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Jan 17, 2014

Minneapolis soil vapor testing more than two-thirds complete

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MINNEAPOLIS -Testing has been completed in more than two-thirds of the homes and buildings being studied for the possible presence of TCE in soil vapor in the Como neighborhood of Minneapolis.

Of the approximately 200 properties in the study area, 143 homes and buildings have already been sampled. An additional 15 homeowners have completed access agreements to allow testing, bringing the total number of access agreements to 158.

Test results are shared with homeowners by phone as soon as they are received from the independent laboratory analyzing the sample.  Copies of the test results are also mailed to homeowners following the phone notification.

Ninety-two properties in the study area have been found to have levels above the very protective screening level set by the Minnesota Pollution Control Agency (MPCA) and have been offered vapor ventilation systems.  Vapor ventilation systems are a proven solution to the issue of vapor intrusion. 

Thirty-seven homes have been found to be below the screening threshold set by the MPCA.   Thirteen additional homes tested between two and 20 micrograms per cubic meter, and all 13 of those homes will be retested.  If the second sample confirms the level is below 20 micrograms per cubic meter of air, no further testing would be necessary, and vapor ventilation system would not be required.

As of today, one test result is awaiting analysis at the independent laboratory, which analyzes samples on a 24-to 48-hour turnaround.

The installation of vapor ventilation systems is also underway.  Thirty vapor ventilation systems have been installed to date, with additional installations being completed weekly.  Seventy-six homeowners in all have scheduled or held design meetings, a step that precedes the system installation, at which a licensed contractor meets with the homeowner to discuss and design a vapor ventilation system and installation plan for the home.  Installations proceed thereafter based on the homeowners’ schedule.

In the soil vapor study, if TCE vapor is found to be present above the screening level set by the MPCA, homeowners are being offered a vapor ventilation system at General Mills’ expense.  Such systems, identical to radon mitigation systems, are “a proven solution to radon and vapor intrusion problems,” according to the MDH.  The cost of offered vapor ventilation systems, if necessary, will be fully paid by General Mills, along with maintenance costs. 

The study, announced Nov. 7, is assessing whether TCE vapor may be present beneath the basement floor or slab of homes and buildings in the study area.  TCE may be present in the soil vapor as a result of historic waste disposal activities at 2010 East Hennepin Avenue, a site owned by General Mills from approximately 1930 until 1977.  TCE is a common industrial solvent and degreaser.  It may also be found in household products such as wood finishes, adhesives, paint removers, lubricants, and cleaners. 

Beginning in the 1940s, until the early 1960s, solvents were disposed in a manner customary for the times in an absorption pit located in the southeast corner of the property.  General Mills sold the site in 1977, but the discovery of TCE in the soil at the historic disposal site in the early 1980s led to extensive clean-up activities.  The disposal area was excavated and the soil was removed.  Extraction and treatment of shallow-level groundwater (non-drinking water) to stabilize and contain the migration of TCE also began in 1985, and continued for 25 years.  Drinking water supplies were not impacted.

Based on extensive groundwater testing over many years, data demonstrated that TCE concentrations had declined to below established cleanup levels for the site.  With approval of the MPCA, the shallow-level groundwater treatment systems were shut down in September 2010.  To address the emerging issue of vapor intrusion, the MPCA requested that General Mills investigate the potential for TCE vapors from the shallow groundwater to accumulate in the soil gas under buildings in the area.  Soil vapor testing was then conducted, and in September 2013, TCE was found to be present in the soil gas in several samples taken on public rights-of-way in the area, prompting this study. 

All activities are conducted by General Mills under the oversight of the MPCA.

As anticipated, as the study has progressed, additional homes have been added to the study area based on the data collected.  As a result, access agreements have been sought for approximately 100 additional properties.  Fifty-five access agreements have been received for those properties, and 39 have already been sampled.  Nine of those properties tested above MPCA screening levels and have been offered vapor mitigation systems.  Nineteen properties tested below the screening threshold set by the MPCA.  An additional seven properties tested below 20, but above 2 micrograms per cubic meter, and will be resampled.   Test results are pending for four additional properties. 

Area residents can ask questions and meet with representatives from the MPCA, MDH, Barr Engineering and General Mills at an additional meeting next week.   Organized as an “open house,” the meeting enables residents to simply come when available during the times listed.  Sampling and mitigation access agreements are also available to review and sign.

An open house meeting will be held:
January 28, 4-6 p.m.
Van Cleve Recreation Center (901 15th Ave SE, Minneapolis)
 
Additional updates will be provided as the study progresses.

Contact:
Kirstie Foster
General Mills
(763) 764-6364