PIMA COUNTY WASTEWATER MANAGEMENT NORTHWEST OUTFALL INTERCEPTOR EMERGENCY REHABILITATION PROJECT

On September 7, 2002 two sinkholes opened on a busy arterial street in Tucson, Arizona. As a result of the sinkholes a major Sanitary Sewer Overflow (SSO) occurred. Public concern generated by this event prompted an emergency rehabilitation design and construction project utilizing cured-in-place pipe (CIPP) technology. The project had two primary goals:Reduce the flows tributary to the potentially damaged interceptor as soon as possible in order to lower the stress on the pipe.Rehabilitate the remainder of the pipe at the earliest possible date.Unique features of the design and construction included:A two-week fast track design period.Installation of a 38 mgd pumped flow diversion along a river park for the entire project length (5.0 miles) to both relieve flow in the interceptor and to minimize disruption in the impacted neighborhoods by allowing CIPP construction with only minor local flows requiring diversion. The solicitation specification was prepared in just 24 hours and the major diversion was up and running only 42 days after notice-to-proceed.Cleaning two double barrel siphons and rehabilitating the associated inlet and outlet siphon structures, as well as rehabilitating all manholes along the 5 mile alignment.Completing a “fast-track” rehabilitation with substantial completion occurring 149 days after notice-to-proceed.At the time of the sinkholes, Pima County Wastewater Management Department (PCWMD) was preparing several projects focused on long-term preventive maintenance, including a 230-mile closed circuit television (CCTV) investigation of the major sewers within the conveyance system. Because of the public concern, special emphasis has been placed on the unlined reinforced concrete pipe identify those areas with the highest priority for rehabilitation.