Interceptor Condition Assessment Program Supports Long-Term Capital Expenditure Planning

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The Metro Wastewater Reclamation District (District) is a regional wastewater treatment authority that was formed by the Colorado legislature as a single purpose special district in 1961.

The District owns and maintains over 250 miles of interceptor pipe ranging in size from 8 to 96-inch in diameter that conveys wastewater from 1.6 million people in a 615 square mile service area that includes most of the Denver metropolitan area. The District developed in-house and implemented an Interceptor Condition Assessment Program (Program) to provide a systematic, consistent and cost-effective approach to assessing pipeline condition and scheduling necessary pipeline rehabilitation for long-term capital expenditure planning.

The Program includes the following basic components:

Closed Circuit Television (CCTV) Recording of the Interceptors

CCTV Videotape Review, Condition Rating Classification and Report

Maintenance of Data in the Interceptor Infrastructure System (IIS) Database

Supplemental Coring Activities on Selected Pipe Segments

Research & Development of New Condition Assessment Technologies

Long-term Capital Expenditure Planning

The objective of the Program is to assess the current condition and rehabilitation needs for inspected interceptors based upon available information, which is primarily CCTV inspection. Review of the CCTV data refines the extent of the rehabilitation requirements, considers the timing of these activities, and estimates the cost of the rehabilitation. CCTV inspection of the interceptors indicates that certain sections are showing signs of deterioration due to hydrogen sulfide corrosion. Funding is then allocated to rehabilitate selected reaches of the interceptor, most likely with a protective lining system (cured-in-place-pipe (CIPP)). The feasibility of utilizing alternative rehabilitation methods is addressed during design of the recommended improvements.

Specific review criteria, developed by the District, that address condition classifications and recommended timing of rehabilitation were developed to provide guidance and direction to the reviewers of the interceptor pipe segments videos. This promotes consistency between reviewers and encourages agreement on similarly rated pipe segments.

Pipe Condition Assessment Reports are prepared to provide a summary of the review including basic background on each interceptor, present pipe condition ratings, recommend a rehabilitation schedule, and provide budgetary cost estimates for rehabilitation in a concise and consistent manner. Cost estimates are developed based on a combination of historical District CIPP projects including bids received and budgetary costs supplied by CIPP contractors. Historical CIPP installation costs are available for pipe ranging in size from 8 to 60-inch in diameter.

In order to further refine the timing, extent and cost of these rehabilitation needs, the Program includes a coring program to core drill samples from points along affected interceptors constructed with concrete pipe. The Program also includes an ongoing investigation of other non-destructive methods to determine pipe condition and remaining pipe wall thickness.

Keywords: Interceptor; assessment; capital; circuit; closed; condition; expenditure; planning; sewer; television

Document Type: Research Article


Publication date: January 1, 2010

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