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Sanitation District No. 1 Implements Innovative and Aggressive Continuous Sewer System Assessment Program

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Many utilities throughout the Unites States are facing the reality that their underground sewer assets are deteriorating and many have reached the end of their useful lives. In addition, the Capacity Maintenance Operation and Management (CMOM) portion of the proposed SSO Rule is being included in many NPDES permits as well as Consent Decrees.

In April 2007, Sanitation District No. 1 of Northern Kentucky (SD1), which serves over 97,000 customer accounts in Campbell, Kenton, and Boone Counties, entered into a Consent Decree with USEPA Region 4 and the Kentucky Division of Water (KDOW) to address CSOs and SSOs in the sewer system. The Consent Decree requires the District to conduct a CMOM self assessment as well as a Nine Minimum Controls Compliance (NMC) Evaluation to document their degree of compliance with NMC and CMOM requirements.

One result of the audit and compliance evaluation was the development of an aggressive and comprehensive Continuous Sewer Assessment Program (CSAP) that will include O&M goals related to the NMC and CMOM in the same program. This presentation will document the development and implementation of the District's CSAP, which began operation in January 2008. The overall goal of the program is to cost-effectively minimize O&M related spills and to implement system renewal and rehabilitation in a way that targets dollars where they have the highest benefit. For the collection system, the benefit is a reduction in sewer failures and failure consequences.

The CSAP comprises six individual O&M programs that include a prioritized, structured, and perpetual approach to preventative O&M, sewer assessment and sewer rehabilitation. The overall structure of the program is based on an Asset Management approach. That is, the program will be set up to prioritize assets based on their consequence and likelihood of failure. This approach helps ensure cost-effective use of rate-payers money considering that there are many other needs that the District must address as part of the Consent Decree implementation. The six individual O;amp;M programs include:

Trouble Call Program (TCP): The trouble call program is the program where the Districtreactively responds to calls from customers who suspect they have a problem related to their sanitary sewer.

Preventive O&M Program (POMP): The Preventive O&M program comprises activities designed to proactively prevent system failure such as pipe collapses and blockages that can cause or exacerbate overflows in the sewers system.

Sonar Program (SOP): The Sonar program is an assessment program the District currently uses for the interceptors in the combined system and large trunk sewers in the separate system with high base flows that preclude CCTV inspection.

Sanitary Sewer Evaluation Survey (SSES) Program: The SSES program comprises activities designed to help find sources of I/I, evaluate the potential to cost effectively remove I/I, and subsequent activities designed to cost effectively remove I/I sources in targeted areas.

Large Diameter Sewer Assessment Program (LDSAP) : The LDSAP program is targeted toward District larger sewers where the consequence of failure (criticality) is high.

Manhole Inspection Program: The manhole inspections will be performed at the same time as the sewer inspections associated with the above sewer programs.

A key feature of the POMP is the priority-basin approach. The Districts sewer system is divided into approximately 250 gravity drainage basins, 182 of which are in the separate sewer system. These 182 basins comprise the priority basin area. The priority basin approach essentially means that assessment and rehabilitation activities will focus on an entire basin at a time. This allows for efficient use of CCTV and engineering resources while still focusing on areas that need the most attention. There are three exceptions to this approach. These are pipes located within 50' of a stream, immediately downstream of an SSO, or pipes within an SSES area. These areas were deemed to be high priority and should not wait for its tributary basin to be completed.

Each basin was given a priority score based on a combination of structural and service condition criteria. These criteria were scored for each basin based on a significant amount of information available from the District's gbaMS (George Butler Master Series) CMMS (computerized maintenance management software) which is used to track the inventory and work order associated with the District's assets. Information used in the analysis included CCTV data, work order histories, failure history, Preventative Maintenance history, and its vicinity to a known SSO.

The CSAP was split into two phases; the Assessment Phase and then the Implementation Phase which includes a Cleaning Program and Rehabilitation Program Component. The program was designed to inspect the entire District's service area at least once within 10 years, but will include the assessment of an equivalent system length within 5 years from reoccurring inspections. This is due to the fact that some critical assets may be inspected twice before some are assessed once. This is the necessary result of the Asset Management approach.

A process flow chart was then developed that includes a detailed decision-making procedure for conducting initial inspections as well as re-inspection and re-cleaning frequencies, which depend on the asset's observed condition and criticality. The process flow chart also includes a method to assign assets a rehabilitation priority score of 1-3 based on several factors. The rehabilitation priority score is one of several criteria that will be used to develop, prioritize and implementrehabilitation projects.

The program also includes the development of an interim access database software tool that will automate the process flowchart that was developed. This tool takes the structural and maintenance SCREAM scores from the CCTV results and then lists the next step in the assessment process with a target date. These dates can then be used to develop timely work orders that will then be tracked in the District's gbaMS CMMS software. The interim tool will be replaced in the near future with a permanent tool that will work with gbaMS to automatically generate work orders for the next action based on the inspection results.

With limited external funding sources for infrastructure improvements, municipal utilities are challenged to develop cost-effective O&M programs. A prioritized and proactive approach for sewer system assessment and rehabilitation provides a way to identify and justify to the stakeholders and regulators those sewers and manholes where rehabilitation dollars will have the greatest benefit.

Keywords: CCTV; CMOM; CSAP; asset management; criticality; sanitary sewer overflows; structural assessment

Document Type: Research Article

DOI: http://dx.doi.org/10.2175/193864709793847339

Publication date: January 1, 2009

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