The characteristics of shallow and deep groundwater in Southern Laizhou Bay

The south bank of Laizhou Bay has abundant types of groundwater. Since the 1970s, a relatively complex groundwater environment has been formed under the background of underground freshwater and brine mining. By collecting available groundwater data and combining them with existing field monitoring data, the hydrochemical characteristics of shallow and deep groundwater in the study area were analyzed. Results show that shallow groundwater is closely related to the outside periphery and is influenced by the combination of precipitation and groundwater mining (continuous and staged), resulting in an overall meteorological-mining pattern. The brine area of deep groundwater presents a mining type, while the remaining areas show a meteorological-mining type. Under the conditions of freshwater and brine mining, two large-scale underground water depression funnels are formed, with the lowest groundwater levels of −8.78 m and −44.60 m, respectively. Based on the distribution of groundwater quality and water level characteristics in the research area, the zoning of groundwater was discussed. From south to north, the shallow groundwater could be divided into groundwater runoff zone (S-1), strongly mixed groundwater zone (S-2), and groundwater seawater interaction zone (S-3). The S-1 zone is affected by rainfall infiltration, lateral supplies from the mountain front, and surface runoff, accompanied by feldspar weathering and dissolution of carbonate minerals. The S-2 zone is controlled by the action of a groundwater depression funnel, causing a strong mixing of fresh and saline water, accompanied by a process of fresh water replenishment. The S-3 zone is significantly affected by the brine groundwater funnel, which can easily cause seawater to backflow into groundwater, leading to the interaction between groundwater and seawater. The deep groundwater could be divided into groundwater runoff zone (D-1), groundwater mixing zone (D-2), and brine storage zone (D-3). The groundwater in the D-1 zone is mainly controlled by the interaction between water and rock during the flow process, which is weaker than that in the S-1 zone. There is a mixture of fresh and saline water in D-2 zone, mainly affected by dispersion effect, and the mixing effect is weaker than that in S-2 zone. The average total dissoloved solid (TDS) value of groundwater in D-3 zone was as high as 119 624.94 mg/L. Under the action of the relative aquifuge, it is in a sealed state and always maintains a high concentration. Due to the influence of underground brine mining, the water level continues to decrease.