Combined sewer overflows (CSOs) have been subject to increasingly intense public and political scrutiny for more than a year amid greater awareness of their use and potentially adverse environmental impact. Most recently, the Wildlife and Countryside Link (WCL) called for increased investment at the next price review to curtail their use and levels of river pollution, for instance.
As reported by Utility Week, the alliance of environmental groups and stakeholders’ Blueprint for Water report outlined the need for an effective enforcement regime as the first step in cutting pollution and stressed that a transparent, well-funded, monitoring regime would drive compliance up and pollution down. The group also urged government to set a wastewater target in the upcoming Environment Bill to encourage water companies to phase out CSO usage.
This news came off the back of a swirling current of scrutiny and opposition which had been in motion for much of the past 12 months.
In November 2020, for instance, Surfers Against Sewage demanded legally-binding sewage emission reduction targets and further transparency from water companies on discharges into rivers and bathing water.
Its Water Quality Report found 2,941 CSO discharge notifications between 1 October 2019 and 30 September 2020 – and the number of notifications falling year-on-year for the majority of firms – the group stated that water companies were still “discharging sewage at alarming rates, polluting the environment, and risking our health”.
In the time since, a public outcry against the use of CSOs led to a private members bill motioned by Philip Dunne, chair of the Environmental Audit Committee. Although it did not complete the passage to law, several of its focal points were added to the Environment Bill – including water companies, the EA and Secretary of State being required to report on the use of overflows.
More recently still, David Black – then interim chief executive of Ofwat – wrote to water and sewerage companies in June 2021 to underline the importance of monitoring storm overflows, asking industry leaders to gain a “full and accurate picture” of performance and stressed the importance of actively considering the environmental impact of CSOs and implementing clear and timely strategy to address shortcomings.
With this in mind, Utility Week Innovate asked a number of water companies to provide updates on their CSO performance and policies over the past 12 to 18 months, and outline what steps are being taken to protect the environment.
The state of play: ongoing work and existing targets
The Environment Agency (EA) has stressed that all overflows must be covered by event duration monitors (EDM), to track how often and for how long they are used, by December 2023.
Generally speaking, the water companies which provided updates on their CSO and network monitoring progress explained that existing regimes offered more than 95 per cent coverage from sensors and EDMs – with aims to reach 100 per cent within the next few years as they worked to scale back the role and repercussions of CSO use.
“We have invested heavily in reducing the impact of our CSOs, are continuing to work on further improvements,” James Harrison, head of wastewater asset management at Yorkshire Water says. “We have increased monitoring significantly, with 96 per cent coverage and reporting in 2020 and an aim of 100 per cent coverage by 2023.
“Current monitoring provides 80 million data points and as a business our focus is on the reporting and validation of data to improve data quality, which will continue to improve as understanding of the data improves.”
James MacLean, technical policy manager at Northumbrian Water – whose network consists of nearly 30,000 km of sewers – explains that the firm is in the midst of upgrading and deploying monitoring devices as it works toward a target of 100 per cent CSO coverage in early 2022.
“Our strategy since 2005 has been to install sewer level monitors at all our network CSOs for pollution prevention and operational reasons,” he explains. “They are typically battery-operated monitors that communicate daily unless triggered by a warning level.”
Likewise, Wessex Water – which treats and supplies drinking water to roughly 1.2 million people and provides sewerage services to 2.5 million – is focused on upgrading its network infrastructure. In fact, Jody Knight, asset technology manager at Wessex, explains that having installed 125 EDMs last year despite the Covid pandemic – 55 more than their target of 70 – they’re on course to provide 100% coverage of EDMs on storm overflows to the environment by March 2023.
Fast facts: Northumbrian Water
The number of data points which have been collected by Northumbrian’s monitoring systems since 2012.
The current level of monitoring coverage across Northumbrian’s 1,520 CSOs. Aiming for 100 per cent in early 2022.
The amount to be spent by Northumbrian between 2020-25 to investigate CSOs and reduce their use
Sense-checking monitoring technology
Diving further into the technology at the heart of Northumbrian’s approach, the firm explains that it is set on implementing state of the art monitoring devices across its network as well as bolstering early warning capabilities.
“Investment also continues in our operational technology programme to replace telemetry equipment with new start-of-the-art technology with increased functionality and data availability,” MacLean says. “This also includes increased visibility of wastewater assets on our eSCADA telemetry system and new low-cost monitoring of sewers near to watercourses.”
What’s more, off the back of a data hack led by Microsoft at its 2020 Digital Innovation Festival discussing how sewer level monitoring data can help tackle environmental challenges, delegates at Northumbrian’s first hybrid innovation festival in October 2021 will continue to explore both mainstream and off-piste approaches to CSOs.
“We are continually investing in alternative options and technologies, recognising the benefits of being open with our data,” MacLean adds.
Similarly, according to Thames Water’s head of environmental engagement, Yvette de Garis, the company serving 15 million customers across London and the Thames Valley is trialing a new generation of sewer level monitors to reduce pollutions from blockages and is on course for 100 per cent coverage by 2023.
Monitors tracking flow rates in sewers and designed to send alerts when blockages are detected have thus far been installed in Henley, South Oxfordshire, and West Ham and Harlesden in London, with larger trials afoot should they prove successful.
Fast facts: Yorkshire Water
The number of data points provided by current network monitoring.
CSO monitoring coverage and reporting registered in 2020. Aiming for 100 per cent by 2023.
The amount to be invested by 2025 in storm overflow improvements.
Use of artificial intelligence and ‘machine learning’
Wessex Water’s Knight adds that the firm is using innovative technology to reduce the number of alarms and, like Northumbrian, strengthen its early-warning capabilities.
“We have carried out an open data trial into AI and machine learning analytics at storm overflow sites in Bath,” she says. “The trial utilised diurnal sewage depths from EDMs and upstream rainfall data and, using machine learning algorithms, established ‘normal operating parameters’ for the sewage for those conditions.
“The system then alarms only when actual depths are outside these parameters – for instance, a downstream blockage or obstruction would cause the actual depth to be higher than the expected upper normal operating parameter, whereas an upstream blockage would be indicated by levels lower than the lower normal operating parameter.”
If a storm overflow is discharging in rainfall, when it would be expected to discharge, no alarm will be generated in Wessex’s control room, she continues.
“Consequently, we have been able to identify blockages before they have caused any premature discharges and consequential pollution incidents. We have also been able to move from time-based maintenance to condition-based maintenance for these assets and have dramatically reduced the number of alarms being received in wet weather.
“We have now completed the trials and are in the final stages of a tender process to roll this capability out across our sewer network over the coming years.”
Fast Facts: Wessex Water
Coverage of event duration monitors (EDMs) on storm overflows to the environment targeted by March 2023.
Number of EDM units installed in 2020 despite the Covid pandemic – 55 more than initial target of 70.
Manageable level of event detection alarms in wet weather is in the 10s per day – rather than 100s or 1,000s currently witnessed, according to Wessex Water.
Influx of predictive and telemetry technology
Northumbrian’s response to pollution incidents is primarily governed by the early notification or detection of issues through monitoring and trend analytics.
“Once we are aware of issues, our people perform a ‘blue-light’ pollution response to all potential incidents and aim to minimise any impacts immediately,” MacLean explains.
“We are then able to respond and resolve problems quickly before they cause an incident. There have annually been hundreds of instances when operators were alerted and attended site to clear a problem before there was an overflow.”
Continued investment in sewer level monitoring technology and trend analytics assists said early detection and prediction of issues including pollution and flooding.
“We constantly use and develop our extensive telemetry eSCADA system, covering over three million data points with associated alarms and early warnings,” MacLean adds. “Algorithms have also been developed for the early warning of issues in our Sewer Network Information Performance Reporting (SNIPeR) system together with rainfall data to identify potential problems.”
This control, business intelligence and monitoring capability covering more than 99% of overflows at sewage pumping stations and treatment works has contributed to the lowest levels of pollution events of any water company in the England and Wales since 2017, as measured by the EA, the spokesperson continues.
Thames Water’s de Garis adds that while EDMs are an industry-wide measure, the firm has approached some areas in “different ways” including attempts to provide the public with live updates.
“For example trialling a system to give river users in Oxford real-time notifications of discharges from six of our nearby sites,” she explains. Such automatic release notifications for local community groups in the Oxfordshire area use information from EDMs to send an email whenever data indicates there’s likely to have been a release.
On top of this, an early innovator in real time reporting to the public, Southern Water, has implemented a Beachbuoy monitoring service – offering real-time information about releases of stormwater or wastewater – which covers all of its designated bathing waters as well as areas such as Chichester and Langstone Harbours which are popular with recreational water users.
Fast facts: Southern Water
Amount that Southern is primed to invest in its water and wastewater services under its Water for Life Business Plan 2020–25.
In 2020, Southern saw a 40 per cent improvement in pollution incidents from wastewater treatment works, and a 10 per cent boost overall.
Southern is working to eliminate all pollution incidents on its network by 2040.
Managing a data deluge
The lynchpin of each of the approaches mentioned – whether real time or predictive – is effectively processing, analysing and utilising data, with Southern Water stating that simply installing monitors equates to roughly a third of the challenge
The company – which provides water and wastewater services for east Kent, parts of Sussex, Hampshire and the Isle of Wight – has grown its Beachbuoy service from manual data entry to a fully computerised system which provides both the EA and public with near real time updates.
However, peripheral challenges spanning both technology and workforce remain once data is collected – for example, how the industry ensures quality and accuracy of data collected, especially when it’s gathered at scale.
Northumbrian Water, for instance, has collected more than 600 million data points via its long-running sewer level monitoring programme since 2012.
“Our wastewater teams review the data from our storm overflows weekly and investigate where we have any that are frequently spilling or have repeated issues (e.g. blockages),” MacLean says.
“In addition, we carry out planned inspections of all storm overflows by using the monitoring data dynamically to focus on the risk and vulnerability of our assets. Proactive activities, such as investigating top blocking/spilling CSOs and pre/post bathing season checks, have also been targeted at particular sites to prevent incidents occurring.”
As a consequence of the scale of said data challenges, Yorkshire Water’s Harrison explains that investment allowing greater automatic analysis and support for internal processes for targeting data anomalies, leading to increased action to improve overall data confidence and accuracy of reporting, is afoot.
“We are continually looking to improve our process and the data we collect, particularly as we gather more information on the performance of the network in a variety of conditions,” he says. “Ultimately, the increased focus and use of data will lead to significant improvements in storm overflow performance and help to deliver positive impacts on river water quality.”
What’s more, the sharing and transparency of said data is a key focus.
“Thames Water, along with other water companies, is publishing annual EDM data online, and areas with designated bathing water status which were receiving seasonal notifications can now expect to see alerts shared throughout the year,” Thames Water’s de Garis says. “The company will also accelerate work to install monitoring devices to create a complete picture by 2023.
“Thames Water has also agreed to publish annual monitoring data on its websites about the use of storm overflows so that progress in reducing their use can be tracked,” she adds. “The EA will compile this data and that from other water companies into an annual report that is easily accessible to the public.”
Fast Facts: Thames Water
Length of the ‘super sewer’ beneath the Thames that will intercept sewage overflows. Expected to be operational by 2025.
Reduction in pollution incidents by Thames Water during the year ended 31 March 2021.
Length of river in Thames Water region to receive environmental improvements between 2020 and 2025.
Number of MPs briefed by Thames Water on efforts to stop pollution into streams and rivers from sewers.
Increased investment and ongoing collaboration
In keeping with comments from environmental groups and stakeholders which called for increased investment to end to river pollution and phase out CSOs, De Garis adds that she believes discharges of untreated sewage are “simply unacceptable”, even when they are legally permitted.
As such, she explains that Thames Water will work with the government, Ofwat and the EA to accelerate work to stop them being necessary and to deliver a five-year business plan featuring environmental improvements to 745km of rivers across its region.
“We have a long way to go – and we certainly can’t do it on our own – but the ambition is clear,” she says.
Yorkshire Water’s Harrison adds that the firm has pledged £137 million in investment by 2025 to overflow improvements, investigations and further monitoring, while Northumbrian has earmarked more than £80 million over the same time period.
“We are also piloting an innovative AI pollution prevention solution in collaboration with Siemens and developing SMART network innovation pilots that will use data to identify problems before they cause environmental harm,” Harrison says. “These specific projects are examples of an increased focus on analytics and machine learning to identify patterns and trends to respond to developing trends.
“Ultimately, we will be using the data to take a systematic approach to the network from sink to sea.”
He adds that Yorkshire is also supporting the government led Storm Overflow Task Force by providing detailed asset information and representation on working groups. “Our storm overflow strategy is closely aligned to the Task Force objectives to eliminate harm from overflows, reduce spills and increase data transparency,” he explains.
On top of this Wessex Water’s Jody Knight, says that her firm will be completing an EDM programme for all storm overflows by December 2023 in line with EA expectations, but caveats that CSO improvements are part of a far broader environmental picture.
“While there is lots of focus on the operation of storm overflows, there is little on the impact they do or don’t have on the environment or public health risk,” she says.
“Currently published data from the government website indicates that only 4% of the reasons for waterbodies not achieving good ecological classification are down to storm overflows.
“As a society we need to invest in a greater network of water quality monitoring so that investment decisions can be targeted in the best place. As a member of the Defra Storm Overflows Taskforce, we have been pushing Defra, EA, Ofwat to recognise this – and they have subsequently just announced such an initiative.”
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