316 



THE COMPOSITION OF THE WATERS OF THE GREAT AUSTRALIAN 

 ARTESIAN BASIN IN SOUTH AUSTRALIA AND ITS SIGNIFICANCE. 



By R. LocKHART Jack, B.E. 



[Read August 9, 1923.] 



During the last thirty years many analyses have been made of waters from 

 springs and bores in the South Austrahan portion of the Great AustraHan 

 Artesian Basin. The bulk of them are by W. S.- Chapman, of the School of 

 Mines, and the remainder by G. A. Goyder and W. A. Hargreaves, Government 

 Analysts, and by Goyder and Hallett. The full analyses of samples taken prior 

 to September, 1921, are to be found in the Reports of the Interstate Conference 

 on Artesian Water for 1912, 1914, and 1921. 



The writer, struck by the variation in quality, and particularly by the fact 

 that the eastern waters carry carbonate in excess, while the western waters carry 

 excess of sulphate over carbonate, set out certain characteristics of the analyses 

 in map form, together with other data. Some very interesting features became 

 obvious when this was done. 



The maps prepared were (1) an isopotential map, on which the carbonic 

 acid and the sulphuric acid radicles were also separately set out in grains per 

 gallon of carbonic acid radicle present, or deficient, as shov/n by excess of the 

 SO4 radicle; (2) plans showing the total salts in grains per gallon; and (3) 

 total chlorine in grains per gallon. 



Curves of equal total salinity and of equal chlorine content were then plotted 

 on these maps. It is much to be regretted that there are some bores and springs 

 from which no analyses are available, and which would have enabled a wider 

 area to be plotted. These samples will be got as opportunity arises and the maps 

 modified. Taking No. 1 map first. 



The isopotential ^^^ lines indicate, in addition to the influx of water from the 

 north-east, that there is a western feeder, or intake, and examination of the 

 salient features of the analyses tabulated on pages 319-321 shows clearly that there 

 are two very distinct types of water in the basin — the carbonated and the sul- 

 phated. The carbonate water is the Queensland water, and the amount of 

 carbonate increases as the water travels south-west. The greater part of this 

 carbonate is assumed, in the analyses, to occur as sodium carbonate, and the 

 sulphates are nearly or entirely absent. The other type of water may contain 

 carbonates also, the bulk of which is assumed to be present as calcium carbonate, 

 but the sulphates are always present in excess. In preparing No. 1 map the 

 sulphuric and carbonic acid radicles (shown in analyses as grains per gallon) 

 were alone considered. To compare them the weight of the sulphuric acid 

 radicle is expressed in terms of the carbonic acid radicle according to their 

 respective valencies. This may be illustrated more simply by an example of 

 two common salts having the same metallic base (sodium, for instance) combined 

 with the carbonic and sulphuric acid radicles. The quantity of sodium that is 

 satisfied or enters into chemical combination with ten parts of the sulphuric 

 acid radicle is satisfied by 6'3 parts of the carbonic acid radicle. So, to get 

 comparable figures for plotting, a water containing 10 grains of sulphuric acid 

 radicle is plotted as a deficiency of 63 grains of carbonic acid radicle. The analyses 

 in which SO4 predominate are plotted with the negative sign preceding the figure. 



(1) Using the heights of the surface above the sea, and the water pressures in the case of 

 flowing bores, or the depth to water level in non-flowing bores, contour lines are drawn through 

 as many points of equal elevation on the water surface as possible. These contours showing 

 the height of the water surface — the isopotential lines — show the height to which water will 

 rise in a new boring, and also the direction of movement of the underground water. This 

 movement is at right angles to the isopotential lines ; that is to say, down the steepest slope. 



