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As of June 20, 2008, U.S. EPA has collected 269 sub slab samples, 220 from residential properties, and 49 from commercial/industrial properties. Fourty-one residential properties had sub slab results over MDH's screening level for PCE and/or TCE. Also, 12 commercial/industrial properties exceeded the MDH's screening levels.
EPA collected indoor air samples at 52 properties; 40 residential, 12 commercial. One residential property owner denied access for the indoor air sampling.
Indoor air sampling results showed exceedances to the MDH's indoor screening level for TCE and/or PCE at 8 residential properties. An additional 3 residential properties exceeded MDH's combined hazard index. Five commercial properties exceeded the MDH's indoor commercial screening levels.
A decision was made to offer a vapor abatement system to all residential properties with sub slab exceedances, regardless of the indoor air sampling results. Installation of vapor mitigation systems at these properties began on March 17, and as of June 20, all 40 systems have been installed.
Abatement system performance sampling began, and so far 33 properties have been sampled. All properties sampled showed dramatic reduction in the levels of VOCs. Three residential properties still exceeded sub slab screening levels, and one property exceeded the indoor air screening level but not the sub slab, which might be indicative of an indoor source.
All 40 residential properties where abatement systems were installed, will be sampled 30 and 90 days after system installation. Any necessary adjustment to the systems will be made after the 90-day performance sample.
Also, during this reporting period, the first round of groundwater samples was collected the week of June 9, and another groundwater sampling event will take place in December 2008, as part of the ongoing groundwater investigation.
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