Case Study 3


Industry: Brownfield Development - Residential

Location: West Wales


Hazrem Environmental was commissioned to conduct the site investigation and advise on remedial treatment works required for a small housing developer in west Wales. In addition to metal contamination the site was also infested with Japanese knotweed.

The phase I desk study highlighted that the site had been used throughout the early part of the 1960’s as a tin plating works. Study of hydrogeological and geological information revealed that the site is underlain primarily by impermeable alluvial clays that are in limited hydraulic continuity with the adjacent estuary.

The ensuing Phase II investigation demonstrated elevated levels of a variety of heavy metals within the soils on the site. The most significant contaminant of concern was shown to be arsenic while there were also marginally elevated levels of cadmium within the soils. Ground waters were shown not to be affected. Quantitative human health risk assessment using the CLEA model was used to derive remedial targets on which the remedial strategy was based.

The remedial methodology consisted of excavation and disposal of the worst affected areas of the site and capping the site with a geotextile sandwich of non-contaminated fill overlain by top soil. 1800m3 of contaminated materials were removed to both non-hazardous and hazardous landfill sites. This stage of the works was integrated with the installation of the roads and drainage at the site and was completed in a matter of 5 months.

Forward planning by the developer enabled a cost effective approach to the treatment of the Japanese knotweed found on-site.

In the late spring of the first year of treatment (April) the JKW foliage was sprayed with herbicide and left for some weeks for it to be absorbed into the plants. Following this the plants were removed to just above ground and sent for disposal to a licensed facility.

Controlled earthworks were then conducted to remove the top 300mm of the soil in the vicinity of the JKW infestation. This is where the most virulent part of the Japanese knotweed plant or rhizomes exists. This material was then placed at the same depth on a geo-textile membrane and both areas were allowed to grow up. During the summer and early autumn the JKW was then sprayed a further 2 times. The most important time being during the plants’ senesce when the herbicide is most likely to have its greatest effect. A further 3 treatments through the next year caused plant growth to be extinguished by the end of this year and no further growth was observed during the following spring.