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- ►CS02 Calderstones Hospital, Whalley
- ►CS03 Manchester Road, Tyldesley
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►CS01 Nell Lane, Manchester
| Development: | 187 Residential properties |
| Year: | 2000-2004 |
| Clients: | David Wilson Homes, George Wimpey and Westbury Homes |
| Development Value: | £26 million (approximately) |
Site History
The site was essentially divided into thirds:-
- the site of a former waste incinerator and later a waste transfer station.
- heavily wooded section with the ground surface heavily undulated due to the spreading of the ash from the adjacent land. A part of this section was utilised as a civil defence station during the Second World War.
- an enclosed field which had not been subject to previous development.
Ground Investigation
Coopers excavated 175 No. trial pits, 4 No. trial trenches, and drilled 7 No. cable percussive boreholes across the site to determine the ground conditions, the depth of fill strata as well as the extent of contamination. During the course of the ground investigation several underground fuel storage tanks were encountered which required emptying for off site licensed disposal, degassing and removal. Hydrocarbon contaminated soils associated with these tanks were removed from site as this was most cost effective considering the volume and the cost of on site/in situ remediation at the time.
Remediation
In the two brownfield parcels of the site we encountered significant deposits of ash and clinker resultant from the former incineration plant which had been present on site. This fill strata were noted to be ubiquitously contaminated with metals and PAH compounds.
The method of remediation for this site was the application of an inert cover system within all gardens. Areas of mobile contamination were remediated by excavation.
All properties were to have ground gas mitigation measures suitable for Characteristic Situations 2 or 3 (in accordance with CIRIA 149 – now superseded by CIRIA C665) due to elevated carbon dioxide concentrations derived from the ash and clinker.
Validation
Coopers validated all gardens within the David Wilson Homes and George Wimpey developments. All inert cover comprised crushed sandstone derived from a quarried source. Quarried sandstone was utilised as the bulking fill as this was obtained directly from the quarry and was considered a virgin source. This material needed little analysis to confirm the product to be ‘inert’ which greatly reduced the cost of chemical analysis and time involved with the validation process. During the initial validation Coopers found that the inert cover provided by the groundworks contractor was as contaminated, or more contaminated than the original fill material. All works undertaken by Coopers were approved by Manchester City Council.