In 1999, the United Stated Environmental Protection Agency (EPA) issued an amendment to the Record of Decision for the Whittier Narrows Operable Unit (WNOU) which identified the need for a groundwater extraction barrier approximately ¼ mile north of the Whittier Narrows Dam to halt the flow of contamination traveling towards Central Basin. To form an effective containment barrier, five or six extraction sites were required to remove and treat a total of about 12,000 gpm extracting from both the shallow and intermediate zone aquifers. Because EPA was implementing this remedy under its “fund lead” authority, the responsibility for administering the design, construction and operation of the comprehensive cleanup facility was EPA. In 2002, EPA finished construction of the comprehensive cleanup facility and it is currently being operated by the City of Whittier.
Prior to the construction of the EPA project, the San Gabriel Basin Water Quality Authority stepped in at the request of EPA to construct a temporary 1,000 gpm early action project to stem a flow of high concentration contaminants in the area. That facility was shut down when EPA had completed the construction of their project.