Geochemical Characteristics of Shallow Groundwater in Jiaoshiba Shale Gas Production Area: Implications for Environmental Concerns

The geochemical characteristics of shallow groundwater are essential for environmental impact studies in the shale gas production area. Jiaoshiba in the Sichuan basin is the first commercial-scale shale gas production area in China. This paper studied the geochemical and isotopic characteristics of the shallow groundwater of the area for future environmental concerns. Results show that the average pH of the shallow groundwater is 7.5 and the total dissolved solids (TDS) vary from 150 mg/L to 350 mg/L. The main water types are HCO3-Ca and HCO3-Ca<bold>Mg due to the carbonates dissolution equilibrium in karst aquifers</bold>. The concentrations of major ions and typical toxic elements including Mn, Cr, Cu, Zn, Ba, and Pb are below the drinking water standard of China and are safe for use as drinking water. The high nitrate content is inferred to be caused by agricultural pollution. The shallow groundwater is recharged by local precipitation and flows in the vertical circulation zone. Evidences from low TDS, water isotopes, and high H-3 and C-14 indicate that the circulation rate of shallow groundwater is rapid, and the lateral groundwater has strong renewability. Once groundwater pollution from deep shale gas production occurs, it will be recovered soon by enough precipitation.