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Inflow and Infiltration Reduction

What is Inflow and Infiltration (I&I)? 

Inflow and Infiltration (I&I) refers to rainwater and groundwater that enters the sanitary sewer through a variety of defects. 

Inflow sources allow rainwater to enter the sanitary sewer directly from the surface through improper plumbing and cross connections. Some examples include downspout and roof drain connections, and catchbasin cross connections. 

Infiltration sources allows the groundwater to seep into the sanitary sewer through cracks or bad joints in sewer pipes and manholes. 

A certain amount of I&I is unavoidable and is accounted for in routine sewer design. However, when I&I exceeds design allowances, sewer capacity is consumed and may result in overflows, risks to health, damage to the environment and increased treatment and disposal costs. 

I&I Reduction, Why Bother? 

I&I sources allow large volumes of clean water into the sanitary sewer system that generally were not designed to handle such volumes. Most of the sanitary network in Peterborough was designed and constructed in 1960s. Many older pipes simply don't have the capacity to deal with the volume of wastewater that now courses through them. Stormwater entering the sanitary sewers, especially in the older parts of the City, overwhelms the sewers. Sewer overload is a frequent cause of basement flooding, which is very expensive and disruptive for those affected. It may also result in sewage surcharge into the lake and rivers. This is a potential reason for the beach closing, and also causes pollution to fish and wildlife. In addition, climate change has been increasing the magnitude of storms and flooding. 

Municipal attempts to prevent flooding and sewer overflows can be enormously expensive. The cost to reduce flooding in a single low-lying area could be hundreds of millions of dollars and take many years to complete. In comparison, I&I reduction is cost effective, helps immediately, and even reduces operational and treatment costs at the Wastewater Treatment Plant. The benefits of I&I reduction has been proven in practice in various municipalities and is strongly recommended by various private and public parties. 

How does the I&I Reduction Project Work? 

In line with the City's Flood Reduction Strategy and according to the 2012 Class EA Master Plan recommendations, the City of Peterborough initiated the Infiltration and Inflow (I&I) Reduction Program in April 2014. The project objective is to identify and remediate sources of extraneous flow into the sanitary system (also known as I&I sources). Three (3) main steps of the project are: 

  1. Source Identification; 
  2. Communication; and, 
  3. Remediation. 

Step 1 is typically performed by the City although the landowner can identify suspected I-I sources on their own property and inform the City. Step 2 is performed by the City. Step 3 is performed by the landowners, however funding may be available through the subsidy program. 

Phase 1 - Source Identification 

Sources are identified in the field through various tests and activities. Prior to field testing, local residents and business owners will be notified. Some activities conducted in the field are: 

  • Rain and Flow Monitoring; 
  • Smoke and Dye Testing; 
  • CCTV Investigation and Pipe Condition Assessment; 
  • Sewer Flushing and Cleaning; 
  • Sewer Joint Testing; and, 
  • Field Survey. 

Types of sources identified in the field are: 

  • Defective manhole covers and risers; 
  • Roof downspouts connected to sanitary sewers; 
  • Catchbasins and roof drains cross connected to sanitary sewers; 
  • Overflow structures cross connected between the sanitary and storm systems; 
  • Foundation Drain Collectors (FDC) and sump pumps connected to the sanitary sewers; and, 
  • Cracks and joints in the sanitary sewer mainline or laterals. 

Phase 2 - Communication 

Confirmed I-I sources during phase 1 will be communicated to the respective landowners. In this phase, the City will communicate the type and location of I-I sources as well as their effect on the sanitary system. Also, the City may provide input on owners remediation options. The owner can communicate to the City if they have identified an I-I source on their property. 

Phase 3 - Remediation

It is the landowner's responsibility to remediate and remove any I-I source within their property. However, given the importance of I-I reduction and its benefit to the public, the City provides financial assistance through the Flood Reduction Subsidy Program. The subsidy program potentially covers up to 100% of the cost of labour and materials used for the remediation. The subsidy limit depends on the cost of remediation and the volume of I&I reduced as a result of the reduction. 

In 2014, the primary focus of the study has been on the Downtown Core Area (DCA). This area endured severe damage during the 2004 storm and therefore was selected as the initial study area. Step 1 of the project has been completed for this area. It is the City's intention to implement Steps 2 and 3 of the project during spring and summer of 2015 and 2016. 

The City is going to continue expanding the study area. Naturally, areas with higher I&I generation potential and historical flooding will receive higher priority. However, the residents are encouraged to contact the City if they are aware of any I-I sources within their property. 

Additional Information