Groundwater chemical characteristics of the Qiaojia district in Jinshajiang river valley, Yunnan, China

The Qiaojia district in Jinshajiang river is about 15 km long, of which the cross section is topographically a trapezoidal valley with a relieved bottom and a maximum corrading depth up to 2,719 m. Along the valley karst aquifers develop well and Quaternary porous aquifers distribute at bottom of the valley. There are a number of springs appearing along the valley, which are main drinking water sources for the local residents. In order to better protect the valuable resources, in this research 38 representative springs in the area were selected for the study of groundwater hydrochemical characteristics. Water samples were collected at the end of the rainy season in November 2015 and the dry season period in April 2016, respectively. The samples were analyzed in Lab of Kunming Mineral Resources Monitoring and Testing Center, Ministry of Land and Resources. Sampling and analyzing of the water samples were carried out in accordance with the groundwater environmental monitoring technical specifications (HJ/T164-2004). The result shows that the groundwater chemical type is relatively simple, dominated by water types of HCO3-Ca, HCO3-Ca?Mg, HCO3-Mg?Ca.Basically, TDS（Total Dissolved Solids）concentration of groundwater presents a gradual increasing trend from slope recharge area to runoff zone and to discharge zone in valley area. The TDS concentration of porous groundwater is significantly higher than that of karst water. TDS in porous groundwater generally is greater than 400 mg/L and the ratio of calcium and magnesium (as Ca/Mg) is smaller than 4. In contrast, TDS in karst water is less than 350 mg/L and Ca/Mg is greater than 4. The major components of groundwater, HCO3-, Ca2+, Mg2+ and SO42-, show a positive correlation with TDS. In addition, based on the dynamics of chemical compositions, the origin and forming conditions of large springs in the Quaternary strata are analyzed as well. It is believed that the big spring water is a mixture of porous water and karst water, which is mainly fed by karst water.