Study On Variation Of Fe And Mn Content In Fluctuation Zone Of Groundwater Level

In groundwater source, the groundwater level rises and falls repeatedly due to theintermittent mining of the production wells, thus forming the fluctuation zone ofgroundwater level. The fluctuation of the groundwater level not only changes thegroundwater dynamic conditions, but also changes the environment and thecomposition of groundwater, which affect the migration and transformation of thegroundwater solute. The groundwater level fluctuation changes the acid/alkaline andthe redox conditions of the groundwater, which leads the occurrence of Fe and Mnreduction-dissolution, oxidation-precipitation and other hydrogeochemical process. Inthe pumping well, the accumulation of the precipitation of the oxidized Fe and Mn onthe well pipes and filters causes the decrease of water conveyance capacity, thereduction of water yield, the well plugging and even abandonment. Therefore, theresearch of the variation of Fe and Mn content in fluctuation zone of groundwaterlevel is the base of ensuring the continued reliable operation of the production wells,and also can provide guidance for rational planning of the water plant.In this paper, based on―Biogeochemical behavior of Fe and Mn in the hyporheiczone affected by groundwater exploiting‖project of NSFC, taking Huangjia watersource of Shenyang as an example, we carry out monitoring in the field, simulationexperiment and numerical modeling indoor aiming at the variation of Fe and Mncontent in fluctuation zone of groundwater level on the base of analyzing thegeological and hydrogeological conditions of the region. Through this study, we candraw the following conclusions:1. The content of Fe and Mn in the groundwater is affected by artificialexploitation. While mining, the groundwater environment and the content of Fe andMn evolve into the background value of the region groundwater. When the miningstopped, the water level recovers, the content of Fe and Mn decreases because of the occurrence of Fe and Mn oxidation and precipitation.2. We determine the forms of Fe and Mn existed in the groundwater effluent areFe(OH)3and MnCO3by the box experiment and speculate that the Fe and Mn havethe following reacting:4Fe2++O2+4H+=4Fe3++2H2O, Fe3++3H2O=Fe(OH)3(S)+3H+,Mn2++HCO3-=MnCO3(S)+H+.3. During the groundwater level declines, there is a mixing between the sand boxoriginal water and the inflow, which makes the groundwater outflow evolve into theinflow. During the groundwater level recovers, affected by the DO、Eh and pH of thegroundwater, the oxidation of Fe(II) and the precipitation of Mn are first enhancedand then weakened, and the content of Fe and Mn in the outflow is first decreased andthen increased.4. In the vertical direction of the groundwater level fluctuation zone, from thebottom to the top, the oxidbillity of the groundwater environment is enhanced, thecontent of Fe and Mn in the outflow is decreased, and the ratio of Fe(III) is increased.In the horizontal direction, from the small amplitude of fluctuation to big, the DO andEh of the groundwater increases, the oxidation and precipitation are enhanced, thecontent of Fe and Mn is decreased, and the ratio of Fe(III) is increased. While thegroundwater level fluctuating, the shorter the production time lasts, the less amount ofFe and Mn participates in reaction, the more content of Fe and Mn is in the outflow.5. The numerical modeling by GMS can reflect the basic characteristics of theflow and the variation of Fe and Mn content in the experiment. It shows that the longtime continuous mining or high frequency mining will make it easier for Fe and Mn inthe groundwater to oxidize and precipitate.