Pretreatment at the new plant will begin with the addition of ferric chloride as a coagulating agent. Following flocculation, clarification will be accomplished with a high-rate DAF process, which allows much higher loading rates than conventional DAF. It will effectively remove solids at a design loading rate of 14 gallons per minute per square foot—as much as 3 ½ times higher than conventional DAF and more efficiently than other clarification alternatives. The treatment plant features the second application of high-rate DAF in the United States.
Clarified water will flow by gravity into eight basins that house submerged ultrafiltration membranes. The complete membrane system—consisting of filtration units, clean-in-place equipment, backwash and compressed-air equipment, and control systems—was chosen through a competitive vendor selection process early in the facilities design. Procurement documents were developed and distributed to five membrane vendors certified by the California Department of Health Services (DHS). Unlike a typical competitive bid situation, the scope of the required response and ensuing evaluation was extended 20 years into the future and included not only membrane equipment costs but also ancillary equipment and operation and maintenance costs. As the selected vendor, Zenon, Oakville, Ontario, was added to the design team and made responsible for pilot testing, design, and membrane-system commissioning activities.
These membranes are suspended in cast-in-place concrete basins, allowing for compact, common-wall construction of the filter complex. Each basin contains seven cassettes of membranes that provide a physical barrier to pathogens such as Giardia and Cryptosporidium. The DHS granted this system its highest rating of 4-log removal of these pathogens.Tapping In and Wrapping Up
Chlorine disinfection and contact time will be accomplished in two 3 million gallon reservoirs following filtration and prior to distribution of the treated water. Approximately 40 miles of transmission pipeline, ranging in diameter from 30 to 54 inches, will transport water to the cities. Running the pipeline through developed areas and over land designated as a floodway affected the program's construction schedule; floodway construction must be halted during the eight-month potential flood season. Three new pump stations and a booster station will help deliver water to the first-phase recipients.
“This project is an integral part of our diverse water supply plan,” said Steve Bayley, city of Tracy deputy director of public works. “The treatment plant incorporates technology that represents the new standard in water treatment and will enable the cities to meet foreseeable as well as current requirements.”
The new system will begin to deliver as much as 40 mgd to Manteca, Tracy, and Lathrop early this summer. Phase II will increase the volume of water in the pipeline and extend the line to Escalon when that city joins the program. Construction of the second-phase facilities is expected to begin between 2010 and 2012. With completion of the first phase imminent, the program participants have already demonstrated that even when there's no well, there's a way.
— Hesby is a vice president and project director, Enson is a project engineer, and Standish-Lee is director of watershed planning with Black & Veatch Corp., Concord, Calif. Kreinberg is program manager with Water Resources Consultants, Sacramento, Calif.