Keeping clear water out of the sewer system
The District’s purpose is to collect and treat wastewater from homes and businesses. But through various ways, excess stormwater and groundwater get into the sanitary sewer system, where it gets cleaned unnecessarily. Reducing clear water coming into the sewer system via inflow and infiltration (I&I) can save money while protecting human health and the environment.
What is inflow and infiltration?
Sewer pipes are designed to keep surface water and groundwater out of the system. This extra water, also called “clear water,” is an unnecessary burden on the wastewater collection system and treatment plant. Clear water can enter the wastewater collection system in two ways:
- Inflow: Rainwater or other surface water that enters the sewer system, often through manholes or, in homes and businesses, connecting sump pumps or downspouts to sanitary sewer drains. (This practice is strongly discouraged.)
- Infiltration: Groundwater that enters the sewer system through damaged areas in underground sewer pipes and laterals.
Inflow and infiltration (I&I) is experienced by District and municipal-owned systems, as well as pipes from private residences and businesses.
Why is I&I problematic?
While some communities have a combined collection system for stormwater and wastewater, the District’s is only a sanitary sewer system. In addition, our collection system and treatment plant both have capacity limitations. I&I, especially during significant storm events, can overload the system and cause costly sewer backups into homes and buildings. I&I can also cause sewer overflows into rivers and lakes.
I&I is costly. The District charges owner communities for the amount of flow that arrives at the Nine Springs treatment plant; I&I in the system from broken home sewer laterals, leaky sewer mains or improper sump pump connections increases flow and sewer bills. In addition, I&I results in more energy usage to pump the flow and the unnecessary treatment of groundwater and stormwater.
Why does I&I matter to the District?
I&I reduces the sewer system’s capacity during heavy rains, which could lead to overflows or backups. Wisconsin Department of Natural Resources (WDNR) rules recognize this problem. State administrative code (NR 210.23) requires that all owners of collection systems have a Capacity, Management, Operation and Maintenance (CMOM) Program. A CMOM program requires system operation and maintenance to handle peak flows and that “all feasible steps are taken to eliminate excessive infiltration and inflow from the system.” The District’s I&I reduction program supports our CMOM by working to eliminate excessive I&I. View our Permits & Ordinances.
The District’s I&I reduction program serves a maintenance function that allows for fiscally responsible long-range capital planning. By maintaining I&I levels within allowable limits, the District can forgo spending money to build infrastructure to accommodate I&I and instead invest in capital projects necessary to address community growth.
What are the sources of I/I in the District’s collection system?
Aging infrastructure
One cause of I&I in the collection system is the District’s aging sewer infrastructure. Some of our pipes are more than 60 years old and have leaky joints. To remedy this, the District has a program to assess the condition of our gravity mains and look for leaks with special cameras. With this information, we prioritize the rehabilitation of the worst leakers; rehabilitation includes grouting leaky joints and installing sewer liners to seal the insides of our pipes.
The District does not own all sewer pipes in our service area, though; communities are responsible for their own sewer infrastructure that connects to the District’s larger sanitary mains. Community sewer pipes are subject to the same issues of aging and leaking.
Manholes
During storm events and snowmelt, water can get into the holes of manhole covers or into leaks and cracks in manhole structures. Flood events can also lift manhole covers out of place.
The District’s Collection System Services team regularly conducts manhole inspections and does repairs as necessary.
Sewer laterals
Sewer laterals are the pipes that connect homes and businesses to your community’s sewer system. Over time, sewer laterals can crack or break due to age. Tree roots can also put pressure on these pipes and cause breakages. When this happens, groundwater can enter the sewer system and contribute to the problems associated with I&I.
In Wisconsin, sewer laterals are the responsibility of the property owner.
Improper connections
Connections between the stormwater and sanitary sewer system, which are prohibited, are significant contributors to I&I. Property owners should not connect sump pumps, gutters, roof drains, foundation drains and other stormwater-handling systems to the sanitary sewer system.
What can I do about I&I?
- 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.
What is the District doing to monitor I&I?
The amount of I&I to the collection system varies considerably across the region and within municipalities and individual neighborhoods. The first step in eliminating excessive I&I is identifying where the problem is most severe. Because of variation in rainfall, it typically requires at least three years of monitoring to quantify I&I in an area.
The District is developing a monitoring program utilizing additional flow meters placed at key points of the collection system. These additional meters supplement existing meters and data from pumping stations. The program will grow gradually, allowing staff to learn valuable lessons about monitoring and data analysis. This data will support the District’s capital planning program, and it will be made available to communities to assist in their planning efforts.
What is the District doing to educate the public on I&I
Education and raising awareness of this issue are key to reducing I&I. It is particularly important because private laterals, which are the pipes that connect homes and businesses to the sewer system, are a significant source of I&I.
To support municipalities in educating property owners about the issue, the District developed the DRIIPS (Disconnect and Reduce Inflow and Infiltration to Private Sewers) program. Through DRIIPS, the District has developed a suite of educational materials, which are available on the DRIIPS webpage.
What are potential options for future I&I work?
There are several options that the District may consider in future years. These may be necessary if the District is unable to comply with WDNR rules. Importantly, no actions are being taken on these at this time.
- Sewer Use Ordinance: It may be necessary to amend the District’s Sewer Use Ordinance to provide greater clarity and stronger restrictions on peak flows or similar factors.
- Community work plans: It may be necessary to require I&I control work by individual communities, including specific work plans and enforcement provisions.
The District does not expect to address private laterals directly. The District has no plans to fund private lateral repairs, either through existing District revenues or through a separate charge to communities.
