7.4.1 Chapter 10: Geology and Ground Conditions of the PEIR assesses the effects on land and groundwater quality, land instability and mineral resources as a result of the Project. It includes an appraisal of baseline conditions informed through collation of data from a range of sources, including published data sources and previous ground investigation and assessment reports.
7.4.2 The assessment includes an evaluation of ground conditions and the nature of any contamination present. Part of the assessment includes a review of existing ground investigation data pertaining to the Project site from which a generic quantitative risk assessment has been carried out in accordance with current guidance and best practice. Chemical analytical data have been compared to published assessment criteria and exceedances identified.
7.4.3 The study area includes the Project site and an additional buffer of up to 500 metres. This is considered to be sufficient to enable the identification of off-site potential sources of contaminants of concern, other factors which may have influenced site conditions and/or sensitive off-site receptors that require consideration.
7.4.4 Baseline information on geology, hydrogeology and ground conditions was collected through a detailed desk review of existing studies and datasets.
7.4.5 A site walkover was also undertaken to validate the information collected from the desk review and to identify any existing sources of potential contamination.
7.4.6 The Project site is underlain by superficial deposits including Alluvium, Head and River Terrace Deposits. The deposits are associated with the surface watercourses that flow across the site and are classified as Secondary A aquifers and have a medium sensitivity. The underlying bedrock comprises Weald Clay, which is classified as an Unproductive stratum and has a low sensitivity.
7.4.7 The Project site is located within a Brick Clay Resource Mineral Safeguarding Area as designated by the West Sussex County Council Minerals Planning Authority.
7.4.8 A review of historic maps shows that the Project site had been developed as an aerodrome by the 1930s and major airport development had occurred by the 1950s. Prior to this, the site was used as farmland, a racecourse and golf course, with a railway line through the site. The airport has been subject to further development, which has been accompanied by an extensive drainage and balancing pond network and hotel, car parking and commercial development.
7.4.9 A number of previous investigations have been undertaken on the Project site, the review of which has focused on the areas of the site proposed for redevelopment. Elevated levels of contaminants were detected in soil, leachate and groundwater samples taken from various locations, together with elevated levels of ground gas.
7.4.10 A site walkover was undertaken in September 2019 in order to ground truth information from the desk study and to identify potentially contaminating land uses.
7.4.11 The desk study and site walkover information was used to identify potentially contaminating land uses. This information was combined together to identify Potential Areas of Concern. A strategic approach has been used to target parts of the Project site where further investigation may be required based on the potential for contamination to exist and the future use of the area.
7.4.12 The approach to mitigation includes ground investigations, together with implementation of a remediation strategy where necessary. The Code of Construction Practice will include measures to prevent and control spillage of oil, chemicals and other potentially harmful liquids, in addition to measures to protect groundwater during construction.
7.4.13 A Materials Management Plan will be prepared to document the management of soils on the site, undertaken in accordance with best practice.
7.4.14 The assessment has considered potential impacts on the underlying aquifers, surface watercourses, human health (construction workers and future site users) and mineral resources. The significance of effect is predicted to range from temporary minor adverse effects during construction where remediation is required, to no change during the operational phase. No significant effects have been identified.
7.4.15 Given the measures in place, the Project is not anticipated to have any significant cumulative effects.