YES was commissioned to carry out a detailed quantitative contamination risk assessment to attain planning at a site known as Battery Mill in St Erth. The resident resided in a small cabin and was constructing a new residential dwelling. The site was a former ironworks and mill and therefore there was a risk of heavy metal, hydrocarbon and VOC (volatile organic compound) contamination. There was also a risk of ground gas from the former infilled mill ponds and landfill on the site.
YES carried out soil sampling at the site and concluded that due to the level of contamination, remedial measures were necessary. During construction a high grade of concrete was required for the new foundations and a barrier pipe (rather than standard blue PVC pipe) was needed for the new water supply. Contaminated soil was able to be moved around and used on-site underneath hardstanding areas. Underneath soft garden areas, contaminated soil needed to be removed and disposed of at a suitable landfill facility. Garden areas required a semipermeable membrane and a covering with 600mm of clean certified topsoil.
YES carried out a detailed water risk assessment for hydrocarbon contamination as the site lies within 250m of three surface water features. During the site investigation, the groundwater encountered in the trial pits was tested and was concluded to be low risk. It was recommended that before, during and after construction, groundwater contamination levels were monitored to ensure that ground disturbance activities did not release contamination. Hydrocarbon levels in the groundwater remained stable and YES was happy to conclude that future risk to the identified water receptors was predicted to remain low and no further action was required.
YES carried out gas monitoring on the site. Three boreholes were installed across the site and were monitored on four separate occasions during 2021. Gas monitoring was carried out during suitable atmospheric pressure conditions. After monitoring, YES was able to conclude that the site was in the lowest risk category for ground gas and that additional gas mitigation measures were not required. A radon membrane was recommended, however in line with Building Regulations.
YES oversaw the remediation measures during construction and issued a Validation Report to essentially ‘sign off’ the site from a contamination point of view.
The client now resides in a beautiful two-bed residential dwelling and is looking forward to employing YES again for her future development plans.
Another job done and another happy customer!