Wastewater networks are home to a plethora of assets, often of varying ages and materials, so tackling inflow and infiltration can seem like an insurmountable task – but this industry expert says every little bit counts.
When rainwater (inflow) or groundwater (infiltration) make their way into a sewer network through pipeline damage or joint defects they’re starting a countdown to asset failure, increased operating costs and worst case – overflows.
ISC Services Owner, Dennis Bentink, explained that while it’s virtually impossible to completely eliminate inflow and infiltration, there’s a lot that can be done to control and mitigate it.
“It’s a difficult problem to tackle, and a lot of people don’t know where to start because it’s such a big animal,” he said.
“There’s a misconception that you can’t make a difference but starting to control inflow and infiltration reduces the ongoing cost and problems – every little bit helps.”
It all adds up
Mr Bentink explained that the most vulnerable part of a sewer network is anywhere there’s a connection or joint.
“Basically, a sewerage network can leak from anywhere, it could be an illegal downpipe connected to the sewer, a mistake during construction or, commonly, failed joints,” he said.
“But a big cause of rainwater getting in the sewer is joints, and particularly maintenance holes.
“The top 300mm of the access chamber is disproportionally high risk because you’ve got a lot of joints very close to the surface. And even in new estates, a new maintenance hole might be vacuum tested and pass, but then a machine or vehicle comes along during building works and disrupts the surface, so your brand-new asset starts leaking.”
Ageing infrastructure is not only prone to inflow and infiltration, but Mr Bentink said the two challenges can exacerbate each other.
“[When] Groundwater [raises and lowers] soils expand and contract, and this movement causes joints to separate and leak and old infrastructure to crack and fail,” he said.
“A major issue is that when water moves it generally takes soil with it. So, this will disrupt the support around pipes, maintenance holes and pump stations – and you can even get roads collapsing.”
But, if sewer systems are designed to handle water, then why is it a problem if water gets in?
Mr Bentink explained that additional water takes up capacity in the network, but another big problem is the soil that inflow and infiltration brings along for the ride.
“The soil also takes up capacity and also causes excessive wear and tear on pumps and equipment,” he said.
“Now the pump stations aren’t just pumping too much water – they’re also pumping soil and sand and grit. This increases both wear and tear and power consumption, but also [utilities are now stuck with the cost of] treating water they didn’t want in the first place.
“Worst case, it ends up overflowing and now you’ve got environmental concerns too.”
Staying afloat
As these networks have a lot of assets in the ground, digging around each one to find out if its compromised is just not practical.
According to Mr Bentink, prevention is always the best solution. Advanced monitoring solutions can be very helpful in providing the data to tackle this challenge, however, this can be costly and time consuming – but Mr Bentink said that there are a lot of ways utilities can use the information they already have to identify inflow and infiltration and mitigate it with simple solutions.
“They’re already going to have a lot of information through pump operations. If they get a rain event and a pump station increases its operation three or four times, then there’s obviously water getting in somewhere. So, they can focus their efforts on that particular catchment [for repairs],” he said.
“Another simple and effective way to identify problems is smoke testing – [which can find] everything from illegal downpipes, leaking maintenance holes and cracked pipes.
“There’s also a lot of valuable knowledge held by the operators. They will have observed issues over the years, so they [will often] know that if there’s a rain event, there’s going to be a problem in a certain area.”
Once the source of trouble has been identified, there are a range of simple yet cost-effective ways to both repair damages and prevent inflow and infiltration.
“Every new asset should start with prevention. Gator wrap is an external joint wrap, which can be placed around the joints of brand-new pre-cast assets to stop water, soil and roots from getting in and stop premature failure of the joints,” Mr Bentink said.
“For assets that are already in the ground, let’s say you’ve got a very fast water leak, you can use something like Aqua Seal – which is an expanding polyurethane foam that you inject in. It will push into the soil around the back of the leak and form a mushroom shaped plug, so the pressure doesn’t allow it to pop out, but it fills that void to reduce any surface damage and stop the active water flow and soil coming in.”
To help utilities tackle inflow and infiltration, Mr Bentink said that he works closely with water authorities to identify appropriate solutions.
“All the products [we have] are ‘tools’, and I’ve tried to have a bunch of different options so [we can help customers] choose the right tool for the job,” he said.
“I start off by looking at what the problem is, what is the customer trying to achieve [and work back from there].
“With the Pro-Ring, for example, the problem was that there are a lot of low maintenance holes – which let rainwater in and, being low, become covered and create access issues – there was a lot of damage to infrastructure and there was a lot of manual handling injuries associated with moving concrete risers.
“I had quite a few people talk to me about wanting to improve safety and stop the leaks in the maintenance hole chimney, so I looked around for a solution to raise maintenance holes, and the Pro-Ring was already proven overseas and had a well-established track record, with its light weight and high strength. There are other materials out there, but I chose this one because of the strength, durability and its ability to properly seal.”
ISC Services has a range of simple, yet clever solutions to tackle inflow and infiltration, but for Mr Bentink, the best thing you can do is start sooner rather than later.
“A lot of people don’t know where to start because it’s such a big problem. But not starting doesn’t help – leaks don’t fix themselves and they just cause more and more damage to the assets over time and downstream,” he said.
“Inflow and infiltration are very difficult to eliminate, but by reducing it, we can reduce the burden on the assets and prevent avoidable overflows.”
For more information, visit iscservices.com.au
