Challenge

From 1970 to 2014, a dry cleaner operated in the City of Watsonville and discharged wastewater containing tetrachloroethene (PCE) to the City sewer during its operations. After the dry cleaner closed, the City needed to assess the extent of impacted soil, soil vapor, and groundwater caused by the PCE from the operation southeast of the former facility near residential properties and commercial businesses.

Solutions

Geo-Logic Associates has provided a range of hydrogeologic services for the City, including groundwater monitoring and analysis, and preparing a Corrective Action Plan (CAP). The CAP was prepared for the City under Regional Water Quality Control Board review and approval that summarized numerous prior efforts to characterize groundwater occurrence and flow direction and address groundwater quality impacts.

GLA conducted a community outreach with Regional Board personnel to inform the community of the upcoming corrective action, including door-to-door visits and mailings to request access to residential properties for environmental sampling. In order to evaluate environmental impacts, GLA analyzed the results of several rounds of sampling in area groundwater monitoring wells, soil vapor probes, subslab vapor probes, crawlspace vapor samples, and indoor air and ambient air samples, and developed groundwater equipotential maps to characterize a flow divide in the area. Our team evaluated potential commercial and residential human health impacts due to groundwater impacts and resulting indoor air vapor intrusion and designed a plan to implement in-situ chemical reduction, reductive dechlorination, micro-scale carbon adsorption, and bioaugmentation for groundwater remediation involving numerous groundwater injection points. A soil excavation and sewer line repair were also completed with backfill material consisting of a zero-valent iron (ZVI) amendment.

Results

Groundwater impacts have declined significantly following the in-situ treatment program and the City is pursuing a reduced monitoring program to support regulatory closure.