Our involvement with this project has ensured both regulatory approval of our approach to ground contamination risk assessment and remediation of contamination and has minimised associated disposal costs and project delays.
Briefly this project comprised redevelopment of an existing housing estate to provide a number of new houses and flats along with gardens, communal soft landscaping, access roads and car parking.
A ground investigation undertaken at the site by others identified asbestos fibres within the made ground soils at several locations. Because of the relatively low sampling density undertaken, the assessment report concluded that all made ground soils to be disposed of should be classified as hazardous waste. In addition to the asbestos contamination, the assessment had also identified heavy metal and polycyclic aromatic hydrocarbon contamination to be present within the made ground soils.
Given that the contamination identified would require the provision of a cover system within all proposed gardens and soft landscaping areas, the requirement to remove a large volume of made ground soils as hazardous waste would have had a significant impact on the costs of the development.
Ashdown Site Investigation was commissioned to carry out a more detailed investigation of the shallow soils across the site. The investigation comprised around one hundred sampling positions at close centres and the testing of a large number of soil samples for the presence of asbestos. Where asbestos was identified, the mass of asbestos present was determined. Following this extensive testing programme we were able to demonstrate that although free fibres were present throughout the majority of the made ground soils, the percentage by mass of fibres present was beneath the 0.1% limit at which soils are classified as hazardous waste.
The made ground soils were therefore able to be removed from the site and disposed of as non-hazardous waste, with the significant reduction in costs to the developer far outweighing the costs of the additional investigation, as well as avoiding unnecessary disposal of soils to hazardous landfill.
We subsequently provided a detailed remediation strategy and, following the successful completion of the works, provided a verification report confirming that the appropriate depth of cover soils had been placed across the site.