There are two types of sewer systems commonly used in residential areas: low-pressure systems and gravity-fed systems. In general, low-pressure systems are used in lower-density areas, and gravity systems are used in higher-density areas.
The type of sewer system being constructed in South St. Andrews is a low-pressure system. This is the type of system most commonly used by municipalities with similar population density to South St. Andrews. Low-pressure systems are in use in many Manitoba municipalities. Gravity systems, in contrast, are typically used in cities and in denser residential areas.
Stantec, the project engineer, evaluated whether a gravity-fed system would be feasible in South St. Andrews. Stantec determined that a gravity system would be approximately three times the cost of a low-pressure system, which would make connection fees cost-prohibitive for most homeowners.
Apart from the comparative affordability of a low-pressure system, a second benefit is that low-pressure service piping is shallower and smaller in diameter, which reduces the impact of construction on existing property and infrastructure.
A low-pressure system requires that each connecting property have a septic tank and small pump, which helps pressurize the sewer line and moves wastewater toward the treatment facility.
In most cases, residents who have an existing two-cell septic tank in good working order can continue using their tank with the new system. Residents with single-cell tanks may be able to have their tanks converted if the existing tank is environmentally sound.
Two types of pump are commonly used in low-pressure systems: either a pump installed inside the home or a pump installed inside the septic tank. The system in South St. Andrews is being designed to accommodate both types of pumps where possible.
As in other municipalities, installation of the pump, a check valve, and the piping that runs on the homeowner’s side of the property line will be the responsibility of the homeowner. Work must be done by a licensed contractor. For homeowners’ convenience, the RM will explore the possibility of working with project engineers to provide a list of pre-qualified companies. Homeowners would remain free to work with any licensed, qualified contractor of their choosing.
A low-pressure system requires that solids in the septic tanks still be pumped out, although required pumping is very infrequent. A family of four typically requires only one pump-out per year.
A typical installation with the pump housed inside the septic tank. The pump can also be located inside the home.