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IntroductionThe Canada wide standard for petroleum hy drocarbons ( PHC) contaminated sites is a tieredframework (CCME 2000)。At Tier 1 the propo nents are required to comply with a set of providedcriteria according to different predefined…　　The Canada-wide standard and Alberta Environment guidelines for petroleum hydrocarbon (PHC) contaminated sites provide a tiered guideline framework。The Tier 2 approach allows the proponents to calculate soil and groundwater criteria based on site-specific conditions。The guidelines provide the models to be used for Tier 2 calculation。These models are all based on analytical solutions,requiring significant simplification of real site conditions。The guidelines also specify how the models should be used in order to simplify the application and approval procedure。The purpose and application procedure of Tier 2 models are different from the conventional modeling methodology for soil and groundwater contaminant transport models。However,in practice these differences are often ignored。Meanwhile,difficulties in model input parameter selection are frequently encountered when applying these simple models to complex site conditions。This paper introduces the Tier 2 method for determining site-specific soil and groundwater criteria to protect a surface water body。It is emphasized that the Tier 2 models should be used only for calculating site-specific criteria,not as general tools to predict contaminant migration。Model calibration is generally not meaningful for Tier 2 models。Examples are provided to demonstrate a method based on Monte Carlo simulation to evaluate and present the effect of model input parameter uncertainty。Model input parameter uncertainties are presented using parameter ranges (or probability distributions),and statistically conservative site-specific criteria are calculated。This method is easy to use,and helps to extend the Tier 2 approach to relatively complex (more real) site conditions。　　【Keyword】：petroleum hydrocarbon (PHC);environmental standard;environmental risk assessment;contaminant fate and transport modeling;model parameter uncertainty;Alberta environment guidelines　　加拿大联邦及Alberta省级环境导则为石油烃污染场地提供了多级环境标准及评价方法。其中二级环境标准评价,准许根据污染场地的实际条件计算土壤和地下水污染限值。环境导则限定了计算污染限值的模型和方法。这些模型大都是基于十分简化的野外条件的解析解模型,并根据导则规定的方法使用,以简化应用与审批程序。这些模型的用途和方法与一般通用地下水和土壤污染物运移模型有所不同,在实际运用时这些差别常常被忽略。同时,在复杂野外条件下运用这些模型时,经常遇到确定模型输入参数的困难。介绍了加拿大环境导则中计算污染场地土壤和地下水污染限值以保护地表水环境的模型方法,强调这些模型方法只适用于计算污染限值的特殊目的,不适用于预测污染物运移或套用一般模型拟和调参方法。结合具体计算实例,探索运用Monte Carlo方法评价与表示模型输入参数带来的不确定性。这种方法用参数变化区间(或概率分布)来表示输入参数的变化或不确定性,以求得具有统计意义的保险污染限值。这种方法简单易行,却将二级环境标准评价方法推广到较为复杂(更真实)的野外条件。