AWWA WQTC60575

Castaic Lake Water Agency was faced with a dilemma: how to support the increasing water needs of a growing population in the Santa Clarita Valley with three to five wells in the area shut down due to the presence of perchlorate. Carollo Engineers was hired to design a treatment program for the removal of perchlorate from Saugus Aquifer. Several unknowns challenged the project including an uncertainty in a regulatory MCL for perchlorate, lack of brine line in the area, and low chloride limits in LACSD sewer lines. One of the selected alternatives was throw-away ion exchange. Selection criteria included cost, minimal formation of wastes and full-scale demonstration of the processes. Bench-scale testing of the ion-exchange resins was conducted over a period of 3 months. Single-use ion exchange resins performed well to remove perchlorate below the detection level. The adsorption cycles of two of the resins lasted more than 70,000 bed volumes before perchlorate was detected in the effluent of the columns (approximately 200,000- 550,000 gal/cu-ft resin). No NDMA was formed as a result of post-chlorination with free and combined chlorine, or as a result of prechlorination with free chlorine. The metals measured in the spent results were well below the TTLC and STLC limits, despite the long run times. Ionexchange is therefore a feasible technology for treatment perchlorate in the Santa Clarita Valley. Includes tables, figures.