Reactive transport modeling for the effect of pumping activities on the groundwater environment in muddy coasts

Intensive pumping activities threaten the coast groundwater environment and have a negative impact on aquifer systems. A comprehensive understanding of these effects is important for the management of coastal ground-water resources. However, this is challenging, particularly for coastal saline groundwater systems due to complex water-rock interactions. In this study, a coupled variable-density flow and hydrochemical reaction model was used to examine the effects of pumping activities on the groundwater environment on the southern coast of Laizhou Bay, China, which is a typical muddy coast. The model successfully captured the hydrodynamic and hydrochemical changes, and the water-rock interactions, during three different exploitation stages: (1) evapo-ration and water-rock interactions were the primary controls on groundwater evolution during the weakly pumped stage (before 1995); (2) the groundwater level began to decrease and saltwater intrusion was aggravated during the small pumping stage (1995-2005); and (3) significant hydrodynamic and hydrochemical changes occurred at the saline/freshwater transition and pumping zones during a period of intensive pumping (after 2005). Our findings revealed that water-rock interactions are the primary drivers of hydrochemical evolution at the saline/freshwater transition and seaward saline groundwater zone, whereas hydrodynamic changes are the main drivers in the pumping and deep saline-brine water zones. Furthermore, we discussed the effects of hy-drodynamic variations and water-rock interactions on the aquifer matrix and identified that irreversible changes occurred mainly in the pumping zone and saline/freshwater transition. In conclusion, our study highlights the importance of considering both hydrodynamic and hydrogeochemical factors when managing coastal ground-water resources. By developing a better understanding of these complex interactions, we can minimize the negative impacts of pumping activities and preserve the long-term sustainability of coastal groundwater resources.