During any “normal” day, the flow rate of water coming to the District plant is under 7 million gallons per day. However this jumps drastically when it rains. During one recorded 2.25-inch rainfall, plant flow reached 40 million gallons per day, as the rain water leaked into the sewer main system from cross-connections with storm sewers and improperly connected or leaking house laterals.
Purpose of SSES Testing
The sanitary mains and the treatment plant weren’t constructed to handle the vast amounts of water carried by the City of DeKalb storm sewer system when it rains. The sewage treatment plant process takes time and the capacity is limited. When the plant fills up and can hold no more water, the collection system itself becomes a holding tank for the excess rain water and sewer backups occur.
Finding and sealing the places where storm water leaks into the sanitary main system is crucial to reducing this impact.
Identifying and correcting these problems benefits everyone. Even if your own lateral system is properly separating sewer water from storm water (so that you are not creating your own backups during rain events), if a neighbor has illegal connections or leaking laterals, area sewers fill with water too quickly for it to be drained away by gravity. As water pours in, first the lowest house in the neighborhood and then the next becomes a holding tank for the neighborhood and experiences a backup of storm water mixed with sewage through the basement floor drain.
Types of SSES Testing
Doing Sewer System Evaluation Survey testing helps the City of DeKalb and the DeKalb Sanitary District find the leaks and fix them to keep storm water where it belongs when it rains.
Cross-flooding is done by introducing dye into the storm sewers. Then closed-circuit television is used to observe any impact on adjacent sanitary sewers. This simulates what happens during rain events.
Dye Tests – Is That Antifreeze?
When the storm water is released, the dyed water can be visible in the Kishwaukee. The dye utilized is not harmful to aquatic life, but has turned the river green during past tests.
There are over 4000 manholes in the DeKalb Sanitary District collection system. Manholes can collapse due to age, geological processes, or traffic. Manholes are inspected to identify those in need of repair and to assure that they are not blocked by debris of any kind.
Smoke Testing is a process in which non-toxic “smoke” is blown into the sanitary sewer mains and used as a visual tracer to help determine the condition of the sewer pipes. If, for example, smoke came out of a storm sewer catch basin, it would indicate a connection to the sanitary sewer, which is something we would want to correct.
No Smoke Enters Properly Connected Buildings
If home plumbing connections are in good condition, no smoke should enter any building. Smoke testing crews do not need access to homes, and no change in water usage patterns is required.
Act to Prevent Problems
If any fixtures or drains have not been used in a while, the water in the water seal traps may have evaporated. This condition would allow smoke to enter the home or business. To avoid annoyance and irritation, it is recommended that water be added to any such drains to avoid the possibility of trap malfunction.
Impact of SSES Testing on Residents
The District adheres to City of DeKalb requirements for signage and blockades at cross-flooding sites. District personnel do block off areas of the streets for short periods of time while actively testing. Crews do not need access to homes, and no change in water usage patterns is required.