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Groundwater is the main source of water in the grassland in eastern China, this region is one of the largest coal bases in China. It is of great significance to study the influence of opencast coal mine exploitation on the chemical characteristics of groundwater in grassland and thus to evaluate the suitability of irrigation water based on changes in the chemical characteristics of water. To study the background values of the chemical characteristics of groundwater and thus to assess the effects of high-intensity coal mine exploitation on groundwater, the water samples in this study were obtained from the mining site, as well as from private wells and rivers. It is found that the dominant hydrochemical types of the local surface water and groundwater are the Ca2+-Mg2+-HCO3–and Na+-Cl–types. The concentrations of Na+, HCO3–and SO42–are relatively high in these water samples, and nearly all of them exceed those in the WHO and GB 5749-2006 standards. Both the shallow aquifer water and surface water samples exhibit high salinity, low and moderate alkalinity, and low conductivity, which indicates that they can be used for irrigation. However, the quality of the deep groundwater samples is Permissible to Doubtful, and the coal seam aquifer water is not suitable for irrigation due to its high salinity, high alkalinity and high conductivity. To guarantee the safe usage of domestic and irrigation water, mine drainage is an important alternative to alleviate the local water usage contradiction. The post-processing drainage of coal seam aquifers should be fully taken into consideration. A groundwater monitoring network around the mining area, including urban areas, should be established and improved. The coal seam aquifer water source should be adequately avoided during future well drilling.

The exploitation of coal resources can lead to change of regional environment, and open-pit mining makes even more direct impact on vegetation, topsoil, surface water and underground water in grass area. Studying the change of hydrogeological condition caused by open-pit mining is beneficial for rational utilization of water resource in grass area and guaranteeing normal exploitation of open-pit mine. In this study, the Shengli 1 open-pit coal mine with typical hydrogeographical features, locating in typical meadow steppe area, was taken as researched area. Through collecting basic mine production data, such as annual output, drainage quantity, water inflow, the water inflow (including static-storage and recharge rate) of mine was predicted and calculated by horizontal catchment channel method, big well method and replenishment quantity method, respectively. This study investigates the hydrogeological condition changes of open-pit coal mine in grass area during production process. Results show that the static storage of hydrogeological unit exerts great impact to coal mine exploitation and production in early stage, while recharge rate exerts continuous influence to the whole mining process. As the quarternary loess in earth surface of steppe area is thick, and phreatic layer has a direct association with mining pit, the replenishment quantity method can achieve the most accurate calculation; the influence of open-pit mining to geohydrologic condition is mainly determined by aquifer hydraulic conductivity and mining depth.