Simple UPSS Petroleum Contamination Groundwater Remediation Solution for Council Depot, Central‑Northern NSW

Project summary

iEnvi provided contaminated‑land consulting services for multiple Council depots in central–northern New South Wales. Services included removal, validation and replacement of underground petroleum storage systems (UPSS/USTs), site assessment, fate‑and‑transport modelling, vapour assessment and a pragmatic remediation strategy combining targeted product removal with monitored natural attenuation (MNA).

Site issues, testing and findings

• Leak from a UPSS resulted in free product (LNAPL) on the water table and a dissolved hydrocarbon plume in groundwater.
• iEnvi completed a site conceptual model, aquifer pump testing and geological assessment to define hydrogeology and contaminant distribution.
• Weekly manual bailing of free product was implemented by trained Council staff; this removed approximately 10% of estimated product on groundwater over 1.5 years (project records supplied by the client).
• Fate‑and‑transport modelling and monitoring data indicated dissolved hydrocarbon concentrations were decreasing in lateral extent and concentration over time, consistent with biological attenuation processes at the site.
• Vapour risk was assessed and concluded to be low given the site lithology and depth to source; vapour mitigation measures were not required for the proposed land uses at the time of assessment.

Remediation strategy and justification

The preferred, cost‑efficient approach combined:

1. Targeted, low‑tech removal of mobile product (manual bailing) to reduce near‑source mass and immediate off‑site migration risk.
2. Monitored natural attenuation (MNA) as the primary long‑term management option for the dissolved plume, supported by monitoring wells, analytical groundwater sampling and fate‑and‑transport modelling.
3. An environmental management plan and monitoring program to track natural attenuation indicators (concentrations, redox parameters, electron acceptors, hydrocarbon breakdown products) and to trigger active remediation if trends reversed or receptors became at risk.

Outcomes and benefits

• Observed reduction in dissolved hydrocarbons and shrinking plume footprint during the monitoring period.
• Practical removal of a measurable portion of the free product using trained Council staff, avoiding mobilisation and cost of continuous mechanical extraction systems.
• Significant cost avoidance relative to large‑scale active remediation options, achieved by using a multiple‑lines‑of‑evidence approach to justify MNA where appropriate.

Practical takeaways for asset owners and developers

• Early, focused site characterisation (conceptual site model, hydrogeology, source strength and vapour pathways) enables lower‑cost, lower‑risk management choices.
• Low‑tech product removal (trained staff bailing or skimming) can be effective at reducing immediate LNAPL mass and buying time while MNA reduces dissolved concentrations — but it must be demonstrated through monitoring and trigger levels.
• MNA is a valid remedial option when supported by multiple lines of evidence (chemical trends, biodegradation indicators, hydrogeology and modelling) and formalised in a monitoring and management plan.

Want help assessing a UPSS, LNAPL or groundwater issue?

iEnvi can prepare a rapid, commercially focused assessment (CSM, monitoring plan and risk‑based remediation options) that clarifies cost, timing and approval risk. Call us on 13000 43684 or visit our contact page to discuss your site.