Condition-Based Asset Management: Investigation, Assessment Of The Oakland Macomb Interceptor System

U-TECH
By John R. Kosnak, P.E., M. SAME and Harry R. Price, P.E., F. SAME | October 2012, Vol. 67 No. 10

Following catastrophic failures encountered by the original owner of the Oakland Macomb Interceptor System -- the Detroit Water and Sewerage Department (DWSD) -- the need for condition-based asset management was identified. At DWSD’s request, NTH Consultants, Ltd. (NTH) performed a condition assessment of the entire Oakland Macomb Interceptor System primarily through the use of closed circuit television.

The Oakland Macomb Interceptor System, which includes approximately 42 miles of sanitary sewer, provides service to 830,000 people in Oakland and Macomb Counties. The interceptor was constructed in the early to mid-1970s by DWSD. Ownership of the system was recently transferred from DWSD to the Macomb County Public Works Commissioner’s Office and an inter-county drain authority jointly owned by the Oakland County Water Resources Commissioner’s Office and the Macomb County Public Works Commissioner’s Office.

The individual interceptor components consist of inside pipe diameters ranging from 36-inches to 153-inches; inverts ranged from 20 to 110- feet below ground surface; and construction materials ranging from cast-in-place non-reinforced concrete, reinforced concrete pipe and concrete cylinder pipe. Installation methods included both tunneling and open-cut construction. The soils around the interceptor are a mixture of granular and cohesive soil, with ground water levels as much as 30 to 80-feet above the invert of the interceptor.

Over the service life of the system there have been three catastrophic failures, each of which resulted in multi-million dollar repair costs. The current investigation, evaluation and assessment program was undertaken after the most recent of these catastrophic failures.

Challenges
The principal challenge to the investigation and evaluation of the interceptor system was that the system had to remain in service during the investigation. As a result, flow levels within the system during the investigation ranged from as low as six-inches to as much as 60 inches. Access to the manholes was a challenge as the alignment of the various portions of the interceptor system are located in road rights-of-way, railroad rights-of-way, through an existing high tension power corridor and easements through both public parks and private property. Work hours were adjusted to take advantage of low flow periods and, when possible, were coordinated with the flow controls used during repairs to what is now the Macomb County-only portion of the system. Work in the areas adjacent to wetlands was scheduled after periods of dry weather to minimize damage to the easements.