North & South Basin Quarterly Update

The Orange County Water District (OCWD; the District) manages and protects the Orange County Groundwater Basin that underlies north and central Orange County, from which 19 cities and water agencies draw up to 77% of their water supply. OCWD implements a proactive groundwater and surface water monitoring program to protect the quality of the Orange County Groundwater Basin and ensure the water it provides meets or exceeds state and federal drinking water standards.

Industrial chemicals have impacted areas in the northern and southern parts of the groundwater basin; North Basin (near Fullerton, Anaheim and Placentia) and South Basin (near Santa Ana, Tustin and Irvine). OCWD is proactively seeking ways to clean up the pollution in a united effort with local and national regulatory agencies. 

Below is an update on activities in and around the North and South Basin sites. OCWD will continue to update stakeholders as the need arises.

North Basin

  • The North Basin Site is anticipated to be listed by the United States Environmental Protection Agency (EPA) as a National Priorities List (NPL or Superfund) site in Fall 2020. If the site is listed there will be a general notice sent by the EPA to potentially responsible parties and stakeholders. The notices sent by the EPA are public. There are additional sites throughout the U.S. that are expected to be in the listing package that will be part of the federal registry.
  • A Draft Remedial Investigation (RI) Report was submitted in late April to EPA and state agencies for review. The RI Report describes the project area hydrogeology and the nature and extent of contamination. The submitted report included updated VOC plume maps. The report will be finalized after comments are received.
  • A Draft Human Health Risk Assessment (HHRA) was submitted in late April to EPA and state agencies for review. It will be attached to the RI report when finalized. The California Department of Public Health (CDPH) is looking at the HHRA and will be submitting comments. The HHRA calculates the health risk posed by the contaminated groundwater if that groundwater was produced. State and federal drinking water standards preclude that from happening for public water supplies. However, it demonstrates that the contaminated groundwater cannot be used without treatment.
  • A Draft Remedial Alternatives Technical Memo was submitted in May to EPA and state agencies for review. It identifies different types of remedies that will be evaluated. A Detailed Remedial Alternatives Technical Memo is in progress and is being worked on by OCWD and its consultants.
  • EPA is preparing the North Basin Community Involvement Plan (CIP). The CIP is in draft final form and will soon be completed. The CIP presents a site-specific strategy to enable meaningful community involvement throughout the remediation process.
  • The EPA plans to form a Community Advisory Group (CAG). The CAG is intended to be representative of various community interests. Once the CAG is formed, the CDPH will present to the group regarding their role in protecting public health.

South Basin

  • OCWD and its consultant completed responses to state agency comments and submitted a link to the Supplemental Remedial Investigation Report to stakeholders on July 8. Comments are to be submitted to OCWD (attention: Roy Herndon) by August 8.
  • As a component of the Supplemental RI Report, OCWD’s consultant performed an assessment of the risk to human health and the environment associated with contaminated groundwater in the South Basin area.
  • To maintain program continuity, OCWD is transitioning the remainder of the South Basin RI/FS activities to a new consultant, Engineering Analytics, where key staff of the previous consultant recently transitioned. With the new contract in place, staff expects the next phase of work (groundwater modeling and alternatives screening) for the Feasibility Study to begin soon. 

Additional Information

For additional information, please contact Roy Herndon, chief hydrogeologist at or (714) 378-3260.