Agenda item

The Committee noted the written update provided by Thames Water. They noted that the update was from 1 October 2022, although data for the whole of 2022 could be provided if requested.

During his update, Andrew Scott reported the following:

·         Since October 2022 there had been no spillage from the storm tanks meaning that everything that had gone into the river had been fully treated; to the River Rye and the Thames. This showed the size of the tanks involved particularly as the area had suffered significant rainfall since October with the wettest March on record. So everything had been fully treated and not blended as previously.

·         Following the incident of 18 months ago, a temporary pumping set up was being installed and due to be commissioned within the next 2 months meaning that the blending operation would take place quicker and be treated without fear of significant pollution. This meant blending some of the partially treated effluent with the final effluent to keep TW within consent. TW realised this was not ideal but was the best of a worse case scenario rather than either spill raw from the storm tank.

·         OHES were an independent laboratory and scientific company used by TW to do water and river sampling. They produce data to TW which then gets reported to the EA.

·         BOD was Biochemical Oxygen Demand. DAM was Discharge Alert Management. UWWR was Urban Waste Water which was a direct urban waste water directive which was a different set of sampling whereby TW had a 24-hour composite sample taken periodically on large sites. SAS was Surplus Activated Sludge.

·         In response to a question about whether there were any other overflows nearby without EDM or if Little Marlow, through the treatment works, was the only one in the area and a question about whether pollution events and storm dust discharges could be distinguished in the EDM data, particularly picking up anything coming out to the river and whether it was as a result of a catastrophic failure or overflow; specifically whether the 27 spills in 2021 were as a result of overflows or catastrophic events. In response to the second question, Andrew Scott responded that not all the flow through could be put through to treatment and therefore it went into the storm tank. The EDM monitor was situated at the back end of the storm tank and so only records any spill from the storm tank and not through the final effluent. This action was taken with the permission of the EA which was the best solution under the circumstances at the time.

In response to the first question, Andrew Scott stated there was a rolling programme and therefore all TW’s sewage works should have EDM’s fitted, the remainder would be some of the combined sewer overflows although the programme may not have been fully rolled out. All the currently installed ones were listed on the map. Andrew Scott agreed to obtain data from the network team or environment team to be able to give a more comprehensive response.

ACTION: Andrew Scott

·         In terms of pollution events, where an unpermitted storm discharge would be a three-times compliance failure, there had been no pollution events recorded on the EA website although one enquiry was received from a customer who was concerned about seeing an outfall. However, on investigation it proved to be the opposite meaning there was a lot of silt being carried by the river at the time and the effluent coming in was clearer and appeared a different colour (darker) from where they were standing; it was actually a trick of the light. It was confirmed that it was not pollution.

·         It was noted that the Little Marlow site manager had been off work with a serious illness and therefore the site was being covered by staff from different areas around the Thames Valley. It was believed to be a good thing, because more colleagues were familiar with the site in case of emergencies.

·         Investment and projects: A blending pump installation was underway and should be commissioned around June time although it was there as a back up and protocols would be put in place with the EA. This mean that it could not be used unless permission with the EA was sought. Therefore, it would only be a catastrophic failure that would cause it to be used. A second piece of equipment related to sludge, particularly as the Little Marlow site did not treat sludge on site although did take out raw sludge from the process. The sludge consisted the raw sludge that settled as part of the treatment process and it was also waste bacteria that was generated as part of the process that killed the pathogens and reduced the organic load to then get to the final stage with clear water. Currently the liquor was returned to the start of the process and de-wartered raw sludge was stored on site, not for very long, and then taken to a thermal hydrolysis plant, near Oxford, where it was converted to advanced digestate. This created green energy as well as fertiliser. Funding of £5million had now been obtained to fix the dilapidated assets on site although it would be an 18-month lead time because of necessary pieces of kit that was needed, although it was hoped this work could be done with a 12-month lead time. The issue was that if the equipment stopped working, then solids would build up and it would be harder to prevent solids from carrying into the river. Therefore this was a necessary piece of work but would need to be managed well. The £5million had been put aside for this project.

·         A question was asked about risk factors for storm overflows being infiltration, misconnection or inundations and which of these three factors were of particular importance at the Little Marlow plant. It had been noted there had been a decrease in dry weather flow in 2022 compared with previous years; down from 30,000 cubic metres a year to 25,000 and which of the infiltration, misconnection or inundation was feeding through to lower this flow? Andrew Scott responded that normally infiltration was at groundwater level, and levels had been seen much lower than in the last two years. This then put a head of pressure in the pipes which then caused water to be forced into the pipes through small cracks. Inundations would be the impact of sudden downpours, which had been experienced in March of 2023.

·         Andrew Scott suggested meeting with Nick Rowcliffe to talk about more sustainable behaviours and, in particular, misconnection in respect of rooftop runoff which was a significant contributor to flow and should advice to change to soakaways or water butts be given.

ACTION: Andrew Scott & Nick Rowcliffe

·         In response to the dewatering project, if was noted that currently the assets were working so there was no change to the issue. However, they were at the end of their working life and having to work harder, therefore, the longer it took to replace the more of a risk to the assets failing. Contractors were still engaged to fix problems when they arose but taking them offline for any period of time was not an option. The site had two assets and it was unlikely they would both be taken offline at the same time. But if one was taken offline, then it was estimated that in the region of ten artic loads (per day) of activated sludge would need to be taken elsewhere for treatment.

·         In terms of the time it would take for the whole project to be completed, it was noted that the finish time would be in the region of 18 months from now.

·         A question was asked about the adjoining country park in Little Marlow which was to be used as a Suitable Alternative Natural Greenspace (SANG) in relation to odour being emitted from the sewage works and whether monitoring was in place and if there were any records of that type. Andrew Scott responded that an external company was commissioned to record levels and data would be made available through an EIR request. There was an odour control unit in place at the composting plant at the rear of the site and was the reason the doors were kept closed, this was a large unit with a big fan and had some media attached to it which all extracted ventilation flowed through. All other tanks on site are uncovered, from inlet to primary and secondary tanks and then tertiary treatment which was not uncommon. TW understood that the tanks produced odours and TW stated they would look at the reports and pull together all affected areas to build up a picture of evidence to be looked at.

·         A comment was made about the odour problem being from when the sludge was composted outside and that the biggest change to the odour in the village, came about when the composting plant was built as it had improved because the site was no longer fully composting. However, there was still an issue when lorries were entering and leaving the site causing odour issues around the whole area. Andrew Scott agreed to take this issue away and agreed that following the next odour survey, this issue would be looked at.

ACTION: Andrew Scott

The Chairman thanked Andrew Scott and Jake Morley for their report, update and response to questions.