Hydrochemical characteristics and formation mechanism of groundwater in Nanning City

For further studying the hydro-chemical characteristics of groundwater,understanding groundwa-ter quality,and revealing the hydrochemical processes that control the evolution of the groundwater quality, we collected 22 sets of pore water and 7 sets of karst water to measue pH,cation and anion,total dissolved solids (TDS)and total hardness,and studied hydrochemical characteristics and formation mechanism.The results show that the average pH of pore water and karst water are both below 7,and the values of TDS and total hardness are almost the same.The most anions in pore water and karst water are both HCO -3 ,with values 68.08 mg/L and 106.68 mg/L,respectively.The cations include Ca2 + ≥Na+ >Mg2 + >K+ ,the aver-age values of Ca2 + are 24.04 mg/L and 31.34 mg/L,respectively.The groundwater hydrochemical composi-tions are formed by the weathered-leached effects and mixing action,groundwater hydro-chemistry type is HCO 3 - Ca type water.The geological environment is a major cause for the generally low pH value of groundwater.The impact of human activity on groundwater is increasingly important.The pH value and change of hydrochemical type are closely related to economic development,population increase,growth of industrial and mining enterprises and other human activity.