This paper contrasts the costs of managing wet-weather-induced inflow and infiltration (I/I) with the policy requirements of the federal and state water quality agencies. The presentation describes the framework in which the study was conducted, illustrates the techniques used for coordinating the study with regulatory agencies during the conduct of the study, and presents the costs of alternative levels of improvements. The 2.5-year study culminated in the preparation of U.S. Environmental Protection Agency (EPA) Step 1 201 Facilities Plan and a state of California required Environmental Impact Report (EIR).1 The East Bay Municipal Utility District (EBMUD) is responsible for the interception and treatment of wastewater flows from a 215-km2 (83-sq mile) tributary area along the eastern shore of San Francisco Bay (Figure 1). Seven collection agencies’ systemas contribute flow to the district’s interceptor system. Prior to the completion of the district’s interceptor and treatment system in 1951, wastewater flowed without treatment directly into the bay. The district interceptor system encompasses over 34 km (21 miles) of large-diameter pipe. The district operates secondary treatment facilities with a dry-weather design capacity of 4.54 X 105 m3/d (120 mgd). The treatment plant hydraulic capacity is 1.10 X 106 m3/d (290 mgd); and during infrequent severe storms, an effluent of blended primary and secondary treatment is discharged at a depth of 12 m (40 ft) in bay waters. Figure 2 depicts the treatment plant process flow schematic.