Mound: Tonka Main Plant

The Tonka Main Plant Superfund Site is located at 5300 Shoreline Drive, between two bays of Lake Minnetonka in Mound. Between 1954 and 1982, the Tonka Corporation manufactured children’s toys, and used the solvent trichloroethylene (TCE) as part of the manufacturing process. In 1986, after the plant closed, TCE contamination was discovered underground. Testing found that contamination moved off the property to the north toward Lake Minnetonka.

Hasbro Inc. purchased Tonka Corporation in 1991, and took responsibility for the required environmental testing and cleanup. To protect the lake and nearby city wells, Hasbro’s contractors constructed a wetland that treats the contaminated groundwater.  Wells that provide drinking water to the city of Mound are not at risk from this contamination.

Map of Tonka Main Plant at 5300 Shoreline Drive, Mound

Hasbro sold the property in 1995. It is now occupied by the Balboa Business Center, and used by several businesses for industrial purposes. This happened before there was an understanding of the risk from vapor intrusion and our current understanding of health risks from TCE. Vapor intrusion occurs when chemicals evaporate and the vapors migrate up through the soil. These vapors can enter homes or businesses through cracks or other pathways through a building’s foundation.

Testing for vapor intrusion began in residential areas adjacent to the former plant in 2011, and did not find a vapor intrusion risk in the residential area. Additional testing in 2012-2013 did discover high vapor levels under the former plant building. Because of high TCE vapor levels and new understanding of the short-term health risks for pregnant women and healthy fetal development from TCE exposure, the MPCA directed Hasbro to take expedited action in December 2016.

Health concerns

Indoor air was tested and the results showed that concentrations of TCE are above levels of health concern, especially for women who are pregnant or may become pregnant. Breathing in TCE during the first 2-3 months of pregnancy may increase the risk of heart defects to the baby. If you are pregnant or trying to become pregnant, the Minnesota Department of Health (MDH) recommends that you avoid spending time at the site until levels of TCE in the indoor air decline.

Other health effects from TCE may occur if people breathe high concentrations of TCE vapors in the air over many years. For more information, please see the MDH fact sheet on TCE in Air.

Health protection measures

Some work has already been done to seal possible pathways for vapors to enter the building. Ten air purifiers were installed in early March as a temporary measure to remove TCE from the indoor air to provide protection for workers in the building.

Additional investigation and evaluation is needed to determine the best long-term solution to vapor intrusion issues at the site. One remedy for these situations is to install a soil vapor mitigation system, which operates like a system used to control radon.

More about vapor intrusion

Groundwater contaminated with TCE or other chemicals can release vapors that could rise through the soil and seep through basement and foundation cracks into homes and other buildings, where it could be inhaled by people.

If a person breathes in low levels of contaminants in indoor air for a long time, there is an increased chance that 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.

For more health-related information, visit the MDH's Vapor Intrusion webpage.


Andri Dahlmeier

Minnesota Department of Health