West Shore Parkway Sewer Extension
City of Langford
The West Shore Parkway Sewer Extension is a proposed sanitary sewer main project that will involve extending sanitary sewer service from the Happy Valley Road / Luxton Road area, north and west along Luxton and Finney Roads and over a portion of Dewdney Flats to connect with existing sewer works already completed at West Shore Parkway and Highway 14. The extension will also provide a sewer connection point for the recently proposed Center Mountain Development to the south.
Westbrook Consulting provided detailed Civil Engineering design services for the project starting in 2017 to the present, as well as construction cost estimates, survey, and inspection services for preliminary earthworks within the sewer alignment. The project is awaiting finalization of lift station designs by another consultant and confirmation of project funding prior to moving into construction of the sewer main.
A portion of the site falls within the Agricultural Land Reserve, which added increased complexity. Prior to Westbrook’s involvement in the project, the route for the eventual West Shore Parkway Extension and the related sanitary sewer through the Agricultural Land Reserve portion was established between the City of Langford, adjacent private land owners and the Agricultural Land Commission. The horizontal sewer alignment was established based on the agreement and was not able to be varied, restricting the design area.
Another complexity to the project is that the sanitary sewer alignment traverses a portion of Dewdney Flats. The existing ground conditions consist of over 4.0 m of compressible peat overlying compressible silt and clay in some areas. Long term settlement is a very significant design concern and monitoring has been established to aid in the prediction of long term movement.
Immediately east of the Dewdney Flats portion of the route, the future West Shore Parkway Extension and sewer entered an area of very deep rock cuts, as high as 18 m deep. Consideration had to be given to both constructing the sanitary sewer, as well as allowing for the future West Shore Parkway Sewer Extension within the restricted corridor.
Throughout the detailed design portion of the project, Westbrook has worked closely with the project geotechnical consultant to confirm the magnitude of potential settlements. As a result, Westbrook proposed an alternate design, which eliminated the gravity sewer through Dewdney Flats and the deep rock cut and replaced it with a second sanitary sewer lift station and related forcemain. The switch to the forcemain reduced the depths of excavation required and provided a degree of flexibility for anticipated long term settlements. The alternate design also resulted in reduced rock cuts along the future West Shore Parkway. As a result, proposed cuts were reduced from as much as 18 m down to 12 m.
Prior to proceeding with detailed design of the alternate concept, Westbrook reviewed the anticipated construction costs of the original option with one lift station and the alternate option of two lift stations, with a forcemain and shallower excavation depths, and was able to confirm that the alternate plan was expected to lower the overall capital cost by as much as $ 1 million.
Preliminary earthworks within the corridor are underway and once funding is secured, the sanitary sewer main will proceed to construction.