research program 3
environmental applications of regolith geoscience
WA Wheatbelt drainage - acidic groundwater - geochemisal risk assessment and evaluation of management options (AG1)
Project Leader : Steve Rogers
Start date and duration: 1.7.04 to 30.6.06 (continuing 06-07)
Participants : CSIRO Land & Water and CSIRO Water for a Healthy Country), Dept of Agriculture WA , Dept of Environment WA
Brief project description :
SUMMARY
This project aims to address the following issues with regard to acid drainage and trace element transport occurring as a result of salinity mitigation engineering drainage schemes in the WA wheat belt:
• Understanding the processes of acidic groundwater in the natural or pre-disturbance regolith, and later, beneath the cleared landscape,
• Forecasting the impacts of engineering drainage on the transport and transformation of trace elements in undrained and drained environments (Geochemical risk assessment).
• Assessment of feasible management options (opportunities and constraints).
• Demonstration/evaluation of appropriate management options including potential productive recovery of minerals, salt and trace elements in drainage waters at relevant scales.
The geochemical risk assessment will involve a consortium of end-users (WA DoE, EEI and WA Agriculture) and research providers (CRC LEME and CSIRO Healthy Country) and will be integrated into the current Avon Regional Drainage Evaluation project undertaken by the WA government - CSIRO Healthy Country consortium.
1. BACKGROUND
Acidic, saline and metal rich groundwater is common is the natural environment of parts of the wheatbelt and southeastern parts of Western Australia . In addition clearing has resulted in further acidification of groundwater and the mobilization of salt, ions, metal and other geochemical elements.
Field observations suggest that the development of acidic seepages in parts of the higher rainfall areas of the wheatbelt is a consequence of groundwater rise. In the northern and eastern areas, acid and saline groundwater enters surface systems as a consequence of engineering drainage. The growing demand to install deep drains and other forms of drainage (eg pumping to protect built and natural assets) highlights the need to better understand and manage acidification, and the potential mobilisation of trace elements, associated with drainage.
The cause of acid groundwater and its further acidification (by either ferrolysis or, sulphide and/or pyrite reactions as a result of acid sulphate soils (ASS) are confusing concepts to the farmer and environmental manager. Research into processes of acidification on the Yilgarn block has identified the cause to be ferrolysis (Mann 1983, McArthur et al, 1991), while on the coastal margins both ferrolysis and ASS are believed to be responsible.
In other words, we have confusion about processes, extent and severity of the issue.
In response to developing salinity and a lack of viable plant based options for salinity management, over 12,000 km of deep open drains have been installed in the wheatbelt. Some of these drains have been found to export waters with a pH of 2-3, a flow of 50 kL/km/day and a salinity of 30,000-50,000 mg/L. Drainage waters in some areas have also been shown to have increased concentrations of aluminium, lead, copper, cadmium, manganese, radionuclides, (eg radium, Dickson 1985) and other trace elements.
Drainage is expanding as a management option of choice and regional drainage proposals has been advanced by several groups ( Avon , Yarra Yarra, Blackwood). One such group, the WA Channel Management Group (representing 400 farmers) wishes to construct a 900 km channel after approval of a 28 km pilot (Farm Weekly 20 April 2004). An evaluation of hydraulic-based elements of this proposal has commenced (NAP-EEI and CSIRO- Healthy Country).
2. GEOCHEMICAL RISK ASSESSMENT
Given the current level of confusion and concern within certain stakeholder groups regarding the potential environmental issues arising from installation of drains in areas of acidic groundwater, it is critical that future NRM decision making is based on sound defendable scientific data and a robust assessment of the potential risks and impacts of a range of drainage scenarios in the wheat belt, with regard to trace element transport and acidity. It is also important that appropriate management strategies are devised for any risks identified.
The specific issues that need to be addressed in the wheatbelt of Western Australia associated with acidic groundwaters are:
• Understanding the processes of acidic groundwater in the natural or pre-disturbance regolith, and later, beneath the a cleared landscape,
• Forecasting the impacts of engineering drainage on the transport and transformation of trace elements in undrained and drained environments, and
• Assessment of feasible management options (opportunities and constraints).
• Demonstration/evaluation of appropriate management options at relevant scales
3. EVALUATION STRATEGY
The proposed acid drainage geochemical risk assessment will be integrated into the current wheatbelt Engineering Evaluation Initiative (EEI), specifically the Avon Regional Drainage Model being developed by the WA government - CSIRO Healthy Country consortium. The current regional drainage model aims to assess the surface and groundwater hydraulics (flows and volumes, salt loads and nutrient loads) resulting from eight different scenarios. This project proposes to undertake a geochemical risk assessment that will provide a forecast and prediction of trace element transportation, transformation and loadings associated with the eight drainage scenario's, identifying if significant risk of trace element transport will occur under any of the planned scenarios. The project will also evalue and demonstrate appropriate management options aimed at minimising environmental risks identified.
4. PROJECT PLAN
The project will comprise four stages.
Stage 1: Data Review
Review of existing data on acid groundwater trace element geochemistry, soil types, regolith architecture, trace element analysis in existing drains, flow regimes and, remote sensing data. This largely desktop study will collate existing monitoring data and results of previous research studies that currently reside with state agencies and various research organisations, and place that data within a GIS framework.
Outputs :
Database and preliminary interpretation. Identification of knowledge gaps and additional data requirements needed to complete regional-scaled risk assessment.
Stage 2: Additional Data Collection
Data required to fill knowledge gaps identified in Stage 1 will be collected in the field in cooperation with EEI and other research activities being undertaken. It is envisaged that this will involve sampling and detailed geochemical analysis of drainage waters, a focussed soil survey (eg of proposed drainage areas), mineralogical analysis of drainage material (Fe precipitates), determination of the presence of secondary sulphide minerals, regolith/landscape models etc. Identification of the detailed data required will only be possible once stage 1 is completed.
Output :
Interim report outlining the geochemical processes, causes and nature of groundwater acidification in the wheatbelt. Complete data set required to calculate trace element transportation, transformation and loadings associated with drainage scenarios.
Stage 3: Integration of geochemical data into Avon Regional Drainage Evaluation scenarios
Calculation of trace element loadings and transport under different Avon regional drainage model scenarios. Integration of geochemistry data into hydraulic scenarios. Identification of potential geochemical risks.
Outputs :
Identification of geochemical risks resulting from wheatbelt drainage scenarios. Application of geochemical risk assessment to inform ecological impact (ecotoxicological) risk assessment. Identification of geochemical risk management options. Reporting consistent with outputs of Avon modelling.
Stage 4: Evaluation and demonstration of options to mitigate or productively utilise acid groundwater, minerals, metals and other constituents .
Examples of potential evaluation/demonstration of options will include:
- Identification of potential environmental impacts resulting from long term storage of trace element rich drainage waters in disposal basins, demonstration of appropriate technologies that minimise any future risks of exposure, transport etc.
- Options for reduction of drainage water pH through mixing with surface run off, demonstration of appropriate mixing ratios and buffering of pH.
- Identification of appropriate technologies for potential, productive recovery of minerals, salt and trace elements in drainage waters
The main aim of Stage 4 will be to demonstrate cost effective appropriate technologies to potential end users in the field with suitable pilot projects.
Outputs :
Recommendation of acid drainage water management options with a focus on technologies appropriate to regional land managers, and community based schemes at appropriate scales
Deliverables (outputs) and expected impacts of research (outcomes):
See above
|
