Our work to protect the natural environment and discharges from Wastewater Treatment Works

Flow to Full Treatment (or FFT) is a measure of the maximum flow a wastewater treatment works is designed to treat.

When wastewater treatment works are built, they are designed to meet a ‘flow’, the volume of water going through the works. The Environment Agency, our regulator, requires water companies to design wastewater treatment works ‘to treat peak dry weather flow and additional flows from light rainfall’.

This involves calculating the dry weather flow (DWF), which helps us understand the minimum volume the plant will need to treat during a period without rainfall. The DWF is then used as a base to help calculate the FFT level that meets the regulatory requirements. This means every treatment works has a unique FFT value. In some cases, this value is included in a permit from the Environment Agency with which a water company must comply. Across our 410 wastewater treatment works, there are 189 which are permitted with an FFT requirement.

While the precise circumstances can differ at individual treatment works, a system is normally designed to treat a flow volume of around three times the maximum dry weather flow (DWF). If this flow is exceeded, for example, by a storm event, snowmelt or flooding draining, then flows in excess of the FFT level are diverted.

This can either be:

• to large tanks where the flow is stored until the storm subsides. When the flow into the works reduces after the storm event has ceased and treatment capacity becomes available, the contents of the storm tanks are returned to the inlet to the works to pass through the treatment process.
• Or, to an overflow on the works, which is usually set to spill over directly to a watercourse when the flow exceeds around six times DWF.

This means that, even if sites were not compliant with FFT, this is unlikely to create any harmful spills to the environment - in most cases, the flows would be diverted to storm tanks and then passed back through the treatment process.

When treatment works were first built, they were designed and engineered to a specific capacity to achieve FFT levels. At the same time, the staff operating these sites will monitor their performance and take corrective action to maintain them, ensuring that they continue to operate effectively. Finally, compliance is also checked externally by our regulators through periodic site visits and assessments.

As part of the industry’s Water Industry National Environment Programme (WINEP) work between 2020-25, an extensive investment programme is underway to improve this monitoring and install MCERTS (the EA’s Monitoring Certification Scheme) approved equipment.

Monitors currently installed can either be at the ‘front-end’, or ‘back-end’ of the treatment works. Front-end monitors' will typically compare information on flows directly to FFT permit requirements. They monitor the flows coming into the ‘front’ of a treatment works at a set time before elements are removed or filtered out in the treatment process. ‘Back-end’ monitors instead look at the volumes leaving the site post-treatment.

Every site has its specific process, equipment and procedures and will treat a varying volume on different days; all of this leads to a length of time for water to pass through the treatment process, and it is very difficult to accurately extrapolate from a back-end monitor what flows were coming into the works at a set point in time.

We are investing £45.56 million in flow measurement schemes up until 2025. This will give us much greater coverage of MCERTS front-end monitoring. We have completed investigations on whether we can install the same monitoring to additional sites for completion between 2025 and 2030.

Our regulators are seeking specific information as part of a cross-industry investigation to check our compliance with a specific aspect of our environmental permit conditions relating to discharges and our related statutory and licence duties. We provided extensive information to the EA and Ofwat in November and December last year.

The water industry, EA and Ofwat have worked closely together to tackle the challenges presented by discharges by developing the Water Industry Natural Environment Programme (WINEP). Investment is allocated between 2020-25 as part of the current business plan period. We are installing new monitoring equipment as agreed with Ofwat and the EA. We have been following a clear plan to address any issues that arise and continuously improve on assuring our environmental performance.

In early March 2022, Ofwat issued a formal notice (a Section 203 notice) requiring us to provide further information with a deadline for submission in early April. This notice is a formal investigatory step and indicates that Ofwat will carefully consider the information in light of our legal obligations. It does not necessarily imply that any enforcement action will follow, but it is a more formal process.

We recognise the issue’s importance to our stakeholders and customers and the gravity of the investigation. We fully complied with the requirements to provide information by submitting our response in April, taking the opportunity to demonstrate to Ofwat that we take our responsibilities very seriously.

We have also subsequently provided an update to Ofwat on our progress which remains on track.

These investigations have shown that overall, across the 189 locations where we have these permits, we identified circumstances where we may not have always achieved the required FFT levels at four smaller sites. We have reacted swiftly to address this, investing in new equipment and improved processes to remove the risk that these four sites were not fully compliant. The sites affected and the actions taken are outlined below:

• Seahouses Wastewater Treatment Works, which serves 2,579 customers, where we installed extra pumps in late March, which brought the works into full compliance.
• Stokesley Wastewater Treatment Works, which serves 8,318 customers, where it appears grit and silt have penetrated part of our system, reducing the available flow. We have corrected this issue and brought this into full compliance by May 2022.
• Togston Wastewater Treatment Works, which serves 628 customers, where we are assessing the effectiveness of recently installed new pumps along with checking for any further hydraulic restrictions on site. This was completed at the beginning of June 2022.
• Newbiggin Wastewater Treatment Works, which serves 37,633 customers, has a unique system for pumped inlet flows. Analysis indicates that it is inconsistent in being fully compliant. We optimised site settings and controls, which enabled us to move the site to consistent and full compliance and supplemented this with a hydraulic study of the site, all completed with the site in compliance in June 2022.

Following completion of the work, we will, over several months, fully verify the compliance of these works, as this requires periods of sustained wet weather to confirm that each works is treating the required volumes before any spills occur.

While these works have been completed on the four named sites, we will continue to scrutinise compliance with our environmental permits at all sites. We will continue to update customers and stakeholders appropriately.

We are very disappointed to have identified the risk of potential noncompliance with the FFT permit requirements at these sites. However, we can find no evidence of any material impact on the environment. The table below shows how the impacted supply areas have had no serious pollution events since 2013 and where appropriate bathing waters have been assessed at least as Good, with all now Excellent.

We have looked closely at our performance, monitoring systems, and standard operating procedures as part of this process. As a company committed to constantly improving our environmental performance, we will continue to update and improve these procedures.

We have found several areas where operational improvement may be possible for sites already compliant with their permit, further improving performance beyond the requirements for environmental benefit, and are implementing this as appropriate. This has included:

• A full review of our wastewater compliance assurance processes conducted by an independent company.
• Improvements to reporting internally of spills, including a senior level monthly review.
• A new trigger process for immediate investigations into any site that shows a risk of non-compliance.
• Increased data transparency planned for customers and stakeholders in line with our pledges.
• Regular updates on this specific topic and increased opportunity for scrutiny from our Water Forums, a Customer Challenge Group.
• Further investment in new monitors across sites beyond our committed projects in our Business Plan.