The Arley Consulting Company Limited was commissioned by Persimmon Homes to undertake a comprehensive ground investigation and contaminated land assessment at the 5 Ha residential development in Bury. The site had formerly been used as a bleach works and a paper works prior to demolition in 2008. The site had been subject to several site investigations over the last 15 years. Key locations at the site included infilled reservoirs, buried tanks, wells and significant areas of hydrocarbon contamination. In addition, Kirklees Brook was located adjacent to the site.
This phase of the study included a review of all previous site investigation information which was used to provide indicative information on the typical ground conditions at various locations across the site. Following assessment of this information, TACCL liaised with Bury MBC and the EA to design a comprehensive site investigation for the whole site. The site investigation works were designed to confirm some of the findings of previous site investigation and to investigate areas previously not covered, all of which considered the conceptual model prepared for the site. The full justification for the site investigation was detailed in the Desk Study report, which was approved by Bury MBC and the EA.
A detailed site investigation was designed based on the findings of the preliminary conceptual model which had identified potential risks to human health, controlled waters and the environment. The investigation comprised trial pits and cable percussive boreholes. Soil and water samples were collected using strict quality assurance procedures and selected samples were analysed for specific chemical contamination.
On receipt of all site investigation a quantified risk assessment was undertaken in accordance with UK legislation and policy. The assessment utilised the CLEA model to determine potential risks to human health and the EA P20 model to determine risks to controlled waters. Potential risks to human health and controlled waters were identified and a pragmatic and effective remediation strategy was prepared. The remediation works were detailed in a remediation strategy for the site which was approved by Bury MBC and the EA.
The remediation comprised the excavation and on site remediation of some 1,500 m3 of organic contamination using bioremediation techniques. TACCL supervised the excavation of the contaminated material and recovered validation samples from the base and extent of each excavation. The excavated material was placed on a treatment area prepared by the remediation contractor. The material undergoing treatment was regularly tested until treatment was completed and the soils were re-used at the site, minimising off site disposal costs and promoting sustainability.
In addition some 25 m3 of hydrocarbon contaminated water was pumped from prepared sumps and removed from site.
TACCL also validated imported material to be used in the capping of the gardens and the landscaped areas and checked correct thickness had been achieved. In addition, TACCL inspected and validated the installation of the gas mitigation measures that were required in all new builds.
As requested by the EA, TACCL undertook routine monitoring of Kirklees Brook during the development works. Samples were recovered every 3 months from upstream, midstream and downstream locations and tested for a wide range of potential contaminants.