An Environmental Site Assessment (ESA) is a systematic evaluation of a property to identify potential or existing environmental contamination that could affect human health, the environment, or the property's value and redevelopment potential. In Australia, the assessment process follows a staged approach under state and federal guidelines.
What Is an Environmental Site Assessment?
Environmental site assessments evaluate whether soil, groundwater, or surface water on a site has been impacted by contamination from past or present activities. They are typically required for:
- Property transactions (due diligence)
- Development applications (council/state requirements)
- Brownfield redevelopment
- Contaminated land investigation
- Environmental compliance
- Site remediation planning
Staged Assessment Process
Stage 1: Preliminary Site Investigation (PSI)
The PSI is a non-intrusive assessment that identifies potential contamination sources without any sampling.
Desktop Study:
- Site history review (aerial photos, historical maps, street directories)
- Land title search — past uses and ownership
- Regulatory database search — known contamination, EPA records
- Council records — development history, approvals
- Geology and hydrogeology review
Site Walkover:
- Visual inspection of the site and surrounds
- Evidence of contamination: staining, odours, distressed vegetation, waste
- Existing infrastructure: underground tanks, chemical storage, drains
- Neighbouring property uses (contributing to risk)
PSI Outcome:
- Conceptual Site Model (CSM) showing sources, pathways, and receptors
- Preliminary risk assessment
- Recommendations for DSI (or no further action)
Stage 2: Detailed Site Investigation (DSI)
The DSI involves intrusive sampling to confirm and quantify contamination.
Sampling Plan:
Developed based on PSI findings:
- Sampling locations targeting identified contamination sources
- Depths based on soil type, contaminant mobility, and target media
- Number of samples based on site area and variability
Sampling Methods:
| Method | Application |
|---|---|
| Test pits | Shallow soil investigation (0–3 m) |
| Boreholes | Deeper investigation, groundwater sampling |
| Hand augers | Limited shallow sampling |
| Direct push (CPT) | Continuous profiling, minimal disturbance |
| Groundwater wells | Water table sampling, monitoring |
Laboratory Analysis:
| Contaminant Group | Common Analytes |
|---|---|
| Heavy metals | Arsenic, cadmium, chromium, copper, lead, mercury, nickel, zinc |
| Petroleum hydrocarbons | TRH (C6–C36), BTEX (benzene, toluene, ethylbenzene, xylene) |
| PAHs | Polycyclic aromatic hydrocarbons (16 priority compounds) |
| OCPs / OPPs | Organochlorine and organophosphate pesticides |
| PCBs | Polychlorinated biphenyls |
| Asbestos | Friable and non-friable asbestos in soil |
| PFAS | Per- and polyfluoroalkyl substances (emerging contaminant) |
DSI Outcome:
- Confirmed presence/absence of contamination
- Delineated extent of contamination (plan and depth)
- Quantitative risk assessment (if required)
- Remediation options and cost estimates
Regulatory Framework
| State | Regulator | Key Guidelines |
|---|---|---|
| NSW | EPA | Contaminated Land Management Act 1997 |
| QLD | DES | Environmental Protection Act 1994 |
| VIC | EPA | Environment Protection Act 2017 |
| WA | DWER | Contaminated Sites Act 2003 |
| SA | EPA | Environment Protection Act 1993 |
| TAS | EPA | Environmental Management and Pollution Control Act 1994 |
| ACT | EPA | Environment Protection Act 1997 |
| NT | DEPWS | Environmental Protection Act 2019 |
National Guidelines
- NEPM (National Environment Protection Measure) — Assessment of Site Contamination
- CRC CARE Guidelines — Technical guidance for assessment and remediation
- ANZG (Australian and New Zealand Guidelines) — Fresh and marine water quality
Risk Assessment
Tier 1: Screening Levels
Compare laboratory results to Health Investigation Levels (HILs) and Ecological Investigation Levels (EILs) from the NEPM.
Tier 2: Site-Specific Risk Assessment
Develop site-specific target levels considering:
- Site geology and hydrogeology
- Land use (residential, commercial, industrial)
- Exposure pathways (ingestion, inhalation, dermal contact)
- Sensitive receptors (humans, ecosystems, groundwater)
Tier 3: Detailed Risk Assessment
Probabilistic or advanced modelling incorporating:
- Fate and transport modelling
- Bioavailability studies
- Ecological risk assessment
Common Contamination Sources
| Activity | Contaminants |
|---|---|
| Service stations | Petroleum hydrocarbons, BTEX, TRH |
| Dry cleaners | Chlorinated solvents (PCE, TCE) |
| Landfills | Metals, VOCs, methane, leachate |
| Manufacturing | Heavy metals, solvents, oils |
| Agriculture | Pesticides, herbicides, nitrates |
| Mining sites | Heavy metals, acid mine drainage |
| Defence / fire training | PFAS, explosives |
| Timber treatment | Arsenic, chromium, copper, PCP |
Management and Remedial Options
| Remedial Method | Applicable Contaminants | Key Features |
|---|---|---|
| Excavation and disposal | All | Complete removal, cost depends on disposal |
| Bioremediation | Petroleum hydrocarbons | Cost-effective, requires time |
| Soil vapour extraction | VOCs, petroleum | In-situ, minimal disruption |
| Chemical oxidation | Chlorinated solvents | Rapid reaction, effective |
| Phytoremediation | Metals, some organics | Long-term, low cost |
| Stabilisation / solidification | Metals | Reduces leachability |
| Monitored natural attenuation | Dilute contamination | Long-term, monitoring costs |
Australian Standards
| Standard / Guideline | Purpose |
|---|---|
| NEPM (2013) | Assessment of Site Contamination |
| AS 1726-2017 | Geotechnical site investigations |
| AS 4482.1-2005 | Guide to sampling and investigation of potentially contaminated soil |
| AS 4482.2-1999 | Sampling of groundwater |
| NSW EPA Guidelines | State-specific contaminated land management |
| QLD DES Guidelines | Planning and assessment |