The City of Phoenix currently owns and operates five surface water treatment plants (WTPs) with a total treatment capacity of 610 million gallons per day (mgd). The locations of these WTPs and their respective raw water sources are illustrated in Figure 1. Three of the five facilities, the Val Vista (140 mgd), Deer Valley (150 mgd), and Squaw Peak (140 mgd) WTPs are located along the Salt River Project (SRP) canal system. In addition to using the SRP canals as a raw water source, these three WTPs also return their residual solids to the canals. Because the US Environmental Protection Agency (EPA) has identified the SRP canals as "Waters of the United States," these discharges are subject to the National Pollutant Discharge Elimination System (NPDES) permitting requirements. Since EPA has no current guidelines for establishing discharge limitations from WTPs, each discharge will be evaluated on a case-by-case basis. The establishment of discharge limits may be determined on a cost effectiveness basis using the Best Conventional Pollutant Control Technology (BCT) procedure as established by EPA. The City's WTPs which operate along the SRP canal system employ conventional treatment processes such as grit removal, presedimentation, chemical addition, rapid mixing, flocculation, final sedimentation, and filtration. At the time of original construction, discharge of waste flow streams to the SRP canals was an acceptable practice, hence no solids handling facilities (SHFs) were initially constructed to process residual waste streams.