Bedford/Sackville Trunk Sewer Study

Project Description
Halifax Regional Municipality (HRM) identified the need to review access to and inspect and map each manhole of the trunk sanitary sewer system for the Bedford / Sackville area. Sections of the system, dating back to the 1960s, extend approximately 10 kms from Millwood Drive in Sackville to the recently upgraded Fish Hatchery Park Pumping Station in Bedford. HRM had minimal information regarding the condition of this pipe and manhole network, due to age and location. Most of the system is located adjacent to the Little Sackville River, as well as the lower reaches of the Sackville River, and access for repairs was difficult. HRM has been initiating programs to reduce infiltration and inflow (I/I) into the municipality- owned sanitary systems. Infiltration and inflow is a result of groundwater and surface water entering the sanitary system in addition to the sanitary sewer loadings. This additional flow can overload the system and possibly result in sewer overflows to the environment.

Services Provided
Terrain Group provided topographical survey information for the entire trunk sewer alignment, including vertical and horizontal locations for each of the 133 manholes. Each manhole was labelled and photographed, inspected for condition and possible I/I causes, and manhole diameters and pipe inverts were measured. During the field investigations, a proposed access route was also determined and noted. Plan and profile drawings were prepared for the entire trunk sewer alignment, which identified the manhole locations, pipe size, slope, and inverts as well as the proposed access route for each of the manholes. Data sheets were prepared for each manhole, including coordinates of the cover, a sketch of the location, depth and inverts, flood elevations, proposed repairs to reduce I/I, digital photograph, and other relevant information. Some of the manholes were inspected during rainfall events to further confirm the causes of I/I. To further understand the impacts, Terrain prepared quantity estimates of the I/I for each manhole. The estimates, ranging as high as 20 l/s per manhole during the 100-year storm event, indicate a significant impact on the system. A hydraulic model of the trunk sewer was built to analyze the existing capacity and pinpoint any constraints in the system. The model was also used to review the effect of I/I reduction and future development.