Flow and rainfall monitoring, and flow modeling can help identify areas of high flows during wet weather, indicating the presence of I/I. Sewer system evaluation surveys (SSES) can also be used to examine the condition of the sewer system and help to identify likely sources of I/I.
Sewer system evaluation surveys
SSES methods include smoke testing, closed circuit television (CCTV) inspection, and occasionally dye testing.
- Smoke testing involves pumping smoke through sewers from manholes in streets and observing where smoke exits. The exiting smoke can indicate a broken pipe or identify where roof or foundation drains are improperly connected to the sewer system. View smoke testing FAQ (.PDF file) for more information.
- CCTV cameras can be robotically sent down sanitary sewer lines and along each side sewer to record a video of sewer conditions. CCTV inspections can identify breaks, root intrusion, leaking water and deteriorating conditions.
- Dye Testing involves pouring non-toxic fluorescent colored dye down roof drains or catch basins to see if that dye makes its way into the sewer. This provides verification that the storm drainage being tested is directly connected to the sewer.