A former manufacturing facility had a long history in supplying hydraulic hose components for the aircraft and automotive sectors, with manufacturing pre-dating the 1940s. Because of the presence of degreasing and chrome plating operations throughout the facility, multiple known and unknown source areas required investigation and characterization. Studies performed by TRC on behalf of the client identified the presence of significant chlorinated solvent contamination in soil and groundwater inside and outside of the manufacturing facility. Concentrations of volatile organic compounds (VOCs) in soil and groundwater underlying the manufacturing facility were above concentrations accepted to be protective of the indoor air pathway. TRC worked with the client during the sale of the facility so that the property could remain in use by the purchaser, while corrective measures were performed.
The project's high degree of complexity required a variety of hydrogeological and engineering skills to mitigate the potential vapor intrusion pathway to levels below the remedial goals (RGs) established for the project. TRC performed final Corrective Measure Implementation (CMI) activities, which included in situ chemical oxidation (ISCO) and in situ thermal desorption (ISTD) to address shallow affected soil and groundwater, and in situ biostimulation/monitored natural attenuation (MNA) of the bedrock aquifer to achieve the negotiated RGs. Groundwater and indoor air monitoring are currently being performed to demonstrate that RGs have been achieved.
The presence of highly affected soil and groundwater under the main site building required the evaluation of the vapor intrusion pathway. Soil gas sampling performed by TRC indicated that soil gas samples exceeded screening levels. Additionally, indoor air samples were collected and submitted for analysis of VOCs. Data showed that, under existing conditions, chlorinated VOC concentrations in indoor air had the potential for long–term risk to facility workers.
Because the facility was in use during the implementation of corrective measures, as a short-term solution, TRC industrial ventilation experts developed a strategy to modify the HVAC operational conditions to reduce indoor air concentrations to levels below the RGs inside the manufacturing facility. During the remediation efforts, indoor air samples were collected on a quarterly basis to ensure that VOC concentrations did not pose an unacceptable risk to workers.
As recommended by TRC, and agreed to by the USEPA, the ISTD that was implemented to treat soil and groundwater beneath the building successfully removed the primary source of VOCs that were volatilizing to indoor air and assisted in achieving the indoor air concentrations protective of workers. In addition, the treatment of soil was completed to levels acceptable to the USEPA. Continued monitoring of groundwater shows that the primary VOC of concern, trichloroethene (TCE), have been reduced to concentrations below the site RGs.
Because the RGs for indoor air established by the USEPA were very conservative, and the floor in the manufacturing facility was in poor condition, the potential for vapor intrusion was not completely eliminated by the operation of the ISTD. Therefore, TRC subcontracted an industrial flooring company to install an epoxy coating over the former plating area (approximately 10,000 sq. ft.) to act as a vapor barrier and assist in mitigating the potential for vapor intrusion. As a result, VOC concentrations in indoor air have met the RGs, and there is no need for long-term vapor mitigation strategies (e.g., sub-slab ventilation or sub-slab depressurization).