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.

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

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.