5 approaches to address inflow and infiltration challenges

Wastewater professionals frequently face inflow and infiltration (I&I) issues. They both involve water getting into sanitary sewer systems. Treatment plant professionals may find their operational costs rising while environmental hazards — including sewer overflows — become more common.

Inflow occurs when surface water gets into the sewage system. High levels of stormwater runoff can make it more likely to happen. Conversely, infiltration concerns groundwater entering the sewage infrastructure, often due to infrastructure faults, such as deteriorated pipes.

Infiltration and inflow can present costly challenges for the conveyence of wastewater. Here are five clever approaches to address the problem.

Use multistep campaigns to identify infrastructural problems

Well-established testing methods can help professionals identify issues that will cause inflow and infiltration challenges.

In Cedar Rapids, Iowa, the sanitary sewage network spans more than 660 miles and has had numerous inflow and infiltration issues over the years. These problems led to overflowing sewers and even caused basement backups in people’s homes.

Officials moved ahead with a two-pronged pilot project for improvement. First, crews would perform door-to-door inspections to find instances of basement sump pumps connected to a house’s sewer lateral. Besides being illegal, those can quickly cause sewers to back up and overflow. That’s why the Cedar Rapids inspectors aimed to find and disconnect such connections at no cost to residents.

Several unpermitted sump pump connections can overwhelm a sewer system faster than many people realize. Washington County, Maryland, has many sewage collection systems that can handle a maximum flow rate of 300 gallons of water per minute. However, a half-horsepower sump pump contributes about 60 gallons of water in that time. In that situation, only five households with illegal connections could overwhelm the system, causing backups and millions of dollars in damages.

The second part of the Cedar Rapids plan involved filling the sewer with a non-toxic and odor-free mist to detect issues by seeing where the substance leaks. Officials were confident that this two-step approach would significantly reduce inflow and infiltration problems, making the infrastructure more resilient.

Support the installation of permeable pavements

Permeable pavements are becoming increasingly popular in areas that typically get heavy rainfall. If people install them properly after thoroughly studying the relevant locations and their rainfall patterns, these surfaces can curb inflow issues by reducing stormwater runoff.

A 2022 study by Australian researchers showed that permeable pavements could halve urban flooding, but only after careful analyses. The team collected data from 107 towns and cities in Australia, and then used that information to create the best permeable pavements, assuming that storms lasted a half-hour and had a 5% probability of excessive rainfall.

Next, the researchers built an algorithm to determine each area’s primary soil type and how well it soaked up water. They aimed to have the pavements absorb 70% of the water, meaning only 30% got released as stormwater runoff. The outcomes showed that ideal was possible, but only if people analyzed the soil type and rainfall trends before selecting the base course layer.

Acting now is critical, especially since scientists believe climate change will result in heavier rainfalls worldwide. As the atmosphere warms, it can hold more moisture, causing storms characterized by above-average precipitation. As one meteorologist explained, an atmosphere with a 68-degree-Fahrenheit temperature has twice as much moisture as one at 50 degrees.

Although wastewater management professionals likely won’t have the direct authority to install permeable pavements in the communities where such additions could do the most good, they can educate relevant stakeholders, such as city planners and other local stakeholders, about how permeable pavement systems can minimize the risk of inflow problems.

Model an area’s sewer system

Sometimes, wastewater management professionals don’t know something’s wrong until inflow and infiltration problems become apparent. However, the better approach is to use technology to gain the necessary visibility for better oversight.

That was the focus of decision-makers associated with the sewer infrastructure of Saline, Michigan. The utilities companies there serve the water, wastewater and stormwater needs of around 8,000 customers. But much of the infrastructure is more than a century old. Until recently, the recordkeeping strategies used in the area weren’t sufficiently current either.

All the city’s documents were in various facilities, and only in a paper format. Although city officials invested in a geographic information system (GIS), employees could not access it, and a third party managed the tool.

However, thanks to an intensive digitalization project, the city has reduced inflow and infiltration events by improving access to details of the water and sewage systems. Now, every employee can quickly access the data they need to do their jobs. A plant technician could pull up information about a specific asset, or a field worker could retrieve system blueprints to speed their workflow.

City officials in Saline plan to eventually create a utilities master plan. They can then use their plan to assess the current state of the infrastructure and tackle particular repairs based on their budgets and team member resources. People involved in the initiative believe it’ll help them get ahead of necessary repair and rework and investigate infrastructural improvements for years.

Purchase specialty equipment

Decision-makers must determine when it makes sense to rely on contractors for wastewater infrastructure inspections and when it might be more cost-effective to buy specialized equipment. The latter option allows people to use the assets whenever needed and not face delays from waiting for busy contractors to have more availability.

Such was the case in a small town where officials had to call contractors up to 12 times a year to do camera-based pipe inspections. Officials realized they could perform those checks on an optimized schedule by purchasing the necessary equipment instead of depending on contractors. They had previously agreed to arrangements that cost hundreds of thousands of dollars but still only inspected 75% of the area’s infrastructure.

Decision-makers overcame those downsides by purchasing a pipe-crawling robot that sent images to users and allowed them to pan around the area or zoom in on specific sections of a pipe. People also received data about how far the robot had moved down a pipe, letting them keep track of progress.

It’s not always easy to make internal changes and get approval for new investments. But this example shows that doing so can often bring better results. That’s particularly true if people take the time to identify the downsides of their current processes and learn how to achieve meaningful improvements.

Invest in smart sensors

Industries ranging from agriculture to manufacturing commonly use smart sensors to collect real-time data for actionable insights. These additions can minimize inflow and infiltration challenges, too.

One example comes from South Bend, Indiana. Aging infrastructure and heavy rainfall there resulted in up to 2 billion gallons of pollution entering the St. Joseph River each year. Officials aimed to solve the problem with intelligent sensors that provided continuous alerts while monitoring the system. This high-tech upgrade caused a more than 70% reduction in overflows. The implementation enabled approximately $1.5 million in annual operating and maintenance savings and $500 million in capital works savings.

Leaders associated with the project were particularly impressed that the changes were relatively affordable and brought such significant gains. They expect that, in addition to the money saved, the sensors will support long-term regulatory compliance and system performance.

Some advanced technologies also use artificial intelligence to help people proactively respond to inflow and infiltration problems. These tools can show utilities professionals how severely specific storms affected their infrastructure and which issues are the most likely to cause issues if not remedied soon. Such technologies also support troubleshooting and resource deployment by displaying maps indicating the locations of possible problems.

Begin tackling inflow and infiltration issues today

Unaddressed inflow and infiltration problems can quickly become incredibly resource-intensive. The best options are typically proactive, and leaders can start making measurable progress by implementing some of the suggestions detailed above.