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Highway 100/County Road 3 Groundwater Plume

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EPA proposes site to National Priorities List; comment period now closed

Update (Feb. 27, 2019):  The National Priorities List (NPL) proposed rule (84 FR 60357), which proposes adding Highway 100 and County Road 3 and four other sites to the NPL, was published in the Federal Register Nov. 8, 2019. The comment period for the proposal, which was scheduled to end Jan. 7, 2020, was extended through Feb. 6, 2020 and is now closed.  Visit Current NPL Updates: New Proposed NPL Sites and New NPL Sites (EPA) to learn more.

EPA proposes site to National Priorities List 
On Oct. 30, 2019, U.S. Environmental Protection Agency (EPA) announced the proposal of the Highway 100 and County Road 3 Groundwater Plume Site to the National Priorities List (NPL), which would make the site eligible for investigation and cleanup under the Superfund program. The City of St. Louis Park is pleased that this process, which was announced to residents in early September, is proceeding. The city is in full support of this action to ensure the ongoing health and safety of residents and that those who caused the contamination are held responsible. Visit Current NPL Updates: New Proposed NPL Sites and New NPL Sites (EPA) to learn more.

In mid September 2019, St. Louis Park residents received a special mailing, St. Louis Park's Industrial Legacy (PDF version), about the site.

History of the site

In April 2004, the Minnesota Pollution Control Agency (MPCA) began searching for the source of vinyl chloride contamination that had been detected in several City of Edina wells that drew water from the Prairie du Chien-Jordan Aquifer. Between 2006 and 2017, following sampling test borings as well as both deep and shallow wells, the source was traced back to an area near Walker and Lake streets in St. Louis Park. While an exact source hasn’t been identified, it’s important to note that the businesses associated with the chemical release no longer operate in these areas; contamination in the groundwater is from previous uses.

In 2007, MPCA sampling of test borings and shallow aquifer wells in St. Louis Park detected high concentrations of certain chlorinated solvents in groundwater, which could cause vapor intrusion into buildings. The MPCA focused on evaluating soil vapor in the residential and commercial neighborhoods north of Highway 7 and south of Highway 7. The data indicated that the trichloroethane (TCE) and percholorethylene (PCE) vapors in the soil were high enough to adversely affect indoor air quality in homes and businesses.

Visit this MPCA storymap for more information.

Health concerns addressed

Any health concerns related to vapor intrusion or drinking water safety as a result of this site have already been addressed by the MPCA, EPA and cities of St. Louis Park and Edina. Since the early 2000s, the city has been working successfully with the MPCA and the EPA to ensure the safety of its drinking water and to protect residents from any adverse effects of this contamination. The City of St. Louis Park is in full support of this step to ensure those responsible for the contamination are held responsible and to ensure the ongoing health and safety of residents.

The current activity is to pursue funding and further investigation into those responsible for the contamination.

Below are activities that have already been completed to protect residents’ health.

Vapor intrusion study/cleanup

In 2008, the EPA assisted in vapor testing 220 homes and 49 businesses in the Lenox, Sorenson and Elmwood neighborhoods, and in parts of the Brooklawns neighborhood. Following testing, 41 homes with elevated levels of volatile organic compounds  (VOCs) in their indoor air or in the soil beneath their homes were offered vapor extraction systems at no charge; 40 homes had the systems installed. Learn more about the study and cleanup.

Water Treatment Plant #4

Water Treatment Plant #4 (WTP4), located at 4701 W. 41st St. in St. Louis Park, was taken out of service at the end of 2016 after aggressive, regular testing showed that while some VOCs were being reduced by an implemented short-term treatment solution, others were increasing. The VOCs were believed to result from the Highway 100 and County Road 3 Groundwater Plume Site.

The city was advised in early 2016 of exceedances of health risk levels, set by the Minnesota Department of Health (MDH) and at much lower limits than those of the EPA, for some types of VOCs at WTP4. At that time, the city had already been working with MDH to develop a short-term solution to lower VOCs at the plant. This short-term solution showed positive results for lowering certain VOC levels, including vinyl chloride, so the plant remained in service. However, later testing revealed an increase in other VOCs such as trichloroethene (TCE); it’s those test results that prompted the decision to take WTP4 out of service.

The decision to take WTP4 out of service was made out of an abundance of caution and to preserve public trust in the quality of the city’s drinking water. Even though water was meeting safe drinking water standards set by the EPA , aggressive, regular testing continued to suggest that water quality at this plant was not where the city wanted it to be.

The city worked with the MPCA and MDH to design and implement upgrades in 2017 and 2018 to treat all identified contaminants, regardless of their source, down to published advisory levels. The upgrades included two air stripper units to treat the VOCs found in the water at this plant as well as many other upgrades, primarily to the interior. Following the re-opening of the plant in early 2019, residents were invited to attend tours at the plant to learn more about WTP4 and how the city produces water.


2004 – MPCA begins searching for source of vinyl chloride contamination in City of Edina wells

2006-2017 – Source is traced back to area near Walker and Lake streets in St. Louis Park

2008 – EPA conducts vapor testing in 220 St. Louis Park homes; installs vapor extraction systems in 41 homes to ensure safe indoor air quality

2008-2018 – MPCA continues investigation

2016 – Water Treatment Plant #4 taken out of service due to an increase in some VOCs

January 2019 – Water Treatment Plant #4 reopens following upgrades to remove VOCs

October 2019 – Highway 100 and County Road 3 Groundwater Plume Site recommended for EPA’s National Priorities List

November 2019 - Published in the Federal Register; comment period opened through Jan. 7, 2020

December 2019 - Comment period extended through Feb. 6, 2020

February 2020 - Comment period closed

Your questions, answered

Is my drinking water safe?

YES! The drinking water in St. Louis Park is safe. Providing safe drinking water is the most important public duty we as a city have to our residents, and we take that duty very seriously. St. Louis Park's drinking water is regularly tested and must meet the drinking water standards set by the federal Safe Drinking Water Act, a requirement of any public water system. The Minnesota Department of Health (MDH) enforces these drinking water standards for public water supplies in Minnesota. MDH enforcement is based on the regular testing and monitoring of drinking water from public water supplies. Results of this testing are available to each consumer through an annual consumer confidence report which is distributed via mail each year to every household in St. Louis Park. View the city's drinking water reports.

Why is the Highway 100 and County Road 3 Groundwater Plume site proposed for the Superfund program’s National Priorities List (NPL)?

In partnership with the cities of St. Louis Park and Edina, the State of Minnesota has agreed to the NPL listing by the EPA because it needs additional resources to investigate and clean up the contaminated area and hold the polluters accountable. The groundwater contamination plume is at a depth of approximately 300 feet below ground and covers an undefined area in St. Louis Park and extending to Edina. The City of St. Louis Park is in full support of this step to ensure those responsible for the contamination are held responsible and to ensure the ongoing health and safety of residents.

The state has dedicated a large amount of funding and staffing to define the area to date; however, much work remains to be done. The amount of resources required to identify the source area, pursue potentially responsible parties and implement a cleanup plan far surpasses the amount of resources received each year by the state’s Superfund program.

Resources from the federal government will assist with additional investigation activities and bring in additional technical expertise and specialized legal counsel to effectively address the complexities of the site in a timely manner. If a potentially responsible party(ies) can be identified, cost recovery efforts can be pursued.

EPA’s Superfund program focuses on making a visible and lasting difference in communities, ensuring that people can live and work in healthy, vibrant places. The goal is to be an asset to the communities and enhance opportunities for growth and prosperity by deploying federal level resources to the valuable ongoing work started by the local and state governments.

Are there other NPL Superfund sites in Minnesota or across the nation that have groundwater plumes that provided a model for this listing?

Yes. Many of the more than 1,300 sites that have been listed on the NPL include a groundwater contamination plume. Two examples in Minnesota are the New Brighton/Arden Hills Superfund Site (also known as the Twin Cities Army Ammunition Plant or TCAAP Site) and the Baytown Groundwater Contamination site. The TCAAP Site plume extends under several cities, including New Brighton, Arden Hills, Columbia Heights, St. Anthony and Minneapolis. The Baytown Groundwater Contamination plume is approximately 5 miles long, covers about 7 square miles and extends from the eastern portion of the City of Lake Elmo through Baytown Township, West Lakeland Township and the City of Bayport to the St. Croix River.

What are the possible health effects of VOCs?

VOCs are typically described as human carcinogens and can also cause problems with liver and kidney function. The potential for VOCs to be a health concern depends on the toxicity and concentration of the contaminant, the exposure conditions, and the duration or exposure. Factors like age, health condition, gender, and exposure to other chemicals can impact potential health effects for individuals. For more information about VOCs visit this MPCA fact sheet and this information from the MDH

What effect does the Highway 100 and County Road 3 Groundwater Plume site have on property values?

We know from past experience with the Reilly site that this is, understandably, of great concern to homeowners. Unfortunately, there’s no clear-cut answer to this question. The EPA suggests that concerned property owners should consult a professional who can give a more accurate response to property value questions and concerns. Nevertheless, it is important to note that the impact of the plume is to the groundwater and not to residential properties’ surfaces. MPCA maps of the area delineate an estimated plume hundreds of feet below the surface and not surface contamination on residential properties. 

What’s the difference between the Reilly Tar & Chemical site in St. Louis Park and the Highway 100 and County Road 3 Groundwater Plume site?

These are two different chemical releases that were caused by different sources.

The Reilly Tar & Chemical Corp. (Reilly) contamination is mainly creosote, which contains polycyclic aromatic hydrocarbons (PAHs) that were at used in wood treating operations. Contamination at the Reilly site is the result of:

  • Wastes discharged directly to a ditch which flowed into a wetland on the southern side of the property.
  • Contaminated soil from leaky pipes and various processes that spilled during operations.
  • Creosote and waste materials that likely seeped down a Reilly process well located on the property.

The Reilly site has previously been listed on the federal National Priorities List (NPL). The EPA and MPCA, in partnership with the City of St. Louis Park, has been overseeing cleanup there since the late 1970s.

The Highway 100 and County Road 3 Groundwater Plume site contamination consists of volatile organic compounds (VOCs), including tetrachloroethylene (PCE), trichloroethylene (TCE), cis dichloroethylene (DCE) and vinyl chloride (VC), collectively known as chlorinated VOCs. PCE is an industrial solvent used to degrease metals. Under the right conditions, PCE can break down in the environment to form TCE, DCE and VC. MPCA staff have conducted investigations to identify the source of the release, but additional work is needed to complete the investigation.

Is the soil in my yard contaminated?

The proposed NPL listing is for the deep groundwater plume. The deep groundwater plume is at a depth of more than 300 feet. Due to its depth, the deep contamination does not affect the soil on individual properties.

The major concern of the deep groundwater plume is its impact to the cities’ municipal wells. To ensure safety of the drinking water, both the cities of St. Louis Park and Edina have installed treatment systems to ensure their drinking water meets the requirements of the federal Safe Drinking Water Act and the state’s drinking water guidance values. Once the site is placed on the EPA’s National Priorities List, the EPA and MPCA will continue working to identify sources of the deep groundwater contamination plume.

Does this mean that the volatile organic compounds (VOCs) are affecting a larger area than initially identified in 2008? 

According to the Minnesota Pollution Control Agency (MPCA), the 2008 vapor study was conducted to evaluate whether or not shallow  (e.g. less than 100 feet underground) groundwater concentrations of tetrachloroethylene (PCE) and trichloroethylene (TCE) were impacting indoor air quality. Deeper groundwater contamination that impacts the municipal wells does not present a risk for vapor intrusion. MPCA conducted additional testing in 2014 and 2015 to verify the extent of the vapor plume; no additional homes or businesses are believed to be impacted by vapor intrusion at this time.

Is a vapor extraction system the same as a vapor mitigation system? 

Although the terms vapor extraction system (VES) and vapor mitigation system are often used interchangeably, they are used for different purposes. VES is a technology to remediate contaminated soil by inducing a strong vacuum to remove volatile organic compounds (VOCs). Vapor mitigation systems are similar to radon systems. Air flow is induced just under the concrete slab floor in a basement or other lower level and discharges the air above the building. This gives the VOCs a preferential pathway outside so they do not accumulate inside homes or businesses.


National Priorities List: the list of sites of national priority among the known releases or threatened releases of hazardous substances, pollutants or contaminants throughout the United States and its territories. The NPL is intended primarily to guide the EPA in determining which sites warrant further investigation. Placement on the NPL make a site eligible for investigation and cleanup under the Superfund program.

Superfund program: EPA’s Superfund program is responsible for cleaning up some of the nation’s most contaminated land and responding to environmental emergencies, oil spills and natural disasters. To protect public health and the environment, the Superfund program focuses on making a visible and lasting difference in communities, ensuring that people can live and work in healthy, vibrant places.

Vapor intrusion: occurs when chemicals such as volatile organic compounds in groundwater give off dangerous gases that can seep into buildings through foundation cracks and holes, causing unsafe indoor air pollution.

Volatile organic compounds (VOCs): Volatile organic compounds are a group of chemicals used in solvents, paints and dry-cleaning fluid.  Breathing low levels of VOCs for long periods may cause an increase in health risks. Find more information at the MPCA and MDH.




City of St. Louis Park

Questions about drinking water, the Reilly site or the Highway 100 and County Road 3 Groundwater Plume Site:
Mark Hanson, public works superintendent

Questions about vapor intrusion related to the Highway 100 and County Road 3 Groundwater Plume Site: 
Brian Hoffman, director of building and energy

Minnesota Pollution Control Agency

Questions about the Highway 100 and County Road 3 Groundwater Plume Site:
Crague Biglow

Minnesota Department of Health

Questions about drinking water, VOCs or other health concerns:

U.S. Environmental Protection Agency (EPA)

Questions about the Superfund process: 
Heriberto León, community involvement coordinator, Superfund Division



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