While the sanitary sewer and storm sewer pipes should not be interconnected, clear water does get into the sanitary sewer system. Clear water that enters into the sanitary sewer system is called Inflow and Infiltration, or I&I.
Infiltration refers to groundwater that seeps into sewer pipes through holes, cracks, joint failures, and faulty connections. Inflow is stormwater that quickly flows into sewers via roof drain downspouts, foundation drains, storm drain cross-connections, and through holes in manhole covers.
Why You Should Care About Inflow & Infiltration
All of the water that comes to our facility needs to be cleaned. Neither the sanitary sewer system nor our treatment facility was designed to handle stormwater, so when all that additional water enters the sanitary sewer system, it flows to our plant and we have to treat it.
Why is I/I Problematic?
- Takes up capacity in the collection system and treatment plant and ends up at the regional wastewater treatment plants where it must be treated like sewage, resulting in higher treatment costs.
- Contributes to sewer system overflows in local homes and the region’s waterways, negatively impacting public health and the environment.
- Results in more energy usage to pump the flow and the unnecessary treatment of groundwater and stormwater.
- If left untreated, I/I could lead to funding a plant upgrade, because influent flows are exceeding permit and design capacity.
What Are We Doing About I/I?
- Main & Lateral Televising – A robot camera with the ability to record, moves through existing openings in the sewer pipe. These cameras are self-propelled and can inspect the sewer main and lateral at the same time. The cameras are an essential inspection tool for identifying infiltration and inflow, solids accumulation, root infiltration, pipe defects, and the structural condition of lateral services and mainline sewers.
- Manhole Inspections – Traditional inspection methods include visual observation by trained technicians along with the completion of detailed inspection forms and supporting photographs. Advanced techniques include the use of cameras that are remotely operated from a vehicle. The units use a telescoping lowering device, a high-powered camera with a remotely adjustable zoom lens, and powerful lighting. The zoom system allows for digitally recording of the condition of the manhole as well as inspection of pipe segments immediately upstream and downstream of the manhole.
- Flow Monitoring – Flow monitoring is an essential procedure to collect data for evaluating and characterizing wet-weather and dry-weather flow conditions in sanitary sewer collection systems. Real-time use of the data for supporting operational decision-making/optimization and in-time maintenance activities.
- Sump Pump Inspections – Most homes built after 1920 have foundation drains that surround the home. These drains collect the groundwater that gathers at the home’s foundation and drains the water away from the home. Many homes in the City of Fond du Lac have their foundation drains directly connected to the sanitary sewer system, rather than being collected by a sump pump system and discharged into a storm sewer or into the home’s yard. Foundation drain connections contribute a considerable amount of inflow into the sanitary sewer system.
- Smoke Testing – Smoke testing is a relatively simple process that consists of blowing nontoxic, nonflammable smoke mixed with larger volumes of air into the sanitary sewer line. Usually induced through the manhole, the smoke travels the path of least resistance and quickly shows up at sites that allow surface water inflow. Smoke will identify broken manholes, illegal connections (including roof drains, sump pumps, yard drains, and more), uncapped lines, and will even show cracked mains and laterals providing there is a passageway for the smoke to travel to the surface.
- Flow Modeling -Rainfall-derived infiltration and inflow (RDII) of extraneous stormwater and groundwater to sanitary sewers can unduly affect the capacity and operation of collection and treatment systems. In many cases, excessive RDII can be a significant cause of sanitary sewer overflows (SSOs) and basement backups. We are investing significant resources on reducing RDII through sewer rehabilitation/replacement and private property efforts to eliminate sources of RDII.
What Can You Do?
- Do not connect sump pumps to the sanitary sewer.
- Do not connect roof drains and gutters to the sanitary sewer.
- Do not connect foundation drains to the sanitary sewer.
- Keep all cleanouts capped, both inside and outside. This will help keep unwanted water out of the sanitary sewer system and prevent sewer gas from entering your home.
- Avoid planting trees/shrubs over your sewer lateral, as tree roots can damage sewer piping.