Assessment of surface–groundwater interactions using hydrochemical and isotopic techniques in a coalmine watershed, NW China

The Kuye River is located in Shenfu-Dongsheng coalfield which is the most important energy center in China. The region climate belongs to arid and semi-arid climate with vulnerable ecological environment. Groundwater dewatering for coal mining may cause stream flow reduction in the watershed. Therefore, the effects of coal mining on surface water–groundwater interactions are of great concern in the watershed. In this paper, descriptive statistical method, stable isotope measurements and Piper trilinear diagram are employed to analyze the interaction among river water, groundwater (both in wells used for drinking water and in mine water discharges) and rainwater. The chemical analysis of water samples shows that all the water sources are dominated by HCO₃⁻ as anions, by Ca²⁺ and Na⁺ as cations. River water has a chemical composition of the Na·Ca–HCO₃·SO₄ facies. The chemical composition of mine water discharges is similar to river water within the range of 5 km from the river course. Similarly, groundwater samples from drinking water wells that are less than 180 m deep and are located within 1 km of the river are similar to that of river water. Groundwater recharge analysis shows rainwater is the main source of drinking water recharge when drinking water wells are more than 180 m and also the main source for mine water discharge more than 5.5 km from the river course.