Hydrocarbon Contamination – Identifying and Managing Petroleum-Impacted Soils

Hydrocarbon contamination is a common consideration on former commercial, industrial and service-related properties across NSW. Historical fuel storage, vehicle and machinery operations, workshops, chemical storage and spills can leave petroleum hydrocarbons in soil and fill.

For developers and builders, identifying hydrocarbon contamination early can help prevent unexpected excavation issues, disposal costs and construction delays.

At Confluence Environmental, we help property owners, developers and contractors investigate petroleum-impacted soils, determine the nature and extent of contamination and develop practical strategies for management or remediation.

Where Does Hydrocarbon Contamination Originate?

Petroleum hydrocarbons can enter soil through activities including:

• Fuel storage tanks and bowsers

• Service stations

• Vehicle and machinery storage

• Mechanical workshops

• Fuel and oil spills

• Chemical storage areas

• Industrial operations

• Leaking underground or above-ground infrastructure

• Historical waste disposal

• Uncontrolled fill

Contamination may be obvious, such as visible staining or a strong hydrocarbon odour, but it can also be present without obvious signs at the surface. This makes historical land use an important part of any contamination assessment.

What Are Petroleum Hydrocarbons?

Petroleum hydrocarbons are a broad group of compounds found in fuels, oils and other petroleum-based products. Environmental investigations commonly assess:

• Total Recoverable Hydrocarbons (TRH)

• BTEXN – benzene, toluene, ethylbenzene, xylenes, and naphthalene

• Polycyclic Aromatic Hydrocarbons (PAHs)

• Volatile Organic Compounds (VOCs)

Different petroleum products behave differently in the environment. Some compounds are more volatile, while heavier hydrocarbons can remain within soil. Understanding the type of petroleum impact is therefore important when assessing potential risks.

What Are Signs of Hydrocarbon-Impacted Soil?

Potential indicators during a site inspection can include:

• Hydrocarbon staining

• Petroleum or chemical odours

• Unusual soil discolouration

• Oily or greasy material

• Buried drums or tanks

• Evidence of historical spills

• Fuel infrastructure

• Stockpiled or imported fill

• Elevated field screening results

A Photoionisation Detector (PID) can be used during intrusive investigations to screen soils for volatile organic compounds and identify areas requiring further assessment. Field observations and PID readings are screening tools. Laboratory analysis is generally required to characterise contamination and compare concentrations against relevant assessment criteria.

How is Hydrocarbon Contamination Investigated?

Investigation should be designed around the site's history, potential contamination sources and proposed future use.

A Preliminary Site Investigation (PSI) typically considers historical aerial imagery, previous land use, environmental records, site observations and potential Areas of Environmental Concern.

Where the PSI identifies potential contamination, a Detailed Site Investigation (DSI) may be recommended.

A DSI can involve:

• Targeted or systematic soil sampling

• Test pits or boreholes

• PID screening

• NATA accredited laboratory analysis

• Assessment of fill and natural soils

• Contamination delineation

• Assessment of potential exposure pathways

The objective is to determine what is present, where it is located, how extensive it is and whether it presents a potential risk.

How Are Hydrocarbon Results Assessed?

Laboratory results need to be considered alongside the site's proposed use, soil conditions and potential exposure pathways.

Assessment may include:

• Health Investigation Levels (HILs)

• Health Screening Levels (HSLs)

• Ecological Investigation Levels (EILs)

• Ecological Screening Levels (ESLs)

• Management Limits

HSLs are particularly relevant to petroleum hydrocarbons because they consider potential human health risks associated with vapour intrusion and direct contact.

Management Limits consider additional factors, including the potential for petroleum hydrocarbons to form non-aqueous phase liquid (NAPL) or affect buried infrastructure.

Managing Petroleum-Impacted Soil During Construction

Construction can change the risk profile of a contaminated site. Excavation, trenching, landscaping and service installation can expose previously buried material.

Before disturbing suspected impacted soil, the project team should understand:

• Where contamination is located

• How deep it extends

• What contaminants are present

• Whether excavated soil can be reused

• Whether waste classification is required

• What disposal pathway is appropriate

A Construction Environmental Management Plan (CEMP) and Unexpected Finds Protocol (UFP) can also provide a framework for managing unexpected contamination during ground disturbance.

How Confluence Environmental Can Help

Confluence Environmental provides practical contaminated land services across NSW, including:

• Preliminary Site Investigations

• Detailed Site Investigations

• Hydrocarbon contamination assessments

• Soil sampling and laboratory analysis

• PID screening

• TRH, BTEXN and PAH analysis

• Contamination delineation

• Waste classification

• Remediation advice

• Validation investigations and reporting

Need Hydrocarbon Contamination Advice?

If you're purchasing, developing or excavating a property with a history of fuel storage, heavy machinery, workshops, industrial activities or suspected petroleum spills, early investigation can help identify risks before they become construction issues.

Confluence Environmental provides PSI, DSI, hydrocarbon contamination, soil, waste classification and validation services across NSW.

Call 1300 855 447 or contact Confluence Environmental to discuss your environmental consulting requirements.