Groundwater quality Alluvial aquifers

The main alluvial aquifers of the subregion are those associated with the Condamine, Maranoa-Balonne and Border Rivers (Macintyre Brook, and Dumaresq and Macintyre rivers) river systems. Other alluvial systems in the subregion are also identified in literature, but these are less developed.

Upper Condamine Alluvium

Groundwater from the Upper Condamine Alluvium is of relatively good quality, being used intensively for irrigation, industrial and stock and domestic purposes. CSIRO (2008) states that the water is suitable for most purposes and that salinity ranges from 900 to 2100 mg/L total dissolved solids (TDS). MDBA (2012) includes a map based on MDBC (2000) data that shows that groundwater salinity in the Upper Condamine Alluvium (see Figure 20) is variable. Along the eastern margin and flanking the main river course, low total TDS concentrations are recorded in the range from zero to 1500 mg/L. Higher TDS concentrations are recorded away from these areas, mostly in the range from 1500 to 3000 mg/L, but in places concentrations in the range from 3000 to 14,000 mg/L are shown.

Kelly and Merrick (2007) highlight that saline water is present adjacent to and overlying the freshwater intervals extracted for irrigation. Some of this water has salinity levels that would affect crop yields and there is concern that heavy extraction might result in salinisation of freshwater sources. Kelly and Merrick (2007) report that Huxley (1982) showed that groundwater evolves along flow paths from low salinity, magnesium bicarbonate – dominated water in the upstream areas associated with Main Range Volcanics Formation to relatively higher salinity, sodium chloride – type water downstream. A similar trend was noted in recent work by the Queensland Office of Groundwater Impact Assessment (2013) that incorporated more recent data. Kelly and Merrick (2007) highlight that a previous study by McNeil and Horn (1997) showed that groundwater salinity may be rising in the area between Dalby and the convergence of the North Branch with the main channel of the Condamine River.

The sodium adsorption ratio of groundwater is generally low, indicating that it is suitable for irrigation. However, Kelly and Merrick (2007) record that Islam (2006) did identify some areas around Dalby and Chinchilla where the sodium adsorption ratio was somewhat elevated.

Kelly and Merrick (2007) raise the issue that since pesticides have at times been detected in the Condamine River, it is likely that some level of pesticide contamination is present in the shallow aquifers in losing stream reaches.

The Office of Groundwater Impact Assessment (2013) analysed water chemistry data of aquifers within the footprint of the Condamine Alluvium using multivariate statistical techniques to identify differences in groundwater chemistry between aquifers, groundwater chemistry evolution within aquifers, and the potential for inter-aquifer connectivity between the Condamine Alluvium and Walloon Coal Measures. Data from 1980 to 2011 were used in the analysis. They concluded that on the basis of hydrogeochemistry, large-scale mixing and flow of water from the Walloon Coal Measures to the Condamine Alluvium is unlikely, although some local-scale mixing could not be ruled out.

Border Rivers Alluvium

Groundwater in the Queensland Border Rivers Alluvium (Figure 20) is shown in MDBA (2012) to be relatively fresh, with TDS concentrations mostly in the range from zero to 1500 mg/L. This generally matches work presented by Please et al. (2000) who identified TDS concentrations in this area of less than 1000 mg/L. Please et al. (2000) indicated that salinity increases significantly downstream, west of these areas. In the east, groundwater had mixed cationic composition (sodium dominant), and whereas shallow groundwater was dominated by chloride anions, deeper groundwater was dominated by bicarbonate. Further west, water was generally sodium- and bicarbonate-dominated, while high salinity areas in the far west had sodium chloride – type waters. Similar findings were reported from a more recent study by Baskaran et al. (2009).

The fact that these groundwater sources support irrigation, stock and domestic use confirms they are of relatively good quality. However, Please et al. (2000) indicate that groundwater does have a high sodium hazard rating in some places, particularly close to the Peel Fault zone (about 45 km east of Goondiwindi) where sodium concentrations are elevated in the alluvial system. This might be due to upward leakage of groundwater from the GAB, which is known to have elevated sodium concentrations.

St George Alluvium

Salinity levels for the deep aquifer in this area generally range from 1800 to 13,300 mg/L TDS (CSIRO, 2008). Although the higher salinity groundwater is unsuitable for stock or irrigation purposes, lower salinity groundwater is present west of Beardmore Dam (Lake Kajarabie) around the lower reaches of the Maranoa River and the upper reaches of the Balonne River. In this area, MDBA (2012) record TDS concentrations in the range from zero to 1500 mg/L based on MDBC (2000) data.

Kellett et al. (2006) show that in the shallow aquifer, electrical conductivity (EC – another measure of salinity), is lowest close to the major rivers, where values below 600 µS/cm were recorded in places. Away from the major rivers, salinity reportedly increases towards the south, with values in excess of 50,000 µS/cm recorded in places. In the lower aquifer in the main paleochannel, the range in salinity is considerably less, increasing from about 3000 to 5000 µS/cm in the north to greater than 10,000 µS/cm in the south.

Kellett et al. (2006) include data showing that where measured, water in the shallow aquifer is predominantly of sodium-bicarbonate-chloride type with a significant portion being of sodium chloride type. In contrast, groundwater from the deeper aquifer is sodium chloride – dominated. The sodium chloride – type waters are typically associated with higher salinity. Fractured rock aquifers

Main Range Volcanics Formation

The main groundwater source in the Main Range Volcanics Formation included in the Basin Plan is the Upper Condamine Basalts sustainable diversion limit unit. MDBA (2012) present MDBC (2000) data showing that groundwater is of low salinity, having TDS concentrations mostly in the range zero to 1500 mg/L, increasing slightly in the north to 1500 to 3000 mg/L. Water quality is generally suitable for all purposes, with salinity in the range from 500 to 1500 mg/L (CSIRO, 2008). Surat Basin

Habermehl (2002) states that groundwater quality of the GAB is variable but salinity is generally in the range from 500 to 1500 mg/L in the Lower Cretaceous-Jurassic aquifers. Groundwater salinity reportedly increases away from the recharge areas in the east and north (<250 mg/L TDS in places) along groundwater flow paths to the south and west to over 2000 mg/L in places (Radke et al., 2000).

Groundwater in the Lower Cretaceous-Jurassic aquifers is typically of sodium-bicarbonate-chloride type (chloride becoming more dominant away from the intake beds), and generally suitable for domestic, town supply and stock use (although elevated fluoride concentrations in places – mostly Queensland – may cause issues for stock watering). However, it is unsuitable for irrigation in most areas due to its high sodium adsorption ratio (Smerdon and Ransley, 2012).

In NSW, the upper confining units of the Surat Basin (managed under the NSW GAB Shallow Groundwater Source Water Sharing Plan to a depth of 60 m) generally consist of low permeability claystone, mudstone, calcrete and shale with minor conglomerate and sandstone (Green et al., 2012). The aquifers they contain are described as sporadic and often low yielding, producing brackish to saline water of limited use. Burton (2011) recognised the uppermost GAB unit as the Griman Creek Formation in northern NSW, noting that underlying units also outcrop in the east and west. At the scale of the Surat Basin, the Griman Creek Formation is described as a partial aquifer by Kellett et al. (2012).

The Walloon Coal Measures (the main lithological unit in the Surat Basin prospective for coal seam gas) contain groundwater of comparatively high salinity, ranging from 950 to greater than 12,000 mg/L TDS and averaging around 4,500 mg/L (Moran and Vink, 2012). The quality of co‑produced water necessitates treatment prior to beneficial use. This process results in saline brines and salt requiring management.

Last updated:
5 January 2018
Thumbnail of the Maranoa-Baloone-Condamine subregion

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