations.
May - December 2014 The MPCA requests access from owners of 18 residential properties to collect soil vapor samples beneath their homes to assess vapor intrusion risks. Fourteen sub-slab samples are collected and mitigation systems are installed at 3 homes.
January – June 2015 More residential property owners provide access to the MPCA for vapor sampling. Four more homes with results above action levels are mitigated by the MPCA. Based on the site investigation results, the area of concern is expanded to include the south-facing Sherburne Avenue properties east to Albert Street. Vapor sampling is also expanded to the commercial properties along University Avenue between Pascal and Albert streets and sampling results where access was obtained identified TCE and PCE concentrations on some properties significantly higher than at the residential properties to the north, suggesting possible sources of contamination.
July – November 2015 MPCA SA Program seeks and obtains additional funding to continue the vapor investigation and to look for contaminant sources.
December 2015 – Spring 2016 MPCA continues to seek access to sample all properties where vapor intrusion risks are suspected. The MPCA will mitigate 5 commercial business properties. Additional investigation is proposed south of University Avenue to help identify contaminant sources.

What owners of residential properties need to do

If the MPCA is seeking access to test the soil vapor at your property, sign the access agreement that the MPCA will be sending you. The MPCA will work with you to schedule a time to sample beneath your home. You will need to be present at the time of the sampling.

If sub-slab levels are exceeded at your residential property, the MPCA will work with you to develop a schedule for installing a vapor mitigation system.

What does sampling involve?

With the permission of you, the residential property owner, the MPCA will sample the air under the building foundation. If test results exceed levels of concern, the MPCA will ask permission to install a mitigation system at no cost to you. Sub-slab sampling is the name given to the process of collecting a vapor sample from directly beneath the basement floor through a small hole drilled in the floor. Collecting a sub-slab vapor sample takes about an hour. The sample results will be provided to you after the sample has been analyzed, which could take a couple of months.

What if the sampling indicates a potential problem?

If the sample results indicate elevated TCE and/or PCE vapor levels, the property and its occupants can be protected by installing a vapor mitigation system. This system is similar to a typical “radon system” installed in homes and buildings in areas where radon is naturally present in the soil. Such systems consist of a hole in the building floor with a sealed pipe that leads to a low-wattage fan in the attic or on the outside of the building. The fan pulls vapors from beneath the floor and discharges them to the atmosphere through a stack on the roof.


Tim Grape

Minnesota Department of Health