Risk Assessment Of Karst Groundwater Of Jinci Spring Area

Jinci spring area is the second largest karst spring area in Taiyuan,which is the significant source of water use in Jinci district and western border mount zone.With the rapid development of social economy since 1980 s, the karst ground water quantity and quality of Jinci spring area have been threatened by a series of problems. Therefore, it is urgent for karst groundwater to be evaluated,protected and repaired.Based on the analysis of physical geography, geological and hydrogeology conditions, human activities in Jinci spring area, this paper modified existing evaluation system, regarding vulnerability and hazard as first grade indexes to built karst groundwater risk assessment model. The second grade indexes of vulnerability including antipollution vulnerability, resource vulnerability and potential vulnerability, and the second grade indexes of hazard including loss of value and status hazard. From the two aspects of water quality and quantity, 17 third grade indexes are selected to build the complete assessment system. The results not only could been applied to karst groundwater resource exploitation,land planning and utilization, but also have guiding value for the protection and restoration of karst groundwater environment in Jinci spring area, meanwhile, it has reference meaning for the other northern karst spring area.Firstly, based on the COPK assessment model, the factor of pollution source is added this model, forming the antipollution vulnerability assessmentmodel(COPKLu) with the other four factors overbite protective layer(O), runoff condition(C), infiltration recharge(P) and karst development degree(K).According to the actual situation of spring area, the resource vulnerability assessment select exploitation coefficient(E), infiltration recharge(P) and mining displacement(Md) to build EPMd model. Aiming at the potential threat of karat groundwater, the potential vulnerability assessment select goaf area(G),the thickness of aquiclude(T) and the water pressure(Pr) to build GTPr model.The antipollution vulnerability, resource vulnerability and potential vulnerability constitute the comprehensive vulnerability of Jinci spring area.Then, the loss of value assessment model consists of water abundance(At),groundwater quality(Al) and groundwater source protection areas(Pa). The status hazard assessment consists of groundwater pollution degree(Po) and amplitude of groundwater level(L). And these two factors constitute the comprehensive hazard. Finally, according to the result of vulnerability assessment and hazard assessment, the risk of karst groundwater in Jinci spring area is evaluated.Due to the multiple attribute of the assessment system, this paper choose iterative indexes method to evaluate. The weights is defined by analytic hierarchy process, and then various distribution map are weighted stack in Arc Gis to get the karst groundwater risk distribution map of Jinci spring area.The result shows that: the overall trend of karst groundwater risk is gradually lower from southeast to northwest. The regions of high risk mainly distributed in limestone exposed area of Fengyu valley, Jinyuan district, the leakage area of Fen River valley, Gujiao city and coal mine goafs distributed area of Wanbailin district. Because the infiltration recharge is large and the pollution source is concentrated in these regions, as well as there is some potential threat from mining. The low risk region mainly distributed in northwest and southwest of the spring area, along the line of Changan-Mayu village toward southwest to theborder of spring area, and the region of Xiazhuang and Ximing village in northeast of the spring area. The reason is that the protective ability of overbite layer is better, and in these regions the water exploitation and coal mining are less. Other regions belong to the medium risk region.