- Meeting of Little Marlow Sewage Treatment Works Liaison Committee, Monday, 2nd August, 2021 10.00 am (Item 4.)
Several questions had been circulated to Thames Water (TW) ahead of the meeting. Full copies of the questions would be appended to these minutes. Mr A Scott answered from his prospective as the TW Regional Operations Manager. He was unable to comment fully on future strategy which was managed by a separate team.
In response to the written questions from Cllr Wilson and questions from the Chairman, Mr Overall and Mr Emmett the following responses were made by Mr Scott:-
1.Prevention - Investment in Capacity, Capability & Processes
- Mr Scott had been working with the engineering and asset management teams at Thames Water to understand the full scope of work needed to future proof the site.
- Initial drafts were for 2 additional asset tanks, 25 meter in diameter with the new equivalents of the necessary inlet, distribution and return activated sludge (RAS) systems.
- Costs would be in the region of £10m which was not included in the latest Assets Management Plan (AMP) cycle (2019-2024). Therefore, there would be an internal TW funding review process to satisfy before works could begin. TW were keen to invest time upfront in getting the right solution before starting works to avoid abortive costs.
- Project timescales had not been defined, responsibility for timescales sat with the TW asset and project definition teams, but the installation of equipment was likely to take 2 years from when work on site began. This was due to the scale and complexity of the engineering work involved.
- In response to challenge Mr Scott stated that with all existing tanks now fully operational there was no reason to believe the site would be regularly pumping raw sewage into local rivers due to lack of capacity while planning and installation was carried out. He noted that the recent mechanical failure was a once in 14-year event.
- Mr Scott did not have figures to hand for the total additional capacity that would be provided by 2 additional tanks but stated they would give capacity for 1 of the 6 tanks to be taken offline entirely at any given time while still coping with maximum flow. ACTION Mr Scott
- At the last meeting it had been stated that during lower flow in summer months the other tanks could be taken offline and drained to allow for a full inspection. Mr Scott explained that instead there had been an inspection of the equipment by the engineering team on site to install the replacement equipment. This had included oil analysis, looking at heat generation, photographic work and vibration monitoring. There were delays bringing the broken tank back online so none of the other tanks were taken offline to carry out these checks.
2. Future proofing - 1000+ Houses and Climate Change
- The site had two strategies relevant to flow in place namely the Ground Water Impacted Management Plan (GISMP) and the Drainage and Wastewater Management Programme. Copies of these would be sought and added to the committee directory. ACTION Mr Scott/Ms Kenward
- Currently more water was being treated than was necessary due to surface and ground water entering the sewer network. The first step would be to limit this water entering the system. This could involve sealing manhole covers and lining sewers to prevent ground water coming through.
- There was a Developer Services team within Thames Water who liaised with developers. A database called Solar was used for predicting future flow including that raised by new developments.
3.Transparency - Alerts and Notifications
The chairman asked Mr Collyer to include in his distribution list the three councillors who were elected to represent Wooburn & Bourne End in May 2021, in future updates on the site. Ms Kenward would share the relevant contact details. ACTION Mr Colly er and Ms Kenward
4. Five Year AMP
The current Asset Management Plan (AMP) came into effect in 2019 and would be reviewed in 2024.
Dating back to 2017 Mr Overall had asked if it were possible to have a containment barrier to prevent overspill from the site escaping into the neighbouring country park in the event that the tanks overflowed. Previously there had been flooding to the anglers’ car park, access road and public right of way. At the time TW had stated this would be too difficult to implement. Mr Overall asked whether something as simple as a ramp could be used to prevent sewage leaving the site.
· Mr Scott would take this suggestion to colleagues for comment. ACTION Mr Scott
· Mr Scott referred to an incident approximately 2 weeks before this meeting where a flock of geese had flown into overhead power lines. The sites backup generator had failed to start automatically due to there being a reduction in power rather than a total outage. It had not been possible to manual start the generator as the high voltage panel had still been receiving some electricity but not enough to power the sites larger equipment. As a result, settled sewage from sediment tanks had overflowed on to local footpaths and private gardens - the clean-up took place within 12 hours. There would now be a full investigation including a review of how the backup generators operate in the event of a power dip rather than a full outage. It was confirmed that the electrical systems on site were considered to be sufficient having been inspected the week before the incident by the TW High Voltage team and independently by SSE.
Mr Emmett had previously toured the site and asked it the storm tanks were still operational.
· There had been no change to storm tank provision on site.
Mr Kershaw asked what the process was for alerting local residents of incidents
· Mr Collyer would check the formal process but stated that after recent incidents both political and environmental stakeholders had been contacted. ACTION Mr Collyer
Mr Scott stated that there were trials in other areas to make on site monitoring available to the public in real time. The Smart Water Programme.