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A City of Cooperation

Inflow/Infiltration (I/I) Reduction Program

Objective

Remove storm water sources from the sanitary sewer system, keep wastewater treatment costs and sanitary sewer rates low, and protect the environment

**A copy of the 2012 Ohio EPA Sanitary Sewer Overflow report for overflows within the City of Oregon is available and can be picked up at the Department of Public Service office between the hours of 8:00am and 4:30pm, Monday through Friday.**

Program Overview

The term I/I is an abbreviation for Inflow/Infiltration and is used to describe the sources of storm water (rain and groundwater) that enter into the dedicated sanitary sewer system.  Sanitary sewers are pipes located under the street, or City right-of-way, and are strictly designed to transport wastewater from sanitary plumbing fixtures, such as toilets, sinks, bathtubs, showers, and lavatories.  The I/I Reduction Program has been implemented to identify and remove I/I sources from the sanitary sewer system.  These sources can overload the sanitary sewer system and cause sanitary sewer backups into homes and businesses, as well as sanitary sewer overflows (SSOs) to nearby creeks.    

Inflow sources are those that flow directly into the sanitary sewer via a defined route (pipe, etc.)  Infiltration sources are those that inadvertently enter into the sanitary sewer via cracks, holes, faulty connections, or other openings.  Inflow sources within the public right-of-way can include sanitary manhole covers and storm water catchbasins that are inadvertently tied into the sanitary sewer.  Private land areas (outside of public right-of-way) inflow sources include roof downspout connections, yard and driveway drains, broken or missing sanitary lateral cleanout caps, and sump pump connections to the sanitary sewer system.  These connections are illegal and can add thousands of gallons of storm water into the sanitary sewer system per household during large rain events.  Inflow sources are usually the easiest to remediate.                 

Infiltration sources within the City right-of-way can include broken or cracked sanitary pipes, deteriorated manholes, and misaligned or faulty pipe joints.  Private infiltration sources can include broken lateral sewers, faulty lateral connections, tree root penetration, and broken cleanouts.  Infiltration sources can be more difficult to deal with due to the fact that the sources occur underground. 

City of Oregon I/I Fact Sheet

Prohibition of Unpolluted Water 

Storm water discharges to the sanitary sewer are illegal within the City of Oregon, as stated by Oregon Codified Ordinance 925.26 PROHIBITION OF UNPOLLUTED WATER:
 
 “No person shall discharge or cause to be discharged any stormwater, surface water, groundwater, roof runoff, subsurface drainage, uncontaminated cooling water, or unpolluted industrial process waters to any sanitary sewer.” (Ord. 155-1977. Passed 8-8-1977.)  

Oregon Sewer Ordinances

Treatment Costs and Wastewater Treatment Plant (WWTP) Expansion

During a rain event, a large amount of storm water (I/I) enters into the sanitary sewer system and is treated as if it is wastewater.  Typically, rain water is clean and does not need any type of treatment.  The unnecessary wastewater treatment of storm water costs the City, and ultimately all sewer users, extra money in wastewater treatment.  Sewer use rates will need to increase if I/I is not reduced to combat the costs associated with treating excess storm water.

The City of Oregon WWTP is a public (non-profit) utility.  Major capital improvements made to the WWTP are financed through a combination of sewer use fees and income taxes.  A major future expansion to the WWTP will be mandated by the Ohio Environmental Protection Agency (OEPA) to eliminate all overflows and water quality violations explained in the next section below.  The size of the plant expansion will be dependent upon the success of this program, thus a smaller plant expansion equals less cost to taxpayers and sanitary sewer users.

Environmental Concerns and Sewer Backups

In addition to extra costs, the OEPA now mandates I/I reduction to reduce illegal sanitary sewer discharges to local rivers, lakes, and streams.  This is due to the amount of water quality violations that occur during large rain events.  Anyone discharging or planning to discharge wastewater from a treatment facility (wastewater treatment plant) into a body of water must obtain a National Pollutant Discharge Elimination System (NPDES) permit from the OEPA.  This permit sets limits on the type and quantity of pollutants that can be discharged.  NPDES permits also set requirements necessary to protect human health and the environment, which includes eliminating water quality violations. 

Water quality violations are a result of sanitary sewer overflows (SSOs) from the collection system and partially treated discharges (bypasses) from the WWTP.  SSOs occur during storm events when too much rainwater improperly enters the sanitary sewer system and the system becomes filled to capacity.  Once filled beyond capacity, the sewer starts to relieve pressure through SSOs and/or backups to the lowest points in the system.  The lowest points in the system are typically near creek crossings or in the vicinity of the WWTP.  Unfortunately, sanitary sewer backups into basements can occur in residential homes and businesses when plumbing fixtures are physically lower in elevation than the top of the saintary manholes outside.         

A bypass of the secondary wastewater treatment process may also occur at the WWTP during extreme rain events.  This is due in part to the plant having a restricted treatment capacity of 8 million gallons per day (MGD), and a total hydraulic capacity of 36 MGD.  Again, the plant capacity was designed strictly to treat sanitary sewage, with limited wet weather I/I.  Once the plant capacity is exceeded by a combination of both sanitary and storm water, influent must be restricted and/or secondary treatment of sewage must be bypassed in order to avoid failure of treatment plant operation.  This secondary bypass is deemed a water quality violation by the OEPA NPDES permit.       

The Sewer and your Home

Milwaukee Metropolitan Sewer District Sanitary Lateral Video

See the following pictures and diagram of common I/I sources:

 

video_infiltration3

 Storm water infiltration into a sanitary sewer pipe at a bad joint

 

4-10-09 001

Groundwater infiltration within a sanitary sewer manhole

 

mass roots

Tree roots within a sanitary sewer pipe, discovered by CCTV (closed circuit television) inspection

 

downspout connection

 A roof downspout connected to the sanitary sewer system, discovered by smoke testing

 

 i-i sources

Diagram of common inflow and infiltration sources

 

 

 

 
© 2014 City of Oregon