The Environment Agency explains that combined sewerage systems take away rainwater runoff as well as wastewater, including human waste, in the same pipe and send them to a sewage treatment works. Storm overflows prevent pipes from being overwhelmed during heavy rainfall by the volume of water, which would otherwise cause wastewater to back up and flood people’s homes and businesses, as well as roads.
The agency arranges permits to limit the impact of storm overflows on the environment. It has made water companies install monitors on all storm overflows to identify how often and how long they discharge using event duration monitors (EDM). The data is then used to identify storm overflows that are spilling too frequently so that water companies can take action (see box, p15).
Nick Mills, head of Southern Water’s clean rivers and seas taskforce, recognises the importance of tackling the issues presented by storm overflows. “This is probably the biggest issue that the industry has faced since privatisation in the late 1980s, which took place at a time when the UK was known as ‘the dirty man of Europe’ because in many cases there was no wastewater treatment.
“The EU introduced the Urban Wastewater Directive which meant we had to treat to a certain standard,” he continues. “The UK decided to privatise the industry to pay for end-of-pipe treatment solutions, and a lot of the improvement we have seen in bathing water since those times is because of this activity.”
The EU introduced the directive in 1991 to protect the environment from the adverse effects of urban wastewater discharges, and discharges from certain industrial sectors by mandating waste collection and treatment in urban agglomerations with a population equivalent of more than 2,000. It requires member states to ensure that national authorities take measures to limit pollution of receiving waters from storm water overflows via collecting systems under heavy rain.
However, Southern Water has also come under fire recently. In July, the company was fined £90m after pleading guilty to causing 6,971 illegal discharges of sewage between 2010-2015. The discharges were made into numerous watercourses, including conservation sites, causing environmental harm to shellfish waters. This negatively impacted businesses and community groups, with discharges causing a deterioration in the shellfish quality – leaving some areas unsuitable for harvesting shellfish for human consumption, according to the Environment Agency (a point disputed by Southern Water).
Mills states that the company is taking steps to make up for its past actions. “We are recovering from a dark period where we got it wrong. We have a new CEO, Lawrence Gosden, and pretty much an entirely new executive team. We have implemented a lot of cultural training, including improvements to whistleblowing procedures.”
DIGITAL INFO
As part of this transition, the utility has adopted a more transparent approach to sharing data via its Beachbuoy digital tool, which provides near real-time information about storm overflows near coastal bathing waters.
Aside from making up for past actions, Southern Water is also responsible for fitting storm overflow monitors provided by Siemens that measure the water level using an ultrasonic device. “We’ll take those readings and send them back to the central server. The data is reported on the Beachbuoy website if it has the potential to impact designated bathing water on the coast while also sending notifications to the Environment Agency.”
Elaborating further on how the sensors work, Adam Cartwright, head of IoT applications at Siemens, explains that the sensors look for reflections that bounce off different materials.
“You have to configure the sensor to understand if the reflection is bouncing off the walls or [the] engine, which is the shape on the chamber that it’s in, which allows you to cut out those reflections that aren’t real. At that point, you have defined the low points when there is no water and the high points as far as it goes, and then you measure the distance in between.”
Every 15 minutes, the telemetry unit powers up and takes the signal from the sensor, and normally sends the data once a day. However, Cartwright points out that a powered site may send signals more frequently, as there is no need to preserve the battery life.
“The standard practice for configuring telemetry units is that if a measurement comes back and it’s at the high point, then instead of waiting a day to send the data point back, it starts sending it back straight away. This is to alert the water company that the water level has reached a certain height.”
Once the high point signal is received, an alarm is triggered in a utility control room where personnel will investigate the alarm and determine whether the system is operating normally or if the signal is reporting a false positive.
Do the monitors come with any specific maintenance requirements? Mills explains that the heads of the devices require manual cleaning when wet wipes wrap around the head of the devices. However, gaining physical access to the sensors, which are sometimes installed underground and only reached via a manhole, can require waiting times of three months to allow for traffic management planning.
“We are requesting nationally a review of this process because three months is not sustainable,” Mills continues. “We do have emergency powers if there is a burst or something that is disrupting people in a big way, but an instrument that monitors the overflow doesn’t currently count as an emergency.”
ON THE RIGHT PATH
Fitting and maintaining monitors are only part of the solution. Another approach relates directly to Mills’ role as head of Southern Water’s clean rivers and seas taskforce, which is charged with delivering at least six pathfinder projects to solve a range of challenges, including surface water and groundwater inundation in sewers, a root cause of flooding and storm overflow use, he says.
The taskforce carries out each project with an initial survey of the catchment area and actions like cleaning screens and pipes to reduce the chance of blockages. It then establishes pilot projects, which can include measures such as controlled improvements on existing assets before carrying out more complex interventions. These can include installing soakaways, roadside swales, rain gardens in schools or highway drainage enhancements.
Among the pathfinder projects, Southern Water is trialling the provision of smart water butts and planters that slow the flow of water running off roofs and into the network in Deal, Kent. It will work alongside Deal’s MP, Kent County Council, Dover & District Council and public representatives.
Also in Kent, the company is seeking to reduce the stress on pumping stations and storm overflows at a combined sewer system in Margate. As part of the work, a sustainable drainage system programme is underway across 19 schools in the area, while the main pumping station has also been upgraded.
Elsewhere in the county, Southern Water is setting out to better manage water flows in Swalecliffe. The company is enhancing a terminal pumping station that receives municipal wastewater from the network pumping stations and optimising the storm tank controls on the main wastewater treatment works to increase the volume stored and treated.
In Pan Parishes, Hampshire, Southern Water is using Tubogel, a two-part liquid rehabilitation solution, to repair broken or fractured household pipes. Once the T2 liquid reaches the residue of the T1 liquid, which has saturated the area surrounding the external area around the breach or break in the pipe, it solidifies, creating a hard seal around the breach.
The water utility is also trialling wastewater pumping control, surface water and storage solutions at Sandown, in the Isle of Wight, while identifying options to reduce the flooding and pollution incidents and the storm loading on the treatment works in Fairlight, East Sussex.
“Some of the work we have been doing at the Isle of Wight in particular shows that these measures really make a difference when you deploy them at a domestic level,” Mills continues. “In one case, the storm overflow would activate with five millimetres of rainfall, typically. We have installed water butts on 70% of the properties in that village, and since we have done that the overflow has not activated.”
The technology is feeding into a regional plan that Southern Water is hoping to release if it gets the approval from regulators. “If it is accepted, we will publish the plan [this] year, so people can see what it means for their particular area, and we will be asking for feedback from our communities.”
While the Environment Agency’s data underscores the urgency of the task at hand, Southern Water has charted a course in the right direction.
BOX: Spill data
In March 2022, the Environment Agency released data from the 2021 EDM storm overflow returns from water and sewerage companies. The Environment Agency data also shows:
12,707 (89%) of England’s 14,470 storm overflows now have monitors, with the remainder due to be installed by the end of 2023The average number of monitored spills per overflow reduced from 33 in 2020 to 29 in 2021. While the trend appears to be going down, this is likely because of drier weather in parts of the country last year than in 2020The average duration of each monitored overflow event was seven hours 5% of storm overflows spilled more than 100 times in 2021; 87% of storm overflows had at least one spill in 2021; and 13% of storm overflows did not spill in 2021