Blackburn Wastewater Treatment Plant Upgrade Study

SECTION 2.0
III MITIGATION MEASURES
2.1 INTRODUCTION
Snowmelt and rainfall that enters a sanitary sewer during wet weather periods can be
categorized as either inflow or infiltration. Inflows are due to direct connections of
rainfall and/or snowmelt and contribute to rapid flow increases, whereas infiltration is
due to indirect sources and produces delayed flows and extended flow increases.
Therefore, inflows are critical for short high intensity as well as for long duration
storms; infiltration would be critical for Iong duration events. Since prolonged wet
weather, due to winter thaws and spring raidthaw conditions, is quite normal in the
BIackbum area, both inflow and infiltration (III) contribute significantly to the
overloading of sanitary sewers.
Excessive H places significant peak flow demands on the sanitary sewer system.
Retrofit measures such as upgrading capacity of pipes, pumpstations, and treatment
facilities can substantially increase the cost of providing sewer service. On the other
hand, realizing the significance of yI and impIementing a program of L'l reduction can
extend the life of facilities by deferring the need to upgrade hydraulic capacity.
Controlling excessive amounts of VI is the single largest demand-side management
issue for any wastewater collection system. Therefore, a planned yI investigation and
analysis methodology can be adopted to: detect and identify these It1 sources on a site
specific basis; quantify their comparative impacts; find appropriate mitigative
measures on a prioritized basis; and implement policies that promotes the reduction of
excessive UI.
A Mica1 I/I mitigation work plan methodology recognizes that:
Within the sewer network, major VI sources can be 'leaky' manholes, poor pipe
joints, poor senice connections, and failed pipes.
High ground water table during wet weather periods can create high hydraulic
heads, which result in continuous UI through the defective components of the
sewer network.
A significant portion of UI is often generated within private property.
Since a major source of the UI can be generated on individual lots, the potential
costbenefits of implementing I/l reduction measures on private property should be
part of the solution.