North and 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 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, now called the Orange County North Basin Superfund Site, was listed by the United States Environmental Protection Agency (EPA) as a National Priorities List (Superfund) site on September 3, 2020. The goal of the Superfund listing is to get contamination contained and cleaned up, and to compel parties responsible for the contamination to implement and pay for the cleanup. Nationally, there are 1,600 sites on the National Priorities List. ­
  • OCWD press release regarding Superfund listing ­
  • EPA press release regarding Superfund listing
  • With oversight from EPA, OCWD is conducting a Remedial Investigation/Feasibility Study (RI/FS) to further characterize areas with elevated contaminant concentrations, and develop and evaluate alternatives for an Interim Remedy that remediate parts of the plume that pose a more imminent threat to local groundwater supplies. EPA will propose a preferred alternative, seek public review and comments on that proposal, and work with potentially responsible parties to implement the Interim Remedy selected by EPA.
  • OCWD has completed the Remedial Investigation for the Interim Remedy, which included installing 23 monitoring wells and sampling approximately 90 new and existing wells. A Draft Interim RI Report is being reviewed by EPA and should be finalized by early 2021. The District is currently working on the Feasibility Study, which is expected to be completed in 2021.
  • EPA is starting a comprehensive RI/FS to address parts of the plume that will not be remediated with the Interim Remedy. In early 2021, EPA plans to install six monitoring wells at two locations. The comprehensive Remedial Investigation will likely require many more monitoring wells. EPA will work with the potentially responsible parties to continue to conduct the comprehensive RI/FS and to implement additional remediation to supplement the Interim Remedy, if deemed necessary.
  • At the Nov. 4, 2020 board meeting, EPA provided an update on the next steps in the Superfund process now that the North Basin site has been placed on the National Priorities List.

South Basin

  • OCWD and Engineering Analytics, its consultant on the South Basin Remedial Investigation/Feasibility Study, are reviewing and developing responses to comments received from stakeholders on the Supplemental Remedial Investigation Report.
  • Engineering Analytics is working on developing a groundwater flow model of the South Basin area for use in evaluating remedial alternatives as part of the Feasibility Study.
  • Engineering Analytics has begun evaluating remedial technologies and will be preparing a draft technologies screening technical memo that will be submitted to state regulatory agencies for their review.

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