On September 22, 2023, the Maryland Heights TCE site was referred to EPA Region 7 by the Missouri Department of Natural Resources (MoDNR) to address vapor intrusion risk associated with a trichloroethylene (TCE) groundwater plume of uncertain origin or extent, with a primary concern regarding a commercial property on Adie Road where soil gas sampling conducted near the building identified elevated TCE concentrations.
On April 17 and 18, 2023, EPA Region 7 mobilized to the site and conducted a removal site evaluation sampling event at the Adie Road property to evaluate the building for vapor intrusion issues. The office area indoor air TCE concentrations ranged from 8.9 to 17 micrograms per cubic meter (μg/m3), exceeding the EPA commercial Removal Management Level (RML) of 6 μg/m3. On May 19, 2023, EPA Region 7 delivered the results of the April 18 sampling event to the property owner which indicated that TCE vapor intrusion was occurring with indoor air concentrations exceeding the EPA commercial RML. Following the transmission of sample results, the owner expressed a willingness to follow EPA recommendations and conduct a PRP removal action.
On July 18, 2023, the Potentially Responsible Party's (PRP's) contractor, Radon Control Services, Inc., installed a depressurization system for the office area. On August 8, 2023, the PRP's contractor, EOI, conducted an inspection of the sub-slab depressurization system and an indoor air sampling event for the office area with the sub-slab depressurization system. On August 25, 2023, PRP delivered the EOI report “Vapor Intrusion Mitigation System Installation/Inspection and Indoor Air Sampling Results” to EPA Region 7 that presented the results of the August 8 PRP sampling event. The indoor air sample results provided in the report summary table indicated that TCE concentrations were all reported as non-detect indicating installation of the depressurization system was successful in addressing indoor air impacts.
The PRP removal action was completed on August 25, 2023. On November 6, 2023, the site was referred to the EPA Site Assessment Program for further evaluation.
