A preliminary investigation of the oxygen and hydrogen isotope hydrology of the greater Cape Town area and an assessment of the potential for using stable isotopes as tracers

Abstract

The oxygen and hydrogen isotope composition of rain-water, groundwater and mains supply water was determined with the aim of assessing the potential for applying these isotope systems to problems of urban hydrology in the greater Cape Town area. Water treatment plants supplying mains water to Cape Town produce water with a seasonal variation in hydrogen (H) and oxygen (O) isotope composition. In September 1996, at the end of the wet winter months, the treated water had δD and δ18O values that were 12 and 2‰ higher, respectively, than the values of April 1996 at the end of the previous summer. The δD and δ18O values of natural springs on the slopes of Table Mountain show a good correlation, with a line of best fit that is parallel to that of the global meteoric water line, but enriched in deuterium. Groundwater from the shallow Culemborg-Black River aquifer and the extensive Cape Flats aquifer have δD and δ18O values which plot closer to the global meteoric water line.

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