Analysis of Origin of Groundwater in Jianghan Plain Based on Typical Drillings

With the increasing demand of groundwater and the continuous deterioration of water quality in Jianghan plain, it is of great significance to deeply explore the causes of groundwater for rational utilization and evaluation of groundwater. Taking YLW01 in central region and HJ007 near Hanjiang river as the study objects, porewater samples were squeezed from the drilled undisturbed soil columns to analyze hydrochemical characteristics and hydrogen and oxygen isotopic characteristics. The results show that:YLW01 porewater samples of sandy soil in middle-deep depth were saline water and the total dissolved solids (TDS) ranged from 1 131 to 4 013 mg/L, while other porewater samples of clay were fresh water; HJ007 porewater samples were all fresh water. The high concentration of SO₄^2- (459~2 124 mg/L) of YLW01 porewater in middle-deep depth sandy soil was caused by Gypsum dissolution; the high concentration of NO₃^- (22~315 mg/L) of HJ007 porewater in middle-deep depth was caused by nitrification in soil. The chemical composition of porewater was mainly affected by mineral dissolution and cation exchange, and the degree of action in the Yangtze and Hanjiang River zone was different. Hydrogen and oxygen isotopic characteristics indicated that porewater came from atmospheric precipitation and the shallow groundwater in Hanjiang River zone was obviously mixed with surface water. The differences in chemical and isotopic concentrations of the two boreholes in Jianghan Plain were controlled by the sedimentary environment, sediment particle size and mineral composition of the Yangtze and Hanjiang River effecting zones.