Influence Of Characteristic Factor Migration On Groundwater Environment In Typical Geothermal Water Areas In Western Sichuan

Western Sichuan has many types of geothermal resources and large reserves,which is one of the regions with rich geothermal resources in China.As a kind of geothermal resource with high development and utilization,underground hot water has made a tremendous contribution to the economic development of western Sichuan.However,due to the relatively high ion content of underground hot water,blindly developing and utilizing underground hot water can make it easily enter the surface water body or underground aquifer,thereby affecting the water environment of the area and destroying fragile ecosystems,and even affecting the local economic development and the normal life of people.Therefore,based on the distribution regularities and hydrochemical characteristics of underground hot water in the western Sichuan Plateau,the influence of underground hot water exploitation on shallow underground cold water is analyzed,which is of great significance for the rational exploitation and management of local underground hot water.Combining the topic selection of the"Survey on Hot Spring Resources in Xianshuihe Fault Zone"project,this thesis chose the western Sichuan Plateau as research area.Through the combination of data collection and field investigations,the data of underground hot water samples in the studying area were obtained.The piper three-line diagram was used to classify chemical types of underground hot water in western Sichuan,and the hydrochemical characteristics of underground hot water were analyzed.Then,the typical research area（typical area）was selected according to results of the hydrochemical analysis.The single factor index method and principal component analysis method were used to determine characteristic influence factors of underground hot water in the typical area.The three-dimensional solute migration model of underground water in the typical area was established by visual modflow software,and the model was verified by the measured data.Finally,two different forecasting schemes were set up to simulate effects of underground hot water on shallow groundwater under the conditions of the instantaneous leakage and the continuous leakage of pollutants.Through the research above,following research results are obtained:（1）The underground hot water in the western Sichuan Plateau is mainly distributed along the fault zone.The enrichment characteristics of the Xianshuihe fault zone,the Ganzi-Litang fault zone and the Jinshajiang fault zone are most obvious.The temperature of underground hot water is between 25℃ and 97℃,mainly medium temperature hot springs,accounting for 48.11%of the total;pH value is between 5.2⁹.2,mainly neutral hot springs,accounting for 52.76%of the total;the mineralization degree is between 1.33 mg/L and 2898.1 mg/L,and the number of light mineral springs is slightly superior,accounting for 52.83%of the total.（2）The hydrochemical types in western Sichuan are mainly HCO₃-Na type water,HCO₃-Na·Ca type water and HCO₃·Cl-Na type water.Among them,HCO₃-Na type water is distributed in all county-level cities in western Sichuan,HCO₃-Na·Ca type water is distributed in most county-level cities in western Sichuan,and HCO₃·Cl-Na type water is distributed in Kangding City.And,the content of K⁺,Na⁺,Cl^-,SO₄^2-,HCO₃^-and H₂SiO₃ in HCO₃·Cl-Na type water in Kangding area is relatively high,and indicators of Na⁺,F^-,Cl^-,TDS and ammonia nitrogen exceed the groundwater class III standard.So the HCO₃·Cl-Na type water has a relatively large impact on the water environment in western Sichuan.（3）According to the results of hydrochemical analysis in Chapter 3,combined with the characteristics of hot spring exposure and the status quo of exploitation and utilization of underground hot water,the Kangding area is selected as a typical area for researching and analyzing,and the single factor index method and principal component analysis method are used to screening the impact factors of the area.Results show that the fluoride and sodium in the underground hot water in the typical area have the greatest impact on the environment,so they are determined as characteristic influence factors of the area,and are also used as simulation characteristic factors for the solute migration model.（4）Under abnormal conditions,ZK01 has a pollutant leakage.It is predicted by simulation that the underground hot water enters the shallow underground cold water and moves downstream with the groundwater seepage field.The geothermal water causes a certain degree of pollution to shallow groundwater due to hydrodynamic action.In the case of continuous leakage,the pollutants spread 128 m in the west direction to the Yulin River within 30 days.The Yulin River has a fast flow rate,a large flow rate,and a strong dilution effect,which prevents further diffusion of pollutants into deep groundwater;however,it is easily contaminated by geothermal water,which may cause more serious consequences.Based on studies of the distribution regularities and hydrochemical characteristics of underground hot water in the western Sichuan Plateau,this paper analyzes the impact of underground hot water development on shallow underground cold water,which is important to the rational exploitation and utilization of geothermal water and groundwater quality protection.