Inflow & Infiltration

Wastewater is delivered to a treatment plant through a system of municipal sewer pipelines. In our community, this amounts to over 140 miles, all connecting each domestic and industrial customer to the Wastewater Treatment Plant at the end of the pipeline. Pipes settle, manholes crack, brick and mortar crumble. No sewer system is ever completely watertight.

Beginning of Sewers

Long ago, as the Jamestown area was settled and developed and so, too, our entire country, a main concern of builders was to drain water away from building and streets as quickly as possible. Ditches and culverts were dug out to drain water efficiently. 

Over the centuries, the land itself was shaped to meet the needs of growing communities; hills were leveled, roads were cut, wetlands were dredged or filled. Forests gave way to farm fields. Dirt roads were paved and parking lots covered open areas around buildings. The surfaces of urban areas became impervious, resulting in more runoff. Diagram of Inflow and Infiltration Process

Communities attempted to solve the runoff problem by installing street drains and miles of storm sewer pipe to shunt the huge volumes of rainwater or melting snow into storm sewers which ran the water directly into lakes, streams and rivers. These storm sewers were different from sanitary sewers that were built to carry away domestic and industrial wastes.

The Inflow & Infiltration Process

Treating the wastewater that comes to the plant via the sewer system should be challenge enough however, in today's world that challenge is heightened by the intrusion of ground and surface water. Inflow is when the water enters the sewer above ground or from connections with storm sewers and infiltration is when it enters the pipes below ground, the process is usually called "I and I."

How much inflow enters the system depends on the number of low lying manhole covers and cross connections with the storm drainage system. The amount of infiltration depends on the number and size of cracks, holes, and leaky joints in the piping. When it rains, large volumes of "I and I" per person per day can add a significant amount to a community's processing costs, costs to treat water that has not been polluted. Treating the water is expensive because usually more capacity must be added to the treatment plant.

The Solution to Inflow & Infiltration

Efforts to correct "I and I" are sometimes ineffective and also expensive. But sometimes 80% of the problem can be corrected by finding and repairing 20% of the leaks. It's hardest to find the right 20%. Finding leaks is sometimes harder than fixing them, but fixing them is even more expensive.

The Board of Public Utilities (BPU) Wastewater Division is attempting to solve "I and I" problems by:

  • Identifying the specifics and exact locations of problems through customer surveys and inspections as well as an inflow and infiltration (I and I) study of the entire sewer system

  • Undertaking corrective measures where identified primarily by diverting roof drains and footer drains away from the sanitary sewer system

  • Working with the affected customers on immediate measures so they can purchase and install necessary materials to help prevent sewer backup

  • Working with the DPW to identify, verify, and correct any problem that may be found in the storm sewer system

Diagram Examples


This following diagram shows the plumbing of a typical house of the 1950s and 1960s. The downspout surface water drains into the sanitary sewer.Plumbing Diagram from a house in the 1950s

Many homes in this area have their roof downspouts and footer drains improperly draining into the sanitary sewer rather than the storm sewers. In times of wet weather, this extra volume of water, multiplied by many homes, could overflow the sanitary sewers causing the system to back up and relieve itself at the point of least resistance, which could be the homeowner's basement.

Sewer Connection

The following diagram shows the first floor and basement elevations of a home with an appropriate connection to the community's sanitary sewer. It also shows an incorrect connection of the house's storm water downspouts to the sanitary sewer. The rain downspouts should have been connected to the storm sewer.                                 

BPU Wastewater Division staff will inspect your home for water drainage free of charge and offer suggestions to Correct and Incorrect Sewer Connectionscorrect any problems found.

Contact Us

No penalty will occur to any homeowner whose storm water is identified as draining into the sanitary sewer, as many homes were purchased with these problems in place. Call 716-661-1651 for more information.