DESALTING RESIDUALS - A PROBLEM OR A BENEFICIAL RESOURCE

The Sweetwater Authority, which serves 160,000 people in southern San Diego County, has adopted a long-range goal to be less dependent on im ported supplies, especially in water-short years. The Authority is act ively developing a program of brackish groundwater and urban runoff de mineralization. Various options have been evaluated for disposal or re use of the concentrate from the proposed desalination plant. These inc lude: 1) discharge to San Diego Bay, 2) reuse in coastal wetlands, 3) discharge to existing or proposed sewer networks, and 4) discharge thr ough deep well injection. Discharge to San Diego Bay may have regulato ry constraints which would be imposed by the San Diego Regional Water Quality Control Board (RWQCB). A unique opportunity exists to utilize concentrate for beneficial uses for wetland habitat development such a s brackish water wetlands within the Sweetwater Marsh National Wildlif e Refuge (NWR). The NWR has expressed an interest in utilizing the con centrate as a continuous water supply. Concentrate disposal into the C ity of San Diego sewer system could only occur through conveyance line s which will not convey sewage to proposed reclamation facilities. Inj ection of concentrate into the San Diego Formation could have a benefi cial effect to the quality of the groundwater in the San Diego formati on if it occurs close to the coast but may have an adverse impact on i nland groundwater. The least expensive alternative is to discharge con centrate into San Diego Bay, however, concentrate recycling would be b eneficial to the natural environment. Brackish coastal wetlands can se rve as receiving waters for the concentrate. This option is somewhat m ore costly but can provide possibilities for mitigation of project env ironmental impacts.