SSO Program (1998 to 2002)

By design, the investigation/prioritization/rehabilitation/evaluation process changes constantly. As the consolidated program has progressed over the past six years, MSD has learned more about how the collection system responds to different remedial techniques and new investigation and remedial technologies have become available—thus the original 15-year plan devised in 1997 has changed dramatically. Success of the program cannot fairly be measured in simplistic terms such as “total number of SSOs reduced per year” simply because the depth of MSD’s investigation process has tended to uncover problems that were unknown in the past.

Between 1998 and the present, the SSO program focus has shifted. Initially, the program was primarily investigation-based—focused on characterizing the system and quantifying/prioritizing the problems. From 2000 to 2002, the program shifted toward large-scale rehabilitation and evaluation, averaging over $8M annually in sanitary sewer rehabilitation projects in order to repair those areas deemed critical during the characterization phase. To determine the effectiveness of these rehabilitation construction projects, MSD used flow monitoring to compare pre-rehab and post-rehab data. The results of these post-construction evaluations have shown that large-scale collection system rehabilitation may not be the most cost-effective method to reduce SSOs and improve water quality. Therefore, beginning in 2003, the SSO, CSO, and MS4 programs were integrated in order to “step back” and evaluate water quality from a holistic, watershed-based approach. Conventional wisdom in SSO reduction/elimination has been moving away from indiscriminate, wide-scale sewer and manhole rehabilitation and toward more targeted, cost-effective approaches to increase conveyance capacity. While traditional sewer rehabilitation techniques are still used to renew deteriorating infrastructure, MSD no longer uses these techniques for the sole purpose of reducing wet weather impact on the collection system.

Related Links

Prior to 1988 Initial CSO Program Efforts
1988 to 1997 SSO Program Efforts
2002 to July 2003 Holistic Watershed Approach

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