Marsh Mills STW – Ground Investigation for Major Stormwater Upgrade, Plymouth
Ground Consultants Ltd were appointed by Galliford Try Construction Ltd, on behalf of South West Water and Arcadis Consulting (UK) Ltd, to undertake a comprehensive Factual Ground Investigation at Marsh Mills Sewage Treatment Works, Plymouth. The works form part of the city’s £multi-million stormwater storage upgrade, designed to increase resilience and expand capacity from 3,108 m³ to 6,500 m³.
Working closely with Arcadis, GCL delivered all investigation works in strict accordance with the Ground Investigation Specification and relevant British Standards, including BS 5930, BS EN 1997-2 (Eurocode 7) and BS 10175. The team maintained continuous communication with both Arcadis and Galliford Try to ensure all technical, safety and environmental requirements were met throughout.
The investigation at Marsh Mills, Plymouth, included dynamic sampling and rotary coring to depths of 27–28 m, Standard Penetration Testing (SPT), and hand shear vane testing for near-surface strength assessment. GCL installed multi-level groundwater and gas monitoring wells to characterise hydrogeological conditions within the Upper Devonian Slate bedrock and overlying alluvial deposits.
Comprehensive geotechnical and geo-environmental laboratory testing was undertaken through UKAS-accredited facilities, including plasticity, particle size, strength, and contamination analyses. The resulting data informed foundation design, tank support options, and environmental risk assessment for the proposed above-ground stormwater tank.
The Marsh Mills Plymouth Ground Investigation highlights GCL’s proven capability to operate within complex, live wastewater treatment environments — safely, efficiently and to the highest technical standards.
Ground Consultants Ltd were proud to be recognised for their contribution in the official case study on Water Projects Online.
For clients across Plymouth, Devon and the South West, GCL continue to support major infrastructure programmes for Galliford Try, Arcadis, and South West Water, providing expert ground investigation, rotary coring, dynamic sampling, and geo-environmental testing services for the region’s most challenging civil engineering projects.
