Selection of Twin Oaks treatment plant doesn't rule out future Weese, Red Mountain facilities

The San Diego County Water Authority authorized a request for proposals to build a water treatment plant at the Twin Oaks Valley Diversion Structure site, but that doesn’t mean the end of possible future treatment plants at the other three sites considered, including the Weese Water Treatment Plant in Gopher Canyon and the Red Mountain Reservoir in Fallbrook.

“We still encourage those things to go forward,” said Rich Pyle, the CWA’s principal civil engineer.

In April 2003 the CWA board approved the initiation of the process which will expand water treatment capacity in North County by 100 million gallons per day, the amount of additional water treatment expected to be needed by Summer 2007. The CWA stipulated the Twin Oaks Valley Diversion Structure site as the preferred location while selecting the Weese Water Treatment Plant (physically located within the Rainbow Municipal Water District boundaries but owned by the City of Oceanside), the Red Mountain Reservoir, and the Olivenhain Water Treatment Plant for study as alternative sites.

Requests by member agency general managers for further analysis eventually delayed the expected completion date to early 2008.

The Twin Oaks Valley site was designated as the preferred location for several reasons, one of which was the ability to treat 100 million gallons per day (mgd) at a single site. Although the original plans called for an initial phase with 50 mgd capacity and eventual expansion to 100 mgd, the CWA’s treated water needs would only be served by the 50 mgd capacity if all elements of its treatment capacity plans are completed on schedule.

“Local supply development is slower than what we thought it was going to be in 2000,” Pyle said.

The reduction from two phases to a single phase is expected to save $27 million in construction costs, and processing one set of proposals instead of two is expected to expedite the eventual completion by saving two weeks to one month of CWA staff time.

The CWA’s treated water costs, which would be incorporated into a melded surcharge rate, would reflect both construction costs and operating costs. Pyle anticipates that an initial 100 mgd plant instead of phased 50 mgd increments would reduce the CWA portion of the surcharge from $170 per acre foot to $166 per acre foot.

The Metropolitan Water District will increase its treated water surcharge to $132 in January 2006, and Pyle believes that the estimated Twin Oaks Valley treatment cost could be lower than the MWD cost. “Our feeling is right now that we could probably beat Met’s cost,” Pyle said.

Even with the completion of the treatment plant Pyle expects that the CWA will take one-third to one-half of its treated water from MWD, thus leading to a melded surcharge rate once the Twin Oaks Valley plant is completed.

The differential between the MWD surcharge and the CWA cost will also determine baseload versus peak hour priorities for the Twin Oaks Valley plant.

“I support going to 100 mgd immediately. I think it’s the right thing to do,” said Fallbrook Public Utility District general manager Keith Lewinger, who is also FPUD’s representative on the CWA board.

Proposals to design, build, and operate the Twin Oaks Valley plant are due April 25. Before the CWA board awards the contract, CWA staff will return to the board with a recommended prioritization policy for untreated water supplies. The CWA will develop that policy with input from the member agency operating heads and general managers.

That prioritization policy will cover member agency water treatment plant facilities, CWA treatment facilities, and local storage. The priorities will likely be different for peak periods when local storage is being consumed than for off-peak periods when local storage supply is being added.

Pyle said that local agency treatment is anticipated to provide up to an additional 50 mgd of treated water. “Oceanside is looking into possibly expanding the Weese plant for their own demands,” he said.

In fall 2004 the Oceanside City Council awarded a design contract for the Weese expansion. “The Weese expansion to us is really a business decision,” said Barry Martin, who is the City of Oceanside’s Director of Water Utilities and also Oceanside’s representative on the CWA board. “We have the option of buying treated water from the Authority, which is more expensive than producing our own water at Weese.”

The Weese expansion will expand the existing facility from 25 mgd to 37.5 mgd. The design phase is expected to take approximately one year. “We’re hoping to have the plant on line by early 2008,” Martin said.

The City of Oceanside has no specific plans for further expansion of the Weese plant. The need for future expansion will depend on such factors as the city’s groundwater desalination program as well as a potential small seawater desalination plant to be owned and operated by the City of Oceanside. “It really depends at this point,” Martin said.

The Olivenhain Municipal Water District has also discussed an expansion of its treatment plant to serve local needs. The Fallbrook Public Utility District is focusing on the Santa Margarita River conjunctive use project but has not ruled out a treatment facility at the Red Mountain Reservoir. “We’ve discussed maybe doing a joint project to enhance that reservoir with Fallbrook,” said Pyle.