AWWA WQTC71492

The Long Beach Water Department (LBWD) is researching a subsurface intake system (under-ocean floor seawater intake) that collects seawater filtered through engineered sand beds at slow rates. The primary goal of this project is to determine if the system can deliver a sustained quantity of water. A secondary goal is to deliver a consistent water quality that can be used as feed water for desalination membranes. This research also tests concentrate discharge to minimize localized environmental effects, and evaluates additional potential benefit of reducing pretreatment processes. The tests are being conducted over 15 months to evaluate differences in influent water qualities at filtration rates ranging from 0.05 to 0.2 gpm/ft². Two tests have been completed to date, and show that infiltration rates of 0.05 and 0.1 gpm/ft² yield flows that are independent of the tide level (except in extreme low tidal conditions). Testing is ongoing to ensure the respective water quality goals of <3.0 SDI₁₅ and turbidity <0.1 NTU are achieved by cartridge filtration. These goals are generally accepted guidelines for influent water quality used with desalting membranes. The water quality comparisons include chemical analyses (general, physical, selected inorganic and organic), and specialized indicators of marine life activity (marine heterotrophic plate count-mHPC, adenosine triphosphate-ATP, assimilable organic carbon-AOC and dissolved organic carbon-DOC). The comparison will help direct the final stages of testing to help identify any gaps or validate the current test plan. This paper presents the results of the side-by-side comparison for the demonstration-scale experiments described above. Includes 5 references, table, figures.