February 2021 – the sewage returns to the Lambourn Valley

Residents of Lambourn will be dismayed, though perhaps not entirely surprised, to learn that further problems with the local sewerage system emerged over the weekend of 13 and 14 February 2021. A Thames Water (TW) spokesperson confirmed to Penny Post on 15 February a sequence of events that’s horribly reminiscent of last year’s debacle: “rainwater and rising groundwater levels overwhelmed our sewers in Lambourn. Sewage, diluted by the surface water, backed up through manholes and spilled out, mixing with the already dirty flood water above ground. Our engineers visited the area and carried out a clean-up yesterday.”

As this won’t be the last time the area has high groundwater or rainfall and as the long-term problems aren’t going to be fixed overnight, the question arises where this water will go. In some ways the answer is obvious. Our river network has been treated as an extension of the drainage and sewage for some time and, under a system that is coming under increasing scrutiny, still is. In these situations, filtration units known as ATACs sieve off most of the effluent, including solids, and discharge the rest into tankers or the nearest available watercourse. In Lambourn’s case, this is the SSSI-protected River Lambourn. This remedial action – an alternative to sewage coming up into houses or the street – is allowed by the Environment Agency (EA). The system is based on the permits, used for more immediate and unpredictable emergencies, known as Combined Sewer Overflows (CSOs), aka consented discharges. (See this page on the EA’s site for more on these.)

CSOs were designed to permit water companies to deal with emergencies caused by rainfall (not groundwater). Over time, groundwater problems appear to have got bolted on to this system, even though their incidence can be predicted and even though the circumstances can persist for months. A private member’s bill in January 2021 (the main provisions of which have been adopted by the government) attempted to limit this extension of the use of CSOs, Many claim that providing a quick solution to a recurring problem, water companies have no incentive to address the underlying issue.

CSOs forbid sewage discharge by water companies until there is actually a problem to deal with. So, in the recent case in Lambourn, TW knew something was about to happen but couldn’t act until it did. However, this time it didn’t happen when it was expected. Probably because of the remedial work that’s been done in the last few months, it appears that the system’s previous maximum level was passed but nothing overflowed. It may be that the corporate eye was slightly taken off the ball in the hope that the problem had been fixed. Then, on Saturday, it seems that the new maximum level of the system was passed and the overflow happened. (A very similar sequence of events happened in Aldbourne a few weeks ago.) In Lambourn’s case, there was also a problem with the ATAC unit immediately malfunctioning after it was switched on, the cold weather being one possible cause. This was unfortunate and not great PR but, despite this, the suggestion is that Thames Water’s work in the area is, finally, moving in the right direction.

Use of the ATAC will result in semi-treated sewage entering the river: without it, untreated water and solids will emerge, possibly into the street, possibly into people’s homes. Neither is ideal, though the former obviously better for residents. One or the other will persist until the groundwater levels fall below the new trigger level, or further remedial work is done to increase the capacity and integrity of the admittedly aged network.

“We were pleased to see that Thames Water had the ATAC units in place to deal with the sewage overflows early this year, but is really disappointing that the unit failed,” said Charlotte Hitchmough from Action for the River Kennet. “It’s also good news that Thames Water is putting a concerted effort into fixing sewers and tracking down sources of groundwater infiltration around Lambourn, but to put a stop to the problem of untreated sewage polluting our rivers we need long-term strategic investment, which needs action from the government and the regulators. MP Laura Farris’ support is a very welcome step in the right direction.”

This “long-term strategic investment’ may require more or less starting again with the sewerage network in places of high groundwater. An incentive for this should be provided by the new legislation (if adopted) which will tighten up on the ability of water companies to use consented discharges as a means of dealing with groundwater infiltration. For the present, one can only hope that TW’s repairs (which seem to have had some positive impact) keep pace with the levels of high groundwater. However, if more homes are built (as the local plan envisages for Lambourn) or if the sewerage network suffers further damage which exceeds the effects of any improvements, or if average groundwater levels rise, the situation will get worse.

In short, it’s all a bit like dealing with the pandemic. You know that a new surge will happen and you probably know roughly when but you can’t be sure how high it will be nor how long it will last. All you can hope is that the precautions you’ve taken will be sufficient to mitigate its worst impacts. Here the analogy breaks down, however. It seems unlikely that we can eradicate Covid: but we can fix the problem of groundwater infiltration, if we are prepared to pay for it and if there’s enough will from the government and the regulators. If this doesn’t happen, expect to be reading a similar story this time next year.

Please feel free to leave a comment using the box below, or email brian@pennypost.org.uk if you have anything you’d like to add to this.

The photograph at the top was taken in Lambourn’s Newbury Road in February 2020

Brian Quinn


5 Responses

  1. In the TW letter to the developers re the land at the rear of Colinridge Farm developement they state “We’re pleased to confirm that there will be sufficient foul water capacity in our sewerage network to serve your development.” This is something which has appeared on every single planning application for at least the last 30 years I have been taking an interest in planning in Lambourn.
    It is now time for WBC to use an expert on sewerage systems to refute this statement as it has been shown to be patently not true. Or is it up to the combined Valley parish councils to do the WBC work for them? We might get an answer then!

    1. Quite. Evidence from Aldbourne suggests that TW’s remedial work has had some benefits so hopefully this can be maintained. One thing that’s been learned is the the filtration units don’t like very cold weather

  2. Excellent summary Brian. Thank you.
    We all have to keep up the pressure on TW and EA, otherwise it will all be forgotten again once the groundwater drops back.

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