Study On Groundwater Environment And Its Pollution Risk Assessment In Ding-Jing Central Region

Ding-Jing area is rich in oil and gas resources with a large mining intensity, which is bound to adversely affect the groundwater in it.The groundwater environment and its pollution risk are studied in this paper based on the test results of 94 groups of groundwater sampled in 2013 as well as the existing data such as geology, environment in this area.The research results can provide a scientific basis for the reasonable groundwater development and utilization as well as pollution prevention and control, in the studied area.Firstly, the groundwater hydrochemistry type and its evolution rules are analyzed.Groundwater quality in the studied area is mainly controlled by native hydrogeological conditions,and local affected by human activities.The phreatic water hydrochemistry type in the east of study area and the north of DingBian region mainly is HCO3, in the southwest of DingBian region mainly is Cl.The quality of confined water is poor than phreatic water,and the hydrochemistry type mainly is HCO3 in the northern region,mainly SO4 in the southeast region,and the type in the southwest region mainly is Cl. Then using PHREEQC software to simulate the hydrogeochemical evolution of two sections in the studied area,and the simulation results show that the water-rock interaction of phreatic water and confined water are almost the same.Along the flow path,the halite and gypsum mainly precipitate from groundwater,the fluorite mainly dissolve into the water.And the precipitation and dissolution rate gradually slowed.Besides, the water-rock interaction of phreatic water is more severely and the change of ion content is more obvious.Secondly, using the methods of Single Index Evaluation Method, Nemerow Index Method and Fuzzy Comprehensive Evaluation Method to assess the groundwater quality and pollution,which respectively based on the "Groundwater Quality Standards" (GB/T14848-93) and the environmental background value in the area.Then using weighted average method to obtain the final results of groundwater quality and pollution evaluation on the basis of those three evaluation results.The final results show that the groundwater quality is poor all over the studied area and the proportions of phreatic water and confined water beyond the specified limits of Class III are over 75%.Besides,the groundwater is contaminated in different degrees in this area.,which mainly distribute the pollution level in mild, moderate and severe, then followed by level in very severe water pollution,the unpolluted water is very little,which should arouse people’s attention.Finally, using the risk index to evaluation the groundwater pollution risk according to the vulnerability of groundwater and the intensity of pollution sources.The areas of very high and high groundwater contamination risk are mainly distributed in the southern loess area of DingBian and the valley area in study regions with intensive pollution sources;the moderate risk of groundwater contamination are mainly distributed in southern loess areas of JingBian with better vulnerability but intensive pollution sources as well as in middle plains of DingBian and northern desert of JingBian with poor vulnerability and less dense of pollution sources;the low risk of groundwater contamination are mainly in northern desert of DingBian with poor vulnerability but less pollution.