In areas with a high water table, or for cities more prone to flooding, your underground infrastructure can become inundated with groundwater and stormwater.
And despite stormwater systems being built for this type of collection, there are a number of things that can go wrong for both types of collection systems underground—and above ground—that can lead to contamination or degraded infrastructure.
Here are a few problems that could arise, and how to deal with them.
Inflow and Infiltration
When flooding or ponding occurs over sanitary manholes, and if there are any openings or cracks in your manhole covers, it will inevitably cause inflow into that system. This is okay if the inflow is into your stormwater system, which was built to collect surface water; but it’s bad news for your sanitary system. Studies have shown that approximately 50 percent of extraneous water has likely found its way into your sanitary collection system through leaks in manhole covers.
As for underground, if collection system pipes are below the water table or if the ground around pipes becomes oversaturated with surface water that has seeped into the ground after a heavy storm, then those pipe systems will be subjected to external water pressure. Leaks can occur through cracks in pipes, because of failed pipe joints, or from insufficient sealing capacity at the pipe-to-structure connections. Underground leaks can lead to soil erosion, and therefore soil entering the pipes, further limiting flow and putting municipalities at risk of pavement damage and worse—sink holes.
Eventually, with all of this extra water entering sanitary collection systems, wastewater treatment plants (WWTP) will be treating excess water at a cost to municipalities. And in larger storm events, a WWTP can reach overcapacity and have to release untreated or partially treated wastewater into waterways. If the plants don’t release these surges into waterways, they will end up in homes or back up through manhole covers as a sanitary sewer backup.
Outflow and Manhole Surcharge
Our waterways are a precious resource, which is why it’s important to keep them free of contamination. Contamination can take the form of sewage and stormwater leaks through damaged or improperly installed or sealed pipes, as well as manhole surcharges. These leaks pose serious threats to the health of your municipality, and risks to your environment.
If your municipality has a combined sewer, these cracks put your system at an increased risk of combined sewer overflows (CSO) should any flood events or 100-year storms occur. If water is leaking in through cracks, the system will reach overcapacity sooner, and ultimately water and sewage combined will have nowhere to go.
Rubber gaskets for joints between pipe sections and rubber connectors for pipe and manhole intersections should be used for all types of water conveyance. They are much more likely to maintain a watertight seal over the lifetime of the pipe system than other solutions. And being flexible by nature, they are able to maintain a seal even if there is movement of the pipe sections or structure due to differential loading or during installation.
Above ground, watertight manhole systems such as Hamilton Kent’s Lifespan® System will keep surface water from leaking in through the top of the manhole. A system like this can to a limited extent also help to prevent surcharging from top of the manhole.
With watertight manhole frames & covers, rubber gaskets and joint connectors, water will remain within the system and ground and surface water will remain out—ultimately protecting your environment, streams, rivers and waterways.
Along with grey infrastructure solutions, is green infrastructure. By including more permeable options into cities prone to flooding, water can be re-absorbed into the ground, ultimately reducing run-off.