Soil And Groundwater Remediation Based On Health Risk Assessment For Contaminant Sites

In recent years, with the development of remediation for types of contaminated sites in China, there is urgent need to study drawing up remediation objectives based on health risk assessment for targeted site. In this paper,based on referencing Canada Alberta "soil and groundwater remediation guidelines (SGRG) " which is a tiered approach model,the exposure pathway of outdoor inhalation was added to this model. The derivation of volatilization factor of high and low volatility chemicals in soils were given, while the computational models of remediation for surface soil,subsurface soil and griudwater were also given. By modifying some parameters in the model, the remediation objectives of soil and groundwater of a insecticide factory were developed. The following conclusions were drawn:(1) By Comparative analysis of exposure pathways in different models, it can be recognized that the outdoor inhalation of contaminant vapors which releaseed from affected soils or groundwater can not be ignored,especially when a land use of the site being an openspace or a work area with no building.(2) By sensitivity analysising of the parameters in the outdoor inhalation exposure pathway model, it showed that parameters such as width of source area parallel to wind flow direction, width of source area parallel to groundwater flow direction, wind speed above ground surface in ambient zone, thickness of capillary fringe, thickness of affected subsurface soils, depth to subsurface soil sources,have greater influence on soil and groundwater remediation guidelines and should be adjusted in Tier 2 assessment.But the latter two can only be considered for high volatility chemicals.(3) System parameters involved human receptor and site characteristics can be established after literature review, which is fit for our country. Tier 1 remediation guidelines for some chemicals in agricultural and industrial land use were derivatived, which contained all exposure pathways. The results show that guidelines of most chemicals are more strict than that of Alberta because of changes of human receptor parameters such as body weight,skin area etc.(4) The concern contaminations of the factory site were 1,2-dichloroethane and 1,2-dichloropropane.After comparing the contaminant concentrations with Tier 1 guidelines,it could be find that exceededances were found in such pathways:soil indoor vapors, groundwater indoor vapors, protecting of DUA, portable water for 1,2-dichloroethane while in protecting of DUA and portable water pathways for 1,2-dichloropropane.The soil guidelines are 6.2μg/kg for 1,2-dichloroethane and 67μg/kg for 1,2-dichloropropane.The groundwater guidelines are 5μg/L for both 1,2-dichloroethane and 1,2-dichloropropane.(5) Tier 2 assessment were taken to adjust Tier 1 guidelines. The more sensitive agricultural land use was chosen to obtain the remediation objectives.It indicate that, in Tier 2,the concentration of 1,2-dichloroethane exceeded objectives in all pathways except groundwater outdoor vapor inhalation, the concentration of 1,2-dichlo-ropropane exceeded objectives in such pathways as protecting of DUA, portable water. The soil remediation objectives are 11μg/kg for 1,2-dichloroethane and 45μg/kg for 1,2-dichloropropane while the groundwater remediation objectives are 5μg/L for both 1,2-dichloroethane and 1,2-dichloropropane. The adjustment of the guidelines is in accordance with the tiered approach theory.