North and South Basin Cleanup Report

The Orange County Water District (District; OCWD) continues to work toward remediating both the North Basin and South Basin groundwater contaminant plumes to protect our local drinking water supplies.  Our work includes many different components. The initial phase is the Remedial Investigation and Feasibility Study (RI/FS), which is now underway for both areas. OCWD has submitted applications for California Proposition 1 grant funding support for the RI/FS for both North and South Basin areas. We also continue to seek financial participation for the investigation and cleanup costs from the parties responsible for the contamination. 

North Basin [Fullerton, Anaheim, and Placentia areas]

Subsurface investigations have been performed in the North Basin for several decades by OCWD and property owners or operators at sites where contaminant releases occurred. The potentially responsible parties (PRPs) have performed limited studies and remedial work on their individual properties. These efforts have largely been driven by a combination of voluntary actions and State regulatory agency directives. Most PRP site investigations have been limited to the affected property boundaries, while OCWD’s investigations, including construction of 70 monitoring wells, have been focused on assessing the extent and magnitude of contamination that has migrated away from those properties.

As part of a previous project in the North Basin area, the District installed six wells designed to extract contaminated groundwater to impede its continued migration. That project was put on hold and is being re-evaluated as part of the RI/FS, along with other alternatives.  The largest of these extraction wells is currently being made operational by OCWD in response to an urgent need to impede the migration of contamination from the Shallow Aquifer to the underlying Principal Aquifer. The need to operate the remaining extraction wells will be evaluated as part of the RI/FS.

OCWD is voluntarily performing the RI/FS under the oversight and direction of the United States Environmental Protection Agency (EPA). The new multipronged approach includes the California Regional Water Quality Control Board (RWQCB) and the Department of Toxic Substances Control (DTSC) agency oversight of the work being done by the PRPs at sites where contaminant releases occurred. Those efforts focus on assessment and remediation of contaminants in the soil, soil vapor, and some local groundwater hot-spot remediation. OCWD’s focus is on the RI/FS for the areas extending away from the many source sites where contaminants have mixed into large comingled plumes. This RI/FS work is being done within a two-party “administrative settlement agreement” between OCWD and the EPA. 

The District’s RI/FS work is rigorous, comprehensive, and compliant with the National Contingency Plan (NCP), which comprises the Federal regulations for addressing the nation’s worst hazardous waste sites.  Working this way assures that the conclusions are defensible, both technically and legally. Upon completion of the FS in 2019, the EPA will propose a remedy and solicit public comments. After that a remedy will be selected.  If the PRPs do not voluntarily agree to implement the selected remedy, the EPA could order them to do so.

As always, the District’s priority in the North Basin is to cost-effectively remediate the groundwater contamination, protect the aquifers used for drinking water supply, and pursue financial contribution from the parties responsible for the contamination. Without PRP contribution, water rates would need to be increased to pay for the remediation, which will remove many millions of dollars from the local economy.

South Basin [Irvine, Santa Ana, and Tustin areas]

The District’s strategy in the South Basin is similar to that in the North Basin, although the South Basin plume isn’t as long, and the geology is different. In the South Basin the plume is two miles long with slower groundwater velocities and plume spreading rates. The contaminants in the near surface groundwater are similar to those in the North, although their concentrations are higher.

As in the North Basin, the South Basin area is the subject of an OCWD lawsuit against former and current industrial operators and their successors. That litigation has moved into the state appellate court and is fully briefed waiting for a court ruling. The Federal EPA has not taken on the South Basin plume, leaving regulatory oversight of both the various source sites and the offsite plumes to the RWQCB and DTSC. 

OCWD, with the cooperation of these two state agencies, is performing a voluntary RI/FS similar to the North Basin, also following the NCP protocol to assure technical rigor and to allow for future cost recovery against those responsible for causing the problem. The study, now underway, includes the installation of “data gap” monitoring wells and the mapping of subsurface hydrogeologic conditions and water quality. The RI will be followed by an FS that will support the implementation of a South Basin Remedial Action Plan (RAP).

It is hoped that many, if not all, of the PRPs for both the North and South Basin plumes will voluntarily join with OCWD in the performance of this needed work for the protection of the water resource.


The District is currently funding the RI/FS work for both the North and South Basins areas from its general fund. To help relieve some of the financial burden from its ratepayers, the District has applied to the California State Water Resources Control Board’s recently enacted Proposition 1 grant funding program. Three “matching funds” applications have been submitted; two for RI/FS planning studies and one for the construction of the initial pumping system in the North Basin. The District hopes to receive funding approval sometime in January 2017.