Storm on the Horizon: Sewage Overflow Is a Problem for Today, Not Tomorrow
Climate change often is depicted as a far-off threat; something for future generations to worry about. However, while politicians continue to debate how to solve this critical issue, the effects of global warming and changing weather patterns are already being felt close to home.
Across France, for example, heavy rainfall, flooding and other extreme weather events are becoming increasingly commonplace, putting further strain on already overworked infrastructure, including wastewater systems.
“Our urban sewage networks are struggling to meet the needs of a 21st-century population,” says Laurent Lefevre, sales manager for Trelleborg’s pipe seals in the east of France. “These networks are typically designed for smaller conurbations with fewer people. As the population has grown, the networks haven’t had the investment they need to keep expanding. They’ve become more and more overworked, and this is when problems arise.”
A Perfect Storm
For these older networks, heavy rainfall and flash floods—such as those experienced by Lyon at the start of 2018—often are the straw that breaks the camel’s back.
Structural issues often play a part. “The dimensions of drainage pipes are typically calculated based on the average rainfall levels for that region,” explains Jean-Jacques Merour, sales manager for Trelleborg’s pipe seals in the west of France. “It means the standard pipe diameters in the south of France are narrower than those in the north. That’s all fine most of the year, but when you have intense periods of rain, the network is quickly overpowered.”
Furthermore, old-fashioned combined sewers, which still are widely used in cities, are ill-equipped to handle heavy rainfall or meltwater, resulting in overflows of mixed water and sewage into rivers and estuaries. As weather patterns continue to change and sewage networks age further, these problems are likely to occur more frequently in the years ahead.
The impact of rainwater mixing with sewage can be devastating on the urban environment. A research program conducted by Lyon’s water authority, le Direction de l’Eau de Lyon Métropole, analyzed the environmental impact of insufficient capacity.
Counting the Cost
After heavy storms, when rainwater enters the sewer system and water-treatment plants reach full capacity, water is diverted into rivers to prevent it from backing up into homes. That’s when fecal pollution in rivers and groundwater occurs.
These sewage overflows can have dire consequences for public health. A study by the University of Illinois at Chicago discovered that emergency room visits for gastrointestinal illnesses rose 13 percent in the days following extreme rainfall events in towns with combined sewer systems. With most health incidents unreported, the real impact is thought to have been far greater.
Health issues impact directly on the public. In addition, there are cleanup expenses and emergency repairs, municipalities often have to count the cost of lost productivity, and, in many cases, depleted fishing and tourism revenues.
While network capacity issues are known to cause urban Sanitary Sewer Overflow (SSO), the situation is being aggravated by the poor state of today’s wastewater networks. An investigation by the U.S. Environmental Protection Agency into the causes of SSO occurrence found that only 7 percent of overflows were caused by insufficient system capacity, while 27 percent of SSOs were due to inflow and infiltration, and 12 percent caused by pipe breaks.
Help Is at Hand
The good news is that pipe cracks, breaks and leaks can be repaired. If sewer networks don’t require expansion or upgrading, this may be a cost-efficient option. But as Lefevre explains, it’s rarely this simple.
“Everyone knows these problems exist, but that doesn’t necessarily mean that everything possible is being done to resolve the issue,” he notes. “Usually, it’s a question of funds: decision-makers are not always willing to spend money on an issue that may only occur a couple of times a year.”
Rather than replacing entire systems, network owners can take measures to rehabilitate pipes using patch-repair methods, cured-in-place pipelining solutions or mechanical seals. Specific sections of the network then can be replaced with stronger, long-lasting solutions to prevent breaks or leaks in critical areas and increase system capacity.
Choosing the Proper Solution
All too often, the pressure on municipalities and network owners to conserve taxpayers’ money takes precedence. Projects are delayed and robust (but more expensive) solutions are rejected in favor of cheaper options.
“What non-specialists sometimes struggle to understand is that not all sealing materials are alike,” says Merour. “To be able to withstand intense pressure year after year, the rubber in pipe seals needs to be of a very high quality. That is why we continually improve our compounds and are having them tested by third-party agencies.”
Another major influence on the reliability and performance of pipeline systems is the competence of the installer. A number of factors can make life difficult for the pipelayer in the trench; however, designing sealing systems to reduce the risk of incorrect or problematic installations can drive significant improvements in laying rates and site safety.
One such solution involves integrating the seal into the socket of the pipe or manhole before it’s delivered to the site. Integrated sealing systems eliminate the chances of seals being lost or misplaced during pipe stocking and transportation, and ensure the proper seal is always correctly positioned in the joint.
An integrated system also will prevent any accidental misfitting of seals onsite while allowing the tolerances of the joint to be more accurately controlled by the manufacturer before the product leaves the factory. What’s more, with the system “locked” into the socket of the pipe or manhole, the seal can’t be displaced during installation. This reduces the need for operators to be physically present in the trench during lifting and jointing: a major plus point in terms of health and safety.
Although price is an important consideration for today’s network owners, the advantages of doing things properly are difficult to ignore.
A Drop in the Ocean
Increasingly, municipalities and water-board authorities are starting to realize the importance of thinking long term and finding new ways to address the problem of fluctuating rainfall and excess water. Salisbury, Australia, for example, is using technology to “harvest” stormwater by saving it for irrigation and industrial uses during dry spells.
Similar techniques are being pioneered in France. In 2017, the Direction de l’Eau de Lyon Métropole launched Project Ville Permeable, a sustainable approach to dealing with the city’s surplus water issues. The concept is based on the idea of “la ville éponge,” the city as a sponge. Rather than being flushed out with storm drains, rainwater is contained within the city and prevented from turning into unusable waste.
The program relies on significant investment, including using precast concrete to store rainwater and make it suitable for reuse. Crucially, the long-term advantages of making these investments may well be a drop in the ocean compared with the cost of dealing with future overflows and contamination. As one member of the project team put it: “Nous n’avons pas assez d’argent pour faire pas cher” or, in English, “We don’t have enough money to do this on