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Wessex Water gets to work on its biggest project so far

Wessex Water is creating a water supply grid in order to meet supply demand for the next 25 years. The £225M project will take eight years to complete. Maureen Gaines has been seeing how work is progressing.

Grid facts
  • A new Optimiser control system has been developed to manage and optimise the transfer of water along the new 74km transfer main
  • Volumes of the new storage tanks along the transfer main have been minimised by dedicating them as transfer storage
  • The supply grid has been designed to allow existing nitrate removal water treatment works and low nitrate water supply sources to be fully utilised
  • Pipeline material varies between polyethylene, ductile iron and steel, with diameters ranging from 200mm to 600mm
  • Open cut techniques have been used, with directional drilling or auger boring where a tunnel or passage is required

Wessex Water is in the process of delivering the biggest and most complex project it has ever done – establishing a water supply grid. The £225M, eight-year project involves the construction of more than 200km of new pipelines, 24 new or refurbished pumping stations and 12 new storage tanks ranging from two to eight million litres.

In fact, the ambitious scheme incorporates more than 50 individual projects, and a key component is a 74km transfer main from Sturminster Marshall, Dorset, to Camp Hill just west of Salisbury in Wiltshire.

Add to the mix the fact that around 50% of Wessex Water’s region is classed as an area of outstanding natural beauty and you wonder how the scheme will blend into the stunning countryside. It does.

The whole region is also “rich with archaeology”.

The water supply grid is Wessex Water’s answer to meeting future demand and ensuring security of supply to customers. It currently supplies about 350Ml of potable water a year, on average, with a patch covering 7,500km2 including Dorset, Somerset, Wiltshire as well as parts of Gloucestershire and Hampshire.

The grid will enable Wessex Water to move water from areas of surplus to where it is needed to improve resilience to drought and unforeseen events. The scheme maximises the existing assets that the company have, says Drummond Modley, who, as grid programme manager, is the man tasked with overseeing the project.

Modley works for Wessex Water’s in-house construction and engineering arm WECS, which is managing the overall delivery project. He says the scheme provides “a backbone that integrates our existing infrastructure, which is very important.

“It means we can move water from where we have it in abundance – from Dorset, for instance, where we have an unconfined aquifer, north to where we have areas of predicted deficit going forward”.
When all the work is done customers will not have to rely on one source of water, he adds. “If something goes wrong with their local source, invariably a borehole [75% of Wessex’s water is from boreholes], water will come from a different direction. As we deliver these projects and certainly by 2018, customers will be able to turn the tap on and water will come out of it, where in the past bottled water would have been supplied.”

By the end of 2017, Wessex Water’s customers will have supply 365 days a year, emphasises Modley.

Modley says the fact that the project is being developed as an integrated grid “is a seed for what the rest of the country could do”. He explains: “Through integration, maximising existing assets and linking them together better you don’t end up having to build new water treatment plants locally to deal with the need because you move water from other areas. You have that flexibility.

“It’s also a seed in the water industry about cooperating with other local water companies. We have agreements with Sembcorp Bouremouth, for example, for reciprocal resilience arrangements where, by linking our systems together, if they need water we can provide it and vice versa.

“There’s water trading potential because legislation so far has had water companies concentrating on their own areas whereas going forward, and I’m a strong advocate through what we’ve managed here, it’s best for customers if water companies cooperate more and share the water they have. It’s a very sustainable approach but it does need water companies to work together.”

The capital cost of the project may be similar to that of local solutions, says Modley, but “what you get with an integrated grid is a holistic approach, you get the flexibility. Even if you do build local treatment plants they could still go wrong and you’re back to the same problem”.

The grid’s engineering design, planning and environmental services are the responsibilities of WECS, Atkins and AECOM. The project contractors are WECS Civils, WECS Mainlaying, Trant Engineering, AECOM, Lewis Civil Engineering and Clancy Docwra.

Modley has about £100M-worth of construction work that is currently in progress, with 24 sites having now opened. He estimates that there is £1M-worth of construction a week for the next three years to deliver what needs to be delivered. “So the more good weather we have, the better.”

Historical heritage
Before construction could start, the project was put through an Environmental Impact Assessment that reviewed potential impacts and concluded that most of these would be temporary during construction and of negligible significance.

Residual permanent impacts have been identified as being limited to minor adverse impacts on ecology, from washout discharges to watercourses, the historic environment and the landscape.

The historical heritage found in Wessex Water’s domain has led to targeted excavation taking place, cataloguing and careful routeing of the pipeline within a 50m planning corridor to accommodate unforeseen areas of archaeological significance.

A major find has been near West Knoyle, where a female skeleton dating back to the Iron Age was uncovered! Also, the scheme will benefit the River Whylye and Bourne as there will be reduced groundwater abstractions for public supply from its more sensitive upper reaches of the river catchment areas.

Construction of the new pipeline projects commenced in 2011. The pipeline material varies between polyethylene, ductile iron and steel and in diameters ranging from 200mm to 600mm. The new pipelines require more than 120 crossings.

With the countryside in mind, the working width for the new pipelines is typically 20-25m with the trenches being 1.2m wide and 1.5m to 2m deep. Topsoil is being reinstated and the ground surface restored to its original condition once the pipe has been laid.

Open-cut techniques are mostly being used, with trenchless technology being employed to overcome obstacles such as primary roads, railways and ecologically valuable hedgerows.

The route of the transfer main, providing the key link between the north and south of Wessex Water’s region, has been strategically chosen to cover existing supply areas requiring additional resilience.
The route was established in collaboration with local groups including landowners and other planning stakeholders.

It was established to avoid environmentally sensitive areas wherever possible, such as Special Areas of Conservation, Sites of Specific Scientific Interest, Count Wildlife Sites and Scheduled Ancient Monuments.

Innovation is being applied as well. A new Optimiser control systems has been devised for that will manage and optimise the transfer of water along the transfer main. it will be controlled centrally, scheduling transfers in the most efficient way while ensuring security of supply, minimising any risk of water quality issues and keeping energy costs to a minimum.

Bi-directional links will maximise flexibility. This means there will be some flow reversals that result in a requirement to reduce the water pressure within the pipeline. There are plans to install energy recovery turbines within the pipeline with the power generated being used to offset power usage at the pumping stations.

The water supply grid has been designed to allow the existing nitrate removal water treatment works and lower nitrate water supply sources to be fully utilised by the targeted blending of the available low nitrate water with sources at risk of exceeding the nitrate standard.

This has been achieved through careful segregation or twinning of pipework to allow blending at critical points.

Supply chain
With the scale of the project being as huge as it is, ensuring the different elements of work is manageable has been vital. For instance, the 74km trunk main, with all its storage tanks and pumping stations, is worth £110M alone. “Breaking down projects into smaller schemes that are worth between £1M and £10M apiece makes them easier to manage through design, procurement and construction,” says Modley.

To ensure security of delivery, Modley believes in having “strength and breadth” in the supply chain. “Not putting all the eggs in one basket ever. I make sure I’ve got several pipeline contractors, I make sure I’ve got several consultants. I make sure I’ve got a stable of horses I can use for different courses. If one goes over or one goes bust because these things happen, there’s still somebody to fall back on.”

Modley estimates that at least 500 people are working on the project at any one time. “I have a highly motivated team because as you can see it’s a very exciting project. I’m one for having the best people in whatever I do. “I’ve been in the water industry 30 years and this is just a wonderful project because it is complex, it’s diverse and at the end of the day you are bringing benefit.”

Winning over the local communities and interested parties has also played an important role in the project. As part of an agreed communication strategy, an interactive website –www.wessexwater.co.uk/grid –was set up. The site contains animated footage showing the construction of a typical pipeline, storage tank and large as well as small pumping stations.

The animations proved “very popular” at the pre-planning submission stage and the pre-construction public exhibitions.

Topic: Pipes & Pipelines
Tags: construction , pipelines , engineering , infrastructure , Water supply , water resource management , storage tanks

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