Hydrogeochemical characteristics of karst groundwater in southern Nanchuan district of Chongqing

This work focused on the karst groundwater in southern Nanchuan District of Chongqing city. We have analyzed hydrochemical components and trace heavy metals in 149 pieces of samples. The results indicate that the hydrochemical types of groundwater are dominated by HCO3-Ca Mg , HCO3-Ca and HCO3·SO4-Ca. Most major chemical components of groundwater are Ca2+，Mg2+，HCO3-and SO42-，which show the corresponding relation with the water-bearing rock groups, i.e. carbonate karst water > carbonate rock and clastic rock water > clastic rock water. The ratio of Mg2+/Ca2+ in underground water shows that the co-dissolution of calcium carbonate and dolomite is dominant in the groundwater runoff process. The content of trace heavy metals is generally on the low side in groundwater. Most of the water quality is within the category III of water standard, only a few contaminated spots lead to some heavy metals on the high side.