Water quality prediction of shallow groundwater recharge in the western suburbs of Beijing

Groundwater recharge can not only cover the deficit of groundwater resources,but also dilute and purify contaminated groundwater.The recharge experiments at Beijing Water Source No.4 Plant and the PHREEQC simulation software were used in this study for water quality mixing simulations and water quality prediction.The results showed that the recharge has a great impact on the water quality of South Well,but limited impacts on that of North Well and East Well.The water quality of South Well was upgraded from Class Ⅲ to Class Ⅱ.The chloride,sulfate,nitrate and bicarbonate were recharged and their the concentration.at the end were very close to those of the recharge wells.The final concentrations of potassium,calcium and magnesium were slightly lower than those of the recharge wells,probably due to cation exchanges.The simulated water quality of mixed water had a good correlation with the observations,and a linear equation of the simulation mixing ratio and recharge time of South Well were obtained.Its coefficient of determination (R2) was as high as 0.999.It predicted that the groundwater in Beijing needed 11 days to be recharged under the same conditions for the water quality being upgraded from the Class Ⅳ to Class Ⅱ.The water quality prediction method of this study can effectively improve the efficiency of groundwater recharge and has useful guideline for groundwater recharge prediction.

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