OPERABLE UNITS
AREA THREE OPERABLE UNIT Investigation Persists The cities of South Pasadena and Alhambra continue operating their water treatment facilities, including South Pasadena’s new Graves facility. The United States Environmental Protection Agency (USEPA), with a new project manager, is focused on gathering more data for the ATOU area; a formal feasibility study for active cleanup cannot be fully assessed until this additional characterization is complete. As of June 30, 2025, the ATOU facilities have treated more than 65,280 acre- feet of water and removed approximately 3,136 lbs. of groundwater contamination.
enhance remediation efforts. Additional extraction and monitoring wells are being installed under the oversight of the USEPA. Furthermore, USEPA and the Los Angeles Regional Water Quality Control Board, with input from the EMOU Stakeholders, continue to coordinate on source property identification, investigation, and remediation within the EMOU. The former Crown City Plating property, believed to be a significant source of groundwater contamination within the EMOU, is finally being addressed with the cooperation of a new property owner, the City of El Monte along with the State. The EMOU facilities have treated 88,399 acre-feet of water as of June 30, 2025, and removed approximately 3,127 lbs. of groundwater contamination. SOUTH EL MONTE OPERABLE UNIT Expanded Treatment and Funding Moving Forward WQA has made great progress on its Proposition 1 Implementation Grant to improve current water extraction efforts at its Whitmore Street Groundwater Remediation Facility treatment project. Permits have been secured and construction contractors have been selected. Additionally, the WQA was successful in reaching a landmark agreement with the Department of Toxic Substances Control (DTSC) securing funding for multiple years for the operation of the SEMOU Intermediate Zone Remedy Projects ensuring that area ratepayers do not shoulder the burden of cleanup costs. As of June 30, 2025, the SEMOU treatment facilities have treated more than 283,102 acre-feet and removed approximately 33,073 lbs. of VOCs. WHITTIER NARROWS OPERABLE UNIT Additional Funding Secured DTSC is making progress on the necessary infrastructure to integrate the water from the Whittier Narrows Operable Unit (WNOU) Intermediate Zone Remedy back into the potable water supply. The SGVWC has finished construction of the required blend line, moving both DTSC and SGVWC closer to this goal. Once the SGVWC’s amended water supply permit is approved, the WNOU remedy will again serve as a safe and dependable source of drinking water. In addition, DTSC was successful in securing supplementary state funding to install an additional extraction well to enhance containment while ensuring added protection to downgradient drinking water supplies. The WNOU facilities have treated 98,461 acre-feet of water and removed approximately 3,536 lbs. of groundwater contamination as of June 30, 2025.
Advancements Forge Ahead
(SZS) Remedy on behalf of Northrop Grumman. The SZS will provide significant contaminant mass removal while preventing migration into less contaminated areas. As of June 30, 2024, the SZS Remedy has treated 89 acre- feet of water and removed approximately 39 lbs. of contamination. Other PVOU IZ facilities including San Gabriel Valley Water Company (SGVWC) Plant’s B7 and B11 have treated more than 99,624 acre-feet of water and removed approximately 5,431 lbs. of groundwater contamination as of June 30, 2025. Carrier Gaining Traction in Shallow Zone North Remedy Carrier Corporation is responsible for Shallow Zone North (SZN) Remedy and continues to move forward with design. Recent activities include the complete delineation of the SZN groundwater contamination, submission of the basis of design with modeling of the capture zone to proposed locations for additional extraction and injection wells. It is anticipated that Carrier will start the Remedial Design of the SZN Remedy in 2026. WQA will continue to help facilitate and coordinate with state and federal agencies to ensure shallow zone remediate stays on track.
The WQA coordinates groundwater cleanup across six operable units (OUs) in the San Gabriel Basin. These six areas are: Puente Valley Operable Unit (PVOU); Area Three Operable Unit (ATOU); Baldwin Park Operable Unit (BPOU); El Monte Operable Unit (EMOU); South El Monte Operable Unit (SEMOU); and Whittier Narrows Operable Unit (WNOU). With a year marked by a significant natural disaster, Basinwide cleanup activities continue to make advancements. PUENTE VALLEY OPERABLE UNIT Milestone of Progress With construction activities on the Intermediate Zone Remedy treatment plant concluded, startup and shakedown testing activities winddown. All components of the required amended water supply permit have been submitted for review to state regulators. In addition to operating the IZ Remedy, La Puente Valley County Water District began operation of the Shallow Zone South
Baldwin Park Operable Unit treatment facility
BALDWIN PARK OPERABLE UNIT Improvements Reap Rewards The five existing remedy treatment plants remain operational. The SGVWC completed construction of the second phase of a highly efficient, third-generation advanced oxidation treatment system at its Baldwin Park Plant B6. This state-of-the-art system uses ultraviolet (UV) light technology to destroy 1,4-Dioxane and NDMA (N-Nitrosodimethylamine) contaminants. Concurrently, the Valley County Water District initiated capital improvements at its Subarea 1 treatment facility aimed at restoring full treatment capacity. The costs for both of these projects were partially covered by federal funding secured by the WQA. The BPOU facilities have treated 1,161,869 acre-feet of water and removed approximately 135,826 lbs. of VOCs as of June 30, 2025. EL MONTE OPERABLE UNIT Progress Intensifies Due to varying groundwater levels, the parties responsible for containing the contamination in the shallow and deep zones of the EMOU are continuing to
Puente Valley Operable Unit treatment facility
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6 ■ SAN GABRIEL BASIN WATER QUALITY AUTHORITY
2024-2025 ANNUAL REPORT ■ 7
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