Inspecting and maintaining the city’s more than 9,000 manholes can be a daunting task. Constantly changing regulations and requirements pertaining to sewer system maintenance only makes it more of a challenge. Fortunately, in today’s sewer maintenance industry, a few repair/rehab techniques are available which makes completing restoration of a manhole cheaper and easier than it has ever been.
Through the years, manholes have been made of various materials, including brick, native stone, concrete blocks and pre-poured manhole castings to name a few. Each type of manhole has its own set of good and bad points. None of them, however are impervious to hydrogen sulfide gas. This gas is present in different concentrations in almost all sewers, however sanitary-only sewers tend to have more of a problem with this than others. This gas is very destructive and can erode even new concrete sewers in a matter of a few years (to say nothing of the damage done to the cast iron ring and lids of manholes).
In St. Joseph, two new types of rehab techniques designed to counteract the sewer gas have been put in place to see which works better. One type uses a bag sewn to fit each manhole and impregnated with fiberglass, which is impervious to hydrogen sulfide gas. Several manholes in town which were being damaged by the gas have been lined using these bags. The first group was installed two years ago, and so far all are performing beyond expectations.
A type of spray-on epoxy liner has also been tried in the last few months, but it is too early to tell how this method will perform. Both of these methods increase the structural integrity of the manhole itself while providing needed protection from the sewer gas.
Sewer maintenance staff are always on the lookout for new products and methods to maintain the collection system in the most efficient way possible and these are just two examples of those efforts.