Hydrochemistry Highlights Potential Management Issues for Aquifers and Springs in the Lake Blanche and Lake Callabonna Region, South Australia Mark Keppel1, Daniel Wohling2, Andrew Love3, and Travis Gotch1 Abstract A hydrochemistry-based study has highlighted potential management implications for selected aquifers and springs located within the Lake Blanche and Lake Callabonna region in the far north of South Australia. The interpretation of hydrochemical and environmental tracers from 14 springs and 17 water wells, as well as historically available data, were used to establish five hydrochemical-based aquifer types for the region: 1. Fractured rock crystalline basement aquifer. 2. Patchawarra Formation (Cooper Basin) aquifer. 3. J-K aquifer (Algebuckina Sandstone, Cadna-owie Formation and lateral equivalents) of the Great Artesian Basin. 4. A sandstone unit or units interpreted to occur within the Neocretaceous Rolling Downs Group, which is informally termed the ‘Rolling Downs Group sandstone (RDGS) aquifer’. 5. Cenozoic aquifer. Two key findings from this study have potential implications for ongoing resource management. First, artesian groundwater conditions were identified for the first time within sandstones found within the Neocretaceous confining layer (the RDGS aquifer). Although the exact stratigraphic nomenclature of this sandstone unit is not yet confirmed, groundwater sourced from this unit is currently being used for stock. Second, the RDGS aquifer may contribute to spring flow at Lake Blanche and Lake Callabonna. Similarly, the fractured rock aquifer may be a source of water for the Petermorra Springs complex. Beyond certain results from these three spring complexes, the majority of hydrochemical and environmental tracer analyses infer that the J-K aquifer is the primary source aquifer supporting spring flow. Keywords: springs, South Australia, hydrochemistry, Great Artesian Basin, Cooper Basin 1 South Australian Department for Environment and Water, 81–95 Waymouth Street, Adelaide, SA 5000, Australia 2 Innovative Groundwater Solutions Pty Ltd., Unit 3, 7 Greenhill Road, Wayville, SA 5034, Australia 3 National Centre for Groundwater Research and Training, and College of Science & Engineering, Flinders University, GPO Box 2100, Adelaide, SA 5001, Australia Introduction understand the source of flow to the springs within The effective management of spring-supported the Lake Blanche and Lake Callabonna region of environments requires a clear understanding of South Australia (Harrington & Harrington, 2015). the groundwater source and system that supply There have been numerous studies characteris ing them. The potential for petroleum hydro carbon the groundwater sources for various Great Arte- develop ments within the Weena Trough of sian Basin (GAB) spring complexes within South the southern Cooper Basin prompted a need to Australia (e.g. Dalla Valle, 2005; Love et al., This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International Licence. Individual articles may be copied or downloaded for private, scholarly and not-for-profit use. Quotations may be extracted provided that the author and The Royal Society of Queensland are acknowledged. Queries regarding republication of papers, or parts of papers such as figures and photographs, should be addressed to the Secretary of The Royal Society of Queensland ([email protected]). PROCEEDINGS OF THE ROYAL SOCIETY OF QUEENSLAND VOL. 126 65 66 MARK KEPPEL, DANIEL WOHLING, ANDREW LOVE, AND TRAVIS GOTCH 2013; Harrington & Harrington, 2015; Keppel et source and therefore provide a line of evidence for al., 2015), although there remains some uncer- identifying the likely source of groundwater sup- tainty as to the groundwater source for some of porting spring flow. these complexes. This uncertainty has implica- tions for water allocation and groundwater resource Materials and Methods management. Location and Physiography By extension, understanding the responses to The investigation area is approximately 600 km and impacts on spring flows from any water extrac- north-north-east of Adelaide and covers approxi- tion associated with potential petroleum hydro- mately 15,100 km2 extending from the northern carbon developments within the southern Cooper Flinders Ranges in the south, past Lake Blanche Basin, which underlies the major aquifers of the to the southern Cooper Basin in the north, and GAB and the Lake Eyre Basin in the region, is east to Lake Callabonna (Figure 1). The area critical for planning, regulatory and management com prises five spring complexes: Lake Blanche, purposes (Harrington & Harrington, 2015). Reedy, Petermorra, Twelve and Lake Callabonna, The objective of this study was to provide an all of which are part of the Lake Frome Springs initial description of the primary groundwater supergroup. According to Gotch (2013), a spring source for springs within the Lake Blanche and complex is a cluster of spring groups that share Lake Callabonna region based on hydrochemistry similar geomorphological settings and broad simi- data, and to determine what implications the con- larities in water chemistry, whereas a supergroup clusions may have for the ongoing management is a cluster of spring complexes. Finally, Gotch of the groundwater resource. Groundwater hydro- (2013) defines a spring group as clusters of springs chemistry and environmental tracers provide a that share similar water chemistry and source their reliable methodology to identify the groundwater water from the same fault or other structure. Figure 1. The study area and hydrochemistry sampling sites. HYDROCHEMISTRY OF AQUIFERS AND SPRINGS IN FAR NORTHERN SOUTH AUSTRALIA 67 The climate is generally arid, with weather Figure 2. The hydrostratigraphic nomenclature pre- pat­­terns dominated by persistent high-pressure sys- sented here represents a simplified version of the tems. Rainfall comes predominantly from weak stratigraphy present in the study area. A summary of winter cold fronts originating in the Southern stratigraphy for the study area is presented in Table 1, Indian Ocean, or sporadic summer monsoon rainfall which will aid the placing of the hydro stratigraphy origi nating in north-west and north-east Australia. discussed into a wider geological context. Rain fall for the nearest weather station at Moomba Analytes measured during this investigation averages 170 mm/year (BoM, 2019), although this include: can vary significantly from year to year. Since • The major ions chloride (Cl–), sulphate (SO 2–), 1996, annual rainfall has varied from 43 mm/year to 4 sodium (Na+), potassium (K+), cal cium (Ca2+), 660 mm/year. magnesium (Mg2+) and alkalinity (as HCO –). Given the arid climate, aeolian-driven erosion 3 Results were rejected if charge balances for as described by Mabbutt (1977) is important in major ions were ±5% or greater. The minor shaping the physiography of the region. The land- ions fluoride (F–), bromide (Br–) and strontium scape is predominantly flat desert consisting of (Sr2+) were also analysed. sand dunes and gibber plains. Exceptions to this • The stable isotopes of the water molecule include the northern Flinders Ranges, a mountain deuterium (δ2H), oxygen-18 (δ18O). range comprising outcropping basement rocks • The isotopic strontium ratio (87Sr/86Sr). that are Archean to Cambrian in age, and silt and • Radiocarbon (14C) expressed as percent mod- clay pans associated with Lake Blanche and Lake ern carbon (pMC). Callabonna, found along the northern and eastern • Chlorine-36 (36Cl/Cl). margins of the study area (Figure 1). The largest town near the study area is Moomba, Scatter plots and a Piper diagram were used to with a population of approximately 1200, largely determine broad hydrochemical characteristics of composed of itinerant petroleum industry workers. the groundwater and interpret the data in relation Innamincka, located to the north of the study to important hydrochemical processes. area, has a population of 43 (ABS, 2016). Parts The stable isotopes of the water molecule, of the Pirlatapa, Wadigali, Dieri, Yawarrawarrka deuterium (δ2H) and oxygen-18 (δ18O), were com- and Adnyamathanha Aboriginal language groups pared to the local meteoric water line (LMWL) for occur within the study area. Alice Springs (Crosbie et al., 2012; IAEA, 2013) to determine the effects of evaporation or mixing Methodology on groundwater samples. The LMWL is derived Hydrochemistry and environmental tracer data from from precipitation collected from a single site or 14 springs and 17 wells were collected between 5 and set of ‘local’ sites (USGS, 2004). Groundwater that 11 June 2015, and 25 and 28 August 2015 (Keppel et has evaporated or mixed with evaporated water al., 2016; Harrington & Harrington, 2015). Where typically plots below the LMWL, along lines that possible, wells where the hydrostratigraphy of the intersect the LMWL at the location of the original completion interval was known were targeted for unevaporated composition of the water (Craig, sampling. Four aquifer types were targeted during 1961; USGS, 2004). The LMWL at Alice Springs the field work campaign: was favoured over Woomera (the nearest town to the investigation area where stable isotopes in pre- • Fractured rock (Precambrian crystalline) base- cipitation have been recorded) because of a limited ment aquifer. stable isotope record at Woomera (Liu et al., 2010). • Patchawarra Formation (Cooper Basin) aquifer. Isotopic strontium (87Sr/86Sr) was used as a • Cadna-Owie Formation – Algebuckina