Appendix Z. Groundwater Assessment Supplementary Report. Document Name i Insert Month/Year

Transcription

1 Appendix Z Groundwater Assessment Supplementary Report Document Name i Insert Month/Year

2 Australasian Groundwater and Environmental Consultants Pty Ltd Level 2 / 15 Mallon Street Bowen Hills, QLD 4006 Australia ABN T F brisbane@ageconsultants.com.au JST/ae (G1438A.Elimatta) 14 November 2013 RE: ELIMATTA COAL PROJECT RESPONSE TO GOVERNMENT SUBMISSIONS 1 INTRODUCTION AustralAsian Resource Consultants Pty Ltd (AARC) is coordinating the environmental approvals process for the Elimatta Coal Project on behalf of New Hope Group. Australasian Groundwater and Environmental Consultants Pty Ltd (AGE) prepared the technical report for the groundwater impact assessment. AARC has now requested AGE respond to submissions from the State Government on the groundwater impact assessment report, which is a component of the Environmental Impact Statement. 2 SCOPE OF WORK The objective of the assessment was to respond to the Government submissions below. The report needs to clearly identify the groundwater flow directions for all the aquifers in the area, both locally and regionally, any impacts of geological structures in the area. Refer also to groundwater-related comments provided elsewhere in this attachment. Regional scale studies in the Surat Basin have generally reported that groundwater flow occurs from the recharge areas (that outcrop in an arc from Warwick to Roma) to the south, south-west and west (QWC 2012). The exception to this, is the northern portion of the Surat Basin that is in Fitzroy River catchment and north the Great Dividing Range. In the Wandoan region (north of the Great Dividing Range), available data indicates groundwater generally flows towards the north, north-east. Hodgkinson et al. (2009) noted that topography controls hydraulic gradients in shallow systems with groundwater flow from recharge areas towards the south, south-west and west, but with a minor northern flow component in some aquifers. Water level measurements in the monitoring bore network installed in the Walloon Coal Measures for the Elimatta Project confirm this northerly groundwater flow direction. Asia Pacific LNG (2012) assessed flow directions in the deeper underlying Hutton Sandstone and reported a northerly flow direction (refer Figure 2.1 below) in the region north of the Great Dividing Range. Head Office Level 2 / 15 Mallon Street, Bowen Hills, QLD 4006, Australia T F brisbane@ageconsultants.com.au Newcastle Office Harbour Pier, Shop 8, 21 Merewether Street, Newcastle, NSW 2300, Australia T F newcastle@ageconsultants.com.au

3 Page 2 Figure 2.1: Groundwater levels in the Hutton Sandstone (from Australia Pacific LNG (2012) The EIS indicates that, groundwater levels indicate topographic control, rather than conductivity variability or faulting as controls on aquifer flow behaviour. It is suggested that this inconsistency be clarified in the EIS, including further details on fault style (reverse), fault mineralisation or evidence of current stress regimes that would make the faulting or conductivity variability appear more likely to impair conductivity. Further clarification is also sought to validate the model used in the EIS in relation to the predicted extent of depressurization. In greenfield areas undisturbed by significant extraction of groundwater, such as in the Elimatta region, the influence of structures such as faults, or changes in hydraulic conductivity on groundwater levels is commonly not detectable in groundwater levels. The effect of structures on water levels in greenfield sites is typically a small scale influence that cannot be detected with widely spaced drilling and monitoring bores installed for an EIS. At the scale of the investigation, topography has the most obvious influence on the groundwater levels and flow directions. It is only when mining commences and depressurisation of the coal seams and overlying strata occurs, that the influence of structure or hydraulic conductivity variability may become apparent. Faults can act as barriers to groundwater flow, or serve to enhance flow along the fault plane, but these local scale effects cannot be observed from widely spaced groundwater monitoring networks or drilling programs.

4 Page 3 Insite Geology (2009) assessed the geotechnical conditions at the Elimatta Project. The geotechnical study identified five main faults interpreted from various exploration programmes at Elimatta. All faults were inferred to be sub-vertical normal faults with the distance of throw from 1 m to 35 m as shown in Figure 2.2 below. The faults generally trend down-dip, and will be gradually removed by mining. During the mining process, the faults will be exposed in the highwall and are likely to drain and depressurise along the fault plane. Features of such fault zones include the undamaged rock, the damaged (fractured) zone and the core (gouge) zone. The hydraulic properties of these zones will control the magnitude of the drainage and depressurisation. The water pressures and the cross sectional area of the fractured material around the fault plane control the volume and rate of water transferred through the fault. The cross sectional area of a fault plane is typically much less than the cross sectional area of other strata exposed by mining (including the coal seams). This implies then that faults typically only contribute in a minor way to the depressurisation and drainage induced by mining. The groundwater model developed for the EIS will be reviewed after ten years of mining to determine if the predicted zone of depressurisation and impacts are accurate. Review and recalibration of the groundwater model will be undertaken as required by the conditions of the Project s Water Licence issued under the Water Act 2000.

5 Page 4 Figure 2.2: Faults and fault throw (from Insite Geology 2008)

6 Page 5 The EIS is suggested to identify the regional groundwater resources that may be impacted by the Project. If the Juandah Coal Measures (JCM) is to be listed as a separate aquifer to the Great Artesian Basin (GAB), please specify the Juandah Coal Measures and the GAB differently. The GAB is not a geologic basin, but a hydrogeological basin comprising various parts of other geologic basins. Within the project area, the GAB includes the Surat Basin and the upper sedimentary sequences of the Bowen Basin. The main aquifer systems in the GAB in the Project area are the Gubberamunda Sandstone, Springbok Sandstone, Hutton Sandstone and Precipice Sandstone. Mining is only predicted to impact on groundwater levels in the Juandah Coal Measures, the upper unit within the Walloon Coal Measures Subgroup. Mining will not impact upon groundwater levels and the availability of water in the aquifers of the GAB. The Gubberamunda Sandstone is remote from the site, and the Hutton and Precipice Sandstones are located at significant depth below the proposed mining sequence. While the Springbok Sandstone is shown on geological maps as being present in the project area, exploration drilling within the lease did not detect an upper sandstone unit that could be classified as an aquifer. 3 REFERENCES Australia Pacific LNG, (2012), Upstream Phase 1 Reedy Creek Aquifer Injection Trial Management Plan Environmental Authority No PEN Q MP-001. Queensland Water Commission, (2012), Underground Water Impact Report for the Surat Cumulative Management Area, 18 July Hodgkinson J., Preda M., Hortle A., McKillop M. & Foster L., (2009), The Potential Impact of Carbon Dioxide Injection on Freshwater Aquifers: The Surat and Eromanga Basins in Queensland, Department of Employment, Economic Development and Innovation, Brisbane. Insite Geology, (2009), Elimatta Coal Project Southern Queensland, Report on Assessment of Geotechnical Conditions for Northern Energy Corporation Limited, February Please contact me if you have any queries, or if any clarification is required. Yours faithfully, JAMES S. TOMLIN Principal Hydrogeologist Australasian Groundwater and Environmental Consultants Pty Ltd