San Gabriel Valley (Area 4) is a federal Superfund site in La Puente, California, covering about 23 square miles across the City of Industry, City of La Puente, and unincorporated Los Angeles County. It was placed on the National Priorities List in May 1984. Contaminated groundwater extends across more than 30 square miles of the broader San Gabriel Valley. Remedial investigation began in 1993, a cleanup remedy was selected in 1998, and construction work started in 2006 but is not yet complete across the full site.
The contamination affects groundwater in both shallow and intermediate water-bearing zones. Volatile organic compounds from multiple facilities are the primary drivers, and four specific contaminants of concern have been identified in the intermediate zone: 1,4-dioxane, chromium(VI), N-nitrosodimethylamine, and perchlorate. EPA determined all four pose unacceptable risks to human health or the environment. Human exposure is currently under control, meaning no unacceptable exposure pathways exist at this time, but contaminated groundwater has not been stabilized and continues to move.
Three groundwater extraction and treatment systems are being built to stop contamination from spreading and protect drinking water supplies. Carrier Corporation is designing and building a system north of Puente Creek that will extract, treat, and reinject water underground. A 2022 plan update added reinjection as a cost-saving measure worth about $10 million. Northrop Grumman Systems Corporation is operating south of Puente Creek, where extraction wells and a treatment plant were completed in 2024 and are currently in startup testing, with EPA certification expected in 2026. Northrop Grumman is also handling the intermediate zone, where a separate system completed in 2024 at the City of Industry is expected to receive EPA certification in 2027. All three systems are expected to run for 15 to 30 years once certified. Water utilities in the area currently provide clean drinking water that meets all state and federal standards.
EPA completed its third five-year review of the site in September 2021, concluding the remedy will be protective of human health and the environment once complete. The fourth five-year review is underway and must be completed by September 30, 2026. Groundwater is sampled and monitored annually each September, with detailed reports available for public review every February. As of December 2024, 17 businesses operate at the site, employing 365 people and generating about $48.7 million in annual sales.
Community members can stay involved by reviewing site documents at three local libraries, Hacienda Heights Library, La Puente Library, and West Covina Library, or at the EPA Region 9 Regional Records Center in San Francisco. The fourth five-year review report will be posted on EPA's webpage and sent to the information repository when complete. Questions can be directed to the site's Community Involvement Coordinator or Remedial Project Manager.
