Impact of coal mining on groundwater of Luohe Formation in Binchang mining area

Abstract Groundwater of Luohe Formation is the main water source for industrial and agricultural and residential use in Binchang mining area, which is one of the key elements to water conservation coal mining. However, few studies are available to document the enrichment characteristics and influence of underground coal mining on groundwater for the Luohe Formation. This study evaluates the changes of groundwater levels and spring flow caused by mining activities to explore the influence mechanism of coal mining on groundwater by comparatively analysing existing mining data and survey data combined with a series of mapping methods. The results show that the aquifer of Luohe Formation are gradually thinning south-eastwards, disappeared at the mining boundary. In the vertical direction, the lithological structure is distinct, due to alternative sedimentation of meandering river facies and braided river facies. According to the yielding property, the aquifer is divided into three sections, namely, strong water-rich section, medium water-rich section, and weak water-rich section, which are located in northwest and central part, southwest, and the rest part of the mining area, respectively. Mining of Tingnan Coal Mine since 2004 has caused a 3.16 to 194.87 meters drop in groundwater level of Luohe Formation. Until 2015, 70.10% of the mining area undergoes a groundwater level drop larger than 10.00 meters. Another influence of underground mining is that the total flow from 34 springs in 8 southern coal mines of the area has decreased by 286.48 L/s with a rate of decrease at 46.95% from 2007 to 2017. The areas that groundwater level falls or spring flow declines are manly located in the mine gob areas. Results also indicate that the ratio of the height of water conducted fracture zone to the mining height in Binchang mining area is between 16.85 and 27.92. This may increase ground water flow in vertical direction, causing a water level in the aquifer system to drop and ultimately decreasing the flow from the springs. The research results will provide data and theoretical support for the protection of groundwater resources and water conservation coal mining of Luohe Formation in Binchang mining area.