Contaminated Soil Assessment in NSW: When Is Testing Required?
A contaminated soil assessment is undertaken where there is a credible reason to suspect that soil may have been affected by historical or current land uses, imported fill, waste, fuel, chemicals, asbestos or other potentially contaminating activities.
In NSW, soil testing is not automatically required simply because land is being developed. The need for a soil investigation should be based on the site history, proposed land use, current site conditions and the contamination risks that need to be resolved.
For some sites, the appropriate starting point is a Preliminary Site Investigation (PSI) to establish whether contamination has the potential to be present. Where credible contamination risks or important data gaps remain, a Detailed Site Investigation (DSI) or another targeted environmental site investigation may then be required.
The key question is therefore not simply:
“Should we test the soil?”
It is:
“What information is needed to determine whether contamination affects the site or proposed development?”
What Is a Contaminated Soil Assessment?
A contaminated soil assessment is an investigation undertaken to determine whether soil has been affected by contamination and what those conditions mean for the current or proposed use of the land.
Depending on the purpose of the assessment, the work may include:
review of the site history;
identification of potentially contaminating activities;
site inspection;
development of a Conceptual Site Model;
identification of Areas of Environmental Concern;
identification of Contaminants of Potential Concern;
intrusive soil investigation;
laboratory analysis; and
assessment of the findings against criteria relevant to the proposed land use.
The scope can range from investigation of a discrete potential contamination source to a broader contaminated site assessment involving soil, groundwater, soil vapour, surface water or other environmental media.
The purpose is not simply to collect samples and produce laboratory results. A useful land contamination assessment should provide enough evidence to determine what contamination is present, whether it matters and what needs to happen next.
When Is Contaminated Soil Testing Required?
Contaminated soil testing may be appropriate where the available information identifies a credible possibility that soil has been affected by contamination.
Common triggers include:
former industrial or manufacturing activities;
mechanical workshops;
service stations or fuel storage;
chemical storage or handling;
imported or uncontrolled fill;
waste disposal or buried material;
demolition debris;
asbestos-containing material within soil or fill;
agricultural or horticultural activities;
pesticide use;
staining or unusual odours;
former underground petroleum storage systems;
previous structures associated with potentially contaminating activities; or
unexpected material encountered during excavation.
Testing may also be required where land is proposed for a more sensitive use and the available information is insufficient to demonstrate that the site is suitable for that use.
Examples include redevelopment for residential, childcare, educational, healthcare or public open-space purposes.
However, the presence of a historical activity does not automatically mean that contamination exists.
The purpose of the assessment is to determine whether there is a credible mechanism through which contamination could have occurred and whether that issue requires investigation.
Preliminary Site Investigations and Soil Testing
A Preliminary Site Investigation is generally the first stage of contaminated land assessment where the contamination status of a site is uncertain.
Preliminary site investigations typically focus on:
understanding current and historical land use;
identifying potentially contaminating activities;
reviewing the surrounding environmental setting;
inspecting current site conditions;
identifying potential contamination sources;
developing a preliminary Conceptual Site Model; and
determining whether further investigation is warranted.
The term preliminary site assessment is also sometimes used more generally, although Preliminary Site Investigation is the terminology commonly used within the NSW contaminated-land framework.
A PSI does not automatically require soil testing.
Where the available site history is sufficiently complete and does not identify a credible contamination issue, intrusive investigation may not be warranted.
Conversely, where the site history is incomplete, potentially contaminating activities are identified or a particular uncertainty needs to be resolved, limited preliminary sampling may sometimes assist.
The important point is that sampling should have a clear purpose.
Collecting several soil samples simply so that a contamination report contains laboratory results does not necessarily establish whether the site is contaminated or suitable for its proposed use.
Where intrusive investigation is required to characterise the nature, extent or significance of contamination, the work will generally form part of a Detailed Site Investigation or another appropriately designed investigation.
When Does Soil Testing Become a Detailed Site Investigation?
A Detailed Site Investigation is generally undertaken where preliminary assessment identifies contamination risks or material data gaps that cannot be adequately resolved through desktop information and site inspection alone.
The DSI uses intrusive investigation and environmental data to test and refine the Conceptual Site Model.
Depending on the site, it may seek to establish:
whether contamination is present;
what contaminants are present;
where contamination is located;
how contamination varies laterally or with depth;
which environmental media are affected;
whether contamination has migrated;
whether relevant exposure pathways exist;
whether the contamination presents an unacceptable risk; and
whether further investigation, remediation or management is required.
A DSI is therefore more than a larger soil-sampling program.
It is a designed contaminated site investigation intended to provide sufficient evidence to support a decision about the site.
How Is a Contaminated Soil Investigation Designed?
A contaminated soil investigation should begin with the Conceptual Site Model (CSM) rather than a predetermined sample number.
The CSM considers:
Source → Pathway → Receptor
Potential sources might include a former workshop, fuel tank, imported fill, waste burial or chemical storage area.
Pathways describe how contamination could migrate or create exposure, such as direct contact with soil, dust generation, leaching to groundwater, vapour migration or surface-water runoff.
Receptors may include future residents, construction workers, groundwater, ecological receptors or nearby surface-water environments.
Once those relationships are understood, the investigation can be designed around the actual questions that need to be answered.
For example, a site containing widespread imported fill creates a different sampling problem from a property containing a single former underground fuel tank.
Likewise, a former workshop may contain several discrete Areas of Environmental Concern, such as maintenance areas, wash bays, fuel storage and waste-storage locations, requiring targeted investigation in addition to broader assessment of site conditions.
The investigation strategy should therefore consider:
the investigation objectives;
site history;
Conceptual Site Model;
Areas of Environmental Concern;
Contaminants of Potential Concern;
spatial distribution of possible contamination;
depth of potential impacts;
proposed land use;
target environmental media;
existing data; and
the uncertainty that the investigation is intended to resolve.
A good soil site investigation should be able to explain why the samples were collected where they were and what question each part of the sampling program was intended to answer.
Does a Contaminated Site Assessment Only Investigate Soil?
No.
Although soil may be the initial focus, contamination can affect or migrate through several environmental media.
Depending on the Conceptual Site Model, an environmental site investigation may also require:
Groundwater Assessments
Groundwater investigation may be appropriate where contaminants are mobile, impacts extend to depth, historical underground infrastructure has been present or groundwater could provide a migration pathway to sensitive receptors.
Groundwater assessments may involve installation of monitoring wells, groundwater gauging, sampling and laboratory analysis.
Surface Water Assessments
Surface-water investigation may be relevant where contaminants could migrate through drainage, erosion, runoff or direct discharge to nearby creeks, wetlands or other water bodies.
Soil Vapour Assessment
Soil vapour may require consideration where volatile contaminants are present and vapour migration could create an exposure pathway to buildings or future occupants.
The assessment should therefore focus on the environmental media relevant to the identified contamination scenario rather than automatically investigating soil, groundwater and surface water on every site.
What Contaminants Are Tested in Soil?
There is no single laboratory suite that is appropriate for every contaminated soil assessment.
The analytical program should reflect the site's history and the potential contamination sources identified through the CSM.
For example:
Fuel storage and service stations may require consideration of petroleum hydrocarbons, BTEXN, PAHs and lead.
Workshops and industrial areas may require hydrocarbons, metals, solvents or chemicals associated with the activities historically undertaken.
Imported or uncontrolled fill may require consideration of metals, hydrocarbons, PAHs, asbestos and other contaminants associated with the source of the material.
Agricultural or horticultural land may warrant assessment for pesticides and metals associated with historical land-management practices.
Other sites may require investigation for PFAS, chlorinated solvents, asbestos, specific industrial chemicals or contaminants associated with a particular process.
Testing every sample for every possible substance is generally unnecessary.
The analytical suite should reflect the contaminants that could reasonably be associated with the identified contamination scenarios.
How Are Contaminated Soil Results Interpreted?
Laboratory results are interpreted in the context of the proposed land use, environmental setting and Conceptual Site Model.
The National Environment Protection (Assessment of Site Contamination) Measure 1999, as varied in 2013 — the ASC NEPM — provides the nationally consistent technical framework for contaminated site assessment.
It includes investigation and screening levels used to assess potential human-health, ecological and petroleum-hydrocarbon risks.
Importantly, these values should not simply be treated as automatic cleanup limits.
An exceedance may indicate that further investigation or evaluation is required, but the significance of the result depends on the contamination scenario.
A single elevated result within a defined hotspot can have very different implications from widespread contamination extending across an entire site.
Interpretation should therefore consider:
contaminant concentration;
location and depth;
surrounding results;
spatial distribution;
proposed land use;
potential exposure pathways;
environmental media affected;
soil conditions;
data quality; and
the broader Conceptual Site Model.
A contamination assessment is therefore an exercise in interpretation and risk assessment, not simply comparison of laboratory numbers against criteria.
What Happens if Contaminated Soil Is Identified?
The presence of contaminated soil does not automatically mean that all affected material must be excavated and disposed of.
The next step is to determine whether the contamination presents an unacceptable risk and what response is appropriate.
Possible outcomes include:
no further assessment;
additional targeted investigation;
further delineation;
site-specific risk assessment;
preparation of a Remedial Action Plan;
excavation and off-site disposal;
on-site treatment;
containment or capping;
management through design;
an Environmental Management Plan; or
ongoing monitoring.
Where remediation is required, the objective is to make the site suitable for its intended use, not necessarily to remove every detectable concentration of contamination.
Following remediation, validation is generally undertaken to demonstrate whether the remedial objectives have been achieved.
Contaminated Soil Assessment vs Waste Classification
Contaminated land assessment and waste classification are related, but they answer different questions.
A contaminated soil assessment asks:
Does contamination affect the condition or suitability of the land?
A waste classification asks:
How can excavated material be lawfully managed, reused or disposed of?
The same material may need to be considered in both contexts.
For example, a Detailed Site Investigation may identify contaminated fill that requires management during redevelopment.
If that material is later excavated and transported off site, a separate waste classification may be required to establish its appropriate disposal or resource-recovery pathway.
Existing laboratory results from a contaminated land investigation may sometimes contribute to waste classification, but they are not automatically sufficient. The results must be representative of the material being classified and relevant to the proposed management pathway.
This distinction becomes particularly important during earthworks, where contaminated land assessment and excavated-material management often overlap.
Contaminated Soil Assessment vs Geotechnical Soil Testing
The term soil testing is used for several very different types of investigation.
A geotechnical investigation assesses ground conditions relevant to engineering design, such as:
foundation conditions;
bearing capacity;
settlement;
pavement design;
slope stability; and
subsurface materials.
A contaminated soil assessment considers whether chemicals, asbestos, waste materials or other contaminants may affect human health, the environment or land suitability.
A development may therefore require both.
Geotechnical investigation should not be assumed to provide adequate contaminated-land information unless the sampling and analytical program has specifically been designed to address contamination objectives.
Likewise, environmental soil sampling does not replace geotechnical investigation where engineering information is required.
What About Contaminated Soil Found During Construction?
Contamination is sometimes first encountered after excavation or construction has started.
Potential indicators can include:
staining;
hydrocarbon odours;
asbestos fragments;
buried drums;
ash;
demolition material;
unusual fill;
waste; or
unexpected underground infrastructure.
Where unexpected contamination is encountered, disturbance within the affected area may need to be stopped or controlled while the material is assessed.
Depending on what has been found, the response may involve:
targeted soil sampling;
asbestos assessment;
waste classification;
additional contaminated land investigation;
remediation; or
implementation of an Unexpected Finds Procedure.
This is one reason potentially contaminated land is best considered before major excavation begins where the site has a history that could reasonably have resulted in contamination.
Do I Need Contaminated Soil Testing for a Development Application?
Not every development application requires contaminated soil testing.
The relevant question is whether contamination represents a credible issue for the site and whether the consent authority has enough information to determine that the land is suitable, or can be made suitable, for the proposed development.
Where the site history does not identify a credible contamination source and the available information is sufficiently complete, a Preliminary Site Investigation may determine that intrusive investigation is not required.
Where credible contamination risks remain, soil testing or a broader Detailed Site Investigation may be necessary before the planning question can be resolved.
A logical assessment pathway is therefore:
Site history → Conceptual Site Model → data gaps → investigation
rather than:
Development application → automatically collect soil samples.
What Should a Contaminated Soil Assessment Report Tell You?
A useful contamination report should do more than reproduce laboratory certificates and tables.
It should explain:
why the investigation was undertaken;
what contamination sources were identified;
what environmental media were considered;
how the sampling strategy addressed the identified risks;
what contaminants were analysed;
what the results mean;
whether the data are sufficient to support the conclusions;
whether contamination affects the proposed land use; and
what should happen next.
The report should ultimately allow the client, Council, regulator or technical reviewer to understand:
What was investigated? Why was it investigated? What was found? Does it matter? What needs to happen next?
Who Should Undertake a Contaminated Soil Assessment?
A contaminated soil assessment should be undertaken by an environmental consultant with appropriate experience in contaminated land assessment, investigation design and the applicable NSW technical and planning framework.
Experienced environmental consultants should be able to explain not only what sampling is proposed, but:
why the investigation is required;
what contamination hypotheses are being tested;
how the sampling program addresses the CSM;
what limitations remain; and
how the results will affect the project.
For more complex sites, the required environmental consulting services may extend beyond soil investigation to groundwater assessment, surface-water assessment, soil vapour, asbestos, waste classification, remediation planning or validation.
The value of an environmental consultancy is therefore not simply its ability to collect samples. It is the ability to design an investigation that produces the information needed to make a defensible decision.
Frequently Asked Questions (FAQ):
Q: Can I just send a soil sample to a laboratory to see if my land is contaminated?
A laboratory can determine the concentration of the substances analysed in that particular sample. It cannot determine whether the sample is representative of the wider site or whether the land is suitable for its proposed use. Sampling locations, depths and analytical suites should be selected for a defined investigation purpose.
Q: Does contaminated soil always need to be removed?
No. The appropriate response depends on the contaminant, concentration, extent, exposure pathways and proposed land use. Some contamination may require remediation, while other impacts may be managed in place or may not represent an unacceptable risk.
Q: How many soil samples are required?
There is no universal number that applies to every contaminated site. Sampling design depends on the site area, contamination sources, investigation objectives, proposed land use, existing information, target hotspot size and variability of the material being investigated.
Q: Can soil testing be completed during a Preliminary Site Investigation?
Yes. Limited sampling may sometimes be appropriate where it addresses a defined uncertainty. Where intrusive investigation is required to characterise the nature, extent or significance of contamination, a Detailed Site Investigation or another appropriately designed investigation will generally be more suitable.
Q: Is contaminated soil testing the same as waste classification?
No. Contaminated land assessment determines the significance of contamination in the context of the site. Waste classification determines the appropriate management pathway for excavated material being reused, transported or disposed of.
Q: Does a Detailed Site Investigation only assess soil?
No. Depending on the Conceptual Site Model, a DSI may investigate soil, groundwater, soil vapour, surface water, sediment or other environmental media.
Q: Is a contaminated soil assessment the same as an environmental site assessment?
A contaminated soil assessment may form part of a broader environmental site assessment. The broader investigation can include soil as well as groundwater, surface water, soil vapour or other environmental media where relevant.
Contaminated Soil Assessments in NSW
Confluence Environmental provides contaminated soil assessments, contaminated land assessments and environmental site investigations across NSW for development, planning, property transactions, infrastructure and construction projects.
Our assessments are developed around the site history, proposed land use and Conceptual Site Model so that investigation effort is directed toward the contamination risks and data gaps that actually need to be resolved.
Where the appropriate starting point is unclear, we can review existing environmental reports, Council correspondence, development plans and available site information to determine whether the project requires a Preliminary Site Investigation, targeted soil investigation, Detailed Site Investigation, groundwater assessment or another form of contaminated land assessment.
Learn more about our Preliminary Site Investigation and Detailed Site Investigation services, or contact our team to request a proposal.