Usually the first step in a soil contamination investigation is a Preliminary Site Investigation (PSI). This involves researching the history of the site to determine whether there have been site uses that would indicate a risk of soil contamination being present. Following legislative guidelines, the investigation includes searching the historical titles of the site, a search of the property files held by local authorities, reviewing the available aerial photographs, interviewing owners, searching available national contamination registers and usually a visit to the site to determine whether there is any evidence of activities which might have caused contamination.

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The outcome of the investigation determines whether a Detailed Site Investigation (DSI) is recommended or whether no evidence of any activities likely to cause soil contamination was found and therefore no further soil investigation is required.​