SURFACE WATER AND GROUNDWATER INTERACTION IN THE UPPER CROCODILE RIVER BASIN, JOHANNESBURG, SOUTH AFRICA: ENVIRONMENTAL ISOTOPE APPROACH

The interaction between surface water and groundwater is a complex process that can potentially deteriorate the quality of water, which is highly needed by communities. An environmental isotope and stream discharge based study has been conducted in the upper Crocodile River Basin, Johannesburg, which is characterized by fractured crystalline rocks and dolomitic aquifers from which groundwater is extracted for diverse economic activities. The seepage of mine water into a dolomitic aquifer in the vicinity of the Sterkfontein cave has been quantified and falls between 24 x 10(6) m(5)/y and 29 x 10(6) m(3)/y. The environmental isotope results also show that the decanting mine water extensively interacted with the shallow groundwater and streams. On the other hand, the dolomites (Malapa area) that lie away from mine areas in different dolomitic compartment contain uncontaminated and old groundwater with low H-5, which indicates long residence time, with depleted O-18 and H-2 indicating a recharge that took place prior to evaporation, and afterwards the recharged water circulated for long period of time. Streams also lose water into the dolomitc aquifer through sinkholes and fractures. Therefore, surface water and groundwater are intimately connected in the area.