Optimizing Arsenic Removal in Peoria, AZ Surface Water Supplies for Blending High Arsenic Wells

摘要

Since the promulgation of the USEPA Drinking Water Regulation for Arsenic, the City of Peoria, Arizona, has been developing system-wide Arsenic mitigation solutions to meet the new maximum contaminant level of 10 μg/L. One solution that can be used to lower Arsenic concentrations in water delivered to the drinking water distribution system is blending. In the development of a blending design, it is necessary to secure a dependable, low Arsenic source water with which to blend. One possible low Arsenic source for the City of Peoria is surface water supplied by Salt River Project (SRP). Peoria treats this water through the Greenway WTP located at the end of the Arizona Canal. If the Greenway WTP were to consistently deliver water with low Arsenic levels, the treated water could be used to blend down the concentration at some high Arsenic wells. SRP water primarily comes from the Salt River, Verde River, the Central Arizona Project (CAP) canal, and SRP groundwater wells that operate based on canal system needs. The percentage of flow contributed to the Arizona Canal from each source varies throughout the year and each surface water source can be the primary contributor to flow. Raw water Arsenic concentrations at the Greenway WTP vary significantly based on source water contributions. The Salt River and CAP Canal have consistently had Arsenic concentrations less than 5-6 μg/L, but the Verde River water has Arsenic concentrations that can vary from 8 μg/L to 18 μg/L. Significant contributions of Verde River water will require improved Arsenic reduction in the Greenway WTP in order for blending to be feasible. Currently the Greenway WTP removes only 10 – 20% of the raw water Arsenic. City of Peoria Utilities Department engaged the services of Damon S. Williams Associates (DSWA) to provide options for dealing with the varying Arsenic levels from the multiple water sources and to provide options and recommendations for the treatment facility to meet future drinking water regulations at a cost effective price. In order to assess the possibility of improved Arsenic removal, a bench scale evaluation was performed. Testing was conducted on the three surface water sources that contribute flow to the Arizona canal: the Salt River, Verde River, and CAP Canal. Two coagulants, Ferric Chloride (Ferric) and Aluminum Sulfate (Alum), were tested at a range of coagulant doses and under three pH conditions. The affect of ozone preoxidiation, which is currently employed at the Greenway WTP, was also tested. TOC removal was evaluated for all tests to ensure continued compliance with the Disinfection Byproducts Rule and associated Surface Water Treatment Rules.