Environmental Science & Engineering - www.esemag.com - September 2003
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City of Ottawa uses cured-in-place lining to rehabilitate sanitary sewer access structures

By Gerald Bauer, P.Eng. and
Phil Reeve, P.Eng.

 
Installing the one piece Poly-Triplex cured-in-place liner.
The City of Ottawa is a major urban community of 785,000 people, covering an area of 276,000 hectares. The City has experienced rapid growth over the last decade, requiring sewers to be extended further from the trunk sewer system and pollution control plant. The local topography also requires a number of pumping stations and forcemains to service the suburban communities. Due to the length of forcemains, detention times and configuration of the main sewers, turbulence is created at forcemain discharges, resulting in elevated levels of hydrogen sulfide in some sewers. This has resulted in accelerated deterioration of concrete access structures at two forcemain discharges, due to biogenic corrosion (i.e. H2S).

The first structure is located on the Stittsville Trunk Sewer in Stittsville, just downstream of a forcemain discharge. A significant amount of turbulence is created due to a 6 m drop into the structure. The second structure is located on the Hines Road Trunk in Kanata. The structure is the discharge point for a 9 km long forcemain that services the Village of Carp. City officials concluded that a longterm rehabilitation solution was needed to protect these two access structures.

The City of Ottawa retained R.V. Anderson Associates Limited, in association with J.L. Richards & Associates Limited, to study the problem and determine a cost-effective solution. The consulting team collected field data on the extent of concrete deterioration and levels of hydrogen sulfide in the system. Collecting and understanding all relevant data was critical to determining a cost-effective solution.

Both access structures are located in residential areas and are constructed of pre-cast concrete with varying dimensions. The Stittsville structure is a 1600 mm by 1750 mm chamber, 9.5 m deep, built in 1977. A short chimney, 762 mm in diameter, provides access to the chamber. Due to the depth of the structure, a safety landing is located in the chamber. The Hines Road structure is a 1520 mm diameter chamber, 6.1 m deep, built in 1980. A short chimney, 762 mm in diameter, provides access to the chamber.

The assessment identified various solutions, including: Information regarding construction applicability and limitations, costing, availability, requirements, experience, local knowledge and timing was obtained from suppliers and contractors, and the various options were carefully assessed. The City required a cost-effective solution able to withstand the corrosive environment at the structure that would last at least 20 years. The Poly-Triplex® cured-inplace liner was recommended as it provided the best long-term rehabilitation option due to the structure size, location, geotechnical conditions, and the corrosive environment. The Poly- Triplex cured-in-place liner provided an impenetrable membrane to the hydrogen sulfide. The project also included replacement of ladders and landing systems in 316 stainless steel with fibre reinforced plastic grating panels.

Both access structures were lined without disrupting the sewage flow in the system, which minimized inconvenience to the area residents and reduced costs. The work was accomplished by constructing a platform over the pipe invert in the access structure. This “trenchless” solution avoided large-scale, expensive, deep excavations in established residential neighbourhoods. The installation for each site took one to two days of preparatory work, one to two days of liner installation and one to two days of site clean-up.

The Poly-Triplex liner installation used low pressure steam for curing the resin but this could be replaced with hot water.

It is estimated that the lining of the two access structures saved the City about $50,000.00 as compared to full replacement. This was the first time that a cured-in-place lining was used to rehabilitate access structures in the Province of Ontario. The work was completed by Supertec Wastewater Services Ltd., of Montana.
Gerald Bauer is an Associate with R.V. Anderson Associates Limited. Phil Reeve is Senior Project Manager with J.L. Richards & Associates Limited.

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