SearchWatermeadow Court
The Challenge:
Cognition Land and Water were contracted by Mount Anvil to undertake remediation and earthworks at Watermeadow Court, Fulham. Cognition was appointed as Principal Contractor to excavate, bioremediate, and treat groundwater encountered on site to enable the redevelopment of residential properties all within a tightly constrained site.
The main source of contamination in the ground at the site were hydrocarbons, particularly free phase product, which was impacting groundwater within the site boundary as well as beyond the site. The site and surrounding areas had been historically impacted by industrial activities and had also been subject to previous remediation works. However, the previous treatment of groundwater to remove free product and non-aqueous phase liquids (NAPL) seemed to have been limited and unsuccessful in terms of observed contamination at the site.
The Approach
Cognition's scope of works comprised of:
- UXO risk assessment and UXO clearance, if required
- Targeting and extraction of free product impacting groundwater using a NAPL Fabric Extraction System (FabEx)
- Site clearance, enabling works, breakout of concrete slabs and obstructions to prescribed depths
- Careful excavation of made ground at upper site levels following a discovery strategy under a watching brief of site chemist
- Processing and segregation of made ground materials to remove deleterious items such as timber, gross contaminated soils and visible asbestos containing materials (ACM)
- ‘Soil flushing’ within shallow groundwater
- Stabilisation to encapsulate soil contaminants and reduce infiltration to site.
- Stockpiling of materials for either direct re-use, processing, treatment, or reject and disposal
- Design and stabilisation of piling mats
- Piling attendance for secant pile wall around basement
- Excavation of basement and export of clean naturally occurring soils
- Installation of capping beam around basement
- Validation and verification reporting upon completion of works
Demolition and Breakout
Cognition removed, crushed and stockpiled on site all obstructions across the site to a depth of 2.5m bgl during the proof digging. All obstructions within the proposed building footprint were removed to the deepest depth possible without the need to install temporary works. Cognition removed obstructions to a depth of 4.5m bgl during the basement excavation. All deeper obstructions that Cognition was unable to remove were surveyed and recorded.
Groundwater Remediation
Cognition carried out groundwater remediation targeting free product which was thought to be migrating onto the site from previously identified plume of non-aqueous phase liquids (NAPL) originating to the north-east of the site boundary. Cognition deployed FabEx units to remove NAPL from the groundwater. Cognition’s approach to groundwater remediation was that of a “betterment approach” with maximising the length of deployment of the FabEx units to ensure that all recoverable free product was extracted from the groundwater. The extended programme allowed considerably more effort to be expended on FabEx extraction.
NAPL was removed from the groundwater between October 2022 and February 2023 in accordance with the methods outlined in the Remediation Implementation Plan. A total of 374 litres of NAPL was recovered using the FabEx system, indicating significant betterment of the groundwater quality beneath the site. All extracted NAPL was exported off-site for disposal.
Groundwater encountered during the works was pumped through a portable water treatment plant and reinjected back into the ground for the purpose of soil flushing to assist in cleaning up both the on-site soils and groundwater. Some treated groundwater was collected and used for dust suppression on-site. Groundwater was chemically tested prior to soil flushing or re-use on site.
The Outcome
Cognition successfully remediated the site with a total of 374 litres of NAPL recovered using the FabEx system, indicating significant betterment of the groundwater quality beneath the site. We successfully completed the excavation of the basement to the full depth of 4.5m bgl. In the demolition and breakout process, all crushed aggregates were chemically and geotechnically tested for suitability for reuse on site. Approximately 1383.35m3 of site won crushed material was processed and produced.
All works were undertaken under appropriate Risk Assessment and Method Statements (RAMS) and, throughout the progression of the project, we undertook environmental monitoring and made careful considerations to limit the impact of dust, odour, noise, and vibrations.
