Characteristics of groundwater circulation and evolution in Yanhe spring basin driven by coal mining

Abstract The Yanhe spring basin located in the Jindong coal base is relatively short of water resources and the ecological environment is fragile. With the large-scale mining of coal resources and the intensification of human activities, the characteristics of regional groundwater circulation have evolved dramatically. In this paper, through the multivariate correlation analysis between spring flow and coal mining volume, karst groundwater extraction volume and atmospheric precipitation, the attenuation mechanism and main controlling factors of large karst springs are revealed. Combined with regional hydrogeological conditions, hydrochemistry and stable isotope characteristics, the mutual transformation relationship between different water bodies was analyzed, and the groundwater circulation model under the influence of coal mining was constructed. The research results show that: (1) The karst large spring flow and karst groundwater level in the Yanhe spring basin generally showed a downward trend. From 1957 to 2017, the spring flow attenuation range reached 75%, The three stages of 1956-1976, 1977-2002 and 2003-2017 were characterized by steady fluctuation, substantial decrease and slight decrease. (2) Coal mining in the central and southern parts of the mining area has a strong impact on karst groundwater. The main way of influence is that coal mining activities cause serious damage to the structure of the overlying aquifer in the karst groundwater recharge runoff area and attenuation of surface runoff, resulting in a decrease in karst water recharge. With the expansion of coal mining to the north, the burial depth of the coal seam increases, and the karst groundwater is a deep stagnant zone, and the influence of coal mining on it is weakened. (3) the hydrochemistry types of karst groundwater in Yanhe Spring basin have gradually diversified and local pollution has increased. (4) The main controlling factor of the karst spring flow attenuation and groundwater level drop is coal mining. In the rapid decline stage, karst groundwater exploitation is also Important factors affecting spring flow attenuation and water level decline. (5) Isotopic calculations show that surface water seepage and pore groundwater overcurrent are important sources of karst groundwater recharge. Coal mining directly affects surface runoff and pore groundwater aquifers, which in turn indirectly affects karst groundwater level and karst spring flow. (6) The groundwater circulation pattern under the coal mining conditions in the spring area can be divided into shallow, deep and local groundwater flow systems. The local groundwater flow system is mainly affected by coal mining, which is manifested as the centralized discharge of groundwater to the goaf.