Characteristics And Controlling Factors Of Groundwater Chemistry Change In Typical Groundwater Exploitation Reduction Area Of Heilonggang

With the further development of groundwater exploitation reduction in the Heilonggang region,the decrease of groundwater exploitation will inevitably lead to the change of aquifer hydrodynamic conditions,and then lead to the change of hydrochemical characteristics.However,it is not clear how groundwater hydrochemistry will evolve under groundwater exploitation reduction.Therefore,it is urgent to find out the variation characteristics and formation mechanism of groundwater hydrochemistry under the current conditions of groundwater exploitation reduction area.This study aims to reveal the variation mechanism of groundwater hydrochemistry in typical groundwater exploitation reduction area of Heilonggang under the influence of both natural and human factors.It is of great theoretical significance and practical demand for the sustainable development and utilization of groundwater resources in the groundwater exploitation reduction area of Heilonggang and other similar areas to further reveal the hydrochemical evolution law in the area under implementation of groundwater exploitation reduction.In this study,202 groups groundwater samples were collected during five field sampling from 2019 to 2021.Heilonggang region in Handan city is one of the first to carry out the pilot area of groundwater exploitation reduction project in the North China Plain.Therefore,the variation characteristics and influencing factors of groundwater hydrochemistry in a representative groundwater exploitation reduction area（the Heilonggang region in Handan city）were investigated by using the multivariate statistical analysis,Piper three-line diagram,fuzzy membership,water quality index,USSL and Wilcox diagram,ion ratio analysis,chloro-alkaline index,Gibbs diagrams and saturation indices method.The results are as follows:（1）The overall order of cation concentration in shallow and deep groundwater is Na⁺>Mg²⁺>Ca²⁺>K⁺,and the order of anion concentration is HCO₃^->SO₄^2->Cl^->NO₃^-,which does not show obvious seasonal variation.The hydrochemical types of shallow and deep groundwater are not easy to change with the seasons,and they are mainly Na-Cl-SO₄and Na-mixed types,which have close hydraulic relationship.（2）The shallow groundwater of poor quality in most areas is not suitable for drinking and irrigation.The shallow groundwater of general quality in a few areas can be used for drinking or irrigation after treatment.The deep groundwater quality of good overall quality is more suitable for drinking water and irrigation sources.The risk of salt damage is great and the risk of alkali damage is small in groundwater.Infants are the group most at risk from nitrates.There are some health risks in Quzhou and Yongnian,and the groundwater is not suitable for drinking.（3）Natural processes such as evaporation,water-rock interaction and cation exchange control the evolution of groundwater hydrochemical.The ions in groundwater aquifer system mainly derived from the dissolution/precipitation of minerals such as halite,gypsum,Glauber’s salt,feldspar,calcite and dolomite.Cation exchange modified the cationic concentrations of groundwater system in the study area,while reverse ion exchange in the shallow groundwater is mainly concentrated in some areas with surplus Na⁺.The weathering dissolution of feldspar consumes CO₂and promotes the precipitation of calcite at the same time.（4）In addition,human activities such as groundwater exploitation reduction,industrial and agricultural activities and domestic sewage discharge also affect the chemical composition of shallow groundwater.In some areas,the shallow groundwater may be diluted by the upward flow of the deep groundwater,salt water evolves to brackish water,and salinity presents a downward trend to a large extent.Groundwater exploitation reduction projects indirectly improves the quality of shallow groundwater.The hydrochemistry of shallow groundwater is comprehensively affected by industrial and agricultural activities and domestic sewage discharge.The salinity of deep groundwater is relatively stable and less affected by groundwater exploitation reduction and industrial and agricultural activities.