Geraldton Port groundwater risk assessment
Client name: Mid West Ports Authority
Duration: 2012 - 2018
Location: Geraldton, WA, Australia
A clear understanding and a strategic risk-based approach resulted in a pragmatic solution for a busy operational Port with minimal logistical requirements and reduced time frames to undertake the investigations
When historical site investigations identified soil and groundwater contamination to be present Mid West Ports Authority engaged Coffey to undertake a detailed site investigation of the fully operational Port to characterise the nature and extent of impacts.
The objective of the investigations was to assist Mid West Ports Authority in meeting Department of Water and Environmental Regulation (DWER) requirements demonstrating that the contamination status of the Port land had been assessed and was being managed in accordance with the CS Act (2003) and other relevant regulations.
The investigation of the complex site conditions resulted in identifying the presence of elevated nutrients in groundwater and subsequently ascertaining the associated ecological risks of the discharge of these nutrients into the marine environment.
Clearly established terms of reference created time efficiencies, cost savings and led to an informed and practical solution
Our team applied a strategic risk-based approach to the project focusing on potential exposure pathways and effects on sensitive receptors, rather than complete site characterisation. This approach, agreed upon with the client, the Contaminated Sites Auditor and the DWER prior to commencement of investigations, lead to time efficiencies and cost savings over the duration of the project.
Gaining an early understanding of the data gaps across the site and then putting them through a thorough analysis enhanced the strategic risk-based approach. It allowed for a more targeted and robust investigation design to be developed leading to increased success in closing out of data gaps.
A practical approach was developed to assess the potential risk to the marine environment
Following the data gap analysis and development of a preliminary conceptual site model, our team undertook a detailed site investigation. This revealed the presence of nutrients in groundwater at concentrations well above assessment criteria, most notably in locations adjacent to the Port’s harbours where historical activities have resulted in increased nutrient loadings in soil and groundwater.
Coffey then conducted a groundwater risk assessment to understand the ecological risk associated with the discharge of nutrients into the marine environment. Focusing on calculating nutrient mass flux concentration and mass discharge rather than localised groundwater concentrations meant we were able to determine risk to the marine environment based on loading at the point of exposure.
By undertaking further investigations to calculate mass flux and mass discharge estimates our team were able to characterise source strength and establish a direct measurement of nutrient loading to receptors.
On a large site like Geraldton Port, this method is particularly useful to better understand the source zone behaviour. In addition, the mass discharge estimate allows for the mixing at the groundwater and surface water interface to be accounted for. Calculating mass flux and mass discharge provides quantifiable lines of evidence enabling the risks to receptors to be better evaluated.
Using the outcomes of the mass flux and mass discharge calculations an assessment of risk to potential down-gradient receptors was undertaken. It revealed no current unacceptable risk to the ecosystem was present based on concentrations of nutrients entering the harbour via groundwater.
Overall this approach improved the evaluation of risk associated with identified source areas and was considered a practical approach to further understanding potential risk to the marine environment.