AWWA ACE68913

The Santa Ana Watershed Project Authority (SAWPA) owns and operates a 72 mile brine line serving groundwater desalination facilities and other industrial and domestic users in San Bernardino and Riverside Counties in California. Problems have been experienced recently with the generation of large concentrations of suspended solids within the brine line, resulting in added maintenance to remove settled solids as well as significant billing issues for the authority. Dischargers to the brine line are charged based on a combination of flow, suspended solids, and biochemical oxygen demand (BOD) at their point of discharge. SAWPA is in turn charged for these same parameters by a downstream sanitation district at the transition from the SAWPA pipeline to the sanitation district's. Suspended solids measured at the downstream monitoring point have been roughly double what they are going into the pipeline, creating concerns about an equitable manner to allocate costs for roughly 4,000 tons per year of solids that cannot be measured at the discharge points. It has been considered that these solids may come from some combination of chemical and biological interactions between the brine flows and domestic wastewater, which currently makes up 40 percent of the brine line water. SAWPA authorized an extensive water quality study to determine and characterize the source or sources of this solids generation. It was determined during the first stage of testing that both chemical precipitation from hardness and silica and biomass formation were significant contributors to the suspended solids generation. Based on these preliminary results, SAWPA instituted a hardness fee to all dischargers in order to help cover the revenue imbalance created by the suspended solids. The final stages of the water quality study are expected to be complete in October 2008 and will include chemical precipitation and biogrowth models to project and verify contributions of suspended solids from each of these sources. Results of this study will be used as the basis for permanent changes to the rate structure for brine line dischargers and will be used to develop a recommended maintenance program to address the solids generation. Includes tables, figures.