Agenda item

In particular implications for investment at the Little Marlow site arising from change of CEO and the utility's emerging financial position.

Andrew Scott explained that they monitor on site for water quality and quantity by online monitoring, which is constant and measured parameters such as flow, compensation flows, outfall solids, outfall authority, ammonia, and storm tank levels. Event duration monitors were also used to detect when they were spilling to the environment. He admitted that they did not measure the volume of storm flows, which was not required by their permit but could have a significant environmental impact. Thames Water would need to implement upstream and downstream monitoring for water quality by 2030 as part of the Environment Bill.

Andrew Scott explained about the monitoring methods and performance of a water treatment site. He showed graphs of suspended solids, biochemical oxygen demand and ammonia, which were the main parameters of their consent. He also explained that they used online and offline tests to measure these parameters and that Thames Water had been complying with the limits. He went on to explain how some events, such as blower trips, could affect the ammonia removal. Andew Scott concluded that the site was operating well and that they would have to meet new requirements in the future.

Andrew Scott went on to explain how Thames Water used ferric to remove phosphorus from the water and monitored the flow and the storm tank spills. He reported that they had achieved very good results in terms of phosphorus and iron levels and that they had not had any spills to the environment in 2022 and 2023. He also showed some examples of false triggers from the EDM monitors, which were caused by various factors such as maintenance, cobwebs or animals. He assured the committee that they had CCTV and storm tank depth monitors to verify that there were no actual spills.

Andrew also explained how quality of the water was monitored and the performance of the treatment process. He showed three graphs that displayed the results for suspended solids, biochemical oxygen demand (BYOD) and ammonia. He stated that the plant met the consent limits for all these parameters, except for one occasion when the blowers that provided air to the aeration lane tripped and caused a spike in ammonia. Andrew concluded that the site was operating well and effectively.

There were no reported pollutions in 2022 and 2023. The EDM going out to storm is not necessarily a pollution but a consented discharge. Andrew also explained that one of the key ways of reporting pollutions is by the local stakeholders or the Environment Agency. Reporting incidents was encouraged as they would be investigated and reported back through the Environment Agency (EA). There was a national incident recording database which was available for viewing.

Andrew explained how Thames Water reported and investigated any pollution incidents that occurred when the water quality exceeded the effluent of concern level, which is higher than the consent limit. He stated that the consent limit was a 95% compliance limit which meant that they could have some variations in the water quality without violating the regulation. He also stated that the effluent of concern level is usually two or three times the consent limit and if they went above that, even for a short time, they had to notify the authorities and find out the cause.

Sam Kershaw asked Andrew Scott under what circumstances would their regular monitoring system fail to identify a pollution incident which would then have been identified by a member of the public?

Andrew explained that they dealt with the possibility of pollution that was not detected by their online monitoring system. He commented that this was very rare, but it could happen if there was something that affected the water course that they were not measuring. He stated that Little Marlow had a sophisticated online monitoring system that was alarmed and checked by a 24 hour centre and that other sites that did not have this facility relied on daily or weekly visits to check on the outfalls.

Andrew also reported on some of the upgrade work that was taking place on site to improve the water quality and prevent pollution. One of the upgrades, the effluent blending mitigation system, was a backup system that could blend the settled sewage with the treated sewage in case of a failure in the biological plant. He stated that this system was used in 2021 when they had a problem with the biological plant, but it caused some concerns from the Environment Agency who expected a higher level of treatment. He explained that this system was a worst case scenario and only protected the river to some extent. The cost of the upgrade work had increased from £5 million to £20 million. The increase was due to engineers had assessed the site which increased the figure which had previously been an estimate.

Thames Water was replacing obsolete sludge presses with a new sludge system that includes chemical dosing. This will help with sludge management within the site and reduce the risk of suspended solids and BYOD spilling from the site. The new system will also enable the production of a better cake product to take off site. The work has been funded, designed, and is in progress. The preliminary work is expected to start in the New Year and will take about a year to complete. Andrew Scott has also introduced a monitoring system called “UMON4” which includes 1/3 and U-14 measures to indicate when anything is going into the storm tanks. The system includes monitors for storm tank levels and when the water goes out to the environment. Additionally, the UMON 4 measures the forward flow to treatment, which is important for demonstrating that the permitted flow treatment is being met. This is a complex project that is still being designed and is expected to be completed by April 2025. The project aims to ensure that the flow of stormwater is accurately monitored and maintained at 1500 leads per second. The project is challenging due to the presence of interstage pumping and the inlet works that do not lend themselves to accurate monitoring of flow. Andrew Scott extended an invitation to anyone interested to take a look around the site.

In response to a question about EDMs on CSOs which was an action for Andrew in the minutes from the previous meeting. He explained that some CSOs not on online map, and then confirmed that all in Bucks were now on the map but that unpermitted CSOs, ones that had been found but that had not been given permits and that TW was not previously aware of, were being investigated and TW had been given until the end of the year to place EDM monitors at those sites, most of which are in the London catchment.

In response to a question about an odour survey, Andrew explained that one would be undertaken sometime after April 2024. Surveys are normally carried out within a 5 year detail and Andrew agreed to respond to the Chairman.

Philip Emmett and Andrew Scott discussed maintenance and repair. Previously, there was no facility to maintain the system, which led to a serious problem. Andrew Scott confirmed that the situation is still the same and if there was a catastrophic failure, they would have to use blending pumps. However, they now have a better understanding of the failure and have implemented a more rigorous condition-based monitoring on their rotating equipment. All M&E site teams, especially at Little Marlow, have the necessary equipment to perform vibration and heat testing which is now done as a routine. There were some repair jobs that could not be maintained due to the size of the equipment. If it was a gearbox issue, then they can be replaced quite easily as they sat above the ground. The previous failure was because the equipment was bespoke and parts had to be made.

It was agreed that some members of the Liaison Committee would visit the site to gain a better understanding of what takes place.

Action: Andrew Scott, David Watson, Liz Hornby

In response to a question on whether E-Coli was measured within their process, Andrew Scott confirmed that TW was doing testing around bathing waters which were the second only inland bathing waters at Port Meadows in Oxford. There was a whole series of sewage treatment works upstream of that which included Cassington as well as Evenlode and Windrush, so sampling for E-Coli was taking place as there was a lack of knowledge in the water industry regarding the fate of viruses and bacteria in sewage treatment and freshwater. Bacteria and viruses are killed or treated at the back end of sewage treatment, but it is unclear how long they survive in fresh water. It was noted that this testing was taking place in conjunction with the EA due to farming run-off. This testing would give a greater understanding of what was going on. It was also noted that there were some community groups, Henley being one of them, who were part-funded by the TW, who were taking samples from the river and sending them to TW’s laboratories for analysis. It should be noted that there were many other things that could cause harm but they were unknown.

Andrew explained that he is part of a round table working group with Professor Sir Chris Whitty and the CMO team, along with other people from water companies, virologists and the science community. They are trying to understand where they are in lieu of a potential waterborne pandemic and what they would do in that situation. If they discharged into a coastal bathing water, they would need disinfection of some sort which would either be chemical disinfection or UV disinfection. Currently that was costly and time-consuming to set up, but was something that would be considered when considering an inland bathing water. A UV treatment was to be installed at Cassington, which is the nearest discharging site to Port Meadows.

In response to a question about whether monitoring points were being installed in the Thames itself, Andrew stated that the Environment Bill that was passed 18 months ago, which mandates water companies to monitor the receiving water course, which requires upstream and downstream monitoring. However, this is fraught with problems as some streams and rivers are easily accessible to the public. The parameters to measure and how to make them vandal-proof are still being worked out. The cost of this is very high, which will ultimately be borne by the customer. This is a requirement across the whole of the water industry and would help understand the impact of upstream and downstream activities of a particular site’s discharges.

In response to a question about the designated bathing area which is located near a sewage works which, in turn, put constraints on TW in terms of monitoring and treatment of that particular stretch of the river, Andrew Scott explained that where there were bathing waters, monitoring took place every year for faecal indicators as well as E-Coli, Streptococcus etc. The system was complicated due to other factors being involved, such as run off from farms and other river users such as marinas.

If the Little Marlow area were to be designated a bathing area, then this would entail implementing the same measures as at Oxford.

Sam Kershaw enquired about the status of a proactive alerting system that was put on hold. People are expected to check the EDM website to identify instances. Where there are any plans to put in place a more proactive system and if so, what is the progress of that initiative. Jake Morley stated that the online EDM map that monitors the river is currently a fair and good way for river users to check the river and how they want to use it. The map is going through an iterative process and consulting groups from Thames Water are being consulted to improve the map. The text messaging service is not a high concern for the groups. The first iteration of the map only had data on when the river overflowed. The map has been updated to include a link to the website’s improvement plans. There is no specific plan to alert immediate users in the area and users are encouraged to go online to check how they want to use their water courses.

Sam Kershaw asked that following a sewage pipe failure that occurred earlier this year in Marlow, which resulted in tankering in of effluent during that time. The compliance assessment report from 2021 stated that tankering should not occur during storm discharge; could TW confirm if during the storm discharge, tankering took place? Jake Morley responded by asking if Sam was referring to the burst rising main and explained that it was simply to get the effluent to the treatment works. Andrew Scott also explained that TW should not be done during storm events is taking in from third party carriers that are going around picking up septic tanks, for instance, and charge them money to tip because it goes straight out to the environment and during storming events, something called a Cess Logger can be cut off which then means that no discharge can be physically released.

In response to a discussion about the Environment Agency not attending this meeting, the Chairman agreed to co-ordinate with the Leader of the Council to try and exert pressure on them to attend future meetings as it was believed they had an important contribution to make.

Action: Cllr D Watson

In response to a question from Nick Rowcliffe in respect of a strip of land along the south side of the railway from Marlow to opposite the treatment works being dug up by a bulldozer, Jake Morley responded that there was a temporary rising main pipe in situ which was waiting for a more permanent fix.

Nick Rowcliffe also asked about why Marlow was showing green on the EDM map during the recent Storm Kieran compared to all coastal areas which showed red. Andrew Scott responded that there was spillage into the storm tanks and not out of and that the storm tanks have very large capacities.

In response to a question in reference to the impact the new film studios, should they go ahead, would have on the sewage works it was noted that there would be concern at the works due to the additional pressures that would be exerted. The issue was a complex one of measuring the population equivalent of a site which is based on the number of households and estimated number of people living in each household. There is also a trade effluent element to it. The load is measured in kilograms of ammonia per day rather than volume. There are two things that can affect the system: hydraulic restriction and ground water impact. The rising main is used to detect ground water impact. Andrew Scott is unsure about the maximum capacity of the asset management team. The team is responsible for monitoring the development of catchments, which can be unpredictable and vary depending on the design horizon. From an operations perspective, it was noted that the team was often playing ‘catch-up’ instead of being proactive.

In response to a question of when 7 stroke 8 is in real terms and when a likely upgrade/improvement would be, it was noted that AMP 7 finishes at the end of March 2025 and AMP 8 is then a 5-year period starting in April 2025.

The Chairman thanked Andrew Scott and Jake Morley for their report and responses to questions.