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The San Diego County Water Authority (Water Authority) is the regional water wholesalerresponsible for ensuring a safe and reliable water supply to support San Diego's $130 billioneconomy and three million residents. The Water Authority imports 75 to 95 percent of the waterused in the region. The Water Authority's 2030Regional Water Facilities Master Plan indicated an immediate regional need for an additional 50to 100 million gallons per day (mgd) of treatment capacity. The Water Authority does not own oroperate water treatment facilities and relies on Metropolitan Water District of Southern California(MWD) and its member agencies to supply all of the region's treated water demands.Approximately 45 percent of all imported water is treated and supplied by MWD and theremaining is supplied by member agency water treatment plants (WTP). Multiple studiesindicated the most effective option for additional regional treatment capacity is to build a newWTP at the Water Authority's Twin Oaks Valley (TOV) site in northern San Diego county.The Water Authority plans to implement the TOV-WTP using the design-build-operate (DBO)procurement method. The type of WTP being implemented, conventional or membrane, will notbe specified in the request for proposals for the project. Therefore, the Water Authoritydeveloped conceptual designs for the WTP to serve as a basis for the California EnvironmentalQuality Act permitting and included development of budgetary cost opinions for comparison toDBO bids. They will also serve as a resource for the DBO entities bidding for the project.Proposed conceptual designs using both conventional and low-pressure membrane technologieswere prepared for the 50 mgd expandable to 100 mgd WTP. To provide adequate information topotential bidders of this project, the conceptual designs were proposed to satisfy the target waterquality goals for the facility. The conventional design included ozone for primary disinfectionand taste and odor removal. The membrane design included granular activated carbon for tasteand odor removal. The proposed designs indicate that the processes are very comparable withrespect to cost and can meet equivalent water quality goals. However, the membrane treatmentprocess may be capable of providing a better barrier against microbial pathogens. The WaterAuthority is conducting pilot-scale testing of low-pressure membrane treatment processes, withand without pretreatment, to evaluate its feasibility for this project.This paper, based on the information developed for the conceptual designs, will present acomparison of cost, ability to meet water quality goals, potential for future expansion, and otherkey criteria. Includes tables, figures.

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Edition: Vol. - No. Published: 11/15/2004 Number of Pages: 19File Size: 1 file , 240 KB