Groundwater and Hydrogeological Investigation of Five Landfills, North of Brisbane, QLD

Project summary

iEnvi was engaged by a Council north of Brisbane, Queensland to review Environmental Authority (EA) compliance, assess groundwater trends and quantify the risk of leachate impact at five council landfill sites. The scope included data compilation, quality review, statistical and geochemical analysis, hydrogeological interpretation, visualisation and clear, practical recommendations for monitoring and risk mitigation.

What we did (methods)

• Compiled and transformed historical groundwater, surface water and leachate monitoring datasets into a consistent, audit‑ready format.
• Completed a data quality review to identify gaps, reporting inconsistencies and potential non‑detect handling issues.
• Performed statistical analyses (basic statistics including average, minimum, maximum, selected percentiles, t‑tests and correlation analysis) to detect significant differences and temporal trends.
• Applied geochemical characterisation (Piper diagrams) to help distinguish groundwater chemistry sources and identify potential leachate signatures.
• Produced time‑series plots, spatial contour maps and drawings using Surfer software to communicate groundwater level and chemical changes over time.

Investigation objectives

• Establish background groundwater levels and water quality for each monitoring bore.
• Assess differences between upgradient and downgradient groundwater and surface water.
• Compare groundwater and surface water monitoring results against leachate chemistry to identify connections.
• Identify increasing or decreasing trends in key chemical parameters in surface water, groundwater and leachate.
• Define indicators of leachate influence and groundwater–surface water interactions.
• Record basic statistics for each monitoring point to support ongoing compliance reporting.

Key findings (high level)

• Compiled datasets enabled consistent comparison of background and receptor conditions across all five sites.
• Statistical tests and geochemical plots identified locations and parameters that merit focused management and closer monitoring.
• Spatial and temporal visualisation clarified where groundwater elevations and chemistry have changed over time, helping prioritise higher‑risk components at each landfill.

Practical takeaways for Council and site operators

• Use a risk‑based approach to monitoring and management in line with the Guideline: Landfill siting, design, operation and rehabilitation (Queensland Government, 2013).
• Prioritise targeted monitoring at bores showing statistically significant changes or geochemical indicators of leachate influence to reduce regulatory and environmental risk.
• Adopt consistent data handling and reporting procedures to support EA compliance and to speed up future reviews or audits.
• Use visual outputs (time series and spatial maps) to communicate risk to stakeholders and to support operational decisions such as containment, leachate management or remediation options.
• Where monitoring identifies likely leachate influence, consider staged responses (increased monitoring frequency, source control, engineered containment or treatment) based on risk, cost and regulatory requirements.

Benefits to the client

• Clear, evidence‑based identification of higher‑risk monitoring locations and parameters to focus limited budget where it reduces the greatest regulatory and environmental risk.
• Improved defensibility of EA compliance reporting through consistent datasets and documented statistical analysis.
• Faster, more informed decisions about operational controls and remediation priorities, supporting development, transaction or licensing processes.

Next steps we recommended

1. Address any identified data gaps and standardise sampling and reporting protocols across the five sites.
2. Increase monitoring frequency or add monitoring points where statistical and geochemical results indicate potential leachate influence.
3. Apply targeted risk mitigation (source control, containment or treatment) at sites or zones with demonstrated impact or an upward trend in key indicators.
4. Maintain visualisation outputs and update analyses periodically to demonstrate trend direction for regulators and stakeholders.

Why iEnvi

We combine hydrogeological interpretation, practical risk management and clear reporting to help councils and developers reduce regulatory uncertainty and support sustainable outcomes for landfill operation, remediation and future land use.

Contact us to discuss a confidential review of your landfill monitoring or compliance needs: Call 1300 043 684 or use our contact page.