Anglian repair challenges partners
A relatively straightforward leak repair in a wastewater treatment discharge pipe was complicated by the need to keep the plant running. Diverting the flow called on all the resources of Anglian's framework partners May Gurney and Syke's Pumps.Out of sight really is out of mind when it comes to water treatment - which is the way it should be. But to ensure that the public enjoys such blissful ignorance, treatment plants have to run without a hitch.
Proper maintenance is vital, and the industry is spending billions on repair, maintenance and improvement. But interruption to services is not an option. For example, all the effluent and wastewater produced by Peterborough is channelled a few miles south to Anglian Water's treatment works at Flag Fen. During recent repairs, no effort was spared to ensure this facility kept working uninterrupted.
Vast volumes of sewage and rainwater run-off are treated at Flag Fen, then discharged into the River Nene. When Anglian detected a major leak in one of the discharge pipes, it had to find a practical and cost-effective remedy quickly.
The 1m concrete pipe was designed to carry flows of up to 1.500l/s. Any interruption of this discharge pipe could possibly bring the entire treatment plant to a standstill.
Anglian framework contractor May Gurney was called in to repair the pipe. An excavation revealed that ground settlement could have resulted in differential movement of two pipe sections. As a result, the joint had opened.
Anglian treatment manager Tom Waylin said: "We knew before the leak was located that we would have to divert the flow to allow May Gurney to carry out the repairs. But to do this would mean over-pumping from several cells."
Framework supplier Sykes Pumps was asked to propose a solution that would allow May Gurney to carry out the repair. This involved over-pumping all six cells of the tertiary treatment plant.
"These cells all gravity-feed directly into the discharge pipe and produce a peak flow of 1,500l/s. When Anglian first told us their requirements, it seemed like a straightforward solution," explains James Stone, area technical sales engineer with Sykes Pumps.
"Originally there were five cells to pump from and, as each of our 8-inch Wispaset super-silenced diesel pumps is capable of 150l/s, I calculated that two pumps per cell - ten pumps in total - would give the necessary 1,500l/s."
But the job was not as simple as it at first appeared. "During the planning stages, it emerged that we'd actually need to pump from six cells, not the five originally expected," says Stone.
It was also considered prudent to increase pumping capability to give the reassurance of plenty of extra capacity. "So instead of two 8-inch pumps per cell, we installed one 8-inch pump and two 6-inch GP150 pumps in each cell," says Stone. Each GP150 pump can deliver 90l/s, giving a total pumping capacity of 1,980l/s - comfortably in excess of Anglian's requirement.
May Gurney's Neil Still was responsible for ensuring the actual repair - which was relatively simple - went smoothly. "The pipe exits from the tertiary plant, and has a 1m diameter under four or five metres' head of water. The pipe discharges into the watercourse about 100m away. We had to dig about 3.5m to reach the leak in an excavation of roughly 5m2," says Still.
Delivering and installing the pumps was considerably more time-consuming and more logistically challenging than the repair work itself.
"It took over a week to assemble all the equipment and get it all set up," says Wayling. "It looked like a load of giant spaghetti."
Despite the quantity of equipment , pumping was relatively simple. "Sykes Pumps was on-call 24/7 but, as it turned out, the whole thing went extremely well," says Still.
The 18 pumps worked at full bore during the actual repair work to ensure no water found its way into the excavation. May Gurney used a waterproof epoxy mortar to mend the ruptured pipe and encased the damaged joint in mass concrete before backfilling the excavation.
"Normally, on an over-pumping operation like this, you'd be dealing with only a proportion of the flow, but in terms of pumping, this job was phenomenal," says Still. "The pipe carries the treated effluent of the population of Peterborough - approximately 200,000 people. Diverting the flow was an exceptional pumping job. However, the actual repair took only about three days to complete."