Underground Petroleum Storage Systems (UPSS): Modern Risk Management, Investigation Strategies and Emerging Technologies

The Changing Risk Landscape of UPSS Sites

Underground Petroleum Storage Systems (UPSS) remain one of the most common sources of soil and groundwater contamination across New South Wales. Legacy service stations, fuel depots, industrial facilities and commercial sites frequently present environmental risks associated with ageing tanks, fuel infrastructure failure and historical fuel handling practices.

While many sites appear stable on the surface, undetected leaks, vapour migration and residual contamination can persist for decades. Modern environmental management of UPSS sites is no longer reactive - it is proactive, risk-based and increasingly technology-driven.

Across Sydney, Newcastle, the Central Coast and regional NSW, regulators, developers and asset owners are shifting toward early detection, structured investigation and long-term risk control to minimise environmental liability and protect land value.

For broader contaminated land context, see our contaminated land services.

Modern Investigation Approaches for UPSS Sites

Traditional investigations focused primarily on confirming the presence of contamination. Today, investigations are designed to understand the full contaminant behaviour and long-term risk profile.

Modern UPSS investigations typically combine:

• Targeted soil and groundwater sampling aligned with Detailed Site Investigation (DSI) frameworks

• High-resolution site characterisation (HRSC) to define plume geometry and migration pathways

• Soil vapour and vapour intrusion assessment where volatile hydrocarbons are present

• Conceptual Site Model refinement using Conceptual Site Model principles

• Assessment of receptors including buildings, utilities, groundwater and ecological pathways

These approaches allow for more accurate delineation of contamination, better remediation planning and reduced long-term uncertainty.

Emerging Technologies Transforming UPSS Assessment

The environmental consulting industry has moved significantly beyond traditional drilling and sampling. Emerging technologies are improving detection sensitivity, reducing investigation time and increasing confidence in environmental decision-making.

Key advancements include:

Real-time field screening tools
Portable PID/FID and advanced soil gas instruments now allow rapid identification of hydrocarbon hotspots and vapour migration zones, guiding targeted sampling.

High-resolution site characterisation (HRSC)
Continuous soil core logging, membrane interface probes and laser-induced fluorescence technologies enable precise identification of fuel contamination distribution.

Groundwater monitoring optimisation
Improved monitoring well design and data logging systems allow better tracking of dissolved phase hydrocarbons and plume behaviour.

Vapour intrusion modelling
Advanced modelling tools help assess indoor air risks and support risk-based remediation decisions for redevelopment sites.

These technologies support more defensible environmental outcomes and improve long-term risk management.

Remediation Strategies for Petroleum-Impacted UPSS Sites

Remediation of petroleum-impacted sites is rarely a one-size-fits-all process. Effective remediation requires a clear understanding of contaminant phase behaviour (free phase, dissolved phase and vapour), plume stability, site geology and receptor risk. In most cases, a structured Remediation Action Plan (RAP) is developed to define the most appropriate, risk-based remediation approach.

Modern remediation typically integrates multiple strategies rather than relying on a single method.

Source Removal and Excavation

Where heavily impacted soils, legacy fuel infrastructure or concentrated hydrocarbon hotspots are present, excavation and source removal remains one of the most effective remediation techniques. This approach eliminates the primary contamination source and reduces ongoing groundwater and vapour migration risk.

Excavation programs are carefully planned to:

• Remove free-phase and highly impacted soils

• Prevent spreading contamination during earthworks

• Manage odour, vapours and worker exposure risks

• Control groundwater inflow where present

• Track contaminated soil using appropriate waste classification and disposal pathways

For many redevelopment sites, targeted excavation significantly accelerates remediation timeframes and reduces long-term liability.

For broader discussion on contamination management during earthworks, see our article on unexpected contamination on site.

In-Situ Chemical Oxidation (ISCO)

In-situ chemical oxidation is widely used to treat dissolved petroleum hydrocarbons within groundwater and saturated soils. Oxidising agents (such as persulfate or permanganate) are injected into the subsurface to chemically break down hydrocarbon contaminants.

ISCO is particularly effective where:

• Dissolved phase plumes are migrating within groundwater

• Excavation is impractical due to depth or infrastructure constraints

• Rapid contaminant mass reduction is required

• Groundwater protection is a priority

Successful ISCO requires careful design based on plume geometry, groundwater flow conditions and oxidant distribution modelling. Improper application can reduce effectiveness or lead to incomplete treatment, highlighting the importance of detailed site characterisation.

Bioremediation and Enhanced Natural Degradation

Bioremediation enhances naturally occurring microbial processes that break down petroleum hydrocarbons into harmless end products. This may involve the addition of oxygen, nutrients or specialised microbial cultures to stimulate biodegradation within soil or groundwater.

Bioremediation is commonly applied where:

• Contamination is widespread but relatively low to moderate concentration

• Long-term plume stabilisation is required

• Site conditions support microbial activity

• Sustainable remediation outcomes are preferred

Bioremediation is often combined with monitored natural attenuation (MNA), where long-term monitoring confirms contaminant reduction and plume stability over time.

Soil Vapour Extraction (SVE) and Vapour Risk Control

Petroleum hydrocarbons often generate vapours that migrate through soil and can pose risks to buildings, confined spaces and underground infrastructure. Soil vapour extraction removes volatile hydrocarbons from unsaturated soils using controlled vacuum systems.

SVE is commonly used where:

• Vapour intrusion risk to buildings exists

• Volatile fuel components are present in shallow soils

• Source removal alone is insufficient

• Long-term vapour control is required

Vapour risk is frequently assessed alongside groundwater and soil investigations to ensure complete risk management. See our discussion on <a href="/news-and-insights/what-happens-after-a-dsi">what happens after a detailed site investigation</a> for how remediation integrates with risk assessment and planning.

Monitored Natural Attenuation (MNA)

In some cases, active remediation may not be necessary where contamination is stable, contained and naturally degrading. Monitored Natural Attenuation relies on long-term monitoring to confirm that contaminant concentrations continue to decline and that the plume is not expanding.

MNA is appropriate where:

• Contamination is stable and not migrating toward receptors

• Natural biodegradation is occurring

• Risk to human health and groundwater is low

• Active remediation would provide limited additional benefit

This approach is often supported by structured environmental monitoring programs and ongoing risk assessment.

Integrated and Risk-Based Remediation

Modern remediation rarely relies on a single method. Instead, remediation strategies are tailored to site conditions and often combine:

• Source removal and targeted excavation

• Groundwater treatment technologies

• Vapour risk management

• Long-term monitoring and risk control

The objective is not simply to remove contamination, but to make the site suitable for its intended land use while minimising environmental impact and long-term liability.

For more on how remediation integrates into the broader contaminated land process, see our article on what councils mean by further contamination assessment.

Managing Long-Term Risk at UPSS Sites

Not all UPSS sites require full remediation. In many cases, long-term risk management is the most appropriate strategy.

Risk management tools may include:

• Environmental Management Plans to control disturbance and exposure

• Groundwater and vapour monitoring programs

• Engineering controls and containment systems

• Site use restrictions or management plans

• Periodic environmental review aligned with regulatory expectations

These approaches ensure environmental risks remain controlled while allowing continued site use or redevelopment.

Regulatory and Financial Implications

Poorly managed UPSS contamination can lead to:

• Regulatory intervention or EPA notification

• Development approval delays

• Increased remediation cost

• Reduced land value or transaction risk

• Long-term environmental liability

Conversely, early identification and proactive management significantly reduce long-term cost and improve planning certainty.

Why Early UPSS Assessment Matters

Across Sydney, Newcastle and the Central Coast, many redevelopment sites include legacy fuel infrastructure or historical petroleum contamination. Early environmental assessment allows:

• Clear understanding of contamination extent

• Risk-based remediation planning

• Integration with development timelines

• Reduced uncertainty and cost

• Improved regulator and auditor confidence

UPSS contamination is manageable - but only when properly understood.

Specialist Support for UPSS Investigation and Management

At Confluence Environmental, we support developers, asset owners and consultants across NSW with:

• Preliminary and Detailed Site Investigations

• High-resolution site characterisation

• Petroleum hydrocarbon assessment and vapour risk evaluation

• Remediation Action Plans and implementation support

• Groundwater and vapour monitoring programs

• Validation and regulatory reporting

We combine practical field experience with modern investigation and remediation strategies to deliver defensible, regulator-aligned outcomes.

Learn more about our UPSS services.