Site Characterization, Interim Remedial Action and Groundwater Monitoring at Former Carpet Cleaner

Multiple environmental investigations performed at this property discovered that environmental media (soil, groundwater, and indoor air) are impacted by volatile organic compounds (VOCs) to such an extent that may represent a risk to human health or the environment. Historical records indicate that releases of tetrachloroethene (PCE) and trichloroethene (TCE) may have resulted from the use of solvents during former carpet and upholstery cleaning operations.

TRC conducted a vapor intrusion assessment, a subsurface investigation, and an interim remedial action at the property. TRC’s investigations confirmed that though indoor air is not impacted, soil is impacted with PCE and TCE to the depth of groundwater and is a source of continuing impacts to groundwater through dissolution and dispersion. Groundwater sample results also confirm impacts by PCE, TCE, and breakdown products cis-1,2-dichloroethene and vinyl chloride. TRC also identified groundwater impacts extending off-property to the west and that impacts may also extend to the south.

Based on the investigation results, TRC conducted an interim remedial action to remove the source areas to limit future dissolution of compounds absorbed to soil. This removal was also intended to allow the off-property impacts to attenuate naturally, decreasing our client’s potential exposure to third-party liability. The excavation was challenging, as it was conducted entirely within the building located on the property. TRC used a licensed structural engineer to assist with designing the shoring design and to identify where temporary structural reinforcements should be placed during excavation. TRC prepared a contained-in determination request that was approved by the Washington State Department of Ecology (Ecology) because the maximum detected concentrations of PCE and TCE were considerably less than the threshold criteria. As a result, the excavated material was able to be disposed at a Subtitle D landfill.

The interim remedial action was completed successfully with performance sampling results clearly demonstrating compliance with the Model Toxics Control Act (MTCA) cleanup levels throughout the excavation area. The first groundwater monitoring results after the interim remedial action showed an improvement in water quality. TRC will conduct ongoing groundwater monitoring to further assess trends in groundwater quality improvement and to identify if enhanced reductive dechlorination (ERD) should be implemented to further accelerate the attenuation of impacts in groundwater at the property.