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Beside the seaside

Margate - Margate will soon benefit from one of the UK's most advanced wastewater treatment schemes. Damian Arnold reports.

A £66M wastewater treatment project, comprising more than 2km of tunnels, open cut pipe trenches, new treatment works and complex marine engineering, will result in cleaner seas around the seaside resort of Margate in Kent.

Whether the joint venture of Black & Veatch and Costain for client Southern Water will help regenerate the languishing resort remains to be seen. But what is indisputable is that the millions of litres of wastewater discharged into the sea near the town will be far cleaner.

The brief for Black & Veatch/Costain (BVC) was to construct a pipeline for partially treated wastewater from treatment plants at Margate and Broadstairs to a new plant at Weatherlees, 11km away, where it will undergo advanced treatment. After the Environment Agency refused to allow the clean water to be discharged into a local river, another pipeline to transfer the water back to Margate for discharge into sea was added. Work on the twin pipelines in open cut through the Kent fields and partly submerged in tunnels under Margate is expected to complete on schedule by March 2007.

Tunnelling through the reliable chalky ground has been relatively straightforward, but the biggest challenge taxing the design team at Black & Veatch is ensuring a robust performance from the eight huge 330KW transfer pumps that will propel the wastewater from Margate and Broadstairs to Weatherlees and back again.

The pumps will be working hard to pump the wastewater to 80m head, and a sustained breakdown would see the partially treated wastewater overflow into the sea off Margate. This would lead to big financial penalties for client Southern Water for breaching the EU Urban Waste Water Treatment Directive.

'These pumps are the heart of the whole process because if you can't pump the wastewater from Margate to Weatherlees and back, it all goes into the sea, and you can forget about the millions of pounds being spent, ' says Black & Veatch design manager Martin Ellis.

BVC embarked on a costly research and modelling exercise to inform on design, specification and positioning of the pumps supplied by Grundfos, and to ensure their bearings are not overloaded.

This included £80,000 spent on four scale models of the pump station. These were physically tested to see how the predicted flows of wastewater would affect them.

BVC was particularly keen to ensure a consistent flow of water in the pipes near to where the pumps are situated because pockets of air caught in the pipes can cause considerable damage to the pumps.

'You can run all the computer programmes you like but there's nothing like building a onetenth size model because you physically see the flows and what's going to happen, ' says Ellis. 'It was money well spent.' Fibreoptic cables inside the pipelines will give continuing data about the how the water is flowing, so Southern Water can monitor the network in real time.

'People think sewage works are quite low technology but that's not the case anymore, ' adds Ellis.

The pumps will propel the wastewater through twin pipelines that are submerged in tunnels at three locations in and around Margate.

The first 450mm diameter section of underground pipeline that runs beneath a golf course between Margate and Broadstairs Wastewater Treatment Works (WTW) was installed using a directional drilling technique.

From Margate WTW through the main town, the two pipelines are routed through a 1.1km long, 2.7m diameter concrete lined tunnel, completed using a tunnel boring machine. Another 600m stretch of tunnel through the suburbs completes the work.

Origninally, the pipelines were also to have been tunnelled under Manston Airport as the alignment runs very close to the end of the runway but, after negotiations with the operator, BVC was able to construct this section in open cut. This will save an estimated £1M, although BVC will pay upwards of £600,000 in compensation for the privilege.

A fourth tunnelling project is the recently completed 600m storm outfall pipe under the seabed. The pipeline was jacked through chalk in a two month operation. A reception pit had been excavated in the seabed at the end of the outfall and lled with gravel. The 70t cutting face was craned onto a jack-up barge from this point once the outfall was complete.

The completed tunnel was ooded to enable the cutting face to be easily extracted.

The pipeline was then sealed with a steel diffuser plate and the water pumped out.

With such complex works successfully completed, it is hoped that the design and build contract, under which BVC and Southern Water share cost overruns and savings, will result in more gain than pain for BVC.

'It's given us a big incentive to value engineer, ' says Ellis.

'We have saved around £2M and we are looking at coming in well under the target cost and months ahead of the October 2007 completion date.

'We already had a lot of contingencies built in, which is a good job because our liquidated damages are £9,000 a day for every day on site over the target date, up to £6.6M.'

Wetherlees WTW A new wastewater treatment works (WTW) to process partially treated wastewater from Margate and Broadstairs WTW is sited next to the existing WTW at Weatherlees, treating wastewater from Sandwich, Deal and Ramsgate. The new plant includes ultraviolet sterilisation that will clean the wastewater to a higher standard under the EC Shellsh Waters Directive, which covers local sea waters.

Margate and Broadstairs WTWs The WTW at Foreness Point is being extended underground and stormwater storage capacity increased by 13,000m 3 by building a 24m, 12.5m diameter storm shaft. It is hoped that increased storage will ensure there are no more than three storm outows of untreated waste water a year, which is allowed under the EC Waste Water Treatment Directive. Other improvements include new screens, odour control and upgraded power supply. Improvements to Broadstairs WTW at North Foreland include new pumps and an upgraded power supply.

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