Inflow and Infiltration

In the 1980s and early 1990s, the City Wastewater Facility would experience very high peak flow rates during rain events, often causing bypasses. At that time, the plant’s NPDES permit allowed a limited number of bypasses, and we were exceeding that amount. A large part of the problem was the combined sewer/storm system in some areas of the city. To address this problem, a Combined Flow Separation Program was initiated in 1994. Twelve projects were developed and about 8,000 Inflow and Infiltration (I&I) points were removed, reducing flow by an estimated 20 million gallons per day (MGD) during heavy rains. 

Although great progress had been made, we recognized that more work needed to be done. In 2010, the City hired a contractor to perform an I&I study on the city’s sewer collection system. The scope of work was later expanded to include identifying source defects and making recommendations for repairs. A five-year plan was developed to address some of the defects found in the study area. This program began in 2013 and encompasses the repair of 1,588 manholes, 17 cross connects, and 116 main lines. They also performed a second sewer system evaluation survey after repairs were made. More detailed information can be found in the presentation that was given at the 2013 Missouri Water and Wastewater Conference.

Because of goals set forth in the Clean Water Act, new regulations and aging sewer systems, I&I flow reduction will most likely be an unending effort.


Smoke Testing Smoke Testing
Smoke testing is an efficient and cost effective way to help identify areas where rain water is entering the sanitary sewer system. Rain water can cause an unnecessary load on the Wastewater Treatment Facility, and could potentially cause sanitary sewer backups. During smoke testing, smoke-filled air is forced through a sanitary sewer line. The smoke under pressure will fill the main line plus any connections and then follow the path of any leak to the ground surface, quickly revealing the location of any defects.