Modesto Ground Water Contamination

Overview

A dry cleaning facility in Modesto, California is the source of soil and groundwater contamination that earned this site a spot on the EPA's National Priorities List in March 1989. The site sits in Stanislaus County and is managed across two operable units. The most recent Record of Decision was issued in August 2021, updating a cleanup plan originally set in 1997. Long-term response actions are expected to continue through mid-2027, and a feasibility study for the overall site is scheduled to begin in March 2025.

The main contaminants are tetrachloroethene (PCE), trichloroethene, and toluene. PCE shows up in groundwater, soil, soil gas, air, and other tested media. Trichloroethene was detected in soil gas, air, and groundwater. Toluene was found only in groundwater. EPA flagged all three because they pose an unacceptable risk to human health or the environment.

An interim remedy has been running since 2000. It includes a groundwater extraction and treatment system that has processed roughly 342 million gallons of water and removed about 720 pounds of PCE. A soil vapor extraction (SVE) system has pulled approximately 3,500 pounds of volatile organic compounds from the soil. The SVE system was expanded in 2008 and again in 2023. The groundwater system gained an extra extraction well in 2012. The 2021 Record of Decision calls for enhancing the SVE system while keeping the current groundwater system in place. A $1.5 million grant from the Bipartisan Infrastructure Law in 2022 is funding improvements that include horizontal extraction wells, a faster blower, real-time gas sensors, automated controls, and a new supervisory control system.

Current performance shows that groundwater migration is not yet under control and human exposure data is insufficient to confirm whether exposure pathways are fully controlled. Physical construction is not complete and the site has not been deleted from the National Priorities List. A Five-Year Review completed in September 2023 offered recommendations for further improvements, and a Record of Decision Amendment is estimated for late 2028. Routine monitoring and maintenance continue under state and EPA oversight. One business currently operates on the site, employing six people and generating about $427,640 in annual sales.

Community members with questions can contact the EPA's Community Involvement Coordinator or the Remedial Project Manager.