Inflow and Infiltration (I/I)

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What is Infiltration/Inflow (I/I)?

Infiltration occurs when groundwater enters the sewer system through cracks, holes, faulty connections, or other openings. Inflow occurs when surface water such as storm water enters the sewer system through roof downspout connections, holes in manhole covers, illegal plumbing connections, or other defects. The sanitary sewer collection system has a maximum flow capacity of wastewater that can be handled. I/I, which is essentially clean water, takes up this capacity and can result in sewer overflows into streets and waterways, sewer backups in homes, and unnecessary costs for treatment of this water. It can even lead to unnecessary expansion and replacement of pipes and interceptors. These costs get passed on to the rate payer.

What is the Town doing to reduce or eliminate Inflow and Infiltration (I/I)?

While it is virtually impossible to eliminate all I/I from any sewer system, the Town of Dedham has begun a program to rehabilitate the existing system in an effort to reduce the amount of clean water entering the sewer system in an effort to improve system reliability and reduce the costs which residents and businesses pay. 

Identifying Inflow and Infiltration (I/I)

The primary method used to locate infiltration is by closed circuit television inspection. During this process a small robotic camera is placed inside the sewer main on a self propelled crawler. The camera displays the internal condition of the sewer pipe to the camera operator who records any defects observed. The report and digital video of the inspection are then reviewed by an engineer who determines the appropriate repair needed for a given defect or defects present in the pipe. 

Additional methods used to locate I/I include manhole inspection, smoke testing, dyed water tracing, and internal building inspections. 

Removing Inflow and Infiltration (I/I)

There are many methods and technologies available to remove and reduce I/I. Modern techniques allow for the sewer lines to be inspected, cleaned, and even replaced or rehabilitated without traditional open-cut excavation. These “trenchless technologies” allow for rehabilitation and repair of sewers without the expense and interruption of conventional open-cut excavation. 

Not only is it more convenient to employ trenchless technologies to rehabilitate the sewer system, but it is also extremely cost effective when compared to open-cut methods.