Study On Accurate Assessment Conceptual Model Of Environmental Risks In VOCs Contaminated Sites

With the accelerated industrialization in China,a large number of contaminated sites have become an important social problem we face.These contaminated sites are left with toxic and hazardous substances stored or used in production activities,which pose potential threats to human health and environmental safety,so we need to conduct environmental risk assessment of contaminated sites.As an important part of environmental risk assessment,conceptual models describe the contamination sources,environmental receptors,migration pathways,exposure pathways and other information of the sites in a generalized manner in the form of text and diagrams to help risk assessment staff grasp and analyze the risk situation of contaminated sites as a whole.The following deficiencies exist in the current conceptual model study:first,no standardized document has been formed to guide the construction of the conceptual model in China,and it is usually constructed by the staff based on their own experience,which makes it difficult to unify the accuracy and standardization of the model;second,the conceptual model is overly generalized,and the influence of building structure on risk is not considered,and the risk assessment calculation model is copied from foreign models,which leads to inaccurate risk assessment results..To address the above problems,this paper carried out the following three aspects of research work:(1)Based on the preliminary research and literature review,the key information for constructing the conceptual model is comprehensively sorted out and refined,and the elements involved in constructing the conceptual model are generalized to form a universal list of conceptual model elements;based on this list,the specific steps for constructing the conceptual model are proposed:a.clarify the scope of conceptual site model;b.organize the site information;c.confirm the contaminant sources;d.identify the potential environmental media and migration pathways;e.confirm the sensitive receptors and exposure pathways;f.update the conceptual model.(2)To address the shortcomings of the general conceptual model of the Guidelines,two conceptual model scenarios of"direct contact between soil contaminated areas and buildings"and"direct contact between groundwater contaminated areas and buildings"were constructed,and derive quantitative indoor exposure risk calculation equations for the"inhalation of indoor gaseous pollutant pathway from subsoil"and"inhalation of indoor gaseous pollutant pathway from groundwater".(3)Using a decommissioned refinery in northwest China as a model site,the above-mentioned conceptual model construction method was used to construct an accurate conceptual model for the site in combination with the specific conditions of the dyed site;the risk values of the two conceptual model scenarios were calculated and analyzed and compared with the risk assessment results using the generic model of the guidelines.The results show that the two scenario risk assessment models constructed in this paper calculate the carcinogenic risk to future site receptors for the contaminants of concern benzene and ethylbenzene in soil and 1,2 dichloromethane and benzene in groundwater are higher than the acceptable level(1×10~6)and there are significant differences between the results of the optimized scenario model and the generic model.Therefore,a reasonable conceptual model should be constructed before the site-specific health risk assessment,and a suitable quantitative calculation method should be selected based on the model to avoid distortion of the final risk calculation results...