Many occur after rain events. As sewer pipes age they can suffer from inflow and infiltration, commonly referred to as I & I (Infiltration and Inflow).
Ground water entering sanitary sewers through defective pipe joints and broken pipes is called infiltration. Pipes may leak because of careless installation; or they may be damaged after installation by differential ground movement, heavy vehicle traffic on roadways above the sewer, careless construction practices in nearby trenches, or degradation of the sewer pipe materials. In general, volume of leakage will increase over time.
Infiltration will also occur where local groundwater elevation is higher than the sewer pipe. Gravel bedding materials in sewer pipe trenches act as a French drain. Groundwater flows parallel to the sewer until it reaches the area of damaged pipe. In areas of low groundwater, sewage may infiltrate into groundwater from a leaking sewer.
Water entering sanitary sewers from inappropriate connections is called inflow. Typical sources include sump pumps, roof drains, cellar drains, and yard drains where urban features prevent surface runoff, and storm drains are not conveniently accessible or identifiable. Inflow tends to peak during precipitation events, and causes greater flow variation than infiltration. Sources of inflow can sometimes be identified by smoke testing. Smoke is blown into the sewer during dry weather while observers watch for smoke emerging from yards, cellars, or roof gutters.
Some occur due to roots in the system.
- Although this occurs for many home owners, it is also a source of problem for sewer collection systems. Where I&I can occur, roots can also grow into the pipes. Roots seek water sources and water can be found in the sewer pipes. As the roots grow, they collect debris which can eventually block the flow in the pipe.
- Mains uses cutters on some trucks to 'cut' the roots from the pipe and flush them through the systems flowing. Also use chemical treatment to assist with root control.
Many occur from the collection of deposits of Fats, Oils and Grease (FOG) in the sewer pipes. The FOG debris coagulates and forms blockages in the pipes.
- Oil and grease has poor solubility in water and tends to separate from the liquid solution. Large amounts of oil and grease in the wastewater cause trouble in the collection system pipes. Grease in a warm liquid may not appear harmful. But, as the liquid cools, the grease or fat congeals and causes nauseous mats on the surface of the interior of pipes. It decreases pipe capacity and sometimes blocks the flow through the pipe. Flow will then back-up in the system until it finds and exit. Either at a manhole or unfortunately sometimes in someone's home.
- Mains uses flushing trucks to break up large deposits of FOG to keep the systems flowing. Also use some chemical treatment to assist with FOG breakup.
- The City also uses public education to try and keep FOG out of the systems.
Flushable wipes are not actually flushable.
- Although marketed to the consumer as biodegradable and convenient, the flushable wipe is a major nuisance for sewer collection systems and the wastewater treatment plants. The fibrous material does not easily break down the way traditional toilet paper does can clog the pipes, pumps and screening equipment at the plants. The wipes can combine with other materials, like congealed grease, to create a sort of superknot clogging the pipe which can lead to an overflow.
- Maintenance Staff for the pump stations has modified pump impellers in areas where there are high volumes of wipes. The City also uses public education to try and keep wipes out of the systems.
How Can I Reduce My Stormwater Fee?
Stormwater fee credits are available to commercial and industrial properties that have on-site storm water controls. Please refer to the Stormwater Fee Credit Application and Stormwater Fee Credit Manual for additional information.