Groundwater Source Contamination Risk And Its Health Risk Assessment In The Karst Area Of North China

Dawu Well Field,a rare and super large size fracture-karst groundwater water source in the north of China,has strategic significance in guaranteeing the drinking water safety and social and economic development of Zibo.Since this water source has suffered from complex pollution which leads to a public health risk,controlling the pollution of the water source is becoming one of the important conditions to sustainable development of Zibo,Therefore,the karst groundwater quality was investigated and assessed,and the temporal and spatial variation of main contaminants and groundwater chemistry characteristics were analyzed.Taking Dawu water-rich zone as the target source,this paper evaluated the contamination risk of the karst groundwater source and its health risk to human.The combined assessment mode of contamination risk and health risk was established,and on this basis a series of groundwater pollution prevention and control measures were put forward.The main results were as follows:First,under the effect of the hydrogeological conditions and human activities,CODMn,petroleum,benzene and NO3-had gradually become major pollution components in the groundwater.From Hougao eastward to Dawu water-rich zone,the concentration of contaminants decrased,while concentrations changed obviously with time.After 1990s,the proportion of Cl-increased and SO42-droped in seriously polluted areas such as Hougao and Xixia.Meanwhile,the groundwater chemistry types varied correspondingly,i.e.,groundwater chemistry zoning occurred along the runoff direction.Second,the karst groundwater source vulnerability assessment method based on hydraulic field had been proposed in this paper.The conclusions indicated that the distribution of the target source vulnerability to pollution was consistent with karst groundwater burial conditions and flow field,demonstrating a decreasing trend from south(naked karst area)to north(covered karst area),from central area(target source catchment)to neighboring areas(non-target source catchment).In addition,the integrated hazard assessment method of pollution sources had been put forward,including point pollution sources and non-point sources.The results showed that sewage ditch,polluted river,major pollution sources and industrial land ranked the highest hazard;road or railway,discharge pipeline to the sea ranked middle;others lower.In the GIS platform,the zoning of contamination risk of karst groundwater source was obtained,by overlaying groundwater source vulnerability,pollution sources integrated hazard and groundwater value.The contamination risk tended to fall from high vulnerability to low vulerability,from first-grade protection zone to quasi-grade protection zone,from high hazard to low hazard.Third,the health risk from polluted karst groundwater source in the research area was evaluated with the application of USEPA health risk assessment model.The results revealed that the health risk in Hougao went much higher than the maxim acceptable level,with major non-carcinogenic and carcinogenic pollutants being benzene and trichlorethylene.In contrast,the health risk in Dawu water-rich zone was in an acceptable range.Thus,from Hougao eastward to Dawu water-rich zone,the health risk was gradually declining.Over the past decade,the health risk of organic pollution material in Hougao increased dramatically,while Xixia's risk greatly dropped,and Dawu water-rich zone kept stable.On the basis of discussion about the driving factors and mechanism of health risk,the fact that the contamination risk of karst groundwater source was the driving force of health risk had been revealed.In a short period of time,the distribution of health risk was closely related to the distribution of pollution sources and their integrated hazard.However,in the long run,the pollution sources,precipitation,extraction and groundwater level were major factors behind the dynamic variation of health risk.