Evolution Of Groundwater Environment And Hydrogeochemical Simulation Of Shihezi City

Shihezi City is located in the south margin of Jungar basin and middle northern slope of Tianshan Mountains, the area is 460km2(the plain area is 377.35km2), which belongs to continental dry climateand. Shihezi City is one of the economic centers of the middle northern slope of Tianshan Mountains. Due to the shortage of surface water resources, the main water supply for domestic and production is groundwater. With the increasing of human activities, the groundwater environment is worsening, and the contradiction between supply and demand of water is increasingly prominent. Water resources shortage is a key issue in economy development of Shihezi City. Further study on groundwater chemical characteristics and mechanism, evolution of groundwater quality and groundwater pollution,and vulnerability of groundwater environmental have an important significance to groundwater sustainable utilization and protection of groundwater environment.31 water samples, which including 18 phreatic water samples, 10 confined water samples and three surface water samples were collected in this study. Groundwater chemical characteristics and hydrogeochemical processes were studied based on the water chemistry analysis of 31 water samples combined with the hydrogeological conditions in Shihezi City using methods of the mathematical statistics, graphic method and hydrogeochemical simulation. The main research results and conclusions are as follows:(1) TDS and total hardness of phreatic water has great spatial variability. There are brackish phreatic water, salt phreatic water and hard phreatic water, extremely hard phreatic water in study area. Phreatic water hydrochemical type is mainly HCO3?SO4-Ca?Na and SO4?HCO3-Ca. TDS and total hardness of confined water is relatively stable.Most confined water is fresh or low hardness, which hydrochemical type is mainly HCO3-Ca?Na and HCO3?SO4-Ca?Na.(2) The results of quality and pollution evaluation of groundwater show that: there are three grade â…£ and three grade â…¤ phreatic water samples, which accounts for 33.4% of the total 18 phreatic water samples. Confined water quality is good in Shihezi city. All of ten confined water samples meet the grade III groundwater quality standard. Phreatic water has generally contaminated.Phreatic water of one monitoring well was unpolluted, which of five,11 monitoring wells were slight and moderate polluted, while one monitoring well was serious polluted. Confined water of six wells were unpolluted and of four wells were slight polluted which accounted for 60.0% and 40.0% of the total number of confined water sampling points, respectively.(3) Organic contaminants of eight groups of groundwater samples were determined. None of the 37 items in these groundwater samples were detected.(4) The hydrogeochemical simulation in typical section of the study area shows: calcite, dolomite, gypsum, CO2 were the main mineral controlling groundwater chemical composition. Ca2+/Na+ exchange interaction was the main hydrogeochemical process.(5) VLDA model was used to evaluate phreatic water vulnerability in the plain area of Shihezi City. The results show that: the area of low vulnerability zone(with vulnerability index of 3.0~4.0), medium vulnerability zone(with vulnerability index of 4.0~5.0) and high vulnerability zone(with vulnerability index of 5.0~6.0) accounted for 3.1%, 34.0% and 62.9% of the total area, respectively. Relatively high vulnerability zone was located in the north of Qingquanji and Gongerlian and the south of No.312 national road.