Karst Spring Water Pollution By Abandoned Coal Mines

In recent years,with the integration of coal resources and the depletion of energy,the number of coal mines closed in China has increased dramatically.The closure of coal mines leads to the pollution of some springs in Karst areas,which seriously endangers the ecological environment of the basin and living of the surrounding residents.Considering the Karst geological conditions and the groundwater runoff patterns,it is necessary to study the problem of spring water pollution caused by shut pit coal mines,so as to provide theoretical support for the protection and treatment of spring water.This paper takes the Longdong spring pollution problem caused by shut pit coal mine as an example,through field work such as the analysis of hydrological geology survey,geopHysical and drilling exploration,field monitoring,combined with indoor data processing,PHREEQC hydrogeochemical simulation,construction of hydrogeological model and other work.The cause of formation of spring water,pollution source of spring water,evolution of acidic water in abandoned coal mine and process of spring water pollution are analyzed.The trend of spring water pollution is predicted.The main conclusions are as follows:1.The formation of Longdong spring is mainly controlled by structure,and Dafeng Tunnel syncline is the water storage area of Longdong spring source;Fault F1 is the water conduction channel,which leads the upper Maokou-Chihsia groundwater to the lower Devonian to supply water for Longdong spring;Fault F3 cuts the stratum to provide a platform for Longdong spring outcrop.Longdong spring recharge area is the outcrop stratum of Maokou-Qixia in the northwestern part of the study area and the river on the right side of F1 fault.Runoff area is the Devonian stratum between F1 fault and F3 fault in the central part of the study area.2.Through the Evaluation of water quality and pollution degree of Longdong spring.The pollutants of spring water are acid water of coal mine whose iron,manganese and sulfate exceed the standard.Through the pollution source exploration,it is determined that the pollution sources of Longdong spring are acid water in Feilong Coal Mine,and the pollution scope is distributed in the middle of Feilong Coal Mine.3.The goaf is oxidized in wet season after coal mine closure,and pyrite is oxidized and cation exchanged to form high iron,high manganese and weak acidic HCO₃·SO₄-Ca·Mg water.In dry season,pyrite is oxidized,gypsum is dissolved and cation exchanged to form SO₄-Mg water with high iron,high manganese,high sulfate and strong acidity.The pollution factor concentration of goaf is affected by the rate and quantity of groundwater recharge,the time of water-rock interaction and the water environment inside the goaf rapidly.4.The goaf of closed pit coal mine provides space for the production and storage of acid water.According to the dynamic characteristics of spring water pollution,it can be preliminarily determined.The groundwater level in Devonian rises when rainfall occurs in the study area,some Devonian groundwater is rapidly poured into the goaf along the weak structure or floor damage zone near the goaf.which is hydraulically related to acid water in the goaf.End of rainfall,mixed acidic water gushes out along the Devonian groundwater intake channel,rapidly replenishing Longdong Spring,and the spring water is polluted.5.Change rate of Fe in water leached from coal gangue with different deposition Years in watershed.The pollution degree of Longdong Spring increases continuously in 17 years after the closure of coal mine,but the increasing trend is different.Among them,the acceleration rate of iron is the fastest in 14 years when the coal mine is closed,and then the increase rate decreases gradually,but the decline rate is slow.