WHAT IS INFLOW AND INFILTRATION (I&I)
There are three components to wastewater flow in the sanitary sewer system, base sanitary (or wastewater) flow, groundwater infiltration and rainfall derived inflow and infiltration, more commonly called inflow. Virtually every sewer system has some infiltration and/or inflow. Historically, small amounts of I&I are expected and tolerated. However, infiltration and inflow may be considered excessive when it is the cause of overflows or bypasses, or the cost to transport and treat exceeds the cost to eliminate it. In cases where the I&I may not be considered “excessive” from a cost-to-eliminate perspective, but causes health or environmental risks, corrective actions are required.
To keep it simple I&I is clear water from rainfall and groundwater entering the sanitary system, and causing excessive flow which can cause back-ups and overflows/bypasses in the collection system and at the Waste Water Treatment Plant.
Municipalities will be well served to understand the dimensions and nature of any I&I problems. A clear set of goals is important for keeping an I&I program focused.
WHAT THE TOWN OF HEBRON HAS DONE
We have begun a multi-step program to reduce and/or eliminate sources of inflow and infiltration.
- In 2015 the Town of Hebron installed a Remote Monitoring Auto Dialer with real time notifications, at the Monroe St lift station, which allows us to respond to problems much sooner.
- In 2016 the Town of Hebron contracted with Midwest Contract Operations. to install flow meters in specific sub-basins of our collection system, to determine the area of the greatest source of I&I.
- Using the information from the flow meters, in 2016, the town smoke tested the areas of the greatest source of I&I.
- Because of multiple power failures at the Monroe St lift station which caused back-ups and bypasses, the Town of Hebron, in 2017, installed a back-up generator to ensure that a power failure would not cause the lift station from operating.
- After the flow metering and smoke testing, the town contracted with McMahon Associates, Inc, in 2017, to clean and video all of the clay sanitary sewer collection system in the Town of Hebron.
- The town surveyed our sanitary sewer system manholes lids and replaced over 100 open pick manhole lids, in 2017, with sealed manhole lids which were in low lying areas and had evidence of ponding.
- Using the information from the cleaning and videoing, in 2018, the Town of Hebron contracted with McMahon and Associates, Inc to begin a multiphase project, beginning with repairing certain areas with observed problems and to line the sub-basin that flows to the Monroe St lift station with cured in place pipe (CIPP).
- In 2020, the Town of Hebron hired Wessler Engineering to Inspect approximately 390 sanitary sewer manholes for structural issues and for inflow and infiltration.
- During the Waste Water Treatment Plant upgrade project in 2020, the Town installed a 1,670,000-gallon flow equalization lagoon, to handle high I&I events. The Town also upgraded the main pumping station and upsized the piping to help eliminate back-ups in the collection system.
- The Town replaced the South Lift Station (which had bypass/overflow issues caused by I&I) in 2020 with a new lift station.
- The Town of Hebron, in 2021, updated their sewer use ordinance and design standards, to provide guidelines and enforcement to prevent illegal dumping into our sanitary sewer collection system.
- In 2023, the Town of Hebron, partnering with Wessler Engineering, and funding with an Indiana Office of Community & Rural Affairs (OCRA) grant, the town has installed approximately 8,500 feet of Cured-In Place Pipe (CIPP) in existing sanitary sewers with known issues. With the use of the manhole inspection we have also repaired approximately 120 sanitary sewer manholes with known problems.
WHAT THE TOWN OF HEBRON IS DOING
The Town of Hebron is committed to improving our Public Owned Treatment Works to protect public health and the environment and to improve our infrastructure to enable long term economic growth.
The Town of Hebron will continue in multiple phases to evaluate and repair areas in the collection system that the town and the engineers decide are the problem areas.
WHAT YOU CAN DO AS A PROPERTY OWNER
No matter how tight we make the sanitary sewer mainline, we have to address the homeowner’s side of the system. Property laterals (service lines) are a major cause of I&I. Laterals made of clay pipe can shift or settle and cause openings that allow groundwater and rainfall to enter the system. Down spouts hooked up to the sanitary system are not only illegal, but can also cause vast amounts of water to enter into the system. Sump pumps are also a large cause of problems if they discharge into the sanitary sewer.
STORMWATER ORDINANCE 04-01-B
“Storm drainage and surface water installations, including roof downspouts, foundation footing drains, and or sump pumps, shall not be connected to or allowed to empty in the sanitary sewer system.”
HELPFUL TIPS
Replacing clay laterals with PVC pipe, during any repair or renovation, will ensure a long-term solution.
Disconnect any down spouts or sump pumps from the sanitary sewer system and divert the water to grassy areas, plantings or gardens.