Characteristics of groundwater circulation and evolution in Jindong large coal base driven by coal mining:An example of Xin’an spring area

Jindong large coal base is very short of water resources and its ecological environment is fragile.With the large-scale coal mining and the intensification of human activities,the characteristics of regional groundwater circulation have changed drastically.Taking Xin’an spring area of Jindong coal base as an example,in view of the characteristics of groundwater circulation driven by coal mining in this area,the correlation and statistical analysis were used to study the effects of coal mining on the regional water environment.By establishing a multivariate correlation analysis between spring flow and mine water drainage,karst groundwater exploitation and precipitation,the attenuation mechanism of karst spring and main control factors were revealed.Based on the surface runoff cutting and calculation of the mixing ratio of hydrogen and oxygen stable isotope,the interaction between different water bodies and the source of mine water were identified.Combined with the characteristics of regional hydrogeological conditions,hydrochemistry and stable isotope,the pattern of groundwater circulation under the influence of coal mining was constructed.The results showed that:① The karst spring flow and karst water level of Xin’an spring area from 1956 to 2017 showed a general downward trend,both of which showed periodic change.The attenuation rate of karst springs flow reached 75% from 1956 to 2017 and karst water level dropped by 29.8 m from 1972 to 2017.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 east of the mining area had a strong influence on karst groundwater.The coal mining activity,as main influence way,has severely damaged the structure of the overlying aquifer in the karst water runoff area and caused the attenuation of surface runoff,resulting in a decrease in the amount of groundwater recharge.As coal mining expanded westward,the burial depth of coal seam was increased and karst water was located in a deep burial stagnation zone,so the impact of coal mining on karst water was weakened.③ The main control factor of the decay of karst spring flow and the drop of groundwater level was mine water drainage.In the rapid decline stage,karst groundwater exploitation was also an important influencing factor for spring flow attenuation and water level decline.④ Isotope calculations showed that the main source of mine water was fissure water,followed by pore water.Leakage of surface water and pore water were important sources of karst groundwater.Coal mining directly affected surface runoff and pore water aquifer,which indirectly affected karst groundwater level and karst spring flow.⑤ The groundwater circulation patterns driven by coal mining in Xin’an spring area could be divided into shallow,deep and local groundwater flow systems.The local groundwater flow system was mainly affected by coal mining,which was manifested as the concentrated discharge of groundwater to goaf.