The challenge
Predicting chemical risks to aquifers adds another layer of complexity to groundwater modelling
Maintaining a sustainable groundwater resource is not only a matter of avoiding depletion of available volumes but also requires that beneficial groundwater meets human health and environmental requirements.
Especially where new industry developments are planned, the risks to groundwater quality need to be understood such that real risks can be differentiated from potential risks. This requires combination of knowledge of industry processes to identify plausible scenarios for quantitative assessment, and of biogeochemical processes occurring in the groundwater and in the overlying unsaturated soil and regolith.
This adds another level of complexity in our assessment approach to the already complex groundwater flow modelling.
The challenge is to develop an as realistic as possible chemical transport model that links seamlessly with an unsaturated and saturated zone flow model, while still being practical and manageable from a data input and computer resources point of view.
Another challenge is to identify for given industries which activities have the highest risk of potentially leading to groundwater contamination such that appropriate mitigation measures can be put in place.
Our response
We develop fit-for-purpose physically-based models of chemical transport
Assessment of chemical contamination risks to surficial groundwater requires adequate models that capture the coupled processes of water flow, chemical transport, and potential biogeochemical reactions that impact the mobility and bioavailability of chemical compounds over short and long timeframes.
Source-pathway-receptor analysis involving solute migration pathways through soil and surficial groundwater are typically undertaken to assess how people and the environment could come into contact with chemicals associated with given industrial activities.
For plausible pathways, we develop state-of-the-art physically-based models that integrate the coupled processes at the proper spatial and temporal resolution to provide detailed insights in the potential of chemicals released into the groundwater to affect human health and the environment.
Chemical reactions are evaluated using geochemical models from which simplified attenuation relationships are derived for inclusion in the advection-dispersion solute transport models.
The results
Detailed modelling of chemical risks underpins decision making
We contributed to the National Assessment of Chemicals Associated with Coal Seam Gas Extraction in Australia which was undertaken in recognition of increased scientific and community interest in understanding the risks of chemical use in this industry. Our models contributed to an improved understanding of the occupational, public health and environmental risks associated with chemicals used in drilling and hydraulic fracturing for coal seam gas in an Australian context. An efficient modelling framework was developed to investigate the risks from the storage and handling of water pumped out of CSG wells (flowback and produced water) that contain chemicals originating from coal seam formations and chemical residues from the hydraulic fracturing operation.
In South Australia we contributed to The Goyder Institute's Research project, 'Sustainable expansion of irrigated agriculture and horticulture in the Northern Adelaide Corridor', a collaboration between SARDI, the University of South Australia, Flinders University, The University of Adelaide, and CSIRO. The recent investment in the Northern Adelaide Irrigation Scheme (NAIS) will deliver an additional 20 GL/yr ‘Class A’ recycled water from the Bolivar DAFF Wastewater Treatment Plant for irrigation. To ensure future water users will have access to comprehensive baseline soil information and management tools in their planning and design of irrigated agriculture and horticulture developments, this Goyder Institute’s project has undertaken soil sampling, chemical and hydraulic analysis and a study of available water sources which served as key input to computer simulation-based assessments of risk to soil health and crop productivity. This provided insights in the long-term safe use of water sources by keeping soils healthy and crop production sustainable, given specific agricultural management practices. Our biophysical models have provided detailed insight into risks of salinization, sodification, and increased levels of boron in soils and surficial groundwater.
In the Geological and Biological Assessment Program we assess the potential impacts of shale and tight gas development in the Beetaloo and Cooper Basins on groundwater and the environment. Our work provides independent scientific advice to governments, industry, landowners and communities. Specifically, our impact analysis and management assessments for the Beetaloo and Cooper Basins investigates the potential impacts to groundwater resources and Commonwealth and Territory matters of environmental significance, to support the development of effective monitoring, mitigation and management measures.
In Western Australia, we analysed for Water Corporation the probabilistic risk of wastewater nutrient contamination in relation to water quality objectives. The purpose of this study was to provide a repeatable methodology that quantifies the probability of nutrient concentrations from groundwater flow and solute transport models in order to delineate probable attenuation zones. This probabilistic method helps the operator assess the environmental impact of wastewater infiltration for regulatory compliance and assists in the determination of necessary monitoring locations. Investigations included several sites along the west coast (e.g., Jurien Bay, Geraldton).