What is a contaminated land site investigation? Why is it needed? What is involved?
A site investigation should be viewed as a process. It is essential that any site investigation is carried out in the correct manner and should follow the appropriate UK Guidelines such as CLR11 in the case of contaminated land. Reports that do not follow this guidance will not be accepted by the regulators.
This means that all site investigations should initially begin with a desktop study also known as a phase 1 investigation. This will use existing data and possibly information gained from a visual site inspection (walkover survey) to allow a preliminary risk assessment to be carried out. If no risk from contamination in soils to site users or the wider environment, then no further action should be required.
Should a potential risk be identified, then an intrusive investigation (or phase 2 investigation) will be required to establish the likelihood and extent of the risk. This can use a number of different methods from hand sampling though to drilling of boreholes with wells installed and must be based on the scope identified in the desk top study. It enables soils (and sometimes rocks) to be sampled and submitted for analysis. This is the stage that is generally thought of when people think of site investigations and may be referred to as soil sampling, a soil survey, soil testing etc. This may also be combined with a geotechnical investigation that allows data to be gathered on soil strength parameters to enable foundation design. The data gathered will be used to refine the conceptual model and risk assessment to establish whether a risk is present.
So why is this necessary? Soils have become contaminated from a number of different uses. Consequently, they may pose a risk to site users and also to the wider environment if they are not dealt with appropriately. These sources are not just restricted to soils in industrial areas. Agricultural land use may have introduced contaminants into soils including old orchards where lead and arsenic were used as a pesticide. There may also be a risk from ground gas arising from landfill sites or filled ground – this may migrate over quite large distances and has been known to cause explosions destroying domestic properties if not dealt with adequately.