Process to Estimate Sanitary Sewer Pipe Remaining Life Provides MWWSSB Remedial Decision Information

A condition assessment study for the Water Works and Sanitary Sewer Board of the City of Montgomery's (MWWSSB's) West Catoma Interceptor (WCI) was conducted in 1998 and 2003. The WCI was evaluated in 1998 using core sampling, closed-circuit television, and manhole (MH) inspections. Approximately 193 MHs and 65,000 linear feet (LF) of pipe were inspected. A subsequent study conducted in 2003 was initiated to establish a protocol for defining the remaining useful life of the interceptor's structural constituents, and determine the rate of pipe deterioration in order to schedule rehabilitation, or replacement, of the interceptor. The 2003 study involved core sampling in locations approximately equal to the 1998 locations, and in additional locations. The standard for making interceptor structural constituent useful life projections was based on comparisons of interceptor and MH core samples taken during 1998 to samples taken during 2003. The data were used to estimate hydrogen sulfide (H2S) corrosion since 1998 and to develop reference criteria for the service life of reinforced concrete pipe and cast-in-place MHs (both rectangular and cylindrical). The condition assessment revealed that much of the interceptor had deteriorated at varying levels of severity because of H2S-induced corrosion. Both the 1998 and 2003 investigations provided information that the MWWSSB used to make corrective action decisions. The studies provided baseline criteria describing the theoretical useful life of the interceptor and its structural constituents. Using figures and comparative legends, the present study demonstrates that 72% of the 65,000 LF of interceptor evaluated has an estimated remaining service life ranging from zero to five years. On the basis of this information, the MWWSSB adopted a corrective action implementation plan for the WCI.