Oldham mill site remediated

Leyden Kirby Associates Ltd (LKA) has recently undertaken site investigations on the site of the former Granville Cotton Mill, Derker, Oldham, to support a future residential development by McInerney Homes. The mill, with the accompanying mill ponds, boiler house, chimney and reservoirs, was unfit for restoration.

The site was investigated through: the sinking of window sample boreholes; the excavation of trial pits; soil and water sample collection; selected for a variety of chemical contamination analysis based on the previous uses of the site; standpipes installed on the site to enable the monitoring landfill gases; and the geotechnical properties of natural ground were derived using in-situ and ex-situ geotechnical testing techniques

Soil sample analysis proved contaminants to be present in levels exceeding Environment Agency soil guideline values and site specific assessment criteria derived by LKA. The gas monitoring exercise showed elevated levels of methane and carbon dioxide to be present and recommendations on suitable gas protection measures were made in line with CIRIA Report 149.

The results of the contamination analyses revealed two hotspot areas containing one or more contaminants in excessive concentrations. Recommendations were made for removal of this material off site.

Statistical analyses of the remaining data showed three further contaminants (arsenic, lead and benzo(a)pyrene) to be present at levels marginally exceeding the appropriate soil guideline values and therefore requiring basic remedial measures. Due to the large areas of infilled land and underground brick structures, such as chimney foundations and an ancient culvert, the geotechnical properties of the ground were deemed to be unsuitable. Leyden Kirby Associates, together with McInernery Homes, devised a remedial strategy which was seconded by the local authority. This incorporated the removal of hotspot contaminated areas in conjunction with the excavation, sorting and screening of the top three to four metres of made ground in the identified areas on the site.

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