Often times, I’m asked “When is it important to complete manhole inspections?” Manhole inspections should be performed during wet weather, or when the groundwater level is at its peak. Ideally, November to May is the best time to perform manhole inspections to detect inflow & infiltration (I/I). With the snow/ice melt in February and March compounded with heavy rains, Cities and Towns will notice flows spike at lift stations and wastewater treatment facilities. The five (5) most important items to take note of during manhole inspections that will help reduce (I/I) and eliminate potential backups are:
1. The Manhole Chimney During Heavy RainOne of the most important manhole components to observe during a manhole inspection is the manhole chimney. As you can see below, this manhole was constructed of precast concrete, with the exception of the manhole chimney which was constructed of brick. During dry weather the chimney may appear to be in good shape; but when the groundwater rises or heavy rains occur, you may see a different story entirely. It is often hard to believe you are looking at the same manhole, under slightly different conditions. For reference, the inflow that was observed to the right was entering at a rate of approximately seven gallons per minute.