This site has been utilised for industrial activities for over 150 years, which have included brickworks, oil works, coal and oil gas manufacture, chemical works, benzole and tar manufacturing, docks and natural gas storage resulting in several distinct sources of contamination, notably Dense Non-Aqueous Phase Liquids (DNAPL) in the groundwater. The site required remediation to enable redevelopment as part of the Southall Waterside regeneration project. Conventional groundwater treatment (pump and treat) was tried but only recovered 1m3 of DNAPL in 18 months along with huge volumes of water so alternative techniques were sought to deliver a sustainable and cost effective solution for the site.
Cognition used NAPL Fabric Extraction Systems (FABEX) to significantly reduce the amount of NAPL on site, demonstrate low NAPL transmissivity to the underlying aquifer and show that pockets of NAPL were recoverable, and once removed, eliminated residual risk.
The works included:
NAPL Fabric Extraction System
This treatment method is significantly more cost-effective than conventional techniques for the remediation of NAPL. By targeting NAPL it eliminates the need to remove vast quantities of groundwater. It works by drawing NAPL from the groundwater using a hydrophobic/oleophilic fabric on a continuous motorised loop (pulley system). The NAPL is then desorbed from the fabric by squeeze rollers and drained into containers prior to off-site disposal.
The benefits over conventional systems are:
Cognition initially performed recovery potential tests to determine the mobility and recoverability of the NAPL and demonstrate if NAPL recovery is sustainable. If sustainable, a secondary objective of the test is to determine the optimal NAPL recovery rate from the geological formation.
If NAPL recoverability proved to be limited or unachievable, COGNITION used the results to demonstrate to the Environment Agency that recovery is not warranted thus enabling sign off.