Hydrochemical Characteristics And Pollution Evaluation Of Groundwater In Xi'an

This paper takes groundwater in the main urban area of Xi'an as the research object.Based on data collection,field surveys,and hydrogeological supplementary surveys,the theoretical methods of hydrogeochemistry,statistics,and groundwater quality and water pollution evaluation are applied to systematically study groundwater in time and space.Water chemistry characteristics and groundwater pollution distribution,and in-depth analysis of groundwater pollution through water quality and water pollution evaluation.The evolution process of groundwater quality under the influence of human activities is revealed,and the main pollution ways and sources of groundwater in the study area are clarified.The main research results are as follows:(1)According to the field investigation and previous data analysis,the main aquifer in the study area is the Quaternary sand,gravel and cobble layer.The main recharge sources of groundwater are atmospheric precipitation,surface water infiltration,sewage and irrigation water from agricultural activities.Groundwater runoff is greatly affected by stratum lithology and topography.(2)Using ion ratio and saturation index methods to study the hydrochemical characteristics and evolution of groundwater.The formation of solutes in most groundwaters is mainly affected by the weathering of rocks.The influence of evaporation-concentration of phreatic water is slightly greater than that of confined water,and only part of the groundwater has a relatively shallow depth of evaporation.In most areas,groundwater has undergone negative cation exchange adsorption,which gradually reduces the content of Na⁺and K⁺in the groundwater,and gradually increases the content of Ca²⁺and Mg²⁺.Dolomite precipitation,calcite balance and the dissolution of rock salt,fluorite,and gypsum have a greater impact on the solute in groundwater.(3)Through graphic method combined with statistics and hydrogeochemical theory,systematically analyze the hydrochemical characteristics of groundwater in the study area.Both diving and confined water in the study area are alkaline water.The average value of diving TDS is 820.27 mg/L,and the average value of confined water is 374.12 mg/L.In most areas,the diving TDS exceeds the sanitary standard for drinking water.The chemical type of diving water along the Weihe River and other local areas has changed from HCO₃ type water to HCO₃·SO₄or SO₄ type water in 1997;the main water chemical types of confined water in the main urban area have not changed,and the spatial distribution is slightly different.Affected by the replenishment of diving over-current,in the area of Chengdong Shuiliu Township-Xinzhu Town-Baqiao-Maoxi Village-Dizhai Street,the confined water changed from HCO₃-Na type water mainly in 1997 to HCO₃-Ca type water.(4)Evaluate groundwater quality based on single component and comprehensive evaluation,and use single point single factor and Nemerow index method to evaluate groundwater pollution.The results show that most of the diving water quality in the main urban area of Xi'an is mainly category III and IV water.Nearly 45%of the diving water quality in the whole area is of poorer category IV water quality;the confined water quality is better than diving,with nearly 70%of the confined water in the area.The water meets Class III and above water quality standards.Exceeding standards of total hardness,manganese,TDS,arsenic,and sulfate in the study area is more serious;exceeding standards of arsenic,total iron,fluoride and manganese in pressurized water is more serious.Arsenic pollution exists in large areas in diving and confined water.(5)Through the analysis of sewage pollution indicators in various places,the results show that surface water quality has a greater impact on groundwater pollution in the main urban area.Human activities such as domestic sewage,industrial wastewater,and agricultural irrigation water directly or indirectly enter groundwater and groundwater exploitation changes groundwater dynamics.