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A contaminated land assessment works out whether soil, groundwater or other material on a site contains contaminants at levels that put human health or the environment at risk, given how the land is used now or will be used.
In Western Australia, assessments follow the national assessment framework (the NEPM) and guidance from the Department of Water and Environmental Regulation (DWER) and the Department of Health, and are carried out by environmental consultants.
These guidelines cover when a site requires one, what it can find, what happens at each stage and what comes next if contamination turns up.
It is a staged investigation of a site’s history and condition. It answers three questions: is there contamination, where is it and how much, and does it pose a risk for the current or proposed land use?
The answers shape decisions about buying, developing, selling or remediating land. Findings are documented in a standard format so that DWER, local government, lenders and buyers can rely on them.
An assessment is usually required when:
You’re buying land: due diligence before settlement shows whether you’re taking on a liability.
You’re developing or rezoning: local government can set an assessment as a planning condition, particularly where land use changes to something more sensitive, such as industrial to residential.
The site has a history of potentially contaminating activities: service stations, fuel depots, workshops, dry cleaners, manufacturing, landfill, market gardens and sites with imported fill.
You’re selling or refinancing: purchasers and lenders often ask for evidence the land is suitable.
DWER requires it: under the Contaminated Sites Act 2003, known or suspected contaminated sites must be reported to DWER, which classifies them and can require investigation.
Something has gone wrong: a fuel leak, a chemical spill or asbestos found during demolition or earthworks.
Assessments test for the contaminants the site history points to. Common ones in WA include:
Hydrocarbons: petrol, diesel and oils from fuel tanks, service stations and workshops.
Heavy metals: lead, arsenic, chromium and others from industry, old paint, fill and some agricultural uses.
Asbestos: fragments and fibres in soil, often from demolished buildings or buried waste.
Solvents: chlorinated solvents from dry cleaning, degreasing and manufacturing.
Pesticides: residues from market gardens, orchards and termite treatment.
Industrial waste: buried waste, ash and slag.
Acid sulfate soils: naturally occurring soils that generate acid when disturbed, common on the Swan Coastal Plain.
An assessment also identifies how contamination could affect human health or the environment, such as through groundwater, vapour or direct contact with soil.
The process usually runs in stages and each stage determines if the next is required.
The consultant reviews the site’s history: historical aerial photos, previous land uses, DWER records, earlier investigations and planning information. A site inspection follows, looking for staining, tanks, fill, waste or damaged building materials. Some preliminary site investigations include limited sampling.
The result is a conceptual site model: a picture of possible contamination sources, the people and environments that could be exposed, and the pathways between them. If the preliminary site investigation shows a low risk, the assessment can stop there.
If the first stage finds potential contamination, a detailed site investigation follows. This involves:
A sampling and analysis plan setting out where, how deep and for which contaminants to sample.
Fieldwork: test pits, boreholes, soil sampling and, where needed, groundwater monitoring bores and soil vapour testing.
Laboratory analysis by NATA-accredited laboratories.
Comparison of results against the assessment criteria for the land use.
The detailed site investigation defines the type, concentration and extent of contamination, both across the site and with depth.
The final document sets out the results, the risk to human health and the environment, and recommendations. Where a site has been reported to DWER, or an approval depends on the outcome, it may be reviewed by a DWER-accredited contaminated sites auditor.
Finding contamination doesn’t automatically stop a project. The next steps depend on the risk and the intended land use:
Risk assessment: a site-specific assessment can show whether contamination above screening criteria actually poses a risk for the proposed use.
Remedial action plan: if remediation is needed, the plan sets out the method, such as excavation and disposal, on-site treatment or capping, and the goals the site must meet.
Remediation: contractors carry out the works under the plan, with environmental oversight.
Validation: sampling after remediation proves the site meets the required criteria.
Management and monitoring: where contamination stays in place, a site management plan sets out controls, and groundwater monitoring may continue.
DWER classification: for reported sites, DWER may reclassify the site based on the validation results.
Assessments are carried out by environmental consultants with experience in site contamination. That could mean environmental scientists, hydrogeologists, engineers and other professionals.
When choosing between environmental consultants in Perth, look for experience with the Contaminated Sites Act 2003 and DWER guidance, use of NATA-accredited laboratories and work that holds up to auditor review.
We’re a specialist, independent environmental consultancy based in Western Australia with over 13 years of experience in contaminated site investigations, soil and water testing, acid sulfate soils and site assessments. Our contaminated land services include:
Desktop assessments and preliminary site investigations.
Detailed site investigations, with sampling and analysis through NATA-accredited laboratories.
Due diligence investigations before purchase or construction.
Underground storage tank and septic tank assessments.
Treatment and remediation, including brownfield sites.
Management plans and ongoing monitoring.
Much of our work is for developers, development consultants, construction firms and purchasers who want a clear answer on a site before they commit to it.
Send us the site address, your plans for the land and any previous investigations, and we’ll come back with a recommended scope.
