The client was an experienced developer who had carried out numerous housing projects throughout the south east of England.
The project comprised the construction of eight houses with gardens, driveways and parking as well as an access road.
The site was previously occupied by small commercial units with asbestos cement roofs that had been used as car repair workshops.
The client had an old Phase 2 report carried out by another engineer that identified asbestos across the site and hydrocarbon contamination in a small area. The investigation method it had used was trial pitting with an excavator. The investigation had been completed at a low density and so the true extent of the hydrocarbon contamination was not known.
The old report suggested removing the soils containing asbestos from the site and laying clean imported soil in their place. The report included no asbestos quantification or waste classification testing. Appropriate testing for disposal of the soil wasn’t carried out, so it was assumed that this material was hazardous waste, attracting high rate landfill tax of around £95 per tonne - so the cost of removing the soil would have been significant.
The local authority also required groundwater testing to be carried out. This had not been done due to the investigation method used – trial pits do not allow for water sampling.
The Soilutions Investigation
Soilutions was initially approached to develop a remediation strategy for the removal of soils containing asbestos.
But having reviewed the project, Soilutions determined further investigation would be more cost eective for the client. This work would determine the extent of the contamination and attempt to retain the majority of the problematic soils on site.
Soilutions carried out a much denser investigation using window sample boreholes – this method allowed them to investigate twice as many locations in the same time as the previous investigation. This allowed Soilutions
to accurately delineate the extent of the hydrocarbon contamination. Its laboratory testing also quantified the amount of asbestos in the soil as well as analysing water samples to satisfy the local authority.
If all this work had been carried out in the initial investigation a second investigation would not have been required and the client would have known immediately about the potential to reduce remediation costs.
The Soilutions Solution
The results of the investigation proved there were dramatically smaller quantities of hazardous waste on site than originally thought. Soilutions worked with the client to design a remediation scheme where hazardous soils were removed from gardens, but stored on site beneath a membrane under the roads. The road levels were increased to allow for this. Residents of the development were protected from harm by a layer of clean imported soil and a geotextile in gardens.
The Benefits Delivered
The cost saving created by Soilutions for its client was in the region of £50,000. This saving came mainly from not having to pay the high rate of landfill tax for the disposal of hazardous soils.