By Jean-Paul Collet, Sewer Network Manager and Andrew Morris, Rising Main HIT Lead
When challenges come in the water industry, they rarely come alone.We faced a unique set of circumstances in the ancient Kent town of Sandwich this year.
The key wastewater rising main, taking waste from the towns pumping station to our wastewater treatment works, suffered from a failure on the section which passes under the river Stour and on the section which runs under the A256 bypass.
The bursts, which occurred within days of each other, had a series of consequences – starting around 5 November 2019, the issues were first identified as flow, normally being pumped at around 130 l/s, was visible at ground level and causing flooding to the bypass and into the river Stour itself.
In the immediate aftermath, we deployed tankers to control the flow directly from the pumping station – as many as 20, weighing around 40 tonnes when fully loaded, were used to ensure that customers facilities were still available and that our impact to the environment was stopped. Working closely with the local highways authority, a carefully managed plan was instigated to ensure that the tanker movement did not cause undue damage or disruption to the ancient town of Sandwich. We also put in measures around liaison with the local community to ensure they were kept up to date and informed on progress regarding the repair work.
Investigations as to the exact location of where the burst was instantly initiated and run as part of our incident management system. When the burst was found, the real challenges began. The damage on the section nearest to the river Stour was found to be under the opposite bank from the pumping station, where the buried main rises up from the river bed.
For reasons lost in history, our predecessors had taken the unusual decision to fill the bottom of the shaft, used to lay the pipe, with concrete. Below water, cased in concrete – a repair was going to be extremely challenging.
Different ideas around repairs or replacement were designed, including the construction of a temporary pipe bridge over the river to convey flow was one option considered. However, with commercial river traffic using the river on a daily basis, the design of the bridge would have meant heights around 20m to ensure access was maintained to the river. Due to the forward flow capabilities of the pumps at the WPS, this was not going to be something that were able to progress. Protected trees, alongside the river, a cycle path and children’s playground splitting the working area and the pumping station, the design solutions quickly moved into permanent replacement options.
Sinking a new pipe into the river bed was suggested and which would mirror the existing arrangement. Archaeologists were brought in to monitor core ground samples being taken and, as well as the problem of the trees and of disruption to economically important river traffic, an ancient boat was found in the area where we needed to install shafts for the new pipe to be laid. As such this option also became a non-starter.
The clear path to success lay in directional drilling a new line from the WPS side of the river, underneath and making connections to the WPS and an undamaged section on the opposite side of the river. Such engineering methods are well understood by our teams from Engineering and Construction and are increasingly the technique of choice – minimising street digging or disruption to sensitive habitats.
If this was a manageable if not significant engineering challenge, there were other issues.
We were forced to accept that tankers would be needed for a considerable period of time. The only viable route for the tankers would be through the heart of the town – much of which was constructed before the discovery of the Americas.
The old houses had rudimentary foundations if they had them at all. Constant tanker traffic literally shook them. Extremely careful customer, stakeholder and media management was going to be as crucial as best engineering practice.
With an elderly population, social media channels wouldn’t be an ideal communications tool. In addition to letter drops and customer visits, we used our relationship with the town council to institute a pen and ink web page – a large poster in the council offices in the historic town centre updated with news on a weekly and occasionally daily basis.
We were also lucky to have a very engaged local media with a reporter following the story closely and keen to really understand what was going on.
While this was happening, we worked to identify the correct drilling site to place the boreholes.
We engaged with Historic England who unsurprisingly had ruled out the area for our drill where the ancient boat was found. While local theories about the boat raged – Viking long ship? Roman galley? Old Kent smuggler?, we concentrated on finding a new site.
To avoid any risk to an ancient monument we were forced to move the drill site some 60 metres, but swiftly gained agreement from local allotment holders and a tennis court to use that area with a sole dissenting voice expressing concern for the impact of our work on worms.
The new site did not lengthen the actual drilling beyond the 120 metres initially scoped. But moving the site to the other side of our pumping station made the hydraulic calculations far more complex. The pipeline would effectively have to loop back round the station before diving beneath the river. This would put additional pressure into the system and careful note had to be taken to ensure we remained within permit by adding air release valves for instance.
The next challenge could have been predicted by no one; the Covid pandemic hit and the first lockdown began. We were in truly in unchartered waters now. There was nothing in the manual about pandemic ways of working but after taking advice from experts and through a Water UK working group we found a way through.
The team from our excellent, long-standing delivery partners Cappagh Brown, their drilling arm Cappagh London and MTS providing the tankering activities, were most affected by the new rules.
The drilling itself was in the end the least of the challenge. It took four weeks to complete, with utter professionalism from the teams. We were finally able to close the project in July 2020, leaving us feeling incredibly proud of how teams from multiple partners performed – not just MTS, whose teams spent 7 months away from home providing the 24/7 tankering of flow during the entire project, or Cappagh Browne but our own Southern Water internal colleagues.