Combined sewers carry sewage and stormwater in a single pipe. Combined sewers work well during dry weather, but during heavy rain can fill up with more water than they can handle. Combined sewers were designed to overflow directly into the nearest body of water to prevent back ups into homes and businesses. While combined sewers are no longer being built, municipalities and Metro Vancouver are replacing combined sewers with separate sanitary and storm sewers.
[Narrator] All is well in this scene, and in this one where underground sewer pipes are at work. Some contain sewer water, gurgling its way from homes and businesses to wastewater treatment plants. Other pipes are ready to collect rainwater from catch basins on the streets, and carry it to waterways through outfalls. And in some older parts of the region, a third type of underground system is gathering both sewage and rainwater in one pipe, which leads to a wastewater treatment plant.
Combined sewers like this work well during dry weather or light rain, but as west coast people know, it rains here. A lot. Especially in winter. Combined systems get overloaded during heavy rainfall, and rather than backing up into homes, the rainwater and diluted wastewater exits through submerged underwater outfalls. These sewer overflows are detrimental to aquatic life and the environment.
That’s why Metro Vancouver and the member municipalities are making changes to the system in a variety of ways. Each year a portion of combined sewers are removed and replaced with separate twin pipes. It is costly so the work is spread out on a multi-year program. Ground water can also overload separated sanitary systems when it builds up from heavy rain or incorrect pipe connections on private property. The ground water seeps into pipes through cracks. The pipes are not built to accommodate this extra water, and with nowhere to go, the overloaded sewer flow backs up into homes or through maintenance holes where it eventually ends up in waterways.
Changes in rainfall patterns due to climate change contribute to sewer overflows too. Sewer overflows can also be caused by power interruptions at pumping stations, damage to pipes, or equipment malfunctions. Metro Vancouver collects and treats more than one billion litres of wastewater every day at its five facilities and protection of human health and the environment is a primary directive for Metro Vancouver and member municipalities.
For aging pump station machinery, pipes, and valves, a program of assessment and replacement or repair is underway. Like this sewer main repair, taking place at night when flows are lower. Long-term planning to meet the needs of a growing population means that expansions are proceeding at facilities like the Northwest Langley Wastewater Treatment Plant, and across the Fraser River, where a new storage tank is being added which will temporarily hold wastewater to prevent overflows during storms. That’s the ‘low-down’ on why sewer overflows happen, and what Metro Vancouver and member municipalities are doing to prevent them.
Learn more about Sewer Overflows including why sewers overflow, how they are monitored and what you can do to help.