Spatial and temporal variability of the chemistry of the shallow groundwater in the alluvial fan area of the Luanhe river, North China

Groundwater in the alluvial fan area of the Luanhe river, north China, was monitored every 2 months for a year. Subsequently, the temporal and spatial variability in the hydrochemical characteristics of the water was investigated using hierarchical cluster analysis (HCA) and a trilinear Piper diagram. It is found that the spatial variability in the groundwater composition from different monitoring wells has obvious differences, even if the distance between many of the wells is small. Also, the difference in the ion concentration was found to be up to fivefold for the same monitored well. Research has indicated that the groundwater’s chemical characteristics are mainly controlled by soil type, the amount of precipitation, the Luanhe river, the groundwater, and human factors. The thickness and continuous distribution of clay influences the velocity and ion exchange rate of the groundwater flow. This results in the amount of total dissolved solids in the groundwater increasing from upstream to downstream. In the flood season (June, July, and August), ion concentration gradually decreases as a result of the increased recharging of the groundwater due to precipitation. Classification using HCA indicates that the samples can be clustered into different groups according to correlation coefficients. Also, the chemical composition of the water from monitoring wells near the Luanhe river is approximately consistent with that from the Luanhe river. This implies that the samples have some compositions resulted from the mixing of groundwater and river water. The Piper diagram indicates that Ca2+, Mg2+, and HCO3− ions are the predominant ones present, i.e., the type of groundwater is of the Ca–Mg–HCO3 type.