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What is I&I?

April 5, 2023

  • I&I, or Inflow and Infiltration, occurs when stormwater enters sewer pipes through cracks, leaky seals, or faulty or illegal connections.
  • Excess water from I&I can trigger Sanitary Sewer Overflows.
  • Water that enters sewer systems through I&I puts costly pressure on wastewater treatment facilities.

What is I&I?

In the sanitary sewer world, problems often occur out of sight and underground. I&I is one of those issues — but what is I&I, exactly?

The first “I” in I&I stands for “inflow,” which refers to stormwater that enters the sewer system through leaky manhole covers, uncapped sewer cleanouts, or rain leaders, basement sump pumps or foundation drains that are illegally connected to sewer laterals or mains.

The second “I” stands for “infiltration.” Infiltration refers to groundwater that seeps into sewer pipes through cracks, holes, leaky joints, and deteriorated or faulty connections.

I&I and SSOs

I&I and SSOs — this alphabet soup of acronyms stand for a far less appetizing type of soup made of sewer water contaminated with human waste. “SSO” stands for Sanitary Sewer Overflow. A Sanitary Sewer Overflow occurs when contaminated sewer water pushes through manholes and overflows into the environment. This is most frequently caused by wet weather events when all the excess water from a storm enters a sewer system through I&I. The excess stormwater overwhelms the pipes to the point that the contaminated water has nowhere to go but up and out the manhole. The sewage spill can spread human waste and disease and can enter nearby bodies of water, polluting downstream drinking sources.

I&I’s Hidden Costs

SSOs created by I&I pose obvious environmental and financial risks. A less obvious, but potentially costly, harm caused by I&I is the pressure that the excess water from I&I puts on wastewater treatment facilities. All the water that enters a wastewater treatment facility must be cleaned and treated before it is released back into the environment, but only wastewater actually needs that treatment. Cleaning stormwater that enters through I&I is a costly business and can ultimately affect the bottom line for ratepayers.

What can be done?

Maintenance is key! MetroConnects performs proactive maintenance and monitoring of service lateral sewer lines throughout Greenville County. Keep an eye out for our crews as they perform smoke and dye testing to look for cracks in pipes and leaky manholes. It is equally important, however, that you also perform routine maintenance and monitoring of your private lateral lines. The portion of the sewer lateral you are responsible for runs from your property line’s right of way, back to your house. What can you do to make sure your lines are not taking in water?

    1. Cap your cleanout. A sewer pipe cap, or a sewer cleanout plug, is a removable cap that provides access to the sewer line when it needs maintenance. It should always be capped, but often those caps can get knocked off by lawn mowers, or damaged by weather or other events. Check your property for your cleanout — it is usually a white 4-, 6- or 8-inch pipe. If you notice the cap is missing, cracked, or otherwise damaged, you can pick up a replacement at your local hardware store.
    2. Check your gutters and drains. Are they connected to a sewer pipe? Then you are inadvertently contributing to inflow! Have them disconnected to prevent an SSO near — or in — your home.
    3. Follow your roots. Take a look at your landscaping. Could your trees or shrubs be causing root intrusion in your pipes? If so, this could be a source of I&I. Make sure to avoid future problems by following sewer-safe landscaping techniques.
    4. Call MetroConnects! We can inspect your lines to see if you have cracks or leaks in your lines and recommend next steps for repair. Call us at (864) 277-4442 or visit www.metroconnects.org for more information.


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