Risk Assessment Of Shallow Groundwater Pollution Under Shale Gas Extraction In Karst Area

Shale Gas as a new energy can effectively adjust our national energy structure,while the exploitation will cause some influence to groundwater environment of both shallow surface layer and deep underground,the objective of this study is to access the ground water pollution risks in the shallow surface layer.we consider the outlet liquid which is storeed at surface as pollutiong risks assessment pollutant.Developing the karst groundwater system pollution risk under the Shale Gas exploitation can provide the basis of groundwater environment protection.According to the analytic result of charactic components in outlet liquid,this study considers chlorid ion,sodion,ammonium ion,barium ion,strontium ion,nickel ion,anti-1,2-two vinyl chloride,carrene.Groundwater pollution risk assessment has two parts,one is essential vulnerability evaluation,and the other is pollution hazard evaluation.The essential vulnerability uses the european model(OCP),by fully considering charactoristics of karst area,this sthdy chooses six indeies,they are overburden type,physiognomy type,soil media type,terrain slope,annual rainfall and aquifer karst development degree.While,the pollution resource hazard evaluation chooses three factors of specific pollutants,which are toxicity,transferability and degradability.The weight use the analytic hierarchy process(AHP)method to figure out.Through using ArcGIS to overlay indeies,we get the result of groundwater pollution risk distribution at karst area under Shale Gas exploitation,which be classified to five degrees.And,It turns out that the high risk area mainly locates at the north side of the study area,little part of the south-west,,few place at the middle part.Little high risk area mainly distributes at the south-east part and few north-west side part,and the distribution is relatively concentrated.The other parts of the study area are moderate,little low and low risk,the distribution is relatively wide,accounted for71.73 proportion.Main factors of high risk area are overburden type and aquifer karst development degree.By concidering geology,hydrogeology and pollutiong resource charactoristic of study area,the result can reflect basic geological survey in karst areaand influence of groundwater enviroment under Shale Gas exploitation,can provide dependence to effective protect and scientific manage of groundwater at Shale Gas exploitation area.