AWWA MTC57541 ✓ Most Recent

The City of Scottsdale, Arizona manages a Centralized Groundwater Treatment Facility (CGTF). The source water to the CGTF comes from four production wells. At this facility, the City employs air stripping to remove trichloroethylene (TCE). The design capacity of the CGTF is 13.5 million gallons per day (mgd) and the average operational flow is approximately 11.5 mgd. The total dissolved solids (TDS) and hardness concentrations of the CGTF effluent are respectively 830 mg/L and 390 mg/L. The City is planning to install a reverse osmosis (RO) treatment plant to treat a portion of the CGTF effluent and blend the RO product water with the CGTF effluent to achieve lower levels of TDS and hardness. In addition to lowering the TDS and hardness, the City expects the RO treatment to reduce the levels of arsenic and nitrate in the blended water to well below their target goals of 6 ug/L and 8 mg/L as N, respectively. The existing pipe in the distribution system that receives the CGTF water is 25-30 years old, galvanized iron pipe. Visual examination of the pipe has shown varying degrees of corrosion and scaling. Corrosion of galvanized iron pipe is the source for iron and zinc, while precipitation from water is the source for calcium and silica. The City wants to avoid upsetting the existing scale or excessively releasing corrosion products when the CGTF and RO blended water is delivered through the old, rusty pipes. This paper outlines a successful approach to identifying water quality conditions that would minimize corrosion and scaling when RO treated water is introduced into the distribution system. Includes 2 references, tables, figures. See more