Study Of Groundwater Hydrochemical Characteristics And Water Quality Evaluation In The Water Source Areas Of The Front And Middle Section Of The Sunite Ancient River Channel

In arid and semi-arid areas,groundwater has become the main source of water supply due to less recharge.With the continuous impact of physical geography and human activities on groundwater,arid and semi-arid areas are facing the problems of scarcity of water supply sources and deterioration of water quality.The groundwater of the Sunite ancient river is the main water supply source along the ancient river.In order to better develop the society and economy of the region,it is necessary to reasonably protect groundwater resources.At present,there are few reports on the research of groundwater in the region.In order to achieve sustainable utilization of groundwater resources,the primary task is to comprehensively understand the hydrochemical characteristics and their causes.On this basis,this study takes the groundwater in the front and middle section of the Sunite ancient river as the research object,combined with relevant literature,and uses mathematical statistics,Piper three line map,and geographic information system（GIS）software to analyze the chemical characteristics of groundwater;Using analysis methods such as Gibbs model,mineral saturation index,and ion ratio coefficient to study the causes of groundwater hydrochemical characteristics;Use single indicator evaluation method and Nemero index evaluation method to evaluate the water quality of groundwater in the study area,and use factor analysis method to analyze the reasons for excessive fluoride ions.The main results were as follows:（1）The content of HCO₃^-,Cl^-,and Na⁺in the water samples of the study area is relatively high,which may be related to the dissolution of aluminum silicate and salt rock minerals in the study area;The content ratio of Mg²⁺and Ca²⁺is not equal,indicating that the source of Ca²⁺and Mg²⁺in the study area is not only the dissolution of dolomite minerals in the aqueous medium layer;The main hydrochemical types of groundwater in the study area are mixed Ca Na HCO₃（III）and Na Cl（II）types,which may be related to the arid climate,strong leaching and evaporation concentration in the study area.The anions are mainly HCO₃^-and Cl^-.Based on the overview of the water source areas in the study area,most of the groundwater levels are shallow and located within the basin,with poor runoff conditions.In addition,the arid climate conditions have resulted in a high content of Total Dissolved Solids（TDS）in the groundwater in the study area;The p H range of the study area is between 6.75 and 7.66,and the p H differences among different regions within the study area are relatively small,with an overall weak alkalinity.（2）The analysis methods such as Gibbs plot,mineral saturation index,and ion ratio coefficient indicate that the chemical composition of groundwater in the study area is mainly affected by evaporation concentration and rock weathering.The study area is located in arid and semi-arid regions,with strong evaporation and less atmospheric precipitation,resulting in a higher TDS content and a higher Na⁺/(Na⁺+Ca²⁺)content ratio in the water sample;The main source of Na⁺in water is the dissolution of salt rock minerals,and the positive cation exchange that occurs in the water is another source of Na⁺.（3）Evaluation of groundwater quality using single indicator evaluation method and Nemero index,it was found that the main indicators that exceeded the standard in the groundwater in the study area were chloride,sodium,and TDS（total dissolved solids）.There were 24 groups of groundwater samples in the study area that belonged to Class IV water,with a proportion of 96%.Overall,the water quality was poor;The factor analysis method was used to analyze the causes of excessive fluoride ions,indicating that the lower concentration of calcium ions in water and natural factors such as mineral weathering,dissolution,and evaporation concentration are the reasons for fluoride ion enrichment.