Ness Regional WTW, Loch Ness, Scotland

WJ are an industry leader in dewatering and groundwater management systems in the UK, and therefore our work regularly takes us from Central London to the northern reaches of Scotland and everywhere in between. One of our most recent projects took us to the shores of the world famous Loch Ness in the Highlands of Scotland for a ‘monster of a project’!

As part of the Scottish Water framework upgrades that are being undertaken at existing Water Treatment Works sites, there has also been supplementary new developments to expand the existing network. One of these great sites is located on the western shore of Loch Ness near to the picturesque village of Invermoriston.

WJ were employed by Morrison Construction, working on behalf of the main client ESD (a joint venture of Galliford Try, Black and Veatch and MWH Treatment) to provide dewatering services to aid the construction of a new approximately 8.0m deep wet well chamber, as part of a new Raw Intake Pumping Station located immediately adjacent to the Loch and the former Invermoriston Pier.

The ground conditions on site were predominately silty sands and gravels with some cobbles and boulders, overlying Psammite. These ground conditions have the potential for high flow rates, however, due to the silty nature of the soils, flows were predicted by the project consultants to be much lower and therefore it was determined that an Ejector dewatering system would be the most practical solution. A decision which was swiftly proven to be correct as flows from a 12no. well system were rarely above 0.7l/s!

With the presence of cobbles and boulders on site, this would have posed a potential challenge for any onsite drilling. However, by the use of an air flush system, we were able to install wells with minimal delays and ensure the clients programme was maintained.

WJ showcased our technical, flexibility and reactive abilities as a number of boreholes had the rock head encountered at a higher level than anticipated when drilled, with additional artesian groundwater pressures. It was therefore necessary to quickly modify our design to ensure the pumping wells terminated at a shallower depth within the sand and gravel, and not toed in to the Psammite as originally planned, likewise modifying the already installed wells. This was necessary to ensure the successful running of the system and secure a dry excavation for the client.

The only downside of the project was that we are unable to confirm any Nessie sightings during our time on site!

• LOCATION: Invermoriston, Scotland
• CLIENT: ESD
• MAIN CONTRACTOR: Morrison Construction