The Arley Consulting Company Limited was commissioned by a large construction company to undertake a comprehensive ground investigation and contaminated land assessment at a site in north Wales. The site was was formerly used as a waste tip by the local council following the end of world war II. Proposals were put forward for a residential development with an additional area of public open space.
Within the study we carried out the following tasks:
The history of the site was derived following the collation and review of all available information on the site. A landmark EnviroCheck Report was acquired, detailing the environmental setting of the site as well as any potentially contaminating activities within 500 m. Information was also derived from a previous site investigation undertaken to determine foundation design for the proposed development. The desk study identified all potential constraints associated with contaminated land to the proposed residential/open space development.
A detailed site investigation was designed based on the findings of the desk study and the previous site investigation. The investigation comprised of trial pits and window sample boreholes. Peat had been identified within the previous site investigation and the investigation was designed to determine the depth and lateral extent of the peat as well as the area of made ground (former tip). Representative soil samples were collected and a selection were analysed for specific chemical contaminants. Elevated concentrations of arsenic, cadmium, lead, nickel, naphthalene and benzo(a)pyrene were recorded. Three gas monitoring probes were installed and a routine gas monitoring programme was implemented to assess the ground gas regime. Elevated carbon dioxide and reduced oxygen levels were recorded.
A quantified risk assessment (QRA) was undertaken in accordance with current legislation and policy. The CLEA model was used to derive site specific assessment criteria for the proposed residential area. A conceptual exposure model was derived for the proposed public open space areas to determine the critical receptor groups for each potential pathway. The data was used within the SNIFFER model for the ingestion and indoor vapour inhalation pathways. All other pathways (except plant uptake: not applicable) were derived from the CLEA model assuming an allotment end use. The risk assessment identified elevated concentrations of metals for both land uses and a pragmatic and effective remediation strategy was designed. The QRA and subsequent remediation method statement were approved by the Local Authority.
TACCL commissioned to manage the remediation works and ensure compliance with the method statement and provide specialist advice throughout the works. Remediation included the excavation and off site disposal of 4,800 m3 of peat (inert waste) as well as 2,000 m3 of non hazardous waste (former tip material). Validation testing was undertaken following excavation and testing was also undertaken on imported materials to assess their suitability. A validation report was submitted to the LA following all remediation works in accordance with the planning requirements.