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Offsite build for Affinity pumping station

Taking a pioneering new approach to a borehole pumping station upgrade in Essex, Affinity Water minimised asset downtime and costs using a strategic offsite build programme.

The pumping station was built and delivered in a self-contained kioskThe pumping station was built and delivered in a self-contained kiosk

The ambitious project combined virtual design technology with modular offsite manufacturing - shifting the mainstay of the construction work to a controlled factory environment.

The challenge

The borehole pumping station and water treatment works supplies 120,000 houses in Saffron Walden and surrounding villages via a nearby reservoir. Rated at 14Ml/day, water is disinfected using hypochlorite dosing and a contact tank then boosted to 9 bar into supply and to a remote reservoir.

To ensure the plant continued to operate at full capacity for the area, Affinity Water needed to replace existing equipment with a new and efficient installation.

Due to limited shutdowns being feasible at the facility, the existing plant would ideally need to remain operational right up until the new equipment had been commissioned and tested – something that would be hard to achieve using traditional on-site techniques.

Affinity Water awarded specialist contractor Nomenca the design and build contract for the new plant. Nomenca proposed an innovative technical approach to the project, employing its Skilled Assembly Factory Environment (SAFE) modular construction.

Moving the building process away from the physical site and into a controlled offsite environment can have many benefits, from improved health and safety to lower costs.

While offsite construction is yet to become the norm for the water industry, it is growing in popularity. Nomenca has already brought its SAFE approach to a number of projects but Affinity Water’s Essex pumping station was the most ambitious project yet.

Gavin Stonard, Engineering Director at Nomenca said: “Offsite construction techniques are in a growth period worldwide – and already delivering efficiency savings in the UK water industry, as well as helping to overcome safety and operational challenges.”

Virtual planning

BIM technology was intrinsic to project delivery from the outset. Nomenca and Affinity Water shared a virtual view of the site and collaborated online to develop a detailed job scope – reducing the need for the 500-mile round trip to the site.

A 3D laser scan using a FARO focus scanner captured the dimensions and positions of all assets on the site. Buried services were then mapped with ground-penetrating radar, and the results brought together to produce a 3D AutoCAD model.

With the extent of the works reviewed, next came a detailed, working 3D design model built within a multi-disciplined Common Data Environment. The model incorporated all the major and minor components and their various interconnections. It featured the chemical treatment plant and borehole pumping kiosks with their pipework, steelwork and electrical installations, the diesel generator and fill point kiosk, and the chemical delivery area along with its drainage, valve chambers and blind tank.

Nomenca’s in-house virtual reality software enabled Affinity Water to walk through the proposed design. The virtual modelling was also used by construction teams, as well as for community engagement with local residents and council planning application meetings.

The technology meant almost every design detail could be checked right at the outset, from the tie-ins to existing service mains and drainage to the location and dimensions of cable ducts and draw pits.

The building process

With detailed designs approved, the AutoCAD model of the upgrade work was laid over the site survey model - ensuring equipment built off site would fit perfectly once in position. This process immediately highlighted where small design tweaks were needed. Dealing with these onsite – as would normally be the case – would have inevitably caused delays and increased costs.

The offsite build took place at Nomenca’s specialist facilities in Warrington. An SR4-rated kiosk was developed to house the UV and hypochlorite dosing systems, through which raw water from the boreholes would be pumped at mains supply pressure. It holds an additional booster pump to an auxiliary reservoir too in case of a network shortage along with other ancillary equipment, building services and the heating and ventilation systems.

The kiosk also includes the new main site Motor Control Centre that powers not only the skid equipment, but also the new borehole pumps and existing surge vessel. Considering the breadth of services it contains, the 20m-long, 4.2m-wide and 3.4m-tall skid is extremely compact compared to conventional onsite installations.
All equipment was installed, electrically connected and every process tested and commissioned before the treatment plant went anywhere near the site. Once complete, it was transported to site, put into position and linked to power and piping – all in a single day.

Mounting the treatment plant on precast concrete supports instead of a poured concrete base further simplified and speeded both onsite works and the installation process. After arriving onsite, the kiosk simply had to be craned onto the supports.

This project also saw Nomenca introduce Saint Gobain’s Universal Rapid Vi Pipe to the UK. The design’s anchored joints employ an innovative gasket and steel teeth to withstand the thrust forces that high water pressures produce around bends. That removes the need for bulky concrete anchor blocks, accelerating installation, minimising space requirements and, again, reducing costs.

The results

The technical innovations drove a number of financial, environmental, safety and time-saving benefits for Affinity Water. The survey techniques produced an accurate digital site plan extremely quickly, while Level 2 BIM technology enabled collaborative working at all stages of the project.

The use of 3D modelling made sure assets built off site fitted with existing site piping and equipment. Testing the treatment plant to high tolerances and identifying and dealing with minor issues offsite all contributed to the success of the project. On installation day, the kiosk lined up within 5mm of the existing pipework.

All upgrading works took place while the legacy plant continued to operate as normal. Only a single brief shutdown was needed to connect the new services, keeping the water supply running to thousands of Essex residents while minimising noise and disruption. The rapid connection also avoided the potentially vast extra costs associated with importing water from elsewhere.

Offsite building allowed parallel working, with the resulting shorter programme of onsite works cutting project timescales and costs. The project realised a 5% saving on the original project CAPEX, with savings of more than £110,000.

The benefits continued with reduced HSE construction risk, as much of the construction work took place in a controlled indoor environment. The offsite construction process also wastes fewer raw materials and has a smaller overall carbon footprint too.

The development is the largest off-site construction project the water industry has yet seen and stands out in the wider construction sector too.

Greg Cameron, Business Lead at Affinity Water said: “The project is the first time we have applied off site build on this scale and has provided numerous benefits. The factory build has allowed us to test equipment and software before it arrives to site, increasing confidence that it will work first time. This technique has reduced the overall construction programme and helped minimise disruption to local residents.”

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