Why Do Contaminated Land Investigation Costs Vary? Understanding Soil Sampling in NSW
If you have received a quote for a contaminated land investigation, you may be wondering why one consultant has proposed eight soil samples while another has proposed 20—or why the investigation scope is greater than you expected.
It is a reasonable question.
Soil sampling, fieldwork and laboratory analysis can make up a significant part of a contaminated land investigation. But the number of samples should not be arbitrary, nor should every site of the same size automatically receive the same investigation.
A well-designed investigation starts with a different question:
What information do we need to make a reliable decision about this site?
The objective is not to collect the most samples possible. It is to collect enough of the right samples, from the right locations, for the right reason.
Why do contaminated land investigation costs vary?
There is no standard price for a Preliminary Site Investigation (PSI), Detailed Site Investigation (DSI) or other contaminated land assessment because the required scope depends on the site.
Two properties of the same size can require very different investigations.
A vacant commercial property containing relatively uniform fill presents a different problem to a former workshop with fuel storage, chemical handling and areas of uncontrolled fill.
The scope can be influenced by:
the size and history of the site;
the number of potential contamination sources;
whether fill is present and how widely it is distributed;
the depth of investigation required;
the proposed development and areas of excavation;
the number of soil samples requiring laboratory analysis;
which contaminants need to be analysed;
whether groundwater, soil vapour or other media require investigation;
site access, drilling and reinstatement requirements; and
whether reliable previous investigation data are available.
This is why comparing two proposals based only on their bottom-line price—or the number of samples included—can be misleading.
A better question is:
What is the proposed investigation intended to establish?
Why do we need to collect soil samples?
Before intrusive investigation begins, an environmental consultant will usually review information such as historical aerial photographs, planning records, previous reports and former site activities.
A site inspection may also identify fill, staining, fuel infrastructure, waste materials or other potential indicators of contamination.
This information helps us understand where contamination could potentially be present.
What it generally cannot tell us conclusively is what is actually present below the ground.
Sampling provides physical evidence.
Depending on the site, we may be trying to determine:
whether imported fill has introduced contamination;
whether a former workshop has affected surrounding soil;
whether a removed fuel tank has left residual contamination;
whether an identified impact is localised or widespread;
whether excavation is likely to encounter contaminated material; or
whether the site is suitable for its proposed use.
The NSW EPA's contaminated land guidance provides a framework for designing sampling programs and reporting information so that decisions about contaminated land can be adequately supported.
Sampling design starts with understanding the site
Before deciding how many samples to collect, the consultant develops a Conceptual Site Model, commonly referred to as a CSM.
At its simplest, the CSM considers:
Potential sourceHow exposure could occurWho or what could be affectedImported contaminated fillExcavation, direct contact or dustConstruction workers or future occupantsFormer fuel tankSoil or groundwater migrationWorkers, groundwater or adjoining landFormer workshopDisturbance of affected soilConstruction workers or future users
The purpose of the CSM is to bring the site history together and identify the uncertainties that actually matter.
Those uncertainties become the data gaps that the investigation needs to address.
For example, if historical information shows a workshop operated in one corner of a property for several decades, there is a logical reason to investigate that area specifically.
If uncontrolled fill has instead been placed broadly across the property and its origin is unknown, broader coverage may be necessary.
This is why sampling design should follow the site history and CSM—not simply the area of the property.
How are soil sampling locations selected?
There is more than one way to design a sampling program.
Targeted sampling
Targeted sampling is used where there is a specific feature or activity that requires investigation.
Examples may include:
a former underground fuel tank;
workshop or maintenance area;
chemical storage area;
transformer;
visibly stained soil; or
suspected waste disposal area.
Where the potential source is known, it is often appropriate to deliberately position samples around that source.
Systematic sampling
Sometimes there is no single feature that can be confidently targeted.
For example, imported fill may extend broadly across a property, but there may be little information about where it came from or where contamination might occur within it.
In these situations, samples may be distributed more evenly across the investigation area.
Systematic sampling provides broader coverage and can assist in detecting contamination that was not identified from the site history alone.
Combining sampling approaches
Most sites are not that simple.
A property might contain:
fill across a large portion of the site;
a former workshop in one corner; and
a former fuel tank near the boundary.
It may therefore be appropriate to use broader systematic coverage for the fill while also specifically targeting the workshop and former tank.
The NSW EPA's current Sampling Design Guidelines recognise different sampling approaches and provide tools for developing sampling programs appropriate to the investigation objectives. The guidance is intended to support sampling that is fit for purpose rather than applying one identical design to every site.
The sampling design follows the site—not the other way around.
Why can't we just collect a few samples?
Imagine a 10,000 m² property where four soil samples are collected.
All four laboratory results are below the relevant assessment criteria.
That tells us something useful:
contamination was not identified at those four locations.
But there is another question:
How well do those four samples represent the rest of the property?
If a small area of contaminated fill or buried waste sits between widely spaced sampling locations, it could potentially remain unidentified.
This is where sampling density becomes important.
Environmental consultants cannot analyse every kilogram of soil on a site. Sampling is therefore used to obtain information about a much larger area.
The design needs to provide an appropriate level of confidence for the decision being made.
That does not mean that more samples automatically equal a better investigation.
It means there needs to be a logical relationship between the number and location of samples, the potential contamination sources and the questions the investigation is trying to answer.
Does the EPA simply specify a minimum number of samples?
Not exactly.
The NSW EPA Sampling Design Guidelines include methods for considering systematic sampling density and hotspot detection.
However, sample numbers still need to be considered in the context of the site history, CSM and investigation objectives.
A known former fuel tank, for example, can be specifically targeted.
Conversely, if fill extends across a large area with little information about its source or distribution, sampling only beside one known feature may provide very little information about the remainder of the site.
This is why a sampling program should not simply be:
“The site is this big, therefore it needs this many samples.”
A competent investigation considers both coverage and identified Areas of Environmental Concern.
Example: a 1,000 m² commercial property
Consider a 1,000 m² commercial property that will remain in commercial use.
The existing building is largely being retained, but the proposed development includes a new car park, stormwater infrastructure and underground services.
Historical information identifies three potential areas requiring investigation:
General site – Imported fill
Imported fill may be present across the property. The investigation needs to determine whether the fill has introduced contamination and whether broader site coverage is required.
Former workshop – Vehicle maintenance
A former workshop was used for vehicle or machinery maintenance. Targeted sampling can help determine whether these activities have caused a localised impact to the surrounding soil.
Rear boundary – Former chemical drum storage
Chemical drums were historically stored near the rear boundary. Targeted sampling can help determine whether storage, spills or leakage have affected the surrounding soil.
It may therefore be appropriate to provide broader coverage of the filled area while also specifically targeting the former workshop and drum storage area.
The investigation may also consider the proposed stormwater and service excavations, particularly where these works will disturb soil.
A well-designed sampling program may also position locations so that one sampling point contributes to more than one investigation objective.
The result is not simply:
“A 1,000 m² site requires X samples.”
Instead, each sampling location should have a clear purpose.
More samples do not automatically mean a better investigation
Collecting samples that do not address an identified contamination source, data gap or investigation objective can increase the scope without materially improving the assessment.
Equally, collecting too few samples can leave important uncertainties unresolved.
Good sampling design sits between these extremes.
Where appropriate, investigation design can be made more efficient by:
making use of reliable existing investigation data;
separating the site into areas with different contamination risks;
positioning samples so they address multiple objectives;
targeting genuine Areas of Environmental Concern;
selecting laboratory analyses based on credible contaminants of concern; and
staging work where initial results will determine the next investigation step.
The objective is proportionate investigation—not maximum sampling.
Why can two consultants provide very different quotes?
Two consultants can review the same property and arrive at different scopes.
One may consider fill to extend across the entire site, while another may have evidence that it is restricted to one area.
One may identify several Areas of Environmental Concern from the historical information.
Another may propose different investigation depths, analytical suites or methods of obtaining the samples.
One proposal may include broader systematic coverage plus targeted sampling, while another may rely predominantly on targeted locations.
This does not automatically mean that the higher-priced proposal is over-scoped.
It also does not mean that the proposal containing the most samples is technically superior.
The important question is:
Can the consultant explain why the proposed work is required?
When comparing contaminated land proposals, it can be useful to ask:
What is each sampling location intended to investigate?
What potential contamination sources have been identified?
Does the proposed program provide appropriate coverage of the areas that could be affected?
What assumptions has the consultant made?
What happens if the investigation does not answer those questions?
The NSW EPA similarly advises people engaging contaminated land consultants to provide detailed site information so consultants can quote accurately and to understand the proposed scope of works when comparing consultants.
Can an investigation be staged to control scope?
Yes.
Staged investigation can be an effective way of keeping work proportionate.
For example, an initial investigation may target a suspected contamination source.
If sufficient evidence is obtained to demonstrate that no significant impact has occurred, additional investigation of that source may not be required.
If contamination is identified, subsequent sampling can then focus on determining its extent.
As new information becomes available, the CSM can be updated and the investigation refined.
This allows effort to be directed toward the areas where it is actually required.
However, staging should not simply defer work that is already clearly necessary to support the project decision.
What should you look for when comparing investigation proposals?
You do not need to be an environmental scientist to determine whether the logic behind a proposal makes sense.
A good investigation scope should allow you to understand:
What could have caused contamination?
Where could it reasonably be present?
What information is currently missing?
Why are the proposed samples being collected?
What will they be analysed for?
How will the results help the project move forward?
There should be a clear connection between:
Site history → potential contamination source → data gap → sampling → results → decision
If that connection can be explained, it becomes much easier to understand what you are actually purchasing.
The objective is confidence—not sample numbers
The success of a contaminated land investigation is not determined by whether 10, 20 or 30 samples were collected.
It is determined by whether the information obtained is sufficient and representative enough to support the decision that needs to be made.
For a developer, that may mean demonstrating that land is suitable for a proposed development.
For a planner, it may mean obtaining the information required to progress a development application.
For a contractor, it may mean understanding the materials likely to be encountered during construction.
Good sampling design is therefore a balance between coverage, targeting and proportionality.
The goal is not to collect the most samples. It is to collect the right samples, from the right locations, for the right reason.
Planning a contaminated land investigation?
Confluence Environmental provides Preliminary Site Investigations, Detailed Site Investigations, Sampling and Analysis Quality Plans and contaminated land consulting across NSW.
Our investigation strategies are developed around the site history, Conceptual Site Model, proposed development and identified data gaps, with a focus on providing clear, proportionate and technically defensible advice.
If you are planning a development, responding to a contamination requirement or comparing investigation proposals, contact our team to discuss your site and an appropriate investigation approach.
References
NSW Environment Protection Authority (2022), Contaminated Land Sampling Design Guidelines – Part 1: Application.
NSW Environment Protection Authority (2022), Contaminated Land Sampling Design Guidelines – Part 2: Interpretation.
NSW Environment Protection Authority (2020), Consultants Reporting on Contaminated Land: Contaminated Land Guidelines.
National Environment Protection Council (2013), National Environment Protection (Assessment of Site Contamination) Measure 1999, as amended 2013.
This article provides general information only. Contaminated land investigation requirements are site-specific and should be determined by a suitably qualified and experienced environmental consultant having regard to the site conditions, proposed development and applicable guidance.