Study On The Chemical Characteristics Of Groundwater In Shijiazhuang Plain

Shijiazhuang is located in front of Taihang Mountain,and the use of water resources is mainly groundwater.In recent years,under the influence of natural factors and human activities,the distribution characteristics and evolution process of groundwater have been affected to a certain extent,causing a series of changes in the chemical characteristics of groundwater.In order to scientifically understand groundwater,rationally develop groundwater resources,and protect the groundwater environment,it is necessary to study the chemical distribution characteristics of groundwater in this area.Relying on the"National Groundwater Monitoring Project"project of Hebei Geological and Environmental Monitoring Institute,taking Shijiazhuang Plain as the research area,this paper deeply studies the chemical characteristics and causes of groundwater in Shijiazhuang Plain by using mathematical statistics,single-factor evaluation,ion diagram,hydrogeochemical simulation and other methods.The results are as follows:（1）Using the comprehensive analysis method and Piper three-line diagram to analyze the basic data of the sample,it is found that the groundwater in the study area is weakly alkaline,and the conventional ion concentration characteristics are mainly SO₄^2->HCO₃^->Cl^-,Na⁺>Ca²⁺>Mg²⁺.The chemical types of groundwater in the shallow groundwater pre-mountain alluvial fan area in the study area are mainly HCO₃-Ca·Mg type,HCO₃·SO₄-Ca·Mg type,which are converted into SO₄-Na·Mg type and SO₄·Cl-Na type in the central plain area;deep groundwater is converted from the alluvial fan area in front of the mountain.HCO₃-Ca water converted into SO₄·Cl-Na water in the central plains.（2）The groundwater ion concentration in the study area is low in the north-west area and high in the south-east area,and there is a low concentration zone in the north-west to south-east.The distribution characteristics are closely related to the flow field.Groundwater flows from west-south to south-east,and the ion components converge in the southeast discharge area.The concentrations of TDS,HCO₃^-,Cl^-,SO₄^2-,Na⁺,Ca²⁺and Mg²⁺of shallow groundwater in the study area have changed,but the distribution characteristics of remain basically unchanged.The NO₃^-concentration shows a downward trend,and factors such as the reduction of groundwater extraction and ecological rehydration are the main causes.（3）Water quality evaluation results:The shallow groundwater quality in Shijiazhuang Plain has shown a better trend over the years.In 2017,the area of shallow groundwater Class IV and Class V water in the research area accounted for 71.6%;in 2021,there was no Class IV water in the research area,and the area of Class V water accounted for 10.12%of the total area of the research area.the decrease of TDS and NO₃^-concentrations is the main reason for the better water quality.In 2021,the water quality of deep groundwater in most areas is better,and the water quality in most areas is better than Class III.（4）The ion diagram analysis shows that the groundwater in the study area is mainly controlled by rock weathering.The pre-mountain alluvial area is affected by the weathering and dissolution of evaporated salt rocks and carbonate rocks,and the dissolution of silicate rocks and evaporated salt rocks in the central plains is relatively large;cation exchange is common in the research area;agro-industrial activities have a certain impact on the groundwater composition in the research area.（5）The reverse simulation of the research area shows that the hydrochemical effects of groundwater in the study area include aquatic rock dissolution,precipitation and cation exchange.On the simulated path,the dissolution of dolomite and salt rock always exists.The dissolution of gypsum occurs in the edge of the alluvial fan,and the dissolution of calcium feldspar is mainly in the central plain.Cation exchange gradually strengthens from west to east,mainly for the analysis of Na⁺adsorbed by Ca²⁺.The distribution of groundwater ions in the Shijiazhuang Plain is closely related to the flow field.In recent years,with the reduction of the impact of human activities the water quality has gradually improved.The dissolution of water rocks and cation exchange are the main causes of hydrochemical components.