EPA selects pump-and-treat with reinjection for North Basin interim remedy

EPA selects pump-and-treat with reinjection for North Basin interim remedyA proposed plan to contain a 6.4-mile chlorinated solvent plume in Orange County favors reinjection over direct potable reuse due to infrastructure capacity constraints.

The EPA's preferred 'Alternative 4' entails extracting groundwater, treating it at a centralized plant, and reinjecting it downgradient.

The system is designed to process 3.3 billion gallons annually (10,700 acre-feet) at a continuous flow rate of 6,546 gallons per minute.

Direct potable reuse alternatives were rejected because local municipal systems could not absorb the additional water volume without major upgrades.

A Record of Decision is targeted for September 30, 2026, with responsible parties expected to fund implementation.

The US Environmental Protection Agency (EPA) has outlined its preferred interim remedy to address the North Basin groundwater plume in Orange County, California, proposing a large-scale pump-and-treat system that utilizes reinjection rather than direct potable reuse. During a January 28, 2026, presentation to the Anaheim Public Utilities Board, EPA Remedial Project Manager Amanda Cruz detailed the agency’s proposed plan for the site, which was added to the National Priorities List in 2020. The North Basin site involves a commingled plume of chlorinated solvents spanning a 6.4-square-mile area beneath Anaheim, Fullerton, Buena Park, and Placentia. The contamination stems from manufacturing industries, specifically metal and electronic circuit board operations, that utilized volatile organic compounds between the 1950s and mid-1980s. Improper storage and disposal during that era allowed pollutants to leach into the soil and groundwater, eventually forcing the closure of six drinking water supply wells in the region. The proposed interim remedy focuses on a specific high-concentration area to prevent the contamination from spreading laterally or migrating vertically into deeper aquifers used for drinking water. The EPA’s objective is to treat the shallow aquifer zone between 80 and 200 feet below ground. Following a feasibility study completed in August 2025, the EPA evaluated several cleanup options against the requirement to manage approximately 3.3 billion gallons of water per year (10,700 acre-feet). The agency selected 'Alternative 4' as the preferred method. This approach involves a groundwater extraction network operating 24/7 at 6,546 gallons per minute, a new centralized treatment plant to remove contaminants to Maximum Contaminant Levels (MCLs), and a network of injection wells to return the treated water to the aquifer downgradient of the plume. Cruz explained that other alternatives were screened out due to feasibility issues regarding the massive volume of water. 'Alternative 2,' which proposed discharging to the sanitary sewer system for treatment by the Orange County Sanitation District and subsequent replenishment, was rejected because existing sewer lines could not handle the volume. Similarly, 'Alternative 3,' which proposed treating the water for direct distribution through the City of Fullerton or Anaheim’s potable systems, was deemed unviable because the cities determined the 3.3 billion gallons would exceed their system capacities and require significant upgrades. 'Alternative 5,' involving surface infiltration basins, was also discarded due to the difficulty of securing the necessary six acres of land in the dense urban area. The selected reinjection method avoids these capacity and land-use constraints while maintaining aquifer levels. The project is currently in the public comment period, which closes on February 19. The EPA intends to issue a Record of Decision (ROD) by the end of the fiscal year on September 30, 2026. Following the ROD, the agency will work with identified responsible parties—currently numbering 58 parties across 34 parcels—to implement the remedial design and construction under the Superfund program's 'polluter pays' model.