Study On Water Quality During The Transformation Of Surface Water To Groundwater Under Different Medium Conditions In Jinan City

The Jinan City has always been known as Spring City,with multi-source water supply pattern of karst groundwater,local surface water,the Yellow River water and the South-to-North water.In recent years,in order to protect the springs in Jinan City,the exploitation of groundwater is restricted and the current and future water supply sources in urban area are mainly based on local surface water,the Yellow River water and the South-to-North water.However,their water quality is worse than that of karst groundwater.Surface water spreading and artificial recharge of managed aquifer recharge technology can effectively improve water quality during the transformation of surface water to groundwater.The A and B reservoirs are the two major Yellow River water diversion reservoirs in Jinan City,but the Yellow River has heavy water pollution.After sedimentation in the sedimentation basin,it still contains fine particles of suspended solids and trace organic matter in the range of micron or even nanometer,but the conventional water treatment technology have insufficient ability to deal with these.There are three recharge projects in the upper reaches of the Yufu River in the west of Jinan,forming a multi-source water supply pattern for recharging aquifer,but in the risk assessment of these three projects,sulphate is still a high-risk item.However,the sulphate content in the source water of South-to-North water has exceeded the quality standard of groundwater III.Therefore,it is necessary to pay special attention to the sulphate in the recharge process of Yufuhe River.The different leakage of the A and B reservoirs and the channel leakage of the Yufuhe River all provide natural sites for the study of the water quality during the transformation of surface water to groundwaterIn this paper,the A and B reservoirs and Yufuhe River are chosen as research sites to study the change of water quality during transformation of surface water to groundwater under three different medium conditions?the transition zone of the Huang-Pan alluvial plain and the piedmont alluvial plain,the Huang-Pan alluvial plain and the piedmont inclined alluvial plain?.In this paper,field monitoring,isotope tracer test and laboratory test are combined to study changes of water chemical composition and its cause analysis,changes of organic matter and particulate matter during the transformation of the Yellow River water to groundwater under two medium conditions?the transition zone of the Huang-Pan alluvial plain and the piedmont alluvial plain,the Huang-Pan alluvial plain?,and to study the change of sulfate in the transformation process of the South-to-North water to groundwater through quaternary sand gravel of the piedmont inclined alluvial plain.The main results achieved are as follows.?1?After the investigation of the surrounding conditions of A and B reservoirs,9 water sample collection points were respectively selected for stable isotope tracer test.The test results show that:in the 9 water sample points of A reservoir,the water in seepage interception ditches of 0+900,1+.800,3+000 and 4+600 and groundwater in reservoir management office are mainly from the reservoir leakage,and water in the seepage interception ditch 7+400 and Jixi wetland are mainly from the local precipitation;in the 9water sample collection points of B reservoir,the water in seepage interception ditches of3+000,7+800,10+200 and 11+000 and the groundwater of reservoir management office and no.2 pumping station are mainly from the reservoir leakage,and the water in seepage interception ditch 5+600 is mainly affected by rainfall.This result provides a basis for selecting monitoring points in subsequent study of water quality during the transformation of reservoir water to groundwater.?2?During the process of water leakage from A and B reservoirs,the change of water chemical composition is as follows.The TDS of the groundwater and the interception ditch water of the two reservoirs all increase compared with the reservoir water,and the up trend of A reservoir showed a slight increase compared with the reservoir water,while the B reservoir showed a significant increase;During the transformation of surface water to groundwater,the main anion of the A reservoir changed from SO₄^2-to HCO₃^-,and the main cation changed from Na⁺to Ca²⁺.The main anions and cations of the B reservoir water are SO₄^2-and Na⁺,respectively,while the main anions and cations of groundwater become HCO₃^-and Mg²⁺,respectively,and the main anion and cations of the interception ditch become HCO₃^-and Na⁺,respectively.The cause analysis of water chemical composition are as follows.The changes of the ion components in A reservoir are mainly affected by the weathering of rock,while the B reservoir is affected by both the evaporation and the soil decomposition;the surrounding groundwater dynamic conditions of B reservoir are worse than those of the A reservoir,so the soluble salt is more likely to remain in the B reservoir zone,resulting in a significantly higher TDS content at each sampling point of the B reservoir than the A reservoir;Ca²⁺,Mg²⁺,HCO₃^-and SO₄^2-in the sampling points of the two reservoirs are mainly from the weathering and dissolution of carbonate minerals and sulfate minerals in coarse sand gravel or soil,the dissolution of carbonate minerals contain the dissolution of dolomite and calcite,and the proportion of calcite dissolution in A reservoir is greater than B reservoir.?3?Changes in organic matter and particulate matter during the transformation of surface water from A and B reservoirs to groundwater are as follows.The organic matter is reduced during the transformation of the Yellow River water in two reservoirs to groundwater through water spreading,the organic matter removal rate in the process of transformation to groundwater is higher than that to seepage interception ditches,and the removal effect of organic matter in B reservoir is higher than that in A reservoir;the organic matter in the water at each sampling point of the two reservoirs is mainly dissolved organic matter,and the proportion of adsorbed organic matter is low;in the process of leakage of two reservoir,the amount of particulate matter in water has been reduced in different orders of magnitude and the reduction amount in groundwater is much larger than that in water of seepage interception ditch;the amount of particulate matter in each water sample is concentrated in the particle size of 2⁵?m and the amount of particles larger than 5?m is extremely low;the particles in the range of 2 to 5?m are easy to migrate and the particles larger than 5?m are prone to deposition and clogging during migration.?4?Owing to large amount of south-to-north water was recharged into groundwater through Yufuhe River recharge projects,groundwater chemical type changed from HCO₃·SO₄-Ca type with background value to SO₄·HCO₃-Ca type after recharge,SO₄^2-changed from secondary anion to main anion,and the content of SO₄^2-in groundwater after recharge was higher than that of background value but lower than that of south-to-north water.Through laboratory experiments,it is found that the decrease of sulfate content is not caused by the action of water and rock and the water and rock action occurring in the experiment will hinder the decrease of sulfate concentration.