Welcome to the Inflow and Infiltration (I/I) Reduction study website. The purpose of this website is to provide information about the I/I Reduction study that is occurring in the Town of Markham. This website contains background information, weekly status updates of on-going testing, and the contacts of this study.

Introduction to the Project

The Town of Markham is working with Cole Engineering Group Ltd. 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 develop a plan to reduce these “extraneous” flows. 

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, rain water infiltrates into pervious areas, such as grassed lawns and gardens. Any rain water 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. Rain water, 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.

Inflow and infiltration (I/I) occurs when rain water or groundwater enters the sanitary sewer instead of the storm sewer network. This can be 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 Town of Markham and Cole Engineering are conducting this program to identify and reduce sources of I/I entering the sanitary sewers. A flow monitoring program will identify areas within the Town of Markham that have high I/I flows and field testing will identify specific sources of I/I. The field testing includes smoke and dye testing and CCTV inspection.

Smoke Testing

The smoke testing consists of blowing a harmless coloured vapour into manholes and pipes and observing where the smoke exits from the system. The smoke is expected to exit primarily out of manholes on the street and plumbing vents stack at the top of buildings. It is also possible for smoke to exit stormwater catch basins and roof downspouts at the side of a house, where inappropriate connection were made to the sanitary sewer.

The smoke used in the test has no odour and is not harmful to your health, and will disappear after a few minutes. For more information on smoke testing, please visit www.smoketesting.com

A connectivity test will be conducted if the smoke test is positive or inconclusive, to confirm if an inlet is connected to the sanitary sewer system. A possible inlet could be the roof downspout or a rear lot catch basin. A connectivity test consists of pouring water into an inlet to confirm its connection visually by a CCTV camera positioned in the sanitary pipe. Cole Engineering will ask permission from the resident to enter on to their property to conduct the test. If the resident is not home, Cole Engineering staff will leave a notice at the residence to arrange for permission to enter the property.

Notices will be distributed to residents in areas where smoke testing will be occurring. On the day of testing, Cole Engineering staff will visit each building to notify that testing will be occurring. Please note that there is no need to be home during testing and that there is no need to enter the building to conduct the test. A second notice will be distributed when testing is completed at your residence. Cole Engineering staff, identified with a company and name tag, will be on site during the entire process of the testing.