Metropolitan narrows desalination scan to three streamlined-permit concepts
Metropolitan Water District of Southern California, California · Meeting date: August 17, 2026 · Published: September 17, 2026
A CDM Smith study authorised in November 2023 has shortlisted expansions or new facilities at Doheny, Port Hueneme and El Segundo, all based on subsurface intakes and brine commingling with wastewater effluent. Metropolitan will continue coordinating with member-agency projects and may undertake further studies or a CAMP4W assessment if directed.
Key points
- The reconnaissance-level Class 5 estimates place capital costs for the three concepts in a $450 million-$1.66 billion range and 30-year lifecycle unit costs at $4,300-$6,600 per acre-foot.
- The shortlist comprises a 10mgd Doheny expansion in Orange County, a 20mgd Port Hueneme facility requiring more than 30 miles of conveyance, and a 10mgd El Segundo concept; 20mgd could remain feasible at El Segundo if land becomes available.
- All three concepts use subsurface intakes and would commingle desalination discharge with wastewater effluent, meeting the state's streamlined permitting-track criteria.
- CDM Smith found offshore desalination promising but did not advance an offshore concept to detailed analysis because of limited data and permitting uncertainty.
Full report
Metropolitan Water District of Southern California has identified three potential seawater desalination projects that conform to California's streamlined permitting track, following a reconnaissance study by CDM Smith authorised by the board in November 2023.
The study, presented to Metropolitan's Engineering, Operations and Technology Committee on 17 August, was intended to evaluate emerging desalination technologies and candidate sites while informing the utility's Climate Adaptation Master Plan for Water (CAMP4W) process. Its specific focus was projects capable of meeting the state's streamlined pathway, which requires subsurface intakes where feasible and commingling of desalination discharge with wastewater effluent, among other criteria.
The three shortlisted concepts range from 10mgd to 20mgd. Their Class 5 opinion-of-probable-cost estimates span $450 million to $1.66 billion in capital expenditure, with estimated 30-year lifecycle unit costs of $4,300-$6,600 per acre-foot. Staff stressed that Class 5 estimates are based on roughly 2% design and carry an accuracy range of minus 50% to plus 100%.
The first concept is a 10mgd expansion of South Coast Water District's 5mgd Doheny Ocean Desalination Project in Orange County, bringing total capacity to 15mgd. The project is in design, and South Coast Water District estimates a 2029 online date. Both phases would use subsurface intakes and commingle discharge with the adjacent J.B. Latham Wastewater Facility. Two local transmission mains cross the property, providing multiple integration options.
The largest option is a 20mgd project at Naval Base Ventura County in Port Hueneme. It would use subsurface intakes and commingle brine with effluent from Oxnard's wastewater treatment plant. The preferred connection point is Lake Bard Water Filtration Plant, but the arrangement would require more than 30 miles of new conveyance.
At El Segundo, the original 20mgd site was found no longer to have feasible or available land during detailed analysis. Four alternatives were identified, each limited to 10mgd. The project would use slant wells and commingle discharge with Hyperion Reclamation Plant effluent, connecting directly to Metropolitan's West Coast Feeder. Staff said 20mgd remains feasible should land become available in future.
The study began with a literature review and emerging-technology scan before assessing eight sites and 12 configurations. CDM Smith identified offshore desalination as a promising concept requiring further validation, but recommended against detailed analysis of the offshore candidate included in the site review because it relied on an emerging technology with limited data and lacked a defined permitting pathway under the Ocean Plan.
Subsurface intake systems constrain capacity and raise costs, staff said. Metropolitan and its consultants treated 20mgd as a practical upper limit for subsurface intakes, although the actual limit could vary by site. Cost uncertainty was also particularly tied to slant wells, estimated at $4 million-$10 million each depending on steel commodity prices and local geotechnical and aquifer conditions.
Metropolitan plans to remain engaged with South Coast Water District's Doheny project and Water Farm One, an offshore subsea proposal involving OceanWell and Las Virgenes Municipal Water District. Staff will also provide input on the Ocean Plan amendment now under way. The shortlisted projects could be used in a future CAMP4W portfolio analysis, although additional technical studies may be needed depending on the assessment requirements.
This summary was generated by AI based on the source document and may contain errors.
Source: Engineering, Operations, and Technology Committee, Metropolitan Water District of Southern California