St. Louis Park solvent plume and vapor intrusion site

The MPCA and U.S. EPA have been working since 2007 on an issue of groundwater contamination in St. Louis Park. The contamination has produced chemical vapors in the soil, and these vapors can make their way into houses and buildings.

Recent activities

  • The MPCA hired AECOM to design municipal water treatment facilities to remove solvent-related chemicals and polycyclic aromatic hydrocarbons from drinking water.
  • In October 2016, the Minnesota Department of Health issued a drinking water report for the city of St. Louis Park.
  • Additional groundwater contaminant plume characterization activities were completed June 2016.  The result of the characterization activities are available in the PDF icon St. Louis Park Investigation — FY16 (c-s3-13h) (July 2106) 
  • Other investigations were conducted in 2015, the results of which include:
    • Verified the soil vapor intrusion mitigation systems installed in residential properties in 2008 were still operating. No vapor intrusion problems were identified.
    • The perchloroethylene/trichloroethylene (PCE/TCE) soil vapor plume in the Lenox, Sorenson and Elmwood neighborhoods appears less widespread than originally documented.
    • The PCE/TCE groundwater contaminant plume appears to originate near the intersection of Walker St. and Lake St. The extent of the contaminant plume is not fully defined at this time.
    • Investigation activities indicate that the National Lead property does not appear to be a source of PCE and TCE releases. Further investigation activities are needed to determine if a PCE release source exists north of Walker St. on Gorham Ave.

PCE and TCE are compounds that belong to a class of chemicals known as volatile organic compounds (VOCs). VOCs get their name from their ability to pass easily from a liquid into a gaseous state.

Commercially, PCE is used in dry cleaning and to degrease metal parts. TCE is used also to degrease metal parts.

The results of the springtime investigation activities indicate that none of the homes tested had elevated PCE or TCE vapor concentrations in their indoor air.

PCE/TCE vapor plume testing results did not identify an extensive vapor plume as had been identified in 2008.

Four commercial properties were identified as PCE release source areas during previous investigations. More testing will be needed at a fifth property to determine whether either PCE or TCE was released there. Characterization activities conducted near the intersection of Walker and Lake streets indicate that a PCE groundwater plume extends off the PCE release site property to the east southeast.

It’s important to note that some of the releases are not associated with the businesses currently operating at the identified release locations. The releases appear to have occurred from the activities of previous tenants.

What’s next?

The MPCA is working to hold any party accountable that is responsible for the spill or other release of PCE or TCE. The MPCA will be notifying responsible parties of their obligation to clean up contamination at the release sites and to take steps to clean up the PCE and TCE contamination in the groundwater. Businesses now at the sites where PCE or TCE had been released may not be responsible if the release occurred when the properties were owned by someone else.

Interactive story map

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St. Louis Park vapor intrusion interactive map

Background: How the source of Edina groundwater contamination was traced to St. Louis Park

In 2004, Edina city officials reported the presence of the chemical compound vinyl chloride in the city’s drinking water wells. Vinyl chloride concentrations in one well exceeded drinking water criteria and the well was shut down immediately. Other city wells in the area did not exceed drinking water standards and continued to be used.

The MPCA worked with Edina to develop a central water treatment facility to remove chemicals, such as vinyl chloride, cis-1,2-dichloroethene (cis-DCE), TCE and PCE, from the water before it is distributed to residents. Four of Edina’s drinking water wells now are connected to the treatment system.

Vinyl chloride, cis-DCE, TCE and PCE are all VOCs. Vinyl chloride and cis-DCE are toxic chemicals produced when chlorinated solvents, such as PCE and TCE, decompose or are broken down by natural processes.

Typically, MPCA staff try to find the sources of contaminant releases so the responsible parties can be identified and a cleanup plan can be developed. MPCA staff collected and analyzed samples from monitoring wells, industrial wells, irrigation wells and other municipal wells located in the western Twin Cities metro area. The results showed a “VOC trail” that allowed the MPCA to trace the contamination back 2.3 miles, to the Highway 7 and Wooddale Avenue area in St. Louis Park.

First on the agenda: protect people in St. Louis Park from vapor intrusion

In 2006, the MPCA identified high concentrations of PCE in shallow groundwater samples collected from a well at the intersection of Walker and Gorham in St. Louis Park. The concentrations were high enough that MPCA staff believed the PCE could volatilize from the shallow groundwater and cause vapor-intrusion problems in residential and commercial buildings.

The MPCA’s investigation activity changed focus from groundwater to the more immediate concern associated with VOCs in vapor phase. Soil gas samples were taken in the rights-of-way of properties in the northwestern part of the Elmwood neighborhood and in the southwest portion of the Sorenson neighborhood (Area A on map #3) and the southern portion of the Lenox neighborhood (Area B).

PCE and TCE vapors may migrate from the groundwater beneath a building and enter the building through cracks and other openings in the slab (basement floor) or the foundation. For an explanation of how PCE and TCE vapors can enter a building, see:

Health effects may occur when PCE and TCE vapors are inhaled in low concentrations for long periods. To learn why health and environmental professionals are concerned about VOC vapors indoors, see:

In February 2007, the MPCA received the results of an investigation in St. Louis Park that found elevated levels of PCE and TCE in the soil vapor. Based on this information, MPCA staff determined that additional testing was needed, and St. Louis Park officials were notified.

Due to the size, complexity and expense of the additional study needed, the MPCA requested assistance from the U.S. Environmental Protection Agency (EPA). The two agencies developed a plan for additional sampling to evaluate the risk to people living and working in the area. Public meetings were held in December 2007 and testing began in early 2008.

With the owners’ permission, the EPA first conducted air and soil sampling at target properties to determine whether VOC vapors were entering indoor air. This involved drilling a small hole in the floor of the slab, basement or crawl space of the building to collect a sub-slab vapor sample.

If analysis of the sample results indicated elevated VOC vapor levels, the EPA double-checked slabs, basements, crawl spaces, and outdoor and indoor air. Staff performed another round of indoor air sampling after removing all household cleaners and paints, which can be a source of VOCs in indoor air.

If VOC concentrations exceeded screening levels, the EPA took all steps necessary to fix any problems found and to protect the health and safety of residents. Sub-slab depressurization systems (soil vapor intrusion mitigation systems) were installed in about 40 homes. Remediation was free of charge to homeowners.

The EPA’s work was completed in June 2008.

Since then, the MPCA has undertaken additional studies to identify chemical release source areas and the parties responsible for the releases. Follow-up work has been done also to assure that the vapor mitigation systems continue to be effective and determine whether the VOC vapors had traveled to other areas.