Former Colliery/Industrial Site, West Midlands

CALA Homes

Geo Environmental Group (GEG) were commissioned by CALA Homes to undertake a Phase I/II Intrusive Investigation assessment and remediation of a 2.0 hectare former colliery and industrial site for a proposed residential development. The site was part of a Colliery in 1887 with associated spoil heaps and mineshafts were shown on the site in 1919 with a Foundry (Light Castings) also in the central part of the site in 1938. Over subsequent years the foundry was further developed before finally closing between 2002 and 2004 and replaced by an engineering works and subsequently a clothes recycling facility. Therefore, given the sites relatively long industrial history, there was significant potential for contamination in addition to the two mineshafts shown to be present on the site.

In environmental terms, the site was determined as moderately sensitive with respect to Controlled Waters (as it was directly underlain by a Secondary ‘A’ Aquifer) and highly sensitive with respect to the proposed residential development. 

GEG reviewed and augmented the previous investigation to determine the extent of contamination together with an assessment of foundation requirements for the proposed housing development. This incorporated a two stage intrusive site investigation comprising trial pits and cable percussive boreholes. The chemical analysis results indicated general slight contamination with isolated very limited areas of gross contamination associated with a former above ground fuel tank and migration from an electricity sub-station which was off-site but adjacent to the site boundary. Therefore, the remediation comprised the localised removal of the gross contamination, the construction of a containment barrier around the electricity sub-station (utilising an appropriate membrane) and the covering of front and rear gardens and landscaped areas of the site with an appropriate thickness of GEG verified inert sub-soil and topsoil. A remediation strategy report incorporating the proposed works was approved by NHBC and the Local Authority and the remediation works were completed in February 2011.   

In terms of mining, the general coal workings were considered too deep to pose a subsidence risk to the proposed development, although two mineshafts identified on the site by the Coal Authority Mining Report required treatment. The proposed grouting and capping treatment was designed by GEG and tendered to GEG approved specialist mine treatment contractors. The mineshafts were located by GEG utilising trial trenches and subsequently grouted to a depth of 96m and capped by the successful specialist contractor. The works were overseen on site by an experienced geo-environmental engineer from GEG and a subsequent mineshaft treatment verification report was approved by NHBC and the Local Authority.

All the GEG works on the site were approved by NHBC, the Local Authority and the Coal Authority and were completed on time and to budget.