The TCE concentrations detected in soil vapor at the greatest concentrations along the sewer line, according to the report, are east of the facility where 1,270,000 ug/m3 was registered and near the Bent Tree manhole where 726,000 ug/m3 was registered.

Soil vapor sample results collected in 2015 and 2016 on the north and east sides of a former manufacturing plant in Camdenton show trichloroethylene (TCE) concentrations ranging from 5.84 micrograms per cubic meter of air (ug/m3) to 1,270,000 ug/m3.

The Missouri Department of Natural Resources (MDNR) is currently reviewing the Phase 1 Sitewide Soil Vapor Investigation Report submitted in August 2017 by CH2M Hill Engineers, Inc. of St. Louis, who were contracted by Modine Manufacturing.

Modine Manufacturing purchased the plant in 1990 and conducted manufacturing operations until its closure in 2012. “TCE has not been used or disposed of at the Sunset Drive facility since Modine took ownership of the facility,” according to Modine documents.

Prior to Modine taking ownership of the plant at 221 Sunset Drive, it was owned and operated by Dawson Metals and Hamilton Sundstrand. Beginning in 1967, these companies used the degreasing chemical to clean metal parts on a regular basis through 1990, according to MDNR records.

While there have been other investigations of TCE disposal in Camdenton, the purpose of this one was to determine the overall presence of volatile organic compounds (VOCs) in soil vapor, soil and groundwater, and assess the migration pathways from the facility toward other offsite properties.

“The investigation was not intended to identify all of the source(s) of TCE detected in soil vapor, but did identify the sewer lines as a likely conduit from which TCE releases to the environment occurred,” the report stated.

In May 2017, investigators used ground penetrating radar to survey the entire building while attempting to locate a previously undetected major source of TCE contamination that was announced in 2016. Data captured by closed circuit television cameras that explored piping discovered 12-feet below ground is being analyzed.

“The driver for this investigation were the results of the previous soil vapor and indoor air investigations conducted at the facility and in the adjacent residential area in 2015 and 2016,” the MDNR report states.

Those results included a total of 285 various samples from indoor air, subslab, soil gas and groundwater that were taken across 24 residences near the facility. Two homes have had mitigation systems installed while eighteen residences have completed the quarterly sampling program. Four remain in the quarterly sampling program. 

Samples collected from the north and east sides of the building included soil boring advancement and soil sampling, monitor well installation, groundwater sampling, vapor sampling, vacuum testing and surveying, according to the report.

A total of 21 soil borings were advanced using rotosonic drilling methods, so samples could be collected from deep borings from the surface and subsurface soil cores. Soil samples were collected from 27 total monitoring wells that were installed during the Phase 1 investigation. Five VOCs were detected, including TCE which was detected in every sample.

“TCE detections in shallow soil vapor range from 5.84 J micrograms per cubic meter (ug/m3) to 1,270,000 ug/m3. TCE detections in deep vapor ranged from 8,030 ug/m3 to 726,000 ug/m3,” according to the results.

“With the exception of one shallow and deep monitoring well pair (MW-113S and MW-113D, near the sewer line and MW-118S), TCE in shallow soil vapor (20 feet below ground surface (bgs) or less) is at lower concentrations than TCE in deeper soil vapor (greater than 20 bgs).”

The TCE concentrations detected in soil vapor at the greatest concentrations along the sewer line, according to the report, are east of the facility where 1,270,000 ug/m3 was registered and near the Bent Tree manhole where 726,000 ug/m3 was registered.

TCE concentrations in subsurface soil ranged from 0.0116 J to 1.26 mg/kg. The highest confrontations of TCE in groundwater was observed in April and October of 2016 at MW-101 and MW-106, located adjacent to sanitary sewer manholes.

“Approximately 18 cubic yards of soil impacted by TCE was removed from the Bent Tree manhole (adjacent to MW-105) in December 2010 by Golder Associates, a City of Camdenton contractor (Golder Associates 2011),” the report states. “However, TCE in soil vapor was detected in well MW-105, adjacent to this soil removal location, at 726,000 ug/m3. This indicates that the contaminated soil removal activity may have been incomplete and residual soil contamination at this location represents an ongoing source of TCE to soil vapor.”

Phase Two for the work plan will involve further investigation underneath the building that is scheduled to begin in early 2018, according to MDNR. 

“TCE (and its associated degradation products) is the site-specific VOC that is most widely present and has the greatest potential for vapor migration. VOC concentrations in surface soil are below residential health-based levels of concerns. TCE concentrations in subsurface soil were, in some cases, above the industrial health-based level of concern,” according to the conclusions and path forward section of the report.