An Environmental Site Assessment investigates whether past or current activities may have contaminated soil, groundwater, surface water, soil vapour or other environmental media. The work is usually staged so the scope of each step responds to the evidence already available.
In Australia, the National Environment Protection (Assessment of Site Contamination) Measure, known as the ASC NEPM, provides a nationally consistent framework. Each state and territory implements contaminated land requirements through its own legislation, policies and planning system.
When an environmental site assessment may be needed
An assessment may support:
- a development application or change of land use
- acquisition, sale or lease due diligence
- redevelopment of former industrial or commercial land
- investigation of a spill, complaint or regulatory concern
- management or remediation planning
- validation after remediation
- assessment of imported fill or waste-related issues
The purpose of the work should be agreed before the investigation begins. A planning assessment, statutory site audit and private transaction can require different scopes and levels of assurance.
Preliminary Site Investigation (PSI)
A PSI develops an initial understanding of site contamination risks and determines whether further investigation is needed.
Typical PSI work includes:
- review of historical aerial photographs, maps, titles and land uses
- searches of relevant regulatory and planning records
- review of geology, hydrogeology, drainage and nearby sensitive environments
- a site inspection
- interviews or review of available operational records
- identification of potentially contaminating activities and contaminants of potential concern
- development of an initial Conceptual Site Model
- identification of data gaps and recommendations
A PSI is often dominated by desktop research and a site walkover, but it should not automatically be described as a no-sampling assessment. NSW EPA guidance notes that preliminary sampling may be necessary where potentially contaminating activities are suspected or the site history is incomplete.
Conceptual Site Model
The Conceptual Site Model, or CSM, connects three elements:
| Element | Question |
|---|---|
| Source | What activity or material could have caused contamination? |
| Pathway | How could a contaminant move or create exposure? |
| Receptor | Who or what could be affected? |
A potentially complete source-pathway-receptor linkage helps define what should be investigated. The CSM should be updated as new information becomes available.
Detailed Site Investigation (DSI)
A DSI uses targeted investigation and sampling to characterise contamination and address the data gaps identified by the PSI.
The scope may include:
- a Sampling and Analysis Quality Plan
- soil bores, test pits or other suitable sampling methods
- groundwater monitoring wells and sampling
- soil vapour or ground gas investigation where relevant
- survey and documentation of sampling locations
- laboratory analysis for contaminants selected from the site history and CSM
- quality assurance and quality control samples
- comparison with criteria appropriate to the proposed land use and exposure scenario
- refinement of the CSM and assessment of uncertainty
Laboratories accredited by NATA for the relevant analysis are commonly used where required by the project, regulator or guidance.
Selecting contaminants and sampling locations
There is no universal analytical list for every site. The investigation should respond to the site history.
Examples include petroleum hydrocarbons and BTEX at fuel facilities, solvents at dry cleaners, metals at industrial sites, pesticides on some agricultural land, asbestos in fill or demolition-affected areas, and PFAS where particular historical uses indicate a plausible source.
Sampling density and depth should be justified by the assessment objective, site variability, potential source areas, geology and the media being investigated. Generic online test frequencies are not a substitute for a defensible sampling design.
What happens after a DSI
Depending on the results, the next step may be:
- no further investigation for the stated purpose
- additional delineation or monitoring
- a human health or ecological risk assessment
- a Remedial Action Plan
- remediation and validation
- an environmental management plan
- review by an accredited site auditor where required
A DSI does not always prove that a site is completely free of contamination. Conclusions are limited by the investigation scope, sampling coverage, analytical suite and information available at the time.
Australian and NSW framework
The ASC NEPM supplies the national assessment framework and investigation levels. It is given effect through state and territory legislation and guidance, so local requirements must also be checked.
In NSW, relevant resources include the EPA statutory contaminated land guidelines and the Consultants Reporting on Contaminated Land guideline. Reports submitted to the NSW EPA must meet applicable requirements, including consultant certification where required. A NSW EPA-accredited site auditor may be needed when an independent statutory review is required.
Investigation levels are screening tools, not automatic clean-up levels. Their selection and interpretation must consider land use, exposure pathways, background conditions, data quality and the complete CSM.
Choosing a Consultant
Look for experience that matches the site history and purpose of the assessment. The project team may need environmental scientists, contaminated land consultants, hydrogeologists, occupational hygienists, laboratories, surveyors and remediation specialists.
Before the appointment, confirm:
- the assessment objective and regulatory pathway
- relevant professional certification
- proposed scope, exclusions and deliverables
- laboratory accreditation and quality procedures
- whether independent site auditor involvement is needed
- how unexpected contamination will be managed during works
External Resources
- Asbestos Identification and Management
- Acid Sulfate Soils Identification and Management
- ENM and VENM Waste Classification
- Hazardous Building Materials Surveys
- Aggressivity Testing and Soil Chemistry
Official Guidance
- ASC NEPM, National Environment Protection Council
- NSW EPA statutory contaminated land guidelines
- NSW EPA consultant certification
- NSW EPA site auditor scheme
This guide is general information, not a regulatory determination. Check current requirements with the relevant authority and a suitably qualified contaminated land professional.