Study On Risk Assessment And Early Warning Of Groundwater Pollution In The Ordos Basin

The Ordos basin is located in the east part of the northwest China, middle reaches of the Yellow River. Recently, with the development of urbanization and industrialization, the groundwater of the basin has being severely contaminated by municipal solid waste, untreated industrial wastewater and excessive using of pesticide and fertilizer. It not only becomes a serious threat to water security and ecology, but also restricts the development of economic. Therefore, it is urgently needed to carry out the groundwater quality assessment, groundwater pollution risk assessment and groundwater pollution early warning, so that it could be a scientific support to planning and exploiting the groundwater resources, and to preventing the groundwater pollution.Aiming the serious problems of groundwater pollution increasingly in the Ordos basin which caused by industrial and agricultural production, energy development and other human activities in recent years, this paper carried out five aspects of research in the Ordos basin. First, this paper collected the data of the natural, geographical conditions and human activities, as well as sampled and tested groundwater quality. Secondly, this paper assessed the groundwater quality and pollution. Thirdly, this paper assessed the groundwater inherent vulnerability, contaminate load hazard, the importance of groundwater protection, and groundwater pollution risk. Fourthly, this paper divided groundwater pollution prevention area. Lastly, this paper carried out groundwater pollution early warning and proposed pollution prevention measures. This paper obtained the following understandings.(1) The results of groundwater quality and pollution show that single-index assessment method is more reliable than comprehensive-index assessment method to guarantee the safety of drinking water of basin residents. In the basin, the proportion of Ⅴlevel groundwater is 31.88% and mainly distributes in the west edge of north of cretaceous groundwater system and the west edge of Cambrian-ordovician groundwater system. the proportion of Ⅳlevel groundwater is 23.48% and wieldly distributes in the basin. The main influence indices of groundwater quality in basin are CODMn、F-、Cl-、As、I-、NO3-、Na+、Cr6+、TH、Mn、Fe、SO42- and TDS. 53.16% of groundwater in basin have been polluted and pollution degree of east area groundwater was higher than west. The main pollution indices were CODMn、NO3-、SO42- and TDS. This phenomenon was closely related to human activities such as the agricultural production in basin and coal mining etc.(2) The results of groundwater inherent vulnerability assessment show that groundwater inherent vulnerability of basin is given priority to slightly lower, next is middle, slightly higher and low inherent vulnerability, the distribution area of high inherent vulnerability is minimum. High or slightly higher groundwater inherent vulnerability are mainly distributed in the sand beach of northwest in Yu Lin city, the north sand beach of cretaceous groundwater system and the northern section of east edge of Cambrian-ordovician groundwater system. The sensitivity analysis results of groundwater inherent vulnerability assessment indices show that groundwater inherent vulnerability is the most sensitive to vadose medium type, next is depth of water table, net recharge of groundwater, aquifer medium type and topographic slope.(3) Groundwater contamination risk assessment results show that groundwater pollution risk of basin is given priority to low pollution risk, next is middle pollution risk, the distribution area of high pollution risk is minimum. The high pollution risk mainly distributes in the north of cretaceous groundwater system. Because the inherent vulnerability of groundwater in the area is higher and industrial and agricultural sources and large centralized water supply sources are widely distributed.(4) Groundwater pollution prevention area results show that the most of area of basin is pollution control zones which mainly distribute in the east of basin. Western basin has a large of protection zones and the important protection areas and general protection areas are main of these areas.(5) The results of Groundwater pollution early warning show that the groundwater pollution is given priority to serious early warning, next is slight early warning and no early warning, the distribution areas of moderate warning is minimum. The cretaceous groundwater system mainly performances serious and slight warning. The Carboniferous-Jurassic groundwater system performances no warning, the CambrianOrdovician groundwater system mainly performances moderate and slight warning.