Inflow and Infiltration
What is Inflow and Infiltration?
Inflow and infiltration (I&I) is rainwater and groundwater that enters sanitary sewer pipes through:
- holes or cracks caused by damage, age, or tree roots
- leaking pipe joints or maintenance hole covers
- roof and foundation drains that are improperly cross connected
The graphic below (PDF) shows some of the issues that cause I&I and the division of public and private responsibility.
Why is I&I a Problem?
Sanitary sewer pipes are designed to accommodate a small amount of rainwater and groundwater, but in cases where sanitary pipes are damaged or improperly connected, rainwater and groundwater takes up space that is intended for wastewater from homes and businesses. This reduces the space for wastewater in the sewers which can result in backups and sanitary sewer overflows (SSOs). Backups and SSOs can cause property damage, send untreated wastewater to the environment causing negative impacts on ecosystems and be a public health hazard. I&I is an especially large issue during rainstorms such as atmospheric river events and the spring snow melt.
I&I is also expensive. In 2024 Metro Vancouver introduced Wet Weather Sewer Pricing, which means cities pay more for excess wastewater treatment during rain events, increasing utility bills for residents.
I&I in Coquitlam
Nearly 50% of the sanitary sewer system is located on private properties and are privately owned. This means that collaboration between the City and property owners is crucial to the management of I&I and sewer system performance. The City inspects the entire municipal sewer system on a 20-year cycle, and invests nearly $1M each year to investigate and address I&I.
Fog Testing
Fog testing is a standard method for confirming the correct operation of connections to the sanitary system and identifying improper connections or defects. During testing, a fog machine and high velocity fan are temporarily installed on municipal maintenance holes, where the fog is pushed through the sewer system. This visible fog is non-toxic, and should vent through the sanitary vent stacks on property roofs. If your neighbourhood is scheduled for fog testing, you will be notified in advance.
Sanitary Connection Grant Program
Coquitlam’s Sanitary Connection Grant Program seeks to support eligible property owners to replace their sanitary laterals by funding 25% of the replacement cost up to $2,000. See the Sanitary Connection Grant Program for more information.
What You Can Do
You can help reduce I&I from your property by:
- Avoiding planting trees or shrubs near sewer pipes
- Having a plumber or drainage specialist inspect your sanitary pipes for damage (Metro Vancouver recommends this should be done at least once every 10 years)
- Checking that your basement and foundation drains are not connected to your sanitary sewer pipes
- Checking that your gutters and outside drains are not connected to your sanitary sewer pipes
- Repairing defective or broken sewer pipes on your property
More Information
Links:
Reports to Council: