Analysis On Hydrogeology Effect Factors Of Pollution And Risk Assessment In Groundwater Well-fields Of Yinchuan

Yinchuan,the political, economic, and cultural center of Ningxia Province. In recent years, with the gradual expansion of the size of population of Yinchuan city, there is an increasing demand on water resources, a gradual increase in supply as well. Because of the large number of groundwater extraction, a deterioration of groundwater quality in urban areas and the expansion trend of the exploitation depression cone have already come about. In order to ensure the sustainable use of groundwater resources of Yinchuan City, this paper is going to analyze the water source protection and the main factors affecting the adsorption capacity of the vadose zone soil and do the risk assessment of pollution, basing on existing data and previous research based on systematic of Yinchuan City. The paper's main contents and conclusions are as follows:(1)Comprehensive analysis of the hydrogeological conditions of phreatic water aquifer of the well-fields of Yinchuan City and the water level gap between phreatic water and the first confined water and the thickness distribution of the first aquitard, calculate the techarge time of phreatic water to the first confined water,we conclude that the penetrate time in eastern well-field is longest, which is best to protection of the confined water, followed by the well-fields of the northern and chemical plant. The penetrate time in southern well-field is shortest, which is worest to protection of the confined water.(2) The paper draws a conclusion that protection capability of the eastern well-field to the vadose zone groundwater is the best, and the southern well-field of better water source, water source protection capabilities in northern well-field comes to the second, and that of chemical plant is the worst from the reference to comprehensive analysis of unsaturated zone lithology and thickness.(3) The time of the equilibrium adsorption of organic matter and Hexavalent chromium is shorterjust 2.5h, and adsorption rate is large. The analysis of this experimental result shows adsorption capability of phenol and hexavalent chromium of vadose zone soils in three well-fields from large to small followed by:the northern, the eastern, the southern.The adsorption capability of diesel of vadose zone soils in three well-fields from large to small followed by:the northern, the eastern, the southern. So the interception capability of vadose zone soils in the eastern and northern well-fields is lager, the southern is smallest.(4) The absorption isotherms of phenol, diesel and other organic compounds and hexavalent chromium in the vadose zone of northern, the eastern and the southern well-fields are available to use Freundlich equation to describ.(5) Based on the collection of buried deep of groundwater level, aquifer medium,and lithology of the vadose zone, use analytic method to structure comparison matrices and then determine the weight of evaluation factors weight.Do the risk assessment of groundwater pollution to Yinchuan City well-fields, arrive at Yinchuan pollution of groundwater mainly in high risk areas and medium pollution risk areas, the southern well-field, the east well-field in high risk area of pollution; the northern well-field, Ningxia Chemical Plant well-field fraction in high risk area of pollution, most of the medium pollution risk areas.(6) So we should increase the yield of phreatic water, reduce level difference between phreatic water and the first confined water, weaken the supply of phreatic water to the first confined water,concerning the east part of the northern well-field and chemical plant well-field.