Study to Evaluate Long-Term Trends and Variations in the Average Total Dissolved Solids Concentration in Wastewater and Recycled Water

This report was funded by the Southern California Salinity Coalition (SCSC). SCSC and its member agencies are dedicated to managing salinity in the water supplies, wastewater, and recycled water. Member agencies include Eastern Municipal Water District (EMWD), Inland Empire Utilities Agency (IEUA), Metropolitan Water District of Southern California (MWDSC), Orange County Sanitation District (OCSD), Orange County Water District (OCWD), San Diego County Water Authority (SDCWA), Sanitation Districts of Los Angeles County (LACSD), and Santa Ana Watershed Project Authority (SAWPA). Daniel B. Stephens & Associates, Inc.

(DBS&A) performed the analysis and is submitting this technical memorandum to address the research questions posed by SCSC and its member agencies. The 2011 to 2016 drought in California, in conjunction with unprecedented statewide conservation legislation, caused several member agencies to face challenges meeting regulatory water quality standards for the salinity of discharge water from wastewater treatment plants (WWTPs). In particular, total dissolved solids (TDS) concentrations have increased, while the operation of WWTPs have remained consistent with prior years. Figure ES-1 is a typical example of TDS trends for WWTPs in Southern California.