What Is a Preliminary Site Investigation (PSI)?
The primary purpose of a Preliminary Site Investigation (PSI) is to determine whether contamination has the potential to exist at a site and whether further investigation is required.
A PSI is the first stage of contaminated land assessment. It establishes the site history, identifies past and present activities that may have caused contamination, considers the environmental setting and current site conditions, and develops a preliminary Conceptual Site Model (CSM).
The assessment is used to identify credible potential contamination sources, Areas of Environmental Concern (AECs), Contaminants of Potential Concern (CoPCs), potential migration or exposure pathways, receptors and important gaps in the available information.
The outcome of a PSI should be clear: is there sufficient evidence of actual or potential contamination to require further investigation or management?
Where the available information does not identify a credible contamination risk, no further contaminated land investigation may be required. Where a significant uncertainty or potential contamination source remains, the PSI provides the basis for targeted further assessment, which may include a Detailed Site Investigation (DSI).
This reflects the NSW EPA objective for a PSI: to assess whether contamination has the potential to exist and whether further investigation is needed.
The Purpose of a Preliminary Site Investigation
A PSI is fundamentally a decision-making assessment.
It is not simply a collection of historical aerial photographs, property records and environmental database searches. Those sources are used to answer a more important question: could previous or current activities have resulted in contamination that matters to the site or proposed land use?
A properly prepared PSI should establish:
how the site has historically been used;
what potentially contaminating activities have occurred on or near the site;
where contamination could potentially be present;
what contaminants may be associated with those activities;
which environmental media could potentially be affected;
how contamination could migrate or result in exposure;
who or what could potentially be affected;
what important uncertainties or data gaps remain; and
whether further investigation is warranted.
The PSI therefore establishes the foundation for any subsequent contaminated land assessment.
It helps avoid under-investigating credible contamination risks, but equally, it should avoid recommending intrusive investigation simply because a historical activity occurred somewhere on the property.
What Does a Preliminary Site Investigation Assess?
A PSI considers contamination in the context of the site history, environmental setting and proposed land use.
The investigation typically considers the following.
Historical and Current Land Use
Understanding how a property has been used is fundamental to assessing its contamination potential.
Depending on the site, the historical review may identify activities such as:
industrial or manufacturing operations;
workshops and vehicle maintenance;
service stations and fuel storage;
chemical storage and handling;
waste disposal or uncontrolled filling;
agricultural or horticultural activities;
demolition and previous structures;
potentially contaminating commercial activities; or
changes in site development and landform over time.
The presence of a historical activity does not automatically mean that contamination exists.
The purpose of the PSI is to determine whether there is a credible mechanism through which that activity could have resulted in contamination relevant to the site.
Surrounding Land Uses
Potential contamination sources are not necessarily confined to the property boundary.
A PSI also considers surrounding land uses that could potentially affect the site through pathways such as groundwater migration, surface-water movement, vapour migration or historical filling.
This may be particularly relevant where the property adjoins former industrial land, service stations, landfills, chemical storage facilities or other potentially contaminating activities.
Environmental Setting
The site's environmental setting helps determine how contamination could behave if it were present.
The assessment may consider:
geology and soil conditions;
topography;
groundwater conditions;
surface water and drainage;
nearby water bodies;
groundwater use;
potentially affected environmental media; and
sensitive human and ecological receptors.
The purpose is not to provide an exhaustive environmental description. The information should help establish whether a credible source–pathway–receptor relationship may exist.
What Does a Preliminary Site Investigation Involve?
A PSI generally combines a desktop and historical review, site inspection, preliminary Conceptual Site Model, and clear conclusions and recommendations.
Desktop and Historical Review
Available information is reviewed to understand how the property and surrounding land have changed over time.
Depending on the site and investigation objectives, this may include:
historical aerial photography;
current and historical land titles;
planning and zoning information;
Section 10.7 Planning Certificates;
previous environmental reports;
NSW EPA contaminated land information;
environmental and regulatory databases;
historical business records;
dangerous goods or petroleum storage information where available;
geology and hydrogeology; and
surrounding land uses.
Historical records are evidence, not conclusions.
The consultant must interpret the available information and determine which activities represent credible potential contamination sources.
Site Inspection
A site inspection is undertaken to compare the historical information with current site conditions.
Potential indicators of contamination may include:
imported or uncontrolled fill;
disturbed ground;
waste or dumped material;
stained soils or surfaces;
unusual odours;
tanks, bowsers or fuel infrastructure;
workshops and maintenance areas;
chemical storage;
demolition material;
asbestos-containing material;
drainage features; and
evidence of previous structures or activities identified during the historical review.
Information from current or previous owners, occupants or other knowledgeable parties may also assist where it is reliable and relevant.
Preliminary Conceptual Site Model
The information gathered during the PSI is brought together in a preliminary Conceptual Site Model (CSM).
The CSM considers:
Source → Pathway → Receptor
A source is an activity or material that may have caused contamination.
A pathway is the mechanism through which contamination could migrate or result in exposure.
A receptor is a person, ecological system, environmental medium or other entity that could potentially be affected.
For example, identifying a former workshop does not automatically mean an entire property requires intensive soil investigation.
The PSI should consider where potentially contaminating activities occurred, what contaminants could reasonably be associated with those activities, whether they could have entered the environment, how they could migrate or create exposure, and whether those pathways are relevant to the proposed land use.
The CSM is therefore central to determining which potential contamination issues actually matter.
The ASC NEPM places the Conceptual Site Model at the centre of the site-characterisation process, with data gaps and subsequent investigation requirements developed from the understanding of potential sources, pathways and receptors.
For more information about Conceptual Site Models, see: What Is a Conceptual Site Model (CSM) in Contaminated Land Assessment? — Confluence Environmental
Areas of Environmental Concern and Contaminants of Potential Concern
Where potentially contaminating activities are identified, they may be defined as Areas of Environmental Concern (AECs).
Associated Contaminants of Potential Concern (CoPCs) are then identified based on the activity and the substances that could reasonably have been used, stored, generated or released.
Examples may include:
a former fuel storage area associated with petroleum hydrocarbons, BTEX compounds and lead;
a workshop associated with hydrocarbons, metals and solvents;
uncontrolled fill associated with metals, hydrocarbons, PAHs and asbestos;
former agricultural land associated with pesticides and metals; or
demolition areas associated with asbestos, lead and other building-related contaminants.
The objective is not to produce the longest possible list of contaminants.
AECs and CoPCs should reflect the credible contamination scenarios identified for the particular site.
Does a Preliminary Site Investigation Include Soil Sampling?
Not necessarily.
A PSI is primarily intended to establish the site history, potential contamination sources and preliminary Conceptual Site Model and to determine whether further investigation is required.
Where a sufficiently complete site history demonstrates that previous activities were non-contaminating, no significant off-site source is identified and the site inspection provides no indication of potential contamination, further sampling may not be necessary.
Where potentially contaminating activities are known or suspected, the site history is incomplete, or a specific uncertainty can be efficiently resolved, limited preliminary sampling may be appropriate. The NSW EPA reporting guidance expressly recognises both circumstances.
The important issue is why the samples are being collected.
Collecting a small number of soil samples simply so that a PSI contains laboratory results does not necessarily demonstrate whether a site is contaminated or suitable for development.
Where intrusive investigation is required to determine the nature, extent or significance of contamination, the work will generally form part of a Detailed Site Investigation or another appropriately designed investigation.
When Is a Preliminary Site Investigation Required in NSW?
A PSI is commonly undertaken where potential land contamination needs to be considered as part of a development, planning or property decision.
Common situations include:
Development Applications;
planning proposals and rezoning;
subdivision;
proposed residential development;
childcare, education or health developments;
changes to a more sensitive land use;
redevelopment of commercial or industrial properties;
former workshops or industrial land;
former service stations and fuel storage sites;
agricultural or horticultural land;
sites containing imported or uncontrolled fill;
property acquisition and environmental due diligence; and
circumstances where Council or another authority requires additional information about potential contamination.
A PSI is not automatically required for every Development Application, for more information about Development Applications, see Do I Need a PSI for a Development Application in NSW? — Confluence Environmental.
Under Chapter 4 of the State Environmental Planning Policy (Resilience and Hazards) 2021, a consent authority must consider whether land is contaminated and, if contamination is present, whether the land is suitable or can be made suitable for the proposed development. Where the available information is insufficient to address potential contamination, further investigation may be required.
The need for a PSI therefore depends on the site history, proposed land use, available information and the requirements of the relevant planning authority.
Preliminary Site Investigation vs Detailed Site Investigation
A Preliminary Site Investigation (PSI) and Detailed Site Investigation (DSI) serve different purposes within the contaminated land assessment process.
A PSI determines whether contamination may be present and whether further investigation is required.
A DSI is undertaken where the PSI, previous assessment or other site information identifies a contamination risk or material data gap that requires intrusive investigation.
Preliminary Site Investigation
A PSI is primarily based on site history, desktop assessment, environmental setting and site inspection.
Its purpose is to identify credible potential contamination sources, Areas of Environmental Concern, Contaminants of Potential Concern and potential source–pathway–receptor relationships.
The PSI develops the preliminary Conceptual Site Model and determines whether:
no further contaminated land investigation is required;
a specific issue requires targeted assessment; or
a Detailed Site Investigation is required.
Detailed Site Investigation
A DSI is used to characterise contamination conditions in greater detail.
It generally involves intrusive investigation and laboratory analysis of soil, groundwater, soil vapour, surface water or other environmental media where relevant.
The DSI tests and refines the Conceptual Site Model and seeks to establish:
what contamination is present;
where it is located;
the extent and significance of the contamination;
whether relevant exposure or migration pathways exist; and
whether further investigation, management or remediation is required.
Not every PSI progresses to a DSI. Where the PSI identifies no credible contamination risk requiring further assessment, additional intrusive investigation may not be warranted.
What Can a Preliminary Site Investigation Conclude?
A PSI should reach a clear and defensible conclusion.
Depending on the findings, the assessment may determine that:
No Further Contaminated Land Investigation Is Required
Where the site history, environmental setting and site inspection provide sufficient evidence that significant contamination is unlikely to be present, the PSI may conclude that further contaminated land investigation is not warranted.
Targeted Investigation Is Required
A specific uncertainty may require investigation without necessarily requiring a broad site-wide DSI.
For example, further work may be directed toward a former tank, workshop, filled area, demolition zone or other defined source. For more information about Soil Testing for Preliminary Site Investigations, see Does a Preliminary Site Investigation Need Soil Sampling? — Confluence Environmental.
A Detailed Site Investigation Is Required
Where credible contamination sources, significant data gaps or potentially complete source–pathway–receptor relationships remain, a DSI may be required to characterise the contamination and assess its significance.
Another Form of Environmental Assessment or Management Is Required
Some findings may be more appropriately addressed through:
asbestos or hazardous materials assessment;
asbestos in soil investigation;
waste classification;
investigation of underground petroleum storage systems;
groundwater assessment;
remediation planning; or
contamination management during future construction works.
The appropriate next step should respond to the issue actually identified, rather than automatically progressing through a predetermined sequence of reports.
What Makes a Good Preliminary Site Investigation?
A good PSI is not measured by the number of historical records reproduced in the report.
It should demonstrate a logical connection between the site history, identified contamination sources, environmental setting, Conceptual Site Model and recommendations.
A technically defensible PSI should:
distinguish credible contamination risks from theoretical possibilities;
explain the significance of historical activities rather than simply list them;
consider both on-site and relevant off-site sources;
identify potentially affected environmental media;
develop a clear preliminary Conceptual Site Model;
identify genuine data gaps;
consider the proposed land use;
clearly explain whether further investigation is required; and
where further work is recommended, explain what that investigation needs to resolve.
The report should allow the client, planning authority or other reviewer to understand what has been identified, why it matters and what needs to happen next.
Preliminary Site Investigations in NSW
Preliminary Site Investigations in NSW should be prepared with reference to the NSW EPA Consultants Reporting on Contaminated Land Guidelines and the National Environment Protection (Assessment of Site Contamination) Measure 1999, as varied in 2013 (ASC NEPM).
The NSW EPA reporting framework identifies the PSI as the first stage in contaminated land management, followed where necessary by sampling and analysis planning, detailed investigation, risk assessment, remediation, validation and ongoing management.
The ASC NEPM provides the nationally consistent technical framework for assessing site contamination, while NSW planning and contaminated-land requirements determine how that framework is applied within the State.
Who Should Prepare a Preliminary Site Investigation?
A PSI should be undertaken by a consultant with appropriate contaminated-land experience and an understanding of NSW EPA guidance, the ASC NEPM and the planning context in which the report will be used.
For contaminated land reports submitted directly to the NSW EPA, the EPA requires the report to be prepared, or reviewed and approved, by a consultant certified under the recognised CEnvP Site Contamination (CEnvP-SC) or CPSS Contaminated Site Assessment and Management (CPSS CSAM) schemes. Requirements for other projects can depend on the planning authority, project and review framework. For more information about CEnvP-SC or CPSS CSAM, visit CEnvP-SC Review: Why Councils Require It & What It Costs — Confluence Environmental.
Technical experience is particularly important where the site contains multiple historical activities, incomplete records, sensitive proposed land uses or complex contamination pathways.
Need a Preliminary Site Investigation?
Confluence Environmental undertakes Preliminary Site Investigations across NSW for development applications, planning proposals, subdivision, property transactions, infrastructure projects and environmental due diligence. Planning a Child Care Centre? Read more Preliminary Site Investigations for Childcare Centres NSW — Confluence Environmental.
Our assessments focus on identifying credible contamination risks, material data gaps and the level of further investigation actually required, providing a clear and technically defensible basis for the next project decision.
Where a PSI has already been requested by Council or another reviewing authority, we can review the available project information and develop an appropriate scope for the assessment.