The following links to pages on the Gov.uk website detail the UK statutory guidance for investigation of contaminated land. Some guidance is available as downloadable PDF documents,
Land Contamination: Technical Guidance
https://www.gov.uk/government/collections/land-contamination-technical-guidance
Contaminated Land Statutory Guidance
https://www.gov.uk/government/publications/contaminated-land-statutory-guidance
Land Contamination: Risk Management (LCRM)
https://www.gov.uk/guidance/land-contamination-how-to-manage-the-risks
Groundwater Protection
https://www.gov.uk/government/collections/groundwater-protection