Abstract
Groundwater is the most important source of water supply in Beijing city. However, groundwater has undergone intensive total hardness pollution caused by water-rock interaction and by human activities. Analysis of monitoring data of 30 years shows that the high concentration of total hardness is relationship with carbonate mineral dissolution and cation exchange. But speciation calculations of two flow path using the hydrogeochemical modeling code PHREEQC indicated that the annual contribution of carbonate dissolution and cation exchange to concentration of Ca2+ and Mg2+ is less than 1 mgâL-1, which was far less than that observed. The results illustrated that carbonate mineral dissolution and cation exchange in aquifers play a small role in the contribution of groundwater chemical evolution, and also imply other anthropogenic sources exist indirectly.
Highlights
The study area is located in the upper and middle sections of the alluvial fan of the Yongding River, this includes several Beijing administrative divisions such as the Shijingshan District, Chaoyang District, Fengtai District and the piedmont region in Haidian District (Figure 1)
For the analyses of water-rock interaction on the total hardness in groundwater, two scenarios of mineral dissolution and ion-exchange + mineral dissolution were used in the simulation
Comparison of simulated values and measured values shows that the concentration of Ca2+, Mg2+ and HCO3- was larger than the measured values of these of point I and II in 2000
Summary
The study area is located in the upper and middle sections of the alluvial fan of the Yongding River, this includes several Beijing administrative divisions such as the Shijingshan District, Chaoyang District, Fengtai District and the piedmont region in Haidian District (Figure 1). In the western study area, the water quality was relatively good. The total hardness and concentrations of NO3-, Cl-, SO42-, TDS, etc are generally higher in the northern and western regions of the confined aquifer. In some eastern parts of the alluvial fan, shallow aquifers with a depth in 0–40 m, have higher concentration of total hardness and nitrate as nitrogen (N-NO3-). Research has shown that the higher total hardness of groundwater in the Beijing urban areas are influenced by anthropogenic activities. The contribution of total hardness from mineral dissolution is the secondary water rock interaction [2]. PHREEQC was used to simulate the impact of mineral dissolution and ion exchange which influence the evolution of total hardness in groundwater quality
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