*2.3. Groundwater*

The flow of groundwater follows the terrain trend from west to east, although the specific direction and conditions of runoff vary across the whole area. In the study area, the groundwater is pore-water, according to the formation conditions and distribution, it can be divided into phreatic and confined aquifers. Hydrogeological conditions in the study area are, of course, controlled by formation lithology. It can be divided into two areas. The west is a single river aquifer, and the East is a multi-layer structure. The thickness of a single aquifer is thickened from north to south, and the general thickness is 230–265 m. The thickness of the phreatic aquifer within the multilayer structure zone is only 20–60 m. This study targeted the Phreatic aquifer. There are two major recharge sources of groundwater in the Yinchuan area: natural and artificial recharge. Natural recharge occurs mainly through atmospheric precipitation, lateral runoff, and flood loss, while artificial recharge occurs mainly through irrigation infiltration, groundwater irrigation recharge, and drainage system leakage. Evaporative discharge, with a proportion of more than 45%, exceeds manual mining and lateral runoff, which are the two other main discharge modes in the region [33]. Lateral runoff mainly occurs toward the Yellow River and drainage ditches.
