Darren Hanson, Xylem Environmental Solutions, examines the current state of quality monitoring in the UK.

Ambitious targets to protect UK rivers, estuaries and coastal zones, set out in the Environment Act 2021, pose significant challenges for water companies.

For example, Part 5 Section 82 of the legislation, which became law in November 2021, requires water utilities to continuously monitor the water quality of all storm overflow and sewage disposal works, which discharge into these waterways.

The regulation requires the measurement of dissolved oxygen, temperature, pH, turbidity and ammonia, and others specified in water across over 20,000 Combined Sewer Overflows (CSOs) and more than 7,000 sewage treatment works in England. This provides a particular challenge to the industry in terms of installation, monitoring and continuous maintenance.

So how do water utilities carry out a large-scale water quality monitoring programme? Firstly, I’ll explain the current situation.

Where are we now?

CSOs collect both wastewater and stormwater through a single pipe, and the combined flow is carried to a treatment plant. Combined sewers are equipped with a relief flow route, so that pipes and treatment plants are not overwhelmed during surge events and potential flooding of homes and commercial premises is avoided.

Because of this, surge events naturally cause discharge. To better understand the impact of these events, the Environment Act set requirements for water companies to install monitors on the vast majority of overflows.

Event Duration Monitors (EDMs) have now been fitted on over 90% of all storm overflows to monitor the frequency and duration of discharges and provide data to the Environment Agency as part of the Water Industry National Environment Programme. This data is valuable in understanding which sites overflow, but EDMs cannot provide the robust water quality measurement as specified by the Environment Act.

To meet the requirements of new legislation, water utilities need to make use of the latest technologies and practices available to them.

Modern day monitoring

The first thing that a large-scale monitoring programme should consider is the monitoring parameters. Section 82 is based on the use of laboratory replacement parameters to ensure that the collected data is defendable using repeatable and traceable methodologies. Practically, this means real-time measurement in the field, directly comparable to laboratory reading of temperature, dissolved oxygen, turbidity, ammonia and pH.

To effectively measure these parameters, water utilities require the latest digital multiparameter sondes such as the YSI EXO2S. These sondes are designed to work directly in the river with in-built anti-fouling to improve data quality whilst extending deployment times.

The sondes are connected to Low Power Sensor Gateways which push secure water quality data to the Cloud every 15 minutes and uses AI logic to present the data including using a traffic light system based on the water quality parameters. Using these solutions together will enable water utilities to securely deploy water quality sondes with real-time alarms and Cloud visualisation.

The highest ongoing cost of large-scale monitoring is data calibration. While most sensors can be calibrated in both the laboratory and the field, errors can occur due to poor sensor cleaning or contamination of solutions. Due to these reasons, central calibration in the laboratory and simple field swap outs of units or sensors is recommended best practice.

Smart sensors which allow for mass calibration in a controlled environment will also significantly lower costs. Calibration in a controlled environment using true smart sensors allows, for example, mass calibration of pH, reducing time and calibration buffer needs. All sensors have META data which identifies when they were calibrated, by whom, their serial number and calibration details. These sondes also have a modular design, which removes the need to build bespoke cabinets for monitoring and allows stations to be configured in minutes. This practical design reduces field repairs and uses common parts.

Many suppliers offer a Data as a Service (DaaS) programme to enable water utilities to outsource calibration, maintenance and field work. Suppliers manage the risk and provide calibrated data to the secure web. DaaS comes in many variations, from in-house calibration services of water company owned instrumentation, all the way up to paying for the data only.

Due to the importance of the calibration, a DaaS programme is a cost-effective option for water utilities setting up a large-scale monitoring programme. But these parameters are not the only thing to think about. There are also many risks, costs and challenges to be considered in the set-up of a successful large-scale monitoring programme, as required by the Environment Act 2021.

Setting up for success

A programme of this scale will take some years to install, so priority sites must be identified and communicated along the supply chain. EDM data collected over recent years will provide a good basis for decisions on risk-based monitoring, while any water bodies used for bathing water should also be prioritised.

By far the biggest challenge of Section 82 is land access. The majority of storm overflow sites are situated on private land, which means water companies will be required to engage with landowners not only for permission to install instrumentation, but also the need for routine maintenance and calibration visits. This challenge is likely to have significant knock-on costs for water utilities.

Section 82 aims to monitor the impact on receiving waters rather than the discharge itself, so careful consideration is needed in choosing the locations for sensor installation. A number of issues should come into this decision, including flow, mixing, aeration, siltation, human and animal activities and unstable banks.

There are many examples of multiple overflows in close proximity to each other. This could lead to excessive numbers of monitors, increasing both costs and maintenance. DEFRA guidance on clustering (distance between storm overflows) should be followed to determine requirements.

Additionally, water utilities should be considering the power requirements of all sites as well as the potential impacts of theft or vandalism, both of which will require solutions. In terms of the installation, early engagement with suppliers is recommended, while the health and safety aspect of the programme should be front of mind; removing the need for the user to enter the water during calibration or maintenance is recommended.

Data integrity

The Environment Act 2021 requires a step-change in the way water utilities monitor the water quality of storm overflow and sewage disposal works. The legislation requires monitoring programmes that are centrally calibrated to known standards for traceable measurements and deployed in the field. While local measurements in the field and local calibration and correlation can improve accuracy, the scale will make this approach prohibitive. Programmes need to be scalable and modular meaning flexible installation methods depending on the location.

Data integrity is everything. It’s crucial to ensure that parameters are traceable and undergo post-calibration to understand potential fouling or drift issues in the field. Ensure that sensors are traceable to the laboratory and uncertainties are understood. This will ensure high-quality data which can feed into control structures to help the understanding of the environment and areas for improvement. Alongside a thorough understanding of where to monitor, water utilities will be in a good position to comply with the Environment Act 2021 and help protect the UK’s waterways.