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Southall
The Challenge:
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.
The Approach
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:
- Installation of recovery wells;Carry out recovery potential tests;
- Extraction of recoverable NAPL using the NAPL fabric extraction system;
- Production of verification reports demonstrating achievement of an agreed remedial endpoint.
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:
- Eliminates the need to pump & treat groundwater;
- Recovers LNAPL & DNAPL from contaminated groundwater direct from wells;
- Can be used to perform recovery potential tests to demonstrate if NAPL is recoverable or not;
- Significantly cheaper than conventional remediation techniques on a project lifecycle basis;
- Delivers endpoint quicker than conventional techniques;
- Unaffected by fluctuating groundwater conditions;
- Small footprint, allowing it to be deployed on operational sites;
- Quick installation and low power/maintenance costs;
- Proven technology used worldwide;
- Solution supported by the Environment Agency.
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.
The Outcome
