Dublin Docklands brownfield project requires major ground investigation and soil sampling

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A major Dublin Docklands brownfield redevelopment project has required an excavation of 17 m below ground level, with RSK Ireland collecting more than 500 soil samples as part of its ground investigation work.

Waterfront South Central is a Ronan Group Real Estate project, with the site set to become Citibank’s new head office. Fellow RSK Group company Minerex Environmental contributed to the project through the management of the high water table.

RSK Ireland Project Manager Ryan Murphy said: “The scale of the excavation is extraordinary. It’s an exciting project to be part of because of the depth being achieved and the close proximity to the River Liffey. Approximately 345,000 m³ of material has been classified for the bulk excavation – most of which will be reused – which at peak times meant 135 articulated truck trips per day. Each truck has taken up to 26 t of soil away from the site.”

On-site Geoenvironmental Consultant Tom Harrington commented: “Brownfield sites such as Waterfront South Central are important developments. Repurposing derelict brownfield sites for residential and commercial units to meet the housing and office demand is more sustainable than using greenfield sites where biodiversity is affected. It improves urban density, making utilities and transport networks more effective. Sites such as Waterfront can be contaminated with petrochemicals or materials containing asbestos, so classifying all the soils on-site and ensuring proper assessment of any hazardous materials are essential cost–benefit activities. RSK Ireland divided the site into 49 cells, with samples taken at depths of up to 17 m below ground level. A total of 562 soil samples were taken from 50 boreholes across the site in 2019 by RSK Ireland’s geosciences team to classify the different layers of soil. RSK Ireland also provided environmental services on an ad hoc basis when contamination was identified.”

Tom added: “Throughout the duration of the works, an engineer remained on-site to oversee the bulk excavation and to identify any signs of contamination that could have changed the classification of the cell. A photoionisation detector was used to identify any gas vapours emitted from the soil that could create human health risks. In total, approximately 10,000 loads of waste material were sent off site, each of which was overseen by one of our engineers.”

Because of the proximity to the River Liffey and the depth of the excavation, the site had to be dewatered. This process was designed and operated by Minerex Environmental. Groundwater is located at a starting level of 6 m below ground, and Minerex installed wells to pump the water into a settlement pond. More than 55,000 m³ of water to date – equal to the volume of 20 Olympic swimming pools – has been discharged compliantly to recharge wells outside the pile wall and to the foul sewer as required. The complex aquifer system required nearly 20 pumps of differing specifications to maintain a dry site and to keep construction on track.

Around 6 to 7 m below ground level, natural soil, consisting of Dublin Boulder Clay and gravels of varying types, was encountered. This soil has been classified as Soil Recovery Facility, meaning it can be reused. Tom said: “Excavated soil is a valuable resource in other projects. The gravels might be reused in roads and construction, and the clay might be used to cap and fill a quarry. It can be more sustainable to use previously excavated soil rather than new soil, which can create a larger carbon footprint. Reusing these surplus materials can reduce costs and save time on other projects, as well as reduce the impact on the environment. In this excavation, more than half of the soil excavated can be reused.”

With the excavation and soil removal complete, the works on-site will begin. Expected to reach completion by 2026, the wider development will have up to 1.25 million ft² of space split among commercial, residential, hotel and other uses and will include several public and community spaces, such as a waterfront town hall space and farmer’s market, as well as numerous on-site amenities, such as cafes, restaurants and creche facilities.

PJ Hegarty and Sons spokesperson Niall Maginn said: “The Dublin Docklands area has been undergoing a dramatic change. Waterfront South Central is the last development site that was sold, and with the ground excavation complete, the final part of the area’s transformation can begin.”