| Daweijia. which is on the west shore of the Bohai Sea. is located in the northwest of Jinzhou District in Dalian city, and the distance from Daweijia to Jinzhou District is 10km. The karst aquifer in Daweijia was the biggest groundwater source in Dalian city, and it was extremely important for water supplying. Due to long term and irrational groundwater development, groundwater source was sustained overdraft for a long periods, and formed a cone of depression. Since 70s of last century, the sea water intrusion had taken place, and the maximum area of seawater intrusion was 26.5km2. the distance was 5.6km. The seawater intrusion made a series of environmental and geological problems, not only water source development was stopped, but also the shortage of water resource, salinization of soil, ecosystems retrogression, and underground pipeline corrosion, and so on. In order to controlling seawater intrusion and groundwater remediation, this paper under the guidance of groundwater theory, according to the facts of study area, studied the geochemical reactions during the course of seawater intrusion in Daweijia. divided the grade of seawater intrusion discrimination indicators. Based on the analysis of dynamic monitoring data, hydro-chemical and isotope data, the geologic and hydrogeological data. It is revealed that the main geochemistry reactions during seawater intrusion process, and analyzed seawater intrusion mode.The major conclusions of this paper can be summarized as below:1,Based on collecting the available research results, geological and hydrogeological conditions were comprehensive analysis, seawater intrusion monitoring profiles were established, groundwater levels were observed automatically and water quality were monitored annually, seawater intrusion evolution processes were analyzed. It was believed seawater intrusion was affected not only by the man-made factors, but also by the topography, hydrogeology and climatic conditions. The data of groundwater level monitoring and the distribution characteristics of hydrochemistry in the study area combined shows that the modes of seawater intrusion in the Daweijia area mainly include seawater intrusion through karst voids in the cone of depression of groundwater level induced by exploitation in the heterogeneous carbonate coast, linear seawater intrusion through conformation, and planar seawater intrusion in the Quaternary heterogeneous aquifer in the river depression.2,Based on the groundwater chemical results, combined the open-field on-site conductivity test results, groundwater was divided to freshwater, brackish water, salt water and seawater by land to sea. Hydrochemical types changed regularly: Cl·Na→Cl-Na·Ca→Cl·HCO3-Na·Ca→HCO3·Cl-Na·Ca→HCO3·Ca. All the above were divided based on Cl-. salinity and conductivity.3,According to analysis the hydrochemical features of groundwater in the study area, it is well known that there are several hydrogeochemical reaction happened. When seawater intrusion occurred, groundwater and seawater mixed at first, and then. cation exchange and minerals dissolution and precipitation happened.4,It was believed that the DaWeiJia area groundwater come from precipitation by comprehensive analysis of isotope test such asδ34SSO4,δ13CHCO3- and Cl-, The variation ofδ2H,δ18O were affected not only by evaporation, but also by mixing between groundwater and sea water and mineral dissolution,δ18O increased with the increasing of groundwater depth,δ34S had a good relation with EC and SO42-. It shows that SO42- of groundwater comes from seawater. It was believed that the change ofδ13C was affected by mixing process of seawater intrusion and weathering dissolving effect of carbonate based on the analysis of variation ofδ13C. The recharge condition, flow condition and the age of groundwater were analysis by the data of tritium combined withδ18O.5,The results of reactive path simulation of inverse geochemistry show that, the main geochemical activities in the transition zone of seawater intrusion in the study area include cation exchange, dissolution of calcite and montmorillonite. and precipitation of illite. plaster and dolomite accompanied with differentiation and extrication of CO2.
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