The impacts of coal resource development in the Maranoa-Balonne-Condamine subregion could either extend beyond the subregion boundary, or not extend as far as the subregion boundary due to remoteness from development. Defining the preliminary assessment extent (PAE) allows the asset register to be compiled in parallel with the assessment of the resource (Sander et al., 2014) and the development of the coal resource development pathway (see pending companion product 2.3 for the Maranoa-Balonne-Condamine subregion as listed in Table 2) for the Maranoa-Balonne-Condamine subregion.
The following were considered in developing the PAE for the Maranoa-Balonne-Condamine subregion:
- the location of CSG and large coal mining developments
- modelling results from the Office of Groundwater Impact Assessment (OGIA; Queensland Water Commission, 2012)
- groundwater management units
- streamflow characteristics.
The Maranoa-Balonne-Condamine PAE (Figure 3) is the extent of groundwater and surface water systems that may potentially be impacted by coal resource developments in the subregion.
Figure 3 Preliminary assessment extent (PAE) of the Maranoa-Balonne-Condamine subregion
Data: Department of Natural Resources and Mines (Dataset 29 and Dataset 30)
1.3.1.3.1 Groundwater considerations
Predicted water level impacts, reported in the Underground Water Impact Report (UWIR) for the Surat Cumulative Management Area (Queensland Water Commission, 2012), were considered in developing the groundwater PAE. The predicted water level impacts were calculated using a regional groundwater flow model (MODFLOW 2005, Queensland Water Commission, 2012) designed to predict the impacts of groundwater extraction by the petroleum and gas extraction industries within the Queensland portion of the Surat and Bowen basins.
The 95th percentile maximum groundwater drawdown areas for the Walloon Coal Measures, Hutton Sandstone, Precipice Sandstone and Clematis Sandstone hydrogeological units (Queensland Water Commission, 2012) were used to determine the lateral extent of the 1 m drawdown boundary for each geological unit (refer to Figure 21 in companion product 1.1 for the Maranoa-Balonne-Condamine subregion (Welsh et al., 2014)). To ensure all potentially affected assets were included within the PAE, a 100 km buffer was applied to the 1 m drawdown boundary for each hydrogeological unit. The resulting 100 km buffer boundaries were combined and the most laterally extensive boundaries were incorporated into the PAE boundary. The eastern PAE boundary, where it extends into the Clarence-Moreton Basin, was a combination of a 50 km buffer of the 1 m drawdown extent and the outer boundary of the Marburg Sandstone (a lateral equivalent of the Hutton Sandstone).
Significantly, a portion of the 1 m drawdown boundary for both the Walloon Coal Measures and Hutton Sandstone extends north, beyond the Maranoa-Balonne-Condamine subregion boundary toward the Hutton Sandstone recharge areas. The PAE boundary in this area follows the northern extent of the Hutton Sandstone geologic unit, which encompasses the northern extent of the Walloon Coal Measures. Drawdown in both the Hutton Sandstone and the Walloon Coal Measures is a result of extraction within the Maranoa-Balonne-Condamine subregion.
It is unlikely that the units underlying the Hutton Sandstone will be impacted by extraction of groundwater from within the Maranoa-Balonne-Condamine subregion. For example, north of Roma, the modelled impact to water levels in both the Precipice and Clematis sandstones is a result of CSG extraction from the Bandanna Formation of the Bowen Basin in the Fairview and Spring Gully gas fields, which are located outside the subregion. Therefore the 1 m drawdown extents for the Precipice and Clematis sandstones north of Roma were not considered in developing the PAE.
The PAE allows full assessment of impacts to the Hutton Sandstone and shallower aquifers as well as those areas of the Clematis and Precipice sandstones that may be impacted by CSG-related groundwater extraction from within the Maranoa-Balonne-Condamine subregion. Furthermore, in the east, the PAE encompasses current operating (Commodore, New Acland, Kogan Creek and Cameby Downs) and proposed (The Range) coal mines.
1.3.1.3.2 Surface water considerations
The CSG and large coal mining developments in the Maranoa-Balonne-Condamine subregion are mostly at upstream and headwater areas of the Condamine-Balonne, Maranoa, Moonie and Weir rivers. To examine their flow volume and seasonal patterns, data from the following stream gauging stations were analysed: Balonne River at Surat (422220A) and at Weribone (422213A); Maranoa River at Cashmere (422404); Moonie River at Fenton (417204), Weir River at Jericho (416205) and Dawson River at Taroom (130302) (Figure 3). These stations are at the most downstream location in the rivers within the Maranoa-Balonne-Condamine subregion. The following summarises their flow characteristics:
- The Maranoa River at Cashmere on average flows for less than 30% of the time, mostly during November to March. On average, river flow is less than 0.080 m3/second (6.9 ML/day) for 80% of days.
- The Condamine-Balonne River at Weribone and Surat gauging stations on average flows for about 75% and 60% of the time, respectively. The median daily flow is about 1 m3/second (86.4 ML/day) and 0.35 m3/second (30.24 ML/day) respectively.
- The Moonie River at Fenton is an ephemeral river flowing for about 40% of the time on average. For some years (e.g. 1971 to 1972, 1974 to 1975, 1990 to 1991) the gauging station recorded zero flow for nine or more months in the year.
- The Weir River is also highly ephemeral, flowing for 32% of the time on average.
- The Dawson River at Taroom flows for more than 95% of the time with median flows of 0.3 m3/second (226 ML/day). This indicates a baseflow contribution to the flow resulting in a sustained dilution capacity throughout the year (DNRM, 2014).
Most rivers in the Maranoa-Balonne-Condamine subregion are ephemeral, with temporary or intermittent surface water flow that varies between seasons and years. Apart from a few wet months (the wet season in this region is October to April), river flow is zero or close to zero, except for the Dawson River. Therefore any potential discharge from developments to these rivers could have a significant impact on the riparian environment. Since there will be little or no natural streamflow for most days of the year, the quality of released water could potentially be changed by evapoconcentration and mixing with remnant water in the river bed or remnant pools. Current regulations on co-produced water from CSG activities in Queensland aim to strategically manage water and saline waste so that it is used beneficially for new or existing water users, water-dependent industries and/or the environment and firstly avoids, and then minimises and mitigates impacts on environmental values (EHP, 2012).
Dilution, evaporation, seepage, chemical transformation or a combination of these make it difficult to predict how far any effluent water could travel in natural watercourses. Influential factors include the quality and quantity of the release or spillage, existing flow in the receiving waters and the prevailing weather conditions.
A buffer of between 5 and 7 km based on the extent of riparian vegetation from the Dawson, Moonie and Weir rivers was used in defining the spatial extent of possible surface water related impacts.
