EPA proposes dedicated treatment plant and injection wells for North Basin Interim Remedy

EPA proposes dedicated treatment plant and injection wells for North Basin Interim RemedyFederal regulators have rejected utilizing the Groundwater Replenishment System for the North Basin cleanup, citing capacity constraints, and have instead recommended a standalone extraction and reinjection strategy.

The EPA's Proposed Plan, released January 5, 2026, selects Alternative 4: groundwater extraction, a new centralized treatment plant, and reinjection wells.

The project aims to treat approximately 10,700 acre-feet per year (3.3 billion gallons) to contain a plume of chlorinated solvents.

Integration with the existing Groundwater Replenishment System (GWRS) and direct service to Anaheim or Fullerton were ruled out due to insufficient capacity.

Costs are expected to be covered by responsible parties under the 'polluter pays' principle, avoiding impacts to local water rates.

A public comment period is open until February 19, 2026, with a Record of Decision expected to follow.

The U.S. Environmental Protection Agency (EPA) has formally identified its preferred strategy for the North Basin Interim Remedy, recommending the construction of a new centralized treatment facility and injection well system to manage a massive volatile organic compound (VOC) plume in Orange County, California. During the January 7, 2026, meeting of the Orange County Water District (OCWD) Board of Directors, EPA Remedial Project Manager Amanda Cruz presented the agency’s Proposed Plan, which was released to the public on January 5. The plan addresses the North Basin site, which was listed on the National Priorities List (Superfund) in 2020. The interim remedy is designed to contain the highest concentrations of contamination within a targeted area to prevent the plume from migrating laterally or vertically into production aquifers that serve approximately 2.5 million residents. The EPA’s feasibility study evaluated five active cleanup options against a baseline of no action. Cruz confirmed that the agency has selected 'Alternative 4' as the preferred remedy. This approach involves extracting groundwater, treating it at a newly constructed centralized plant, and discharging the treated water via injection wells located outside the target area. This method ensures the water is returned to the aquifer for reuse rather than being wasted. The scale of the remediation effort drove the decision-making process. The system must manage approximately 3.3 billion gallons of water annually, or 10,700 acre-feet per year. Cruz noted that other alternatives were screened out due to significant infrastructure limitations. Alternative 2, which proposed routing extracted water through sanitary sewer lines to the district’s Groundwater Replenishment System (GWRS), was rejected because the existing system lacks the capacity to handle the additional volume. Similarly, Alternative 3, which involved direct service of treated water to the cities of Anaheim or Fullerton, was deemed unfeasible as neither municipality could accommodate the capacity within their current systems. Alternative 5, which utilized infiltration basins, faced logistical challenges regarding land acquisition in the dense urban corridor. 'Finding size for a treatment plant and the infiltration basins in a highly developed area in Orange County with the suitable hydrology was a little bit tricky,' Cruz told the Board. The EPA emphasized that the financial burden of the project will not fall on OCWD ratepayers. The agency intends to enforce the 'polluter pays' principle, working with responsible parties to fund and perform the cleanup. The interim action is intended to stabilize the site while a final, site-wide remedy is developed. The EPA is currently soliciting public feedback, with a comment period open through February 19, 2026. Following the review of public input, the agency will issue a Record of Decision to formalize the remedy selection. In related water quality news, OCWD General Manager John Kennedy reported that the District received notification of an additional $1.5 million in funding from the State Water Resources Control Board to assist with PFAS remediation efforts. Administered by the Division of Financial Assistance, these funds are drawn from a combination of state General Fund appropriations and federal grants targeting emerging contaminants. Kennedy noted that this latest addition brings the total state-managed funding for the District’s PFAS program to approximately $110 million.