Alternative Intake Project is Dedicated
Contra Costa Water District’s (CCWD) Alternative Intake Project was formally dedicated on July 20, 2010, at the Middle River Intake and Pump Station. The facility is about to begin the commissioning stage, which is the final testing prior to operation this summer.
This project is the most significant Delta drinking water quality project to complete planning studies, design and begin construction in the past decade. Water quality at the pumping station located on Old River declines in late summer and early fall, when saltwater from the Bay enters the Delta. The new station will provide fresh water during those months, while also providing benefits for important Delta fish populations.
The new $99 million pump station is located on a levee at the south end of Victoria Island along Victoria Canal in San Joaquin County, California. The pump station is capable of pumping 250 cubic feet of raw water per second through 12,000 feet of 72-inch pipeline across the island to the existing Old River Pump Station Pipeline Facilities. The 900-foot crossing of Old River required installation of a 96-inch-diameter steel casing using microtunnel pipe-jacking techniques and two watertight shafts: a 92-foot-deep jacking shaft and a 49-foot-deep receiving shaft. Microtunnel installation of the casing was halted about 185 feet into the drive beneath the river in order to retract the microtunnel boring machine (MTBM) and 30 feet of casing. After the MTBM was straightened out and the articulating joint at the casing connection was "locked" in place, the microtunnel drive was completed within line and grade tolerances.
The contractor chose the cutter-soil-mixing (CSM) method for the shaft construction. This was the second known application of CSM technology in the U.S. for construction of a microtunnel shaft, and the first known use for applying shotcrete for secondary wall reinforcement. Because of the CSM method’s unknown nature, Jacobs Associates provided full-time construction monitoring during shaft construction, excavation, and shotcreting.
Jacobs Associates prepared the plans and specifications for the tunnel design and a Geotechnical Baseline Report for construction of the shafts and tunnel. Jacobs Associates also provided full-time construction monitoring during microtunnel installation of the casing, and during the machine and casing retraction process.
The project was recognized as the 2009 “Project of the Year” by the Northern California Chapter of the Construction Management Association of America. A technical paper was prepared on the CSM construction method and presented in 2009 at the Australian Society for Trenchless Technology conference, and in 2010 at Portland's ASCE Section meeting of geotechnical engineers and geologists, at the Construction Institute of Northern California, and at the recent North American Society for Trenchless Technology Conference. The project was also submitted for consideration as Trenchless Technology Magazine's Trenchless Project of the Year. The selected projects will be announced in the October 2010 issue of the magazine.
