HARRISON GROUP ENVIRONMENTAL were requested to conduct a site investigation at Gap Farm, South Wooton, to assess the suitability of the site for future residential use.

Site History
The site had been used as a farm and more recently as a general municipal waste landfill which ceased operating in the 1960s. As it was in operation prior to the licensing of landfill sites, it was anticipated that a wide variety of waste streams would be encountered.

Scope of Work

• Desk study was undertaken to delineate the areas of concern and to segregate them into zones associated with their previous site usage
• The intrusive phase of site investigation included trial pits, cable percussive boreholes and a geophysical survey

The trial pits and cable percussive boreholes were carried out to assess the composition of the landfill and the surrounding area. The geophysical survey results were combined with those of the cable percussive drilling to provide an estimation of the volume of waste within the landfill.

Remediation
From the results of the investigation a remediation method statement was drawn up which detailed the activities to be undertaken by the developer in the area of the landfill and the detailed environmental monitoring techniques to be undertaken during the removal operation.

This included: -

• During excavation samples were taken from the base and side of the excavation for analytical analysis, which was on a strict 5 day turnaroud to minimise disruption
• Sump was excavated to allow waste material to drain before removal to minimise landfill costs
• Materials encountered were general municipal wastes, laboratory wastes (including chemical jars), medical wastes (including syringes, needles and medicinal ampoules) , hazardous wastes (asbestos sheeting and furnace slag) and animal by - products (gelatinised fats from rendering plants)
• The landfill was backfilled with a minimum 1m thick compacted clay liner, over which was laid crushed limestone to within 1m of the finished level. This was capped with a suitably designed cover system, suitable for gardens and other high exposure areas
• Some of the landfill material was unable to be removed as it extended outside of the site area. A physical barrier was installed to prevent migration and contamination of the remediated site
• After removal and backfilling, groundwater and ground gas monitoring standpipes were installed. Groundwater samples were taken and analysed to assess the effects on groundwater quality

The site has now been successfully redeveloped.