Storm overflows – SOs – are a part of the way wastewater networks across the UK and Europe function, operating as a relief valve that protects the homes of customers and the environment from sewer flooding. However, the rates of discharge have reached worrying levels. The Environment Agency estimates that raw sewage was dumped into UK waters more than 400,000 times in one recent 12-month period, across more than 3.1 million hours.
Severn Trent is just one water company guilty of illegal sewage discharges. In December 2021, the firm was fined £1.5 million by a court for discharges from four sewage treatment works in Worcestershire (between February and August 2018) after failing to respond to alarms warning of a blockage and also failing to adequately manage sewage sludge. About 360,000 litres of raw sewage were illegally discharged as a result of the breaches.
“The current levels of storm overflow discharges into rivers cannot continue, and the water sector must tackle this,” warns David Black, interim chief executive of Ofwat. “As part of our recent price review, we required [water] companies to reduce pollution incidents by 30% by 2025 and to improve 12,000km of rivers. We also backed investment of around £1 billion every year for water companies to improve the natural environment by increasing the capacity of the wastewater system to meet growing demand.”
For the 2020-2025 period, £4.8 billion of investment is being made to deliver the National Environment Programme (NEP) for Wales and the Water Industry National Environment Programme (WINEP) for England, of which £1.2 billion is specifically for storm overflow-related improvements.
Perhaps most notably, when it comes to ensuring accountability, water companies are also accelerating work to install monitoring devices across all storm overflows by 2023 in England and by March 2022 in Wales. This, says the Environment Agency, is fundamental to understanding and improving the environment. “Over the past 30 years, the work of the EA has directed £30 billion of water company investment in infrastructure, including improvements, to over half of the 15,000 storm overflows in England. Key to these improvements is event duration monitoring (EDM) data. This provides a robust and consistent way of monitoring how often and for how long storm overflows are used, and underpins our planning, compliance and enforcement work.”
Working with water companies, the agency has concluded a programme to install monitors on over 12,000 storm overflows. By the end of 2023, the remaining 3,000 will also be monitored, to provide a complete picture of permitted storm overflows in England.
TASK FORCE LAUNCHED
In 2021, the government launched the Storm Overflows Task Force. Yorkshire Water, for one, is working closely with the task force to deliver a range of short-, medium- and long-term improvements. The company has invested heavily in reducing the impact of its CSOs (combined sewer overflows) and is continuing to work on further improvements, says James Harrison, head of wastewater asset management. “We have increased monitoring significantly, using Point Blue [Metasphere] devices, with 96% coverage and reporting in 2020, and an aim of 100% coverage by the end of this financial year. 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.”
Yorkshire Water is investing £137 million in storm overflow improvements, investigations and further monitoring by 2025. “We are also rolling out an AI blockage predictor tool that will help reduce pollution, in collaboration with Siemens, and developing SMART network innovation pilots that will use data to identify problems before they cause environmental harm,” adds Harrison. “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.”
MAJOR INVESTMENT
For its part, Northumbrian Water recognises that storm overflows need updating and is working to make improvements through more than £80 million of investment in its current 2020-25 operating period and as part of the Storm Overflow Task Force.
“Since 2006, we have installed sewer level monitors (SLMs) on 98% of our SOs and are on track to reach 100% by March 2022,” a spokesperson confirms. “When we first installed SLMs in 2006, we used the IETG Hawkeye monitors. In 2015, we started a replacement programme, installing Technolog Cello monitors and are now in the process of replacing these with Point Blue monitors. These sewer-level monitors all work in a similar way, but the regular upgrade process and maintenance carried out across the asset base enables us to ensure we maintain a high level of operability.”
The SLMs are battery operated, due to the lack of power supply to the majority of the company’s SOs. These loggers contain a SIM card and communicate with the SCADA system via mobile phone networks. An ultrasonic sensor head is fitted above the flow and this can tell the depth of the water by measuring the time it takes for a signal to bounce off the surface of the water.
“Triggers are set at 80% of the weir height, as an early warning, and also at 100% to confirm when the SO is overflowing,” explains the spokesperson. “When an alarm comes in from these triggers, we analyse the date to see if the increase in levels correlates with rainfall in the area. If it does not, it is an indicator that higher levels are potentially caused by a problem such as a blockage.”
Also, Thames Water is spending more than £1.25 billion at its sewage treatment works during the company’s current five-year business plan to deliver a number of benefits, including increasing capacity, better monitor readings and efficiencies in its operations, it says. “We have a long way to go – and we certainly can’t do it on our own – but the ambition is clear.”
To that end, it is conducting a trial at six sites around Oxford, providing real-time alerts of discharges using event duration monitor (EDM) data. “We are learning a lot from the trial, with the help of the user group,” states a spokesperson. “From this, we are developing a system that will enable us to provide notifications for all the 500-plus sites where we have EDMs by end of 2022.”