Impacts of Aquitard Properties on an Overlying Unconsolidated Aquifer in a Mining Area of the Loess Plateau: Case Study of the Changcun Colliery, Shanxi

Quaternary unconsolidated porous aquifers are crucial to industrial, agricultural, and domestic water as well as ecological requirements in semiarid regions. Underground mining can influence aquifers even when they are located out of the fractured zone. Slight but continuous leakage should not be ignored. This study focused on the flow from a leaky aquifer. The deformation and fissure distribution characteristics and changes in the water resistance of a clay aquitard underlying an unconsolidated aquifer were studied by physical modeling, and the impacts on the unconsolidated aquifer were analyzed. Considering the mining-induced changes in the overburden hydraulic conductivity, we used numerical groundwater flow simulations of an unconsolidated aquifer to predict the flow dynamics of the aquifer for different scenarios. The influences of aquitard thickness and permeability on the groundwater flow regime of the regional unconsolidated aquifer under the mining area were quantitatively analyzed. This case study shows that the degree of coal extraction influence on the leaky confined aquifer depends on the properties of the aquitard beneath the aquifer. When the thickness was as high as 40 m and the hydraulic conductivity was as low as 10 −6 cm/s, the aquitard could effectively prevent a water level depression. The results have practical implications for coal mining with water resource conservation.