What Happens After a Preliminary Site Investigation?

A Preliminary Site Investigation answers one question: based on the site's history, is there a plausible reason to think contamination is present? What it doesn't do and isn't designed to do is tell you whether contamination actually exists, how bad it is, or what to do about it. That's where a lot of confusion sits, because a PSI report lands on a desk looking conclusive, when really it's a decision point.

Once a PSI is complete, a site heading through the NSW contaminated land framework will land in one of three outcomes. Which one depends entirely on what the desktop review and site walkover actually found.

Outcome 1: No Further Assessment Required

If the PSI's review of historical land use, aerial imagery, and site walkover finds no evidence of potentially contaminating activities, and no reason to suspect asbestos, filling, or other legacy risk, the report can conclude that the site is considered suitable for the proposed use without further investigation.

This is the outcome most applicants hope for, but it needs to be earned by the investigation rather than assumed from a "clean-looking" site. A PSI that concludes "no further assessment" without genuinely testing the history — building age, prior approvals, adjoining land uses, fill history — is a report that won't hold up if a council or auditor looks closely at it later.

Outcome 2: A Detailed Site Investigation (DSI) Is Recommended

This is the most common outcome where a PSI identifies a credible contamination hypothesis, a former service station, historical industrial use, undocumented fill, or asbestos risk from demolition history, for example. The PSI doesn't confirm contamination; it identifies enough uncertainty that intrusive investigation is needed to resolve it.

A DSI moves from desktop research to physical sampling: soil, groundwater, or building material testing, depending on the hypothesis. It builds a Conceptual Site Model (CSM) and assesses risk against relevant criteria and it's the stage that actually tells you whether there's something to manage, and how much.

This is also where a well-scoped PSI pays for itself. A PSI that clearly identifies every plausible contamination pathway lets the DSI be scoped precisely, right sampling locations, right analytes, right depth, rather than under-scoped and needing a costly second mobilisation once something unexpected turns up.

Outcome 3: Immediate Management Is Required

Occasionally a PSI walkover identifies something that can't wait for a staged DSI — visible asbestos-containing material at the surface, evidence of illegal dumping, or a clear and immediate exposure risk. In these cases, interim management measures (site access controls, immediate removal of visible hazards) may be recommended alongside the DSI, rather than deferred until the next stage is complete.

Why the PSI Outcome Matters for Project Timing

Because development consent and construction timelines are usually built around an assumed pathway, the PSI's outcome has real downstream consequences:

A "no further assessment" outcome can let a project proceed largely on schedule, provided council or the assessing authority accepts the conclusion.

A DSI recommendation adds a distinct assessment stage, sampling, laboratory turnaround, reporting, that needs to be built into the program from the point the PSI is scoped, not bolted on afterwards.

An immediate management finding can affect site access and program before any further investigation even begins.

This is why a PSI shouldn't be treated as a compliance box to tick before an application is lodged, its outcome genuinely shapes what the rest of the project's environmental pathway looks like.

Frequently Asked Questions

If my PSI says "no further assessment required," is that the end of it? In most cases, yes, provided the conclusion is well-supported and accepted by council or the relevant authority. It isn't automatically final if new information (an unexpected find during works, for example) later contradicts it.

Does every PSI lead to a DSI? No, a PSI recommends a DSI only where the history and walkover identify a credible reason to suspect contamination. Many sites, particularly greenfield or well-documented sites, conclude with no further assessment needed.

How long does the gap between a PSI and a DSI typically take? This depends on scoping and site access, but a DSI recommended by a well-documented PSI can usually be scoped and mobilised quickly, since the hypothesis and sampling rationale are already established.

Can a PSI outcome be challenged by council? Yes, council or an assessing officer can request additional information or a more conservative conclusion if they consider the PSI's reasoning insufficient, which is why the quality of the underlying investigation matters more than a confident-sounding conclusion.

Working With Confluence Environmental

Confluence Environmental prepares Preliminary Site Investigations across the Central Coast, Newcastle, Sydney and regional NSW, scoped so that whichever outcome the site lands in, cleared, DSI-recommended, or requiring immediate management, the next step is already clear and ready to move on.

If you're not sure which outcome your site is heading toward, talk to our team before you lodge your development application.