EPA Superfund Site

ORANGE COUNTY NORTH BASIN

CA | EPA ID CAN000900251

About this site’s exposure pathways: As of October 2025, the Orange County North Basin Superfund site is considered “Insufficient Data to make a Human Exposure evaluation” (HEID). Orange County North Basin Superfund site was recently finalized on the NPL on 09/03/2020, and there is an ongoing comprehensive evaluation of the human health exposure risks.

EPA uses this Human Exposure status when there is insufficient data/evidence to determine whether actual or reasonably anticipated human exposures are occurring, and/or whether those exposures are above acceptable risk-based levels. The planned activities to collect sufficient information to make a human exposure evaluation include the Orange County Water District conducting an interim, limited scope Remedial Investigation/Feasibility Study in the most contaminated part of the Site under EPA oversight. Although EPA has not evaluated all human health exposure pathways, all drinking water is provided by water purveyors and meets all federal and state standards. EPA has not investigated the vapor intrusion pathway; however, this investigation will be carried out in coordination with State partners. EPA currently anticipates that there will be sufficient data to make a Human Exposure determination by 2026 because the Remedial Investigation is anticipated to be complete by then.