Hydrochemical Characteristics And Hydrochemistry Processes Of Groundwater In Anyanghe River Alluvial Fan

Located on the eastern Taihang Mountain of the North China plain,Anyanghe river alluvial fan(ARAF)is one of the typical piedmont river alluvial fans with its groundwater is the main supplying water resource in Anyang city.The groundwater in the ARAF is chronically extensive exploited with the deteriorating quality.Likewise,the deep confined aquifer in the distal fan of the ARAF has experienced increasing intensity of exploitation which dramatically improves the contamination risk.Researches on characterizing isotopes and hydrochemistry and analyzing geochemistry processes of groundwater will provide guidance for groundwater quality protection and reasonable exploitation,however,the systematical study still remains unclear.Therefore,based on the consequently hydrogeology field survey and analysis on collected precipitation,surface water,and groundwater samples,the hydrochemical and isotopic characteristics and hydrogeochemical processes of groundwater in alluvial and diluvial fan of Anyang River were systematically studied.The results are summarized below.(1)The seasonal effect of the stable hydrogen and oxygen isotopes in precipitation was considerable,rainy season were much negative than that of the other season.A local meteoric water line was determined to be?D=(7.33±0.37)?¹⁸O+(5.97±2.46)‰by applying unary linear regression on the data of stable hydrogen and oxygen isotopes of precipitation.The annual tritium content in precipitation varied slightly,it was greater than 10 TU from April to June but lower than 10 TU from July to October.Characteristics of stable hydrogen and oxygen isotopes of surface water were controlled by the local precipitation and affected by the effects of evaporation and concentration while the surface water flows from the upper reaches to the middle-lower reaches.Moreover,Xiaonanhai spring acts as a key role to relieve the water quality deterioration of the Anyanghe River.(2)(2.1)The confined groundwater system in the proximal fan of the ARAF hosted with modern groundwater,it has local precipitation infiltration as the most important recharge source,closely followed by river water seepage.The hydrochemistry type was HCO₃·SO₄-Ca and total dissolved solids(TDS)was 0.622g/L,respectively.(2.2)The confined groundwater in the medial fan of the ARAF was modern groundwater featured by strong renewable ability.(2.2.1)In the areas near the hilly area and the proximal fan,the hydrochemistry types were HCO₃-Ca and HCO₃·SO₄-Ca,and TDS was 0.4-0.7 g/L.(2.2.2)In the central area of the medial fan,the hydrochemistry types of the confined groundwater were HCO₃·SO₄-Ca,HCO₃·Cl·SO₄-Ca,and HCO₃·SO₄·Cl-Ca,respectively and TDS increased to 0.7-1.0g/L.(2.2.3)In the transition between the medial fan and the distal fan,the confined groundwater hydrochemistry was characterized as HCO₃·Cl-Ca and HCO₃·Cl-Ca·Mg with TDS decreased to 0.7-0.9 g/L.(2.3)The deep confined groundwater in the medial and distal fan had isotopic characteristics of?D-76.7--66.9‰,?¹⁸O-10.3--9.2‰,and was free of tritium.The hydrochemistry types were HCO₃-Ca·Mg,HCO₃-Ca·Na,HCO₃-Na·Mg·Ca,and HCO₃-Na·Ca·Mg with TDS was about 0.5 g/L.This deep confined groundwater was originated from the precipitation events during the Late Pleistocene epoch(15 ka B.P.).(3)Ions ratio,hydrochemistry diagrams,and isotopes methods were employed to investigate the dissolution reaction.The results showed that(3.1)the dissolution reaction of carbonate minerals is the foremost factor determining the hydrochemical compositions of the Xiaonanhai spring and the groundwater in western hill of the ARAF.(3.2)The groundwater hydrochemistry of the southern and northern hills as well as the proximal fan was mainly influenced by the dissolution reaction of carbonate and silicate minerals.Furthermore,the contribution of silicate minerals was greater for the quartic water than the confined groundwater.(3.3)The dissolution reaction was attenuated steadily from the hilly area to the proximal fan.(4)Na/Ca value and the Reverse Mass Conservation Simulation of PHREEQC were employed to analyze cation exchange reaction.The results showed that the cation adsorption reaction was considerable when deep confined groundwater flows laterally from the medial fan to the distal fan.There are two groundwater flow paths,from sampling sites 33 to 45 and GW26,respectively.The amount of Na⁺transferred from clay into groundwater was 0.870 mmol/L and 1.583 mmol/L for the first and second flow path,respectively.The mass of Ca²⁺or Mg²⁺precipitated from the groundwater was about 0.430 mmol/L or 0.790 mmol/L for the first and second flow path,respectively.(5)A multi end-member mixing model run by MATLAB was developed based on the mass balance law and math model of quadratic programing..The hydrochemical characteristics of the shallow confined groundwater system in the medial fan were controlled by the mixing of multi end-members.The shallow confined groundwater system within the region of the first to the fourth water supply plants was considered as a mixing cell.This mixing cell has six recharge end-members,(?)lateral flow from the proximal fan,(?)mountain front recharge form southern and northern hilly areas,(?)lateral flow from the northern edge of the medial fan,(?)Anyanghe river water seepage,and(?)precipitation infiltration,respectively.The results of the multi end-member mixing model programing showed that their contribution proportions were 0.48,too small to ignore by comparison,0.13,0.18,0.12,and 0.08,respectively.