**2. Background of the Study Area**

The Shuangqiao River originates from the northern foot of the Xiaoqinling Mountains and is formed by the confluence of Mayu, Taiyu, Shancheyu, Dongtongyu, and Xiyu. region (Figure 1c,d [46]). Its flow direction is from south to north, with a length of 14.8 km. It

belongs to the warm temperate continental monsoon semi-humid-humid climate zone, with dry winters and little rain, and humid and rainy summers. The annual precipitation is 587.4 mm and the evaporation is 1193.6 mm. At present, it is mainly used for industrial water. Shuangqiao river channel has not been fully regulated by 2020. The groundwater types in this area are mainly Archean bedrock fissure water and quaternary pore water. There are complex hydraulic relationships among different geological and geomorphological types (alluvial fan, loess plateau, and river alluvial terrace) in the study area. The field investigation found that there was a phenomenon of water-saturated zone-aeration zone-upper stagnant zone-relative impermeable zone-aeration zone-saturated zone in a river in the Little Qin Mountains region. According to the shallow water level in the middle and lower reaches of the river in the mining area, the groundwater is not polluted in the area with good hydraulic alternation between the river and groundwater in the alluvial-alluvial slope.
