Wallis Road, Hackney Wick.
Land Contamination Risk Assessments
Jomas Associates were commissioned to undertake phased land contamination risk assessments, and geotechnical investigations, for a proposed redevelopment of a historic oil refinery and chemical works at Wallis Road, Hackney Wick, in East London.
Preliminary Risk Assessment / Phase 1 Desk Study
Jomas Associates undertook an in depth Phase 1 Desk Study, which included a review of previous reports undertaken at the site, historical maps, aerial photographs online history archives, environmental database searches, and liaison with local stakeholders such as local environmental health officers and the London Fire Brigade.
The Desk Study identified that the site had been established for distilling and refining of mineral oil in 1859, and became the leading distillery in the UK for American crude oil, and made advances in refining coal tar and shales. During World War II the site’s output included production of TNT. After World War II the site focussed on production of special boiling point spirits, with production ceasing in the 1970s, with the site used since as a yard area.
From investigations undertaken by Jomas Associates and others on adjacent sites, it was considered likely that significant contamination was present in the soil and groundwater underlying the site.
A detailed Conceptual Model was produced, on which a Scheme of Investigation was based, which outlined Jomas’s intended approach to further investigate the site and assess identified pollutant linkages.
An intrusive ground investigation was undertaken which included a series of window sampler boreholes and cable percussive boreholes. The investigation identified significant contamination, including within shallow soils, as well as perched groundwater and the underlying aquifer within the Alluvial soils & River Terrace Deposits underlying the site.
A generic quantitative risk assessment was undertaken, which concluded that potential pollutant linkages to human health (including adjacent site users via vapour inhalation pathways) and to controlled waters (including a Principal Aquifer within the deeper Thanet Sand Formation, a nearby public potable abstraction, and surface waterways in the site vicinity). The investigation also identified potential risks to nearby residents and members of the public from vapour risk and nuisance odours during any remedial or ground works, unless works were suitably managed and controlled.
Detailed Quantitative Risk Assessments
Detailed risk assessments were then undertaken by Jomas Associates. Risks to controlled waters were found to require remediation and robust remedial target concentrations were derived and agreed with the Environment Agency.
An assessment of chronic vapour risks concluded that despite the extent and severity of the contamination beneath the site, chronic risks to future users of the site and adjacent site users did not require specific remediation (although it was noted that remediation would be driven by the removal of free phase product and reducing risks to controlled waters, which would achieve a simultaneous reduction in potential risk to human health receptors).
A detailed assessment of acute and sub-chronic vapour risks and nuisance odour risks was also undertaken, considering short term effects associated with short to medium term ground disturbance (such as remediation and ground works). The results of this assessment allowed for formulation of robust management plans and controls to limit vapour and odour releases during such works, and monitor such releases to ensure all persons involved are not exposed to potentially unsafe vapour concentrations or offensive odour levels.
A Remediation Strategy was derived to remediate the site to render it suitable for the proposed use. The methodologies to be employed included bulk excavation of grossly contaminated soils, skimming and pumping of free phase product, and chemical oxidation of contaminated groundwater.
During all phases of assessment, liaison was undertaken with key stakeholders as part of the planning process to ensure prompt approval by regulatory authorities of the relevant documentation. The proposed remedial works are intended to commence in Spring 2020.