Clients often ask whether they need a Preliminary Site Investigation (PSI), a Detailed Site Investigation (DSI), or both. The answer depends on what decision you are trying to make, what the site history suggests, and what council, a lender or a vendor is asking for.
What a PSI is for
A preliminary site investigation is a screening step. It reviews site history, aerial photographs, databases and registers, and usually includes a site walkover. The output is a conceptual site model and advice on whether intrusive investigation is warranted.
A PSI is commonly enough for:
- early due diligence on a property purchase
- council pre-lodgement advice where contamination risk is uncertain
- deciding whether a DSI is proportionate before you commit to sampling cost
What a DSI is for
A detailed site investigation involves physical sampling of soil and/or groundwater to confirm whether contamination is present, define extent, and support risk assessment or remediation decisions.
A DSI is usually required when:
- a PSI identifies potential contamination sources or pathways
- council or a regulator requires sampling before a change of land use
- a transaction or refinancing depends on quantified contamination risk
- remediation or validation scope cannot be defined from desktop work alone
How the two fit together
In most Australian contaminated land matters, the PSI comes first. If the PSI concludes low risk and no further work is needed, that may satisfy council for some proposals. If potential sources are identified, the DSI follows with a sampling programme tied to the conceptual site model.
Skipping the PSI and jumping straight to a DSI is sometimes justified on high-risk sites with obvious contamination, but it can also mean over-spending on sampling where a desktop review would have narrowed the scope.
What to ask before you commission work
- What land use is proposed and what approval pathway applies?
- Is there a vendor report, council letter or lender requirement already specifying PSI or DSI?
- What is the site history (industrial use, filling, service station, landfill, asbestos)?
- Who needs to rely on the report (council, auditor, purchaser, financier)?
iEnvi scopes PSI and DSI work with fixed-fee proposals where possible. If you are unsure which step applies, a short scoping discussion against the site history is usually enough to set the right programme.
Contact iEnvi to discuss a PSI or DSI for your site.
Need advice on this issue? iEnvi provides practical, senior-led environmental consulting across contaminated land, remediation, ecology and environmental risk.
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