Sewage Sludge Soil Contamination

Case Study

We were asked to carry out a site investigation for a mineral extraction company, in order to assess the nature and extent of potential soil contamination. Our approach to delineating the areas on the site where contamination was present resulted in cost-effective sampling. As a result, a materials handling plan was produced to ensure that risks to the environment arising from historical sewage spreading would be properly managed during and after mineral extraction operations. The plan was given to the landowner in order to aid land purchase negotiations.

A major quarrying client was applying for planning consent to extend their current operations into a pocket of previously unavailable land. We were commissioned by the client to assess the nature and extent of soil contamination at the site that may exist as a legacy of previous site use.


The need for the investigation arose as a result of contamination discovered on adjacent land used previously for sewage sludge spreading. To assess the extent of possible contamination at the site, a field investigation programme was designed and implemented. This site investigation was designed to delineate areas of the site (both horizontally and vertically) where contamination was present.


To enable an efficient site investigation to be undertaken, the programme of intrusive trial pitting and chemical analysis was agreed with the Environment Agency prior to commencement of site works. The chemistry of the samples was used to assess the extent of contamination from historic sewage spreading activities. Samples for leaching tests were selected based on the bulk chemistry of the samples and were chosen to include varying levels of contamination.


Based on the results of the site investigation, we proposed a suitable approach to site management, materials handling, and a post quarrying restoration plan, which would safeguard the environment and ensure that development of the site was in a manner consistent with best practice for environmental protection.


A report of the results and recommendations of the handling scheme was submitted to the land owner in order to negotiate purchase of the land and to assure the Environment Agency and Planning Authority that the risk of contamination from the proposals was being addressed.


A previous investigation on adjacent land had shown that a small area of the site contained materials where the leachable quality exceeded Environment Agency guidelines and were to be removed from the site. These materials had been excavated and stored to prevent cross contamination with other soils. The client commissioned us to design a programme to retest the soils and delineate areas of the mound where there was no significant contamination.