Subject: Trunk Sanitary Sewer, Operations and Management
Keywords: condition assessment, trunk sanitary sewers, CCTV inspection

The Regional Municipality of Peel is located on the west side of the City of Toronto adjacent
to Lake Ontario. Peel’s wastewater scheme consists of 2 major drainage systems (the East
and West systems) each of which outlets to a treatment plant located on the shores of Lake
Ontario. The lake-based wastewater system currently services approximately 1 million
people.

In 1997 the Region commenced a pilot program to inspect two large diameter trunk sanitary
sewers using combined Closed-circuit Television (CCTV) and Sonar equipment. Successful
completion of the pilot program lead the Region to initiate a comprehensive Trunk Sewer
Inspection and Condition Assessment Program to address the needs of the entire trunk
sewer system. This involves some 210 km of pipes ranging in size from 750 mm to 3050
mm in diameter (see summary in Table 1). Based on known needs and available
technology a multi-year, staged program was developed. Approximately 50,000 m of
pipeline and some 500 structures have been inspected each year since 1997. Stage 1 of
the annual program involves an initial “First Order” inspection of the assigned sewers and
manholes for that year.

In Stage 2, assets are rated according to a defined set of criteria,
needs are identified and priorities ranked. For the most part condition assessment results
are clear cut with the majority of pipelines and structures found to be in good condition
while only a few need obvious repair or rehabilitation. However, in some cases the
implications of the First Order inspections are not obvious and further detailed
investigations are warranted in order to finalize condition assessment conclusions; these
detailed, “Second Order” investigations are carried out in Stage 3. Selecting from a menu
of available techniques, detailed investigations are tailored to suit site specific problems
and objectives. These have involved in-depth hydraulic analysis, monitoring of corrosive
environments, person-entry inspections, concrete coring and detailed structural
investigations.

The Stage 3 findings are then used to finalize and update the Stage 2
condition assessment rankings. Finally, in Stage 4, findings are compiled and feasible
remedial techniques are programmed into the next year’s Capital Budget.

The purpose of this paper is to explain the importance of a systematic and proactive
approach for managing large diameter trunk sewers. The paper highlights how this program
has evolved to become an important tool in developing and prioritizing the Region