Understanding and Assessing Impacts
Wet weather sanitary sewer overflows are typically the result of excessive amounts of rainwater inflow and groundwater infiltration entering the sanitary sewer system. Increased frequency and severity of rainfall events—a direct consequence of a changing climate—means both young and older communities are at risk of excessive inflows in their sewer systems. These inflows can occur when roof drain leaders, foundation drains and drainage catch basins are incorrectly connected to sanitary sewers instead of storm sewers. Further, cracks and loose joints in storm sewer laterals can lead to exfiltration into the sanitary system. As climate change makes this a more pressing issue across Canada, one of the challenges in confronting this problem is that losses resulting from excessive inflow and infiltration are frequently misidentified by the public to be exclusively the result of municipal infrastructure failure. In reality, as local officials in Surrey identified, 30 to 70 percent of inflow/infiltration originates from private sewer laterals. That is, problems with sewer connections and laterals on private property have the potential to cause damage to the community as a whole. While owners are responsible for repairing or replacing their sewer connection so no rainwater or groundwater enters the system, the City of Surrey found that a significant and growing volume of rainwater has been entering the sanitary sewer system through private connections. This posed a unique challenge to the local government in Surrey. They had to devise a proactive approach that would inspire private property owners to assess the state of their sewer laterals for the benefit of an entire community. Upon understanding the issue and the obstacles that needed to be overcome, the City of Surrey began to plan out a program that would facilitate the mandatory replacement of private sewer laterals in desperate need of improvement.