St. Paul: Pierce Butler Rte. vapor intrusion site

A mixed commercial/residential area just southwest of Pierce Butler Route and Victoria Street South in St. Paul was historically used as a dump, and there are concerns about contamination of surface soils and resulting soil vapors. Common soil contaminants in former dumps include metals such as arsenic, lead, and mercury, and poly aromatic hydrocarbons (PAHs) and perchloroethylene (PCE, also called tetrachloroethylene). Shallow soil testing and soil vapor testing done by an MPCA contractor in 2015 found metals and PAH contamination in the shallow soils and isolated PCE contamination in soil vapors. Additional soil vapor testing done in February and June 2016 identified three buildings where vapor intrusion may be occurring. The MPCA installed vapor ventilation systems on all nine units in the three targeted buildings in June 2017. Starting in November 2017, Braun Intertec Corp. will be excavating contaminated soil in two main areas of the site where there are playgrounds.

The issues: Shallow soil contamination and vapor intrusion

Shallow soil contamination: In certain areas, the shallow soil — soil up to four feet deep — is contaminated with metals and PAHs. Ingestion of contaminated soil and dust is the main exposure route for metals and PAHs. The exposure risk is reduced by covering bare areas with clean soil, mulch and grass. The MPCA has identified 10 areas in Wilder Square where there is shallow soil contamination. A cleanup plan has been prepared and approved by the MPCA. Cleanup will occur in three stages.

Vapor intrusion: Groundwater contaminated with PCE could release PCE vapor that can rise through the soil and seep through basement and foundation cracks into homes and other buildings, where it could be inhaled by people. This is known as “vapor intrusion.” If vapor intrusion is occurring, it is likely that vapors are higher in basements than on upper floors. The MPCA identified three buildings in the Wilder Square site where vapor intrusion may be occurring.

The remedy for the situation is installing a vapor ventilation system, which operates like a radon mitigation system. If a building has a radon mitigation system that was installed by a certified contractor and is functioning properly, it is likely that the problem of PCE vapor in the building’s indoor air is being addressed.

Long-term exposure to low levels of contaminants from shallow soil or indoor air increases the risk that some people might experience health effects. However, the amount of contaminants that may be ingested or breathed in at this site is expected to be small and not likely to result in health impacts. Although the risk is currently believed to be small, it is avoidable. The MPCA wants to identify and take steps to reduce or eliminate contact with contaminated soil and vapor intrusion where possible.

The MPCA installed vapor ventilation systems in each unit of the three buildings in June 2017, and verification testing was completed in August 2017.

Contaminated soil removal

Based on site uses and cost, the MPCA and Braun Interec divided the soil cleanup into three stages. Stage 1 begins in November 2017, funded by the Ramsey County Environmental Response Fund, and targets the two playground areas. These areas are used most often and risk topsoil erosion that would expose contaminated soil. The work is being coordinated with stormwater work in the area.

Most of the areas targeted for soil cleanup are currently covered with topsoil, but removing contaminated soils will ensure residents' safety going forward. Stage 2 is planned for late 2018 and Stage 3 will begin in late 2019.

Map: Pierce Butler/Wilder Square Co-op site

The map below shows which buildings are in the mitigation area.

Pierce Bulter site map


Time period Activity
May 2015 Sampling shallow soil and soil vapor investigation
September 2015 Development of shallow-soil cleanup plan
February 2016 Resampling for vapors under designated buildings
May-June 2016 Resampling southern townhouse building in Area C
September 2016 Addendum to shallow-soil cleanup plan
February 2017 Wilder Square awarded soil cleanup grant from Ramsey County
June 2017 Vapor ventilation systems installed in each unit of three buildings
November 2017 Stage 1 of shallow soil cleanup begin in conjunction with stormwater improvements


On vapor intrusion site

On health issues related to this site

  • Minnesota Department of Health: Daniel Peña (651-201-4920)