A Southern California water utilitys $3.2-billion capital improvement project includes what will be the nations largest submerged-membrane water treatment plant. San Diego County Water Authority last month awarded CH2M Hill Constructors Inc., Denver, a $159-million design-build-operate contract for a 100-million-gallon-per-day plant in Twin Oaks Valley, north of San Marcos, Calif. Completion is scheduled for spring 2008.
Fine screening will eliminate large particulates before 14 separate 7-mgd submerged-membrane plants force water at a flux rate of 20 to 32 gallons per sq ft of membrane surface per day through pores ranging from .04 to .1 micron. This will screen out giardia, cryptosporidium and other organisms, which can range from 2 to 10 microns. "The combination of processes was designed to meet the water quality characteristics," says Bob Chapman, CH2M Hill project director.