By Automated Environmental · For Victorian property owners, buyers and managers. Last reviewed August 2026.
The three are different instruments for different questions, and confusing them is expensive. A Preliminary Site Investigation (PSI) is a desktop-based screening that tells you whether contamination is plausible. A Detailed Site Investigation (DSI) is intrusive sampling that tells you whether contamination is actually present and at what levels. A routine compliance check is a recurring visual and documentary screening that tells you whether a site is meeting its stated obligations — it is not a contamination assessment at all.
Choosing the right one first is the difference between a proportionate spend and paying for a detailed investigation your site never needed.
A PSI is the usual starting point. It is a desktop review plus a site inspection: the site's history, past land uses, surrounding land, available records and a walk-over, assembled into a view of whether contamination is plausible and where it would most likely be. A PSI does not involve sampling or laboratory analysis.
You would typically commission a PSI for due diligence ahead of a purchase or lease, in response to a planning trigger, or to establish a baseline. It answers the question: "Is there a reason to look further?"
A DSI is the follow-on when a PSI (or another trigger) says there is a plausible issue worth confirming. It is intrusive: soil, and often groundwater, is sampled and analysed, so a DSI produces hard data on what is present, at what concentration, and whether it poses a risk to human health or the environment.
A DSI is a materially larger commitment than a PSI. It is the right instrument when you genuinely need to characterise contamination — for a transaction, a clean-up decision or a regulatory requirement — and the wrong one when all you needed was a screening.
A routine compliance check is a different category altogether. It is a recurring, fixed-fee screening of a site against its stated obligations — the clauses in a lease, the conditions of a licence, the duties under the Environment Protection Act 2017. It is photo-evidenced and produces a short, dated summary, with every finding traceable to its source obligation.
Two things are important to be precise about. A compliance check is not an intrusive contamination assessment, and it offers no opinion on contamination status. It does not substitute for a PSI or a DSI. What it does is give an owner or manager a standing, documented view across a site or portfolio — and a clear, early signal when something genuinely warrants a PSI.
The proportionate sequence, most of the time, is this:
For a portfolio, the logic scales: routine checks across every site identify the small number that genuinely need a PSI, and only findings escalate to a DSI. You stop paying for assessments you didn't need and start catching the ones you do.
Costs vary with site size, history and complexity, so any figure is indicative only. As a broad guide, a desktop-based PSI is commonly priced in the low thousands of dollars, while a DSI with sampling and laboratory analysis runs considerably higher. The point of sequencing correctly is to avoid paying DSI money where a PSI — or a simple compliance check — would have answered the real question.
No. A compliance check is a visual and documentary screening against stated obligations. It offers no opinion on contamination status and does not replace a PSI. Where a check observes something that needs assessment, it triggers a scoped PSI proposal.
No. Many PSIs conclude there is no plausible contamination issue, and that is the end of it. A DSI is only warranted where the PSI or another trigger identifies something that genuinely needs confirming with sampling.
Common triggers are a planning application for a sensitive use, a transaction (purchase, lease or refinance), a lender or legal requirement, or an EPA interaction. It is also a sensible baseline for any industrial or legacy site.
A recurring compliance check per site is the proportionate option. It keeps a dated, source-traceable record across the portfolio and escalates to a PSI only where a finding warrants it — far cheaper than periodic intrusive assessments of every site.
Related reading: Section 39 explained, landlord liability for tenant contamination, and our Preliminary Site Investigations service.
This article is general information only, not legal advice. Costs are indicative and vary by site; confirm the right instrument for your situation with a qualified practitioner before acting.