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Inflow And Infiltration

House
Inflow and infiltration (I&I) happen when water from the environment that does not need to be treated enters the sewage system. Infiltration refers to groundwater entering the system. Inflow refers to rainwater (stormwater) entering the system.

The RDN and member municipalities have a separated sewer, made up of two sewer systems:
  • Sanitary sewer: designed to carry sewage to facilities that treat the water before returning it to the environment.
  • Storm sewer: prevents streets from flooding by draining and carrying excess stormwater (from rainfall and snowmelt) to streams, lakes or the ocean.

Understanding I&I (from the Capital Regional District)

Part 1: Introduction
Part 2: The Impact of Rainwater Entering the Sanitary Sewer System
Part 3: How Property Owners Prevent Rainwater from Entering the Sanitary Sewer System
Part 4: How Municipalities Prevent Rainwater from Entering the Sanitary Sewer System

Potential Sources of I & I
Potential sources of I&I
(Image courtesy of the Capital Regional District)

What are sources of I&I?

Examples of sources of I & I include:

Why is I&I a Problem?

Inflow and infiltration are problems because they: Historically, the RDN trunk sewer system has received very high wet weather flows from the City of Nanaimo's sanitary sewer collection system. The largest wet weather flow on record, from December 1997, had a peak flow nearly six times the average dry weather flow. However, since 1997, peak wet weather flows have been significantly lower. While rare, sanitary sewer overflows have occurred from the RDN system in the past - during extreme rainfall events. The frequency and likelihood of these overflows are greatly diminished as I & I are reduced.

How Can We Fix I&I?

The City of Nanaimo has undertaken a rehabilitation program for the City's sanitary sewer collection system. Replacement or repair of leaking pipes and manholes provides positive benefits in terms of I&I reductions. However, a quantifiable trend is not yet apparent in the RDN's flow records due to the variability in annual rainfall, intensity and geographic distribution of individual storms, as well as gaps in flow and rainfall data records. If you need help, contact your local plumber, municipality or the RDN for assistance.

Wastewater Services | 6300 Hammond Bay Road | Nanaimo, BC V9T 6N2 | E-mail: rcu@rdn.bc.ca
Telephone: 250-390-6560 (Nanaimo) 250-954-3792 (Oceanside) 1-877-607-4111 (Toll Free)
1-800-862-3429 (Emergency) | 250-390-1542 (Fax)
Last Modified:  Aug 18, 2014
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