Groundwater Hydrocarbon Sheen vs. Measurable LNAPL: What’s the Difference and When Must You Notify the EPA in Australia?

Understanding the Difference

Undissolved hydrocarbon (i.e. fuels and oils) contamination in groundwater may appear as either a sheen or measurable Light Non-Aqueous Phase Liquid (LNAPL). Knowing the difference is critical for assessing risk and ensuring compliance with Australian environmental regulations.

Feature	Hydrocarbon Sheen	Measurable LNAPL
Appearance	Thin, iridescent film on water	Distinct /field-measurable floating layer of hydrocarbons
Thickness	<0.001 mm (microns)	1 mm to several cm’s or more
Measurement	Visible, but not measurable	Measurable using an oil-water interface probe
Risk Level	Low to moderate	High – ongoing contamination source
Regulatory Reporting Required	Case-by-case	Mandatory in all Australian states & territories

⚠️ A sheen may indicate nearby LNAPL. Further assessment (e.g., groundwater sampling or additional wells) may be required to confirm contamination and determine if notification is needed.

When Is Notification Required?

The risk of harm to human health or the environment determines whether contamination must be reported as well as state-specific regulations relating to NAPLs. Key risk factors include:

✅ Proximity to sensitive receptors – drinking water bores, wetlands, or surface water.
✅ Potential vapour intrusion – enclosed spaces where hydrocarbon vapours may accumulate.
✅ Groundwater use – is the aquifer used for drinking or irrigation?
✅ Migration potential – hydrocarbons moving offsite to neighbouring properties.
✅ Fire or explosion hazards – volatile hydrocarbons in confined spaces.

Even a thin sheen can signal underlying contamination. If LNAPL is measurable, in many cases it should be reported – see below.

Regulatory Notification Requirements by State

State/ Territory	Hydrocarbon Sheen Notification	Measurable LNAPL Notification & Responsible Parties	Key Legislation/Agency & Relevant Sections/Publications	Notes on Reporting Responsibilities
VIC	Required if contamination meets ‘notifiable contamination’ criteria under the Environment Protection Act 2017.	Presence of LNAPL in soil/groundwater is considered notifiable contamination; the person in management or control of the land must notify EPA Victoria.	Environment Protection Act 2017; Environment Protection Regulations 2021; EPA Victoria	Person in management or control of land is responsible. Consultant advises. Auditor’s reporting depends on engagement and findings.
NSW	Not necessarily required; assessment determines if significant risk exists.	Generally required if significant risk is identified; reported by site owner or polluter to NSW EPA.	Contaminated Land Management Act 1997; NSW EPA	Owner or polluter is primarily responsible. Consultant advises. Auditor has specific reporting requirements.
QLD	May require notification based on risk assessment.	Generally required if significant risk is identified; reported by site owner, occupier, or person responsible to Department of Environment, Tourism, Science and Innovation (DETSI).	Environmental Protection Act 1994; DETSI	Owner, occupier, or person responsible is primarily responsible. Consultant advises. Auditor’s reporting depends on engagement and findings.
WA	Case-by-case basis; determined by risk assessment.	Generally required if significant risk is identified; reported by site owner, occupier, or person with knowledge to Department of Water and Environmental Regulation (DWER).	Contaminated Sites Act 2003; DWER	Owner, occupier, or person with knowledge is responsible. Consultant advises. Auditor’s reporting depends on scope of engagement.
SA	Further testing or assessment usually required to determine reporting obligation.	Generally required if significant risk is identified; reported by site owner, occupier, or person responsible to EPA SA.	Environment Protection Act 1993; EPA SA	Owner, occupier, or person responsible is primarily responsible. Consultant advises. Auditor has specific reporting requirements.
TAS	Generally required; assessment needed to confirm reporting obligation.	Notification required within 7 days of awareness. Relevant persons, including infrastructure owners, system operators, and landowners, must notify EPA Tasmania.	Environmental Management and Pollution Control Act 1994 (EMPCA) & Regulations; EPA Tasmania	Infrastructure owner, system operator, and landowner are responsible. Consultant advises. Auditor’s reporting depends on scope of engagement.
ACT	Case-by-case basis; determined by risk assessment.	Generally required if significant risk is identified; reported by site owner or occupier to EPA ACT.	Environment Protection Act 1997; EPA ACT	Owner or occupier is responsible. Consultant advises. Auditor’s reporting depends on scope of engagement.
NT	May require notification based on risk assessment.	Generally required if significant risk is identified; reported by the person responsible to NT EPA.	Waste Management and Pollution Control Act 1998; NT EPA	Person responsible is primarily responsible. Consultant advises. Auditor’s reporting depends on scope of engagement.

This table is a simplified overview and IS NOT legal advice. Environmental regulations are complex and fact-specific.

Environmental consultants play a crucial role in identifying and assessing contamination and advising clients on compliance with environmental laws. However, they are generally not legally obligated to report contamination directly to environmental authorities.

Asite owner or operator that finds out they do have reportable contamination, does however generally have a legal obligation to report the contamination to the environmental regulator in the state. From there they regulator may take weeks or even years to follow up on the site depending on the risk level, and the regulator’s resources.

Characterising suspected groundwater contamination is also mandatory in most states. iEnvi has a long history of completing investigations, risk assessment, remediation and expert advice for petroleum, chemical and other fuel leaks across Australia and internationally.

If you have a problem with petroleum/fuel or other chemical leaks, speak with iEnvi by emailing us at [email protected] and one of our expert consultant will be able to steer you in the right direction.

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