Preliminary Site Investigation (PSI) for Development Applications in NSW: When It’s Required and What Councils Are Looking For
If you are preparing a Development Application, rezoning land, buying a development site or responding to a Council request, you may have been told that you need a Preliminary Site Investigation (PSI).
But what is a PSI actually trying to achieve?
A Preliminary Site Investigation is generally the first stage of contaminated land assessment. It is used to understand the history and environmental setting of a property, identify activities that may have caused contamination and determine whether further investigation is warranted.
Importantly, a PSI is not simply a collection of historical searches, and it should not automatically result in soil sampling, remediation or a Detailed Site Investigation.
A good PSI should answer a more useful question:
Based on the available evidence, is there a credible contamination issue that matters to this property and its proposed use?
Answering that question properly requires more than knowing what businesses once occupied the site. The consultant needs to understand where potential contamination may have originated, how it could move through the environment, who or what could be exposed to it, and whether enough information is available to support a decision.
Why Are Preliminary Site Investigations Undertaken?
In NSW, contaminated land is considered through both the planning system and environmental regulation.
For development and rezoning, contaminated land considerations are incorporated into Chapter 4 of State Environmental Planning Policy (Resilience and Hazards) 2021. These provisions replaced the former SEPP 55 framework that may still be referenced in older reports and planning documents.
The underlying planning principle is straightforward: where contamination may be relevant, the suitability of the land for its proposed use needs to be appropriately considered.
The Contaminated Land Management Act 1997 has a different role. It provides the NSW Environment Protection Authority with powers to regulate contamination that is significant enough to warrant EPA involvement.
Technical contaminated land assessment is also informed by the National Environment Protection (Assessment of Site Contamination) Measure 1999, as amended in 2013, commonly known as the ASC NEPM.
The ASC NEPM provides the national framework for assessing site contamination, including site characterisation, Conceptual Site Models, investigation levels, laboratory analysis and risk assessment.
In NSW, consultants also work with the EPA's Consultants Reporting on Contaminated Land: Contaminated Land Guidelines, which establish expectations for the content and structure of contaminated land reports.
Together, these frameworks are intended to ensure that decisions about potentially contaminated land are based on appropriate evidence rather than assumption.
What Is a PSI Actually Trying to Determine?
At the preliminary stage, the consultant is generally trying to establish:
how the site has been used historically;
whether potentially contaminating activities have occurred;
where those activities occurred;
what contaminants could reasonably be associated with them;
whether contamination could have migrated onto or away from the site;
what people or environmental receptors could potentially be affected;
what information is currently missing; and
whether further investigation is necessary.
This is why a PSI should be more than downloading a few database searches and reviewing historical aerial photographs.
Those pieces of information need to be interpreted together.
Why Is Site History So Important?
Contamination is often associated with activities that are no longer visible.
A modern warehouse may once have contained a mechanical workshop.
A vacant development site may previously have operated as an orchard.
A grassed paddock may contain imported fill or a former dam that was filled decades ago.
A former service station may have been demolished with little visible evidence of the underground tanks, pipework and fuel dispensing infrastructure that once existed.
Understanding site history is therefore fundamental to a PSI.
Depending on the property, the investigation may consider:
historical aerial photographs;
land title information;
historical planning and development records;
former business activities;
NSW EPA records and databases;
dangerous goods or petroleum storage information where available;
previous environmental investigations;
historical maps;
surrounding potentially contaminating land uses; and
information provided by owners, occupants or other relevant parties.
However, finding a potentially contaminating historical activity does not automatically mean that contamination is present.
The consultant still needs to determine whether that activity represents a credible contamination issue.
A Former Workshop Does Not Automatically Mean a Site Is Contaminated
Consider a historical aerial photograph showing a workshop on a property in the 1980s.
A simplistic assessment might conclude:
Former workshop → hydrocarbons and metals → further investigation required.
A more useful investigation asks:
What activities actually occurred in the workshop?
Where was the workshop located?
Was vehicle or machinery maintenance undertaken?
Were fuels, oils or chemicals stored there?
Was the area sealed or unsealed?
Were pits, drains or waste-storage areas present?
How long did the activity operate?
Is there evidence of spills, staining or waste disposal?
Is the area affected by the proposed development?
Are there other lines of evidence supporting a potential contamination source?
The distinction is important.
A PSI should not attempt to list every theoretical contamination possibility imaginable.
It should identify credible potential contamination sources and determine whether they matter to the proposed use of the site.
The Conceptual Site Model: Bringing the Evidence Together
One of the most important outputs of a Preliminary Site Investigation is the Conceptual Site Model, or CSM.
At its simplest, a CSM considers:
Source → Pathway → Receptor
For example:
Source: Petroleum hydrocarbons associated with a former underground fuel tank
Pathway: Impacted soil, groundwater migration or vapour
Receptor: Construction workers, future occupants or groundwater
Another example might be:
Source: Asbestos-containing demolition material within fill
Pathway: Disturbance of shallow soil during excavation
Receptor: Construction workers or future site users
The CSM helps the consultant determine whether a potential source actually creates a plausible contamination risk.
It also provides the framework for identifying data gaps.
For example, historical records may confirm that a fuel tank once existed but provide no evidence that the tank was appropriately removed or that the surrounding soil was validated.
The data gap is therefore not simply:
“There used to be a fuel tank.”
It is:
“We cannot currently demonstrate whether the former fuel infrastructure resulted in residual contamination.”
That distinction is what allows the next stage of investigation to be properly designed.
Why Are Off-Site Contamination Sources Considered?
A PSI does not stop at the property boundary.
Some contaminants can migrate from neighbouring land through:
groundwater;
soil vapour;
surface water;
drainage systems; or
movement of contaminated material.
A neighbouring former service station, dry cleaner or industrial facility may therefore be relevant to the assessment.
That does not mean every industrial property in the surrounding suburb should automatically be treated as a contamination risk.
The consultant needs to consider factors such as:
distance from the site;
relative elevation;
geology;
groundwater conditions;
contaminant behaviour; and
whether a plausible migration pathway exists.
The objective is again to identify credible source-pathway-receptor relationships, rather than simply generate a long list of possible concerns.
Why Do Geology and Groundwater Matter in a PSI?
Clients sometimes wonder why a desktop PSI discusses geology, topography, groundwater or nearby surface water when no drilling has taken place.
These factors help the consultant understand how contamination could behave if it were present.
For example:
permeable soils may allow some contaminants to migrate more readily;
shallow groundwater can create a potential contaminant migration pathway;
volatile contaminants may create vapour considerations;
creeks, wetlands or other surface-water bodies may represent environmental receptors; and
topography and drainage can influence surface-water movement.
The PSI does not necessarily need to resolve every hydrogeological question.
It needs enough information to determine whether these factors are relevant to the site's contamination risk and whether they create a data gap that requires further investigation.
Does a PSI Include Soil Sampling?
Not always.
A Preliminary Site Investigation is primarily focused on understanding the site's history, identifying potential contamination sources and determining whether further investigation is needed.
Where a sufficiently complete site history demonstrates that potentially contaminating activities are unlikely to have occurred, there are no credible off-site impacts and the site inspection does not identify evidence of contamination, intrusive investigation may not be warranted.
In other circumstances, limited sampling may be useful where it can efficiently answer a specific question.
Where significant intrusive investigation is required to establish whether contamination is present and determine its nature and extent, this will generally be undertaken as part of a Detailed Site Investigation (DSI) or another targeted assessment.
The important question is not:
“Does every PSI need samples?”
It is:
“Will sampling at this stage provide enough meaningful information to answer an identified question?”
Taking a handful of arbitrary soil samples does not automatically make a PSI more robust.
PSI vs DSI: What Is the Difference?
The easiest way to understand the difference is through the question each investigation is trying to answer.
Preliminary Site Investigation
Could contamination reasonably be present, and does it require further investigation?
The PSI focuses primarily on the site history, environmental setting, potential sources, pathways, receptors and data gaps.
Detailed Site Investigation
Is contamination present and, if so, what is its nature, extent and significance?
A DSI generally involves intrusive investigation such as:
boreholes;
test pits;
soil sampling;
groundwater monitoring;
soil vapour assessment; or
other environmental sampling.
A good PSI therefore helps make any subsequent DSI more targeted and proportionate.
The objective should not be to undertake more investigation than necessary.
It should be to understand exactly what the next investigation needs to determine.
What Can a PSI Conclude?
A PSI does not automatically finish with:
“A Detailed Site Investigation is recommended.”
There are several possible outcomes.
No Further Contaminated Land Investigation Is Warranted
Where the site history is sufficiently complete and the available evidence does not identify a credible contamination issue requiring further assessment, the PSI may conclude that further contaminated land investigation is not warranted.
That conclusion still needs to be supported by adequate evidence.
Further Investigation Is Required
A credible potential contamination source or important data gap may remain.
Examples might include:
a former underground petroleum storage system with no validation records;
widespread uncontrolled fill;
a historical workshop;
former agricultural chemical use;
suspected waste burial; or
a potentially contaminating neighbouring land use.
The PSI should clearly explain what needs to be investigated next and why.
Another Form of Assessment or Management Is Appropriate
Sometimes an issue identified during a PSI is better addressed through another process, such as:
an asbestos in soil assessment;
hazardous materials survey;
waste classification;
UPSS assessment;
acid sulfate soil assessment;
remediation planning; or
construction environmental management measures.
The next step should respond to the actual issue identified, rather than automatically progressing through a predetermined sequence of reports.
What Makes a Good Preliminary Site Investigation?
The NSW EPA's contaminated land reporting guidance sets out the information expected within a PSI.
However, simply completing a checklist does not necessarily produce a good report.
A strong PSI should demonstrate clear reasoning from the investigation objective through to the final conclusion.
1. Clear Objectives
The report should explain why the investigation is being undertaken and what decision it is intended to support.
A PSI for a proposed childcare centre may have a different decision context to a pre-acquisition PSI for an industrial property.
Without a clear objective, it becomes difficult to determine whether the investigation has actually done enough.
2. A Site History That Is Interpreted
A report should not contain 15 historical aerial photographs without explaining what they show.
The consultant should identify:
what changed → when it changed → why it matters.
Historical information is useful because of what it tells us about potential contamination sources—not simply because it has been collected.
3. Clearly Defined Areas of Environmental Concern
Potential contamination sources should be specific enough to be useful.
For example:
“Historical commercial activity”
provides little information.
Whereas:
“Former mechanical workshop and associated waste-oil storage within the south-eastern portion of the site”
provides a much clearer basis for further assessment.
4. Relevant Contaminants of Potential Concern
Potential contaminants should follow logically from the identified activity.
The contaminants associated with a former service station are different from those associated with an orchard, dry cleaner, workshop or demolition fill.
A good report explains this relationship rather than presenting a generic contaminant list.
5. A Site-Specific Conceptual Site Model
The CSM should demonstrate which source-pathway-receptor relationships are considered credible, which are incomplete and what uncertainty remains.
It should reflect the actual site rather than being a generic table copied between projects.
6. A Meaningful Site Inspection
The site inspection should test the assumptions developed during the desktop review.
For example:
Can the historical workshop location still be identified?
Is fill visible?
Are tanks, vents, pits or drains present?
Is the current site level consistent with historical filling?
Is demolition material or asbestos-containing material visible?
Are adjoining land uses relevant?
The walkover is an opportunity to confirm, refine or challenge the desktop findings.
7. Conclusions That Follow the Evidence
If further investigation is recommended, the reader should understand exactly why.
If no further investigation is considered necessary, the report should explain why the available information provides sufficient confidence to support that conclusion.
Recommendations should flow logically from the evidence.
8. Clear Discussion of Data Gaps and Uncertainty
No environmental investigation removes all uncertainty.
A strong report identifies uncertainty and then considers whether that uncertainty matters to the decision being made.
A missing piece of historical information does not necessarily justify further investigation if it has no material bearing on the contamination risk.
Conversely, a missing validation report for a former underground fuel tank may be highly significant.
What Does a Poor PSI Look Like?
Some common warning signs include:
generic text that could apply to almost any site;
a limited or poorly explained site history;
no meaningful Conceptual Site Model;
every conceivable contaminant or receptor being listed without site-specific reasoning;
Areas of Environmental Concern that are not clearly defined or mapped;
recommendations for a DSI without explaining what the DSI needs to determine;
arbitrary sampling that does not relate to the CSM;
conclusions that do not follow from the evidence;
no meaningful discussion of uncertainty; or
no clear answer to the investigation objectives.
A longer report is not necessarily a better report.
A better measure is whether you can follow the reasoning from:
Site history → potential source → pathway and receptor → data gap → conclusion → next step
Why Does the Quality of a PSI Matter?
The PSI establishes the foundation for everything that follows.
If an important potential contamination source is missed during the preliminary assessment, it may only be identified after intrusive investigation has already been completed—or even during construction.
That can mean:
another site mobilisation;
additional drilling or test pits;
additional laboratory analysis;
amended reports;
Council Requests for Information;
unexpected remediation;
redesign;
construction delays; or
additional waste-disposal costs.
The opposite can also occur.
An overly conservative PSI can recommend intrusive investigation that does not materially improve the understanding of the site.
Good contaminated land consulting therefore requires balance.
The objective is not the smallest investigation possible, nor the largest. It is the right investigation for the question being asked.
What Does Council Need From a PSI?
For development matters, Council ultimately needs enough information to determine whether potential contamination has been appropriately considered in relation to the proposed use of the land.
Depending on the site, that may involve understanding:
whether potentially contaminating activities have occurred;
whether the historical information is sufficiently complete;
whether contamination could affect the proposed development;
whether significant data gaps remain;
whether intrusive investigation is necessary;
whether remediation or management may be required; and
whether the site can ultimately be demonstrated to be suitable for the proposed use.
Individual councils may also have their own contaminated land policies, technical guidance or reporting requirements.
This is why a consultant needs to understand both the technical contaminated land framework and the planning purpose of the report.
A technically complicated report that never clearly answers the planning question is of limited value.
Does a PSI Need CEnvP(SC) or CPSS CSAM Review?
Not every PSI prepared for a Development Application in NSW automatically requires formal certified consultant endorsement.
The requirement depends on the circumstances of the project and the requirements of the authority receiving the report.
The NSW EPA currently recognises two contaminated land consultant certification schemes:
Certified Environmental Practitioner – Site Contamination [CEnvP(SC)]; and
Certified Professional Soil Scientist – Contaminated Site Assessment and Management [CPSS CSAM].
Contaminated land reports submitted directly to the NSW EPA under its certification requirements must be prepared, or reviewed and approved, by an appropriately certified consultant.
Some councils also require certified consultant involvement through their own contaminated land policies or project-specific requirements.
Even where formal certification is not required, senior specialist peer review can provide valuable additional quality assurance.
At Confluence Environmental, we regularly involve CEnvP(SC) and CPSS CSAM practitioners in the technical review of our contaminated land work, including on projects where formal certified endorsement is not specifically required.
The purpose is not simply to obtain another signature.
It provides another opportunity to challenge the CSM, investigation logic, assumptions and conclusions before the report reaches the client or reviewing authority.
A PSI in Practice
Consider a commercial property proposed for redevelopment.
Historical research identifies:
a former mechanical workshop;
a former underground fuel tank; and
imported fill across part of the property.
A useful PSI does not simply conclude:
“Workshop, tank and fill identified. DSI required.”
Instead, the consultant should ask:
What activities occurred in the workshop?
Where exactly was it located?
Was vehicle or machinery maintenance undertaken?
Were fuels or chemicals stored there?
Where was the former tank, pipework and dispensing infrastructure?
Are tank removal or validation records available?
What is known about the source and extent of the fill?
Which areas will be disturbed during the proposed development?
What contaminants are credibly associated with each potential source?
Are groundwater or vapour pathways potentially relevant?
What information is still missing?
Only after those questions have been considered should the consultant determine what, if anything, needs to be sampled.
This is why the quality of the PSI has such a large influence on the efficiency of everything that follows.
How Much Does a Preliminary Site Investigation Cost?
There is no standard price for a PSI because sites vary considerably.
The scope may be influenced by:
site size and number of lots;
complexity of historical land uses;
availability of historical records;
number of potential contamination sources;
whether Council files or specialist searches are required;
whether limited sampling is appropriate;
certification or specialist-review requirements;
site location; and
project timeframes.
A relatively small property with a straightforward and well-documented history may require significantly less work than a former industrial property containing multiple historical activities, fill and fuel infrastructure.
When comparing PSI proposals, it is therefore useful to compare what each consultant is actually proposing to investigate, rather than looking at price alone.
How Should I Choose a PSI Consultant?
A contaminated land consultant should be able to explain:
what information they intend to review;
what the PSI is intended to determine;
how the scope relates to the site's history and proposed development;
what relevant NSW guidance will be applied;
how the Conceptual Site Model will be developed;
how the report will be technically reviewed; and
what happens if a significant data gap is identified.
Relevant contaminated land experience matters.
The consultant should also be able to explain their reasoning in language that the client, planner and reviewing authority can understand.
The Bottom Line
A Preliminary Site Investigation is not simply another report required because Council asked for one.
Done properly, it establishes the foundation for the contaminated land assessment process.
A good PSI:
establishes how the site has been used;
identifies credible potential contamination sources;
considers how contamination could affect people or the environment;
develops a site-specific Conceptual Site Model;
identifies the important data gaps; and
provides a clear recommendation about what needs to happen next.
Sometimes that recommendation will be further investigation.
Sometimes it will not.
The objective is neither to minimise investigation at all costs nor to recommend every possible environmental assessment.
It is to obtain enough reliable information to make a defensible decision about what the site actually needs.
Need a Preliminary Site Investigation?
Confluence Environmental provides Preliminary Site Investigations for Development Applications, rezoning, subdivision, property acquisition and environmental due diligence across NSW.
Our approach focuses on clear site histories, practical Conceptual Site Models, proportionate investigation and technically defensible conclusions.
Our contaminated land reports undergo technical quality assurance appropriate to the complexity of the project, and we regularly involve CEnvP(SC) and CPSS CSAM practitioners in the review of our work.
If you have received a Council request for a PSI or are planning a development or property transaction, contact our team with the site address, proposed development and any available Council correspondence or previous environmental reports.
Learn more about our Preliminary Site Investigation services.
Key References
NSW Environment Protection Authority, Consultants Reporting on Contaminated Land: Contaminated Land Guidelines (2020).
NSW Environment Protection Authority, Contaminated Land Sampling Design Guidelines – Part 1: Application (2022).
National Environment Protection Council, National Environment Protection (Assessment of Site Contamination) Measure 1999, as amended 2013.
NSW Department of Planning, Housing and Infrastructure, Contaminated Lands – NSW Planning Framework.
This article provides general information only. Contaminated land assessment requirements are site-specific and should be considered having regard to the site's history, proposed use and the requirements of the relevant planning or regulatory authority.