Remediation of the former St Peter’s Wharf gas works by E-Clay stabilisation and installation of a PRB
Site Overview
The site was situated adjacent to the River Medway on the location of a former gasworks and brewery. It was extensively contaminated with hydrocarbons and to a lesser extent cyanide from the gas production process.
Objective
The remediation strategy for the Maidstone site was designed to address the on-site source contamination and indirectly the pathway contamination issues with the intention of protecting both human health and
groundwater/surface water receptors; in particular the adjacent River Medway.
The agreed remediation strategy was source treatment by E-Clay stabilisation and groundwater treatment through the design and installation of an E-Clay Permeable Reactive Barrier.
Treatability trials were undertaken at the request of the Environment Agency together with groundwater modelling via Modflow.
Remediation works
The remediation work was conducted in two stages; the first phase was based on excavating and treating materials from the former gasholder bases and from hotspots in the vicinity of the former purifier boxes. The second phase involved the installation of the barrier consisting of sections of permeable reactive barrier and sections of low permeability cut off walls.
Validation
Validation of the treated material was carried out leach testing a number of representative samples and comparing to the agreed remediation target criteria.
The reactive barrier system performance was monitored for two year post remediation by independent consultants.
The scheme was subsequently signed off by the regulators.
A comprehensive Validation Report was completion following the remediation works were complete.
