An Intrusive Investigation includes trial pits, boreholes, groundwater well installation, sampling and chemical analyses to allow a Site Contamination Risk Assessment (SCA) to be carried out.

The programme for this phase has to be approved prior to commencing the work by the Local Authority and the Environment Agency (if there is likely to be an impact on the groundwater regime). For a detailed site contamination assessment, it is usual to carry out an initial screening of the site with samples recovered at several horizons, but this sampling regime will depend on the general sub-soil characteristics, the extent and depth of any areas of potential contamination and also the presence of made ground.

Following sampling, it is recommended that the shallower samples recovered from less than 1.0m depth are first analysed as an initial assessment. A full environmental suite of analyses is usually performed, although additional analyses may be required, depending on the likely contaminants, particularly lubricants, fuel or heating oil, coal tar, cleaning fluids, PCB’s etc. The results of the analyses are compared with Generic Assessment Criteria (GAC) or where possible Site Specific Assessment Criteria (SSAC) obtained using the Contaminated Land Exposure Assessment (CLEA) model, SNIFFER and HSE guidelines, the former covering site end use whilst the HSE relates to operatives working on site. Should any of the determinands exceed the soil guideline values (sgv’s) given in these guidelines, then additional sampling and/or analyses may be required.

If the samples from the initial horizon indicate that there is no potential contamination present, then it is not usually necessary to perform similar analyses on the samples from any deeper horizons sampled.

The scope of work required on a particular site can vary greatly; it is strongly recommended, therefore, that your requirements are discussed with us at an early stage.

Since the costs of chemical analyses and the site supervision are relatively expensive, TSL use a pragmatic approach to potential contamination issues and would be pleased to provide a detailed and economic budget cost estimate, which will satisfy the particular requirements for your site.

Since the sampling requirements are similar, the site contamination assessment can often be combined in a cost effective manner with a geotechnical appraisal, should this be required, in order to assist with foundation and infrastructure design.