Why is infiltration and inflow a problem?

We estimate that I/I makes up 75% of peak flows during winter. Much of this comes from private property. A regional I/I control program helps protect the environment and decrease wastewater treatment costs.

Sewer system overflowing through a manhole during a storm.

Extra water in the sewer system is a problem because it:

• Takes up capacity in the sewer pipes and ends up at the regional wastewater treatment plants where it must be treated like sewage, resulting in higher treatment costs.
• Requires new and larger wastewater facilities to convey and treat larger volumes of flow, resulting in higher capital expenditures.
• Contributes to sewer system overflows into local homes and the region's waterways, negatively impacting public health and the environment.

Impacts of peak I/I on wastewater flows

I/I flows are a major reason why portions of the conveyance system are at or near capacity and require capital improvements.

The following figure demonstrates how much peak I/I flows can exceed base flows: