Inflow & Infiltration (I&I)


Why is I/I a problem?

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.

I/I flows contribute to sewer system overflows into local homes and the region's waterways, negatively impacting public health and the environment.

We estimate that inflow and infiltration makes up 75 percent of peak flows during winter, and much of this comes from private property.

Protecting the environment and decreasing wastewater treatment costs are the benefit of a regional I/I control program.

Impacts of peak I/I on wastewater flows

While there are multiple reasons why portions of the conveyance system are at or near capacity, a major contributing factor is the capacity taken up by I/I flows in the system. Several capacity related capital improvements are needed in the regional system that are directly related to excessive I/I entering the system upstream of the needed improvements. The following figure demonstrates how peak I/I flows can far exceed base flows.

I/I that enters the collection and treatment system also triggers higher operating costs for the region. Operating costs for conveyance facilities such as pump stations are proportional to flow volumes passing through the facilities. I/I also increases treatment costs because more chemicals and electricity are used during peak flows at the treatment plants.

What can you do?

Here's what you can do to reduce inflow and infiltration in the sewer system, to help boost our capacity to treat wastewater during the wet season.

Inspect your roof gutters and downspouts to see if they are connected to the sewer system. If so, have them disconnected.

Direct downspouts onto lawn and garden beds or hook up a rainbarrel or cistern to your downspouts.


How I&I Impacts Conveyance Facilities

I&I Chart

Copyright 2018 by City of Proctor, Minnesota
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