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TCE soil vapor in the Como neighborhood of Minneapolis

Update on access agreements and mitigation

  • Number properties/buildings with sub-slab sample results: 318
  • Number properties/buildings over 20 ug/m3: 153
  • Number properties/buildings less than 20 ug/m3: 165
  • Number of properties/buildings within mitigation area this week: 146
  • Number of properties/buildings with mitigation complete in mitigation area: 81
  • Percent of properties/buildings in mitigation area that have mitigation complete: 55%
  • 177 access agreements signed in the original study area (91% of the 195 properties)

General Mills vapor study community office hours

April 29 and May 27, 4-6 p.m.
Van Cleve Recreation Center (901 15th Ave SE, Minneapolis)

This type of outreach is targeted for one-on-one communication with residents and property owners. Representatives from the Minnesota Pollution Control Agency, Minnesota Department of Health, Barr Engineering and General Mills will be available to answer any questions, address concerns, and make the sampling and mitigation access agreements available to review and sign. The format will be like an open house — attendees may come at any point during 4-6 p.m.

Next steps in process

Click image for a larger view

general-mills-site-timeline-530

Current maps of sampling

The following map shows the status of sampling in the Como neighborhood study area. Note, we will update the map every two weeks. Click image for larger view.

Below is the building mitigation status map. The purpose of the map is to show which buildings are in the mitigation area, where additional investigation is needed and where long-term monitors will be installed. Click image for larger view.

TCE Como building mitigation status map

The following map shows the sampling status.  Click image for larger view.

Map of Minneapolis Como neighborhood TCE vapor intrusion sampling

The following map shows the sampling range of properties that have TCE levels above 20.  Click image for larger view.

Map of sampling range of properties that have TCE levels above 20

Area of concern

The following map shows the area of concern in the Como neighborhood of southeast Minneapolis.

Map of Como neighborhood of SE Minneapolis with area of concern

Notice to residents and property owners

On Wednesday, November 6, 2013, the Minnesota Department of Health (MDH) and Minnesota Pollution Control Agency (MPCA) sent a joint letter to owners and occupants of residences in part of the Como neighborhood of southeast Minneapolis to alert them to an ongoing investigation of potentially harmful trichloroethylene (TCE) vapor from contaminated groundwater that may be intruding into their homes. TCE is a commonly used cleaning solvent and degreaser. The priority testing area is shown on the map.

The letter informed residents that although there is no immediate or urgent health concern — more investigation and testing needs to take place in their residences to evaluate actual risk and determine the correct response.

TCE was used as an industrial solvent at a former General Mills Inc., research facility at 2010 E. Hennepin Ave. in Minneapolis in the 1940s until the early 1960s. During that time, waste TCE was disposed of in a pit on the property. The contaminated site has been known about for more than 30 years.

Cleanup of former General Mills site

General Mills, under the oversight of the MPCA, pumped and treated groundwater for 25 years at the Hennepin Avenue site to remove the TCE from it. Based on extensive groundwater testing over many years, data demonstrated that TCE concentrations in the groundwater significantly declined and the groundwater plume has stabilized. With approval from the MPCA, the treatment systems were shut down in September 2010 and monitoring was increased to determine whether the system can remain shut down.

 

Drinking water in the area was never a health issue because this area is served by city water and there were no wells that drew from the contaminated plume.

Soil vapor testing was required as part of this process. In October 2013, data showing TCE in soil gas samples taken on public rights of way in the area prompted the alert to property owners and residents.

How vapor intrusion happens

diagram showing vapor-intrusion from groundwater through soil to basement of house

Investigating houses for vapor intrusion

At the open houses on November 12, residents and property owners will be informed of the testing locations and procedure as well as the potential health risks of TCE. Environmental testing at the properties will be performed in the method approved by the MPCA. Testing of the soil gas below the houses will begin as soon as testing and mitigation plans are approved and access agreements are signed by property owners.

If TCE levels in the soil beneath any building or home are above the safe level set by the MPCA and the MDH, General Mills has agreed to install vapor ventilation systems, which work like radon mitigation systems. Such systems are a proven solution for vapor-intrusion problems; homes with existing radon mitigation systems may already be effectively mitigated for TCE in indoor air.

The MPCA and MDH are asking for the public’s assistance in this process. To ensure quick response times, officials with the MPCA and the MDH encourage all residents and property owners to cooperate by allowing access for tests inside their residences.

There will be no cost to residents or property owners for testing or mitigation. Vapor intrusion mitigation systems will be offered and installed at no cost in affected homes. Access agreements will be available at the public meetings as well as on this webpage.

Project teams will visit homes and buildings in the study area during the next several weeks seeking access to complete the appropriate tests in the soil beneath certain homes in the area of concern. Officials with the MPCA and MDH are encouraging residents and property owners to cooperate by allowing access for tests inside and around their residences.

There will be no cost to residents or property owners, and vapor-intrusion mitigation systems will be offered and installed at no cost in affected homes. The sub-slab (below basement floor) testing will begin November 18, 2013, provided property owners have signed access agreements.

Questions and answers for property owners and residents

Why am I being asked to participate?

Your property is in an area that the MPCA and the MDH have identified as the investigation area to test for elevated levels of TCE.  Tests also found TCE vapor in public rights of way, south and west of the Hennepin Avenue site.

Why are we concerned about TCE vapors in indoor air?

MDH staff has reviewed the soil-gas data collected at this site and are concerned that vapor intrusion may be occurring.  Once inside the building, vapors can be inhaled by residents.  If vapor intrusion is occurring, it is likely that vapor levels are higher in basements than on upper floors.

The groups considered to be more sensitive to potential health effects from breathing in TCE vapor include unborn children, infants and children, and/or people with impaired immune systems. Because of the risk of heart defects occurring in developing fetuses, MDH is concerned about TCE exposures in women who are pregnant or who may become pregnant. 

If I can't smell TCE in the air, am I being exposed?

Some people may be able to detect TCE at levels lower than the reported odor threshold, and some people may only detect it at higher concentrations. Just because you can’t smell TCE doesn’t mean there is no exposure. Sampling and testing is the best way to know if TCE is present.

How will the sampling be done?

With the owner’s permission, licensed contractors will conduct sampling at the target properties to see whether contaminated soil vapors are potentially underneath your home or building. The first step in sampling each residence will be to collect a sub-slab vapor sample. This involves collecting a vapor sample from directly beneath the basement floor through a small hole drilled in the floor, which takes about 45 minutes. Sub-slab samples can be more accurate than indoor air samples, which can be cross-contaminated by common household products, such as cleaners and adhesives.

If TCE is detected at my property, how will it be cleaned up?

If the sample results indicate TCE vapor levels above MPCA screening levels, licensed contractors will install a sub-slab ventilation system in the overlying structure.  This system is the same as a typical “radon system” commonly 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.

Contacts

For more information or if you have questions or comments, contact these representatives:

Minnesota Pollution Control Agency (for project or testing questions)
Edward P. Olson, CEP, Project Manager, Site Remediation 1, 651-757-2627, edward.olson@state.mn.us
Fred Campbell, Site Remediation 1, 651-757-2260, fred.campbell@state.mn.us
Hans Neve, Site Remediation 1, 651-757-2608, hans.neve@state.mn.us

Minnesota Department of Health (for health-related questions)
Rita Messing, 651-201-4916 or Emily Hansen, 651-201-4602
Site Assessment and Consultation Unit, 651-201-4897 or 800-657-3908
Email: health.hazard@state.mn.us
website: www.health.state.mn.us/divs/eh/hazardous/topics/tce.html

To schedule sampling, call Barr Engineering, 952-842-3505.

To contact General Mills, call 763-293-1165.

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Last modified on April 14, 2014 10:46

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