Inflow and Infiltration


Municipal Office

395 Mulock Drive P.O. Box 328 Station Main, Newmarket, Ontario
L3Y 4X7

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​​Inflow and infiltration (I/I) happens when water from the environment enters the sewage system for treatment. Inflow is when there is a rapid flow of storm water in the sanitary sewer system. Infiltration is the gradual downward flow of water from the surface of the earth into the soil and into the wastewater collection system.

Inflow and Infiltration occurs through through cracks or holes in the pipe network or through inappropriate connections such as catch basins or roof downspouts. I/I increases the flow and volume in the sanitary sewer and reduces the capacity of the pipe and the treatment plant. The result is a higher risk of overloading the pipe network leading to potential basement flooding, and increased flows and volumes that must be treated at the plant.

The sanitary sewer system is an underground pipe network that collects wastewater produced by houses, businesses, and institutions. The purpose of the pipe network is to direct the wastewater to a treatment plant where the water is treated before being discharged into Lake Ontario. 

The storm sewer system is an underground pipe network that collects rainwater runoff. During storm events, rainwater infiltrates into pervious areas, such as grassed lawns and gardens. Any rainwater that does not infiltrate will turn into runoff that will flow down impervious areas, such as roads and parking lots. Catch basins and other inlets are designed to collect the rainwater runoff and convey the water through a storm sewer system. Rainwater, unlike wastewater, does not need to be treated by a plant and can be treated by on-site controls such as a stormwater management pond or an oil and grit separator. Therefore the purpose of having a storm and sanitary sewer system is to separate these flows prior to treatment and discharge to the environment. 

The Town of Newmarket is currently working with Civica Intrastructure on a Inflow and Infiltration reduction study. 

Inflow and Infiltration (I/I) Reduction Study 

The Town of Newmarket is working with Civica Infrastructure Inc. on an Inflow and Infiltration (I/I) reduction study. The study’s objectives are to identify sources of I/I entering the sanitary sewers and to develop a plan to reduce these “extraneous” flows. A flow monitoring program with field testing is being conducted to identify sources of I/I entering sanitary sewers. The flow monitoring program will identify general areas within the Town of Newmarket that have increased I/I. Additional field testing will then be conducted in these areas to identify the specific sources of I/I.  

Exterior Property Asessements in your neighbourhood 

Civica Infastructure will be conducting exterior property assessments in select neighbourhoods between the hours of 9 a.m. to 5 p.m. 

Exterior property assessments are visual assessments of the outside of your home to note any drainage features which may discharge to the sanitary sewer. Common drainage features include roof downspouts, basement access drains, driveway drains, etc. Civica Infrastructure staff will walk around the exterior of your property and note any drainage features that do not drain to the surface (i.e. lawn, garden, driveway, etc). Exterior lot assessments typically take less than 10-15 minutes to complete. Staff will not need to enter inside your house to conduct the assessment. 

On the day of the assessment, Civica Infrastructure staff will knock on the resident’s door, stand at least 6 feet back to maintain physical distancing and inform the resident that the exterior property assessment will be occurring. You do not need to be home for the exterior property assessment, but you can be home while the assessment is occurring.