Study Onhydrochemical Evolution And Groundwater Circulation In Guyuan Salt Mining Area, The South Of Ningxia

Guyuan Salt Mining Areawhich located in the south of Ningxia, is rich in rock salt mining resources and has brought an new opportunity for the development of the society and economy of Guyuan region. However, Guyuan as a region which is one of the areas seriously short of water in China, is shortage of surface water resources and the water quality is poorer. Qingshuihe Plain lies in the eastern part of The rock salt mining area is abundant of quaternary pore water in loose rock mass and has become the main source of water for local industry, agriculture and domestic use. In recent decades, as the result of the excessive expolitation of groundwater, the water level has dropped sharply and the quality of groundwater has deteriorated continuously. So to find out the water cycle and water chemistry of groundwater formation mechanism in the salt mining area is of important guiding signifinance for the rational development and utilization of rock salt mining and groundwater. In this paper, the distribution characteristics of water chemical composition and isotope in the western mountainous area and eastern plain were analyzed respectiely. The hydrogeochemical evolution and circulation mechanism of groundwater is analyzed by integrated use of the distribution of chemical composition, ion composition and ratio, mineral saturation indices, stable isotopes, radioactive isotope, and profile modeling. The results show the following conclutions:1.Surface water in the eastern is mainly controlled by the evaporation and concentration, surface water in the western mountainous area, in addition to the evaporation and concentration, it is also affected by groundwater recharge. According to the correlation analysis and mineral saturation index method, leaching is the main action that control the water chemistry in the western mountainous area, in the proccess of runoff, shallow groundwater mainly occurs the dissolution of mirabilite, gypsum and a little amount of feldspar and calcite, deep groundwater mainly occurs the dissolution of soluble salt such as gypsum, mirabilite and halite. In the eastern plain, brackish water is widely distributed, water chemical composition is mainly controled by mixing processs, in addition, in the proccess of runoff cation exchange function occurs significantly.2.The distribution characteristics of stable isotopes(δD and δ18O) of surface water and groundwater indicate that surface water in the study area is influenced by evaporation significantly, groundwater in the western mountainous and eastern plain has a close hydraulic connection. Deep groundwater in the western mountainous area was recharged before a long time and almost don’t participate in groundwater circulation.3.In order to further determine the effect of western mountainous groundwater on groundwater in eastern plain, 3H and 14 C is used to groundwater dating analysis. The tritum content in groundwater indicates that most of the groundwater is recharged before 1957 or after 1982.In addition to individual samples, the age of groundwater of most samples is older than 60.14C is used to old groundwater dating analysis, the results show that, the water in Qingshuihe Plain characterized by ancient water is older than 10000, waters in shallow wells and descending springs in the western mountainous area are characterized by modern water. The age of water distributed near the fault near Taozitan and Shangdianzi is between 5000 and 10000 years.4. 3H and 14 C was used to calculate the renewal rate of groundwater, the results show that the renewal ability of groundwater in the study area is poorer, groundwater update rate is less than 1% every year.5.The profile modeling results show that, groundwater flow system in the salt chemical industrial base can be divided into the local water system, middle water system and regional waer system. The local water system is mainly located between peaks and valleys in the western mountains with good radial flow condition, fast infiltration rate and big runoff intensity, and the circulation depth is less than 300 m, the circulation depth of groundwater in intermediate water system is less than 600 m, groundwater in regional water system, the circulation depth is deep, the water flow is sluggish and runoff flow intensity is weak.