Santa Ana Region -


Orange County North Basin Regional Groundwater Plume

On September 1, 2020, the United States Environmental Protection Agency (USEPA) announced the addition of the Orange County North Basin (OCNB) site in southern California to the Superfund National Priorities List (NPL). The OCNB includes parts of Anaheim, Fullerton and Placentia, and is part of the larger Orange County Groundwater Basin. For more information related to the OCNB and the NPL listing, please see the links to documents and websites section below.

Information on Proposed National Priority Listing

On January 18, 2017, the USEPA opened a Comment Period for the proposed addition of the OCNB to the NPL. The Site, located in Northern Orange County, is a comingled groundwater plume of chlorinated solvents and other contaminants covering more than 5 square miles, primarily beneath the cities of Anaheim and Fullerton, California.

As of March 8, 2018, EPA gave all interested parties an additional 60 days to submit comments related to OCNB proposed NPL addition. The public comment period ended on May 18, 2018.
As of August 13, 2018, EPA is providing a notice of data availability for documentation supporting the proposal of the Orange County North Basin Site.  This notice provides an opportunity to comment on the additional reference documentation only. The comment period closed on September 12, 2018.

The Orange County North Basin Community Meeting was held at Fullerton Public Library, 353 W. Commonwealth Avenue, Fullerton, CA on Wednesday, November 14, 2018.
The purpose of the meeting was to discuss site activities; promote meaningful community involvement; share information about the NPL, Superfund Alternative Approach, and interim Remedial Investigation (RI); explain site cleanup activities; learn about the public health assessment activities that will be conducted; and hear the community’s health and exposure concerns related to the site.

Ongoing Investigations and Cleanup Activities

In 2014, the State of California referred the OCNB Site to the USEPA to prevent further migration of contamination into the groundwater, which is the primary drinking water source for Orange County. In 2016, the USEPA became the lead agency for the OCNB commingled plume project.

Under USEPA oversight, the Orange County Water District (OCWD), is currently conducting an interim remedial investigation and feasibility study (RI/FS) to address groundwater contamination in the OCNB. As of April 2018, 13 monitoring wells have been constructed and sampled and an additional 8 monitoring wells are planned for construction. The data collected as part of this study will provide the USEPA with the information needed to develop an initial remedy that will prevent further vertical and horizontal migration.

While USEPA is taking the lead in overseeing the investigation of the regional groundwater contamination, the Santa Ana Regional Water Quality Control Board (Regional Board) and the California Department of Toxic Substances Control are lead agencies in overseeing the investigation and cleanup of contamination at individual industrial properties suspected of having contributed to the regional groundwater contamination.

USEPA Project Contacts

USEPA Community Involvement Coordinator:
Carlin Hafiz
(213) 244-1814

USEPA Remedial Project Managers:
Kathleen Aisling
(213) 244-1823

Additional Contacts:

Orange County Water District
Dave Mark, Project Manager

Santa Ana Regional Water Quality Control Board
Maile Gee, Site Cleanup Case Manager
(951) 782-4379

California Department of Public Health
Beth Saiki, MPH, Health Educator
(510) 620-5764


This page contains links to websites and documents pertaining to the proposed project.

Interested parties are invited to subscribe to the Regional Board's E-Mail Notification System.

Links to Documents and Websites



Documents on the page are in Adobe Acrobat. Get the free reader below:

Click here to Get Acrobat Reader