MWD, CWA staff discuss Pipeline 6 alignments

Staff from the Metropolitan Water District of Southern California and the San Diego County Water Authority met in late October to discuss possible alignments for the south reach of the future Pipeline 6 which will bring water from Temecula’s Lake Skinner to northern San Diego County.

“In a way it was kind of a kickoff meeting,” said Tobin Tellers, MWD’s project manager for Pipeline 6.

Pipeline 6 is expected to carry between 470 and 630 cubic feet per second (cfs) of water and would connect Lake Skinner with the County Water Authority’s Twin Oaks Diversion Structure. The 470-630 cfs rate equates to 300 to 400 million gallons per day (mgd), and the 400 mgd figure would increase the CWA’s imported water pipeline capacity by 45 percent. Pipeline 6 is expected to be an untreated water pipeline, which would allow the conversion of one of the existing untreated water pipelines to a treated water pipeline. That would increase treated water capacity from approximately 600 cfs to approximately 900 cfs while untreated water capacity would increase from less than 800 cfs to about 1,000 cfs.

The north reach of the project, which will serve Temecula, covers the first seven miles between Lake Skinner and Anza Road at De Portola Road in Temecula. Actual water delivery in the north reach is expected to begin later this month. “We’re just going through the final stages of opening it up right now. The pipeline’s full of water,” Tellers said.

The southern portion which would serve San Diego County is not currently needed, so financial priorities have been placed elsewhere although right-of-way acquisition has begun to allow needed easements to be obtained at a lower cost and other work on the future pipeline is in progress. A worst-case scenario incorporates a nine-year timeframe for the south reach, and Pipeline 6 is not expected to be needed prior to 2018. If the CWA can implement a seawater desalination program Pipeline 6 can be delayed until 2025.

“Right now according to our latest studies the total pipeline would need to be on line by 2018,” Tellers said. “We have to maintain a schedule that can ensure that we can bring it on line at the earlier date.”

The total length of Pipeline 6 is approximately 31 miles. “The remaining portions are the subject of a feasibility study where we’re looking at alternative alignments,” Tellers said. “We’ve learned a lot more about what it would cost to build a tunnel.”

The construction plans envision mostly open trench construction primarily within existing or planned streets for the first 12 1/2 miles from Lake Skinner, and the next portion of the pipeline from would be installed in a tunnel approximately 6 1/2 miles long. The MWD responsibility area is currently terminated near the south tunnel portal just north of the San Luis Rey River, and the CWA would construct the remaining 11.7-mile portion from that point to the Twin Oaks Diversion Structure.

The pipeline was identified as being nine to ten feet in diameter when the 1993 environmental impact report for the pipeline was certified by the MWD board of directors and also approved by the CWA board of directors. Part of the easement in the 1993 EIR is on a property which has since been purchased by the Pechanga Indian Reservation. That purchase makes acquisition more difficult, and MWD is looking at an eastern bypass around that area which would connect to the EIR-stipulated alignment south of the border between Riverside and San Diego Counties. That option could move the tunnel portal to south of the county line.

While the CWA portion is not expected to be affected by alternative alignments and the CWA has been acquiring right-of-way, MWD has held off on right-of-way acquisition until completing the studies to determine the specific alignment. “That’s holding us up,” Tellers said.

MWD also wishes to conduct additional geotechnical and hydrogeological studies for the tunnel area. The additional field investigations and a recommendation on the eventual alignment are expected to take between 18 and 24 months. A technical review workshop was held in November 2005 to assess alignment information and project timing.

“We really need to take a better look at some of the impacts to right-of-way and environmental impacts,” Tellers said.