Simulation Of Hydrogeochemical Process Of Quaternary Pore Water In The Northwest Of Ili River Valley

Huocheng is located in the northwest of Ili Valley.Because of its special geographical position,this region has gradually become a key area of Northwest China for economic development and environmental protection,in recent years.Groundwater is the most important part of water resources in this area for human survival,agriculture,forestry,animal husbandry,industrial development and maintaining ecological stability.To clear and definite its quality,hydrogeochemical composition and its formation and evolution of the water storage in different sections and different layers,this study consulted the application of mature research,carried on discussion and analysis of its hydrochemical characteristics and hydrogeochemical process of groundwater occurred in the Quaternary aquifer,in Huocheng County Plain,northwest of the study area,based on comprehensive investigation and evaluation of geology,hydrogeology,groundwater resources and environmental problems:?1?On the basis of geological conditions analysis,the plain is divided into five types of water-bearing media,I-coarse granular aquifer with single structure,II-coarse grained confined aquifer in a single structure of overlying fine soil,III-confined aquifer with coarse and fine grained interbedded structure,IV-confined aquifer with fine soil and V-medium and fine grained confined aquifer;the three-dimensional geological structure model of the quaternary system shows the spatial distribution and attribute feature of the sandy loam,silty clay,gravel,pebbles,coarse sand and loess.?2?On the premise of clear groundwater recharge,runoff and discharge conditions,research the origin and transformation process of the groundwater by using environmental isotope method,it shows that surface water and groundwater in this area were originated from atmospheric precipitation,but the main supply source is surface runoff from the mountain area in the Northern.The recharge source infiltrated directly into the lower aquifer through the single structure of the alluvial floodplain gravel;Affected by evaporation,?D and?¹⁸O values of shallow water were significantly higher;spatial variation of ³H value shows that the process of groundwater recharge experience different time for groundwater in different sections,and there is a big difference;with the increasing of depth,groundwater circulation speed is relatively slow;impeded by surface eolian sand,groundwater under the desert resulting in atmospheric precipitation and surface water can not form an effective recharge of it,and the groundwater renewability is poor.In addition,artificial mining is the most important way of groundwater discharge in the area,the mining process accelerated the update rate of groundwater,and change the natural conditions of groundwater circulation.?3?Analysis of the chemical characteristics of groundwater shows that the dominant cationic in groundwater are Ca²⁺and Mg²⁺,however,dominant anion are HCO₃^-and SO₄^2-,the main chemical type of groundwater are Ca·Mg-HCO₃and Ca·Mg-HCO₃·SO₄,those two types of groundwater accounted for 42.86%and 34.29%of the total groundwater in this area.From the north of the plain to the lower reaches of Ili River,total dissolved solids of groundwater is gradually increasing,affected by evaporation,total dissolved solid content of groundwater within depth of 20m was significantly higher than that of deep groundwater.?4?Identification of ion sources shows that the main controlling factors of groundwater chemical composition in the study area is rock weathering and evaporation crystallization;opposite to deep groundwater,shallow water is more significantly effect by evaporation crystallization.The Cl^-/Na⁺?mmol/L?relationship of groundwater shows that there are other sources of Na⁺in groundwater,except for the dissolution of halite,and the Na⁺in the deep water of those source is more than that of the shallow water.Proportional relation of?(Ca²⁺/Na⁺)/?meq/L?,?(Ca²⁺/Mg²⁺)/?meq/L?and?(Mg²⁺/Na⁺)/?meq/L?showed that the exchange between the cations is one of the main factors controlling the formation of groundwater,resulting in the proportion of Na⁺in groundwater increased in the whole section;and dissolution of a large number of minerals such as dolomite is the main source of Mg²⁺in underground water.In addition,of Inverse Hydrogeochemical Simulation showed that the halite,gypsum,calcium-montmorillonite and potassium feldspar has always been dissolved minerals,the dissolving process lead H₂SiO₃ to saturation and the formation of large amounts of H₂SiO₃ also contributed to precipitation of illite and quartz.