Study On The Chemical Characteristics And Simulation Of Groundwater In Overdraftedzone Of The Hutuo River Basin

The Hutuo River alluvial plain is the most intense area of human activity in the North China Plain,with depleted surface water.Groundwater is the main water supply source,which accounts for more than 80%of the total water supply.Full fresh water area of shallow groundwater has produced a regional groundwater drawdown funnel,as a result of severe over exploitation.Groundwater depth in the center of funnel is reduced from the initial 7.8m to the current 50m.The average dry thickness of aquifer is about 21m,and the influence area of the funnel is 474km².Monitoring shows that the content of characteristic component groundwater is significantly higher than the surrounding,with showing a rising trend.Therefore,it is an important scientific basis for the control of water resources in the area to study the change of the hydrodynamic field and the water chemical field and the coupling mechanism.The author collects 114 groups of groundwater samples in the study area.According to the hydro geochemical theory,using the mathematical statistics,correlation analysis,ion ratio and water chemistry analysis,it is found that the groundwater chemical types in the study area with HCO₃-Ca·Mg and HCO₃·SO₄-Ca·Mg type water,are mainly influenced by the upstream surface water containing sulfate impact.And it forms a strip of HCO₃·SO₄-Ca·Mg type water along the Hutuo River.From 1970s to 2012,the distribution range of HCO₃ type water and HCO₃·Cl type water are decreased,while HCO₃·SO₄ type water distribution range shows an increasing trend.The author evaluates the shallow groundwater quality in the study area by using the evaluation method of single index and comprehensive index:I^III type groundwater accounts for 51.75%of the total sampling point,IV type groundwater accounts for 41.23%,and V type groundwater accounts for 7.02%.The groundwater regime and water quality monitoring data show that,the change of groundwater level is very consistent with the change of water chemistry in the study area,and the groundwater under this environment in this area has experienced the period of complementary and discharging balance,the initial period of abnormal change,the period of abnormal change and the period of slow change.The total dissolved solids,total hardness,Cl^-and SO₄^2-are positively correlated with groundwater depth in the study area,and the correlation coefficients are 0.879,0.8046,0.9,0.8334.In wet years,the contents of the main ions show a downward trend due to the influence of the water level rise.The groundwater in the study area is mainly affected by rock weathering.Weathering dissolution of rock-forming minerals,such as quartz,feldspar,amphibole,mica and other silicate,aluminum silicate,calcite,dolomite and other carbonate,and salt rock,are the main sources of ions in the regional water.The author use PHREEQC to establish a model of water-rock migration in the funnel area,and simulates three periods of the water level drop,the water level rise and the slow decline.Under the condition of a substantial reduction in the groundwater level,dolomite,fluorite and gypsum are precipitation,and calcite and carbon dioxide are in the state of dissolution.The simulation in water level rise period shows that the mineral phase has a great change compared with the other two periods in the aspects of migration and migration status.