Conducting a Desk Top Study.

A desk top study is a good way of identifying past use of land that may have led to contamination (not necessarily actual contamination as this is often hard to prove).  Sensibly it should start with a collation of a variety of historic sources: historic Ordnance Survey maps are good for this as well as any trade directories.  The full list of sources can be found in Contaminated Land Research Reports No 2 & 3 (http://www.eugris.info/envdocs/CLR03_00.pdf (NB this document is over 11MB in size).

The British Standard BS 10175 2011 is an excellent Code of Practice for the investigation of contaminated land. It cannot be downloaded but has to be bought from the BSI bookshop (http://shop.bsigroup.com/en/Navigate-by/Membership/Benefits-and-services-/BSI-Knowledge-Centre/). Alternatively you may be able to find a copy in the reference section of your local library.

The Environment Agency has prepared a Model Procedure for Site Investigation. You can access it here. http://publications.environment-agency.gov.uk/PDF/SCHO0804BIBR-E-E.pdf
(this document is 2Mb in size)

Once the historic, geological and other data has been sifted what’s called a Site Specific Conceptual Model (CSM) needs to be produced.  Again, there is guidance in the above documents but what this is, is a means of identifying all likely sources of contamination (given past use); the receptors (things that may be affected if they come into contact with the contaminants) and the pathways, of methods by which the receptor may be harmed by the source.

As some source-pathway-receptor pathways will be quite tenuous, you then need to evaluate how likely each source-pathway-receptor is to create harm by assessing the likelihood of the occurrence against its severity.  This will usually give a reading of low, medium and high risk.  Anything with a medium to high needs further consideration.

This will usually entail movement to a site investigation taking actual samples of soil gas, soil and groundwater (depending upon what your CSM reveals) If your CSM and risk assessment demonstrate no or low risk there is may be no need to go onto the next level. However you may need to carry out targeted sampling to confirm your predictions (e.g. that the protective geology you believe to be present at depth is indeed as predicted.

There are many environmental consultancy agencies and organisations that may be able to do the whole investigation for you, or specified parts. Following this link will take you to advice as to how to find them and key questions to ask.
http://www.iwight.com/living_here/environment/environmental_health/Environmental_Protection/Contaminated_Land/