基于特定污染场地的蒸汽入侵模型研究

Case Study on Vapor Intrusion Model Based on Specific Pollution Site

对某化工厂搬迁后拟建的商业住宅用地所在区域地下水开展污染调查,采样结果表明,拟建住宅区存在甲苯、乙苯、二甲苯3种苯系物污染,可能通过蒸汽入侵途径对居民造成健康风险。该研究场地地下水水位2.67 m,地下室埋深3.66 m,地下室底板位于地下水水位以下,导致《污染场地风险评估技术导则》中建议的基于地下室在地下水水位以上的通用污染概念模型不适用于该污染场地。文章创新性地构建了基于地下室底板低于地下水水位的蒸汽入侵模型,该模型根据蒸汽入侵方式的不同,可分为地下室进气污染概念模型和地下室渗水污染概念模型。以该污染场地的实测数据为基础,采用该模型进行室内浓度计算,并与通用污染概念模型的计算结果进行比较,结果表明通用污染概念模型由于存在包气带及裂隙的衰减,导致计算的污染物浓度偏低,比渗水模型少400倍以上,远远低估了污染物侵入室内的浓度。由此可见,在对该污染场地进行风险评估时,直接套用现有的通用污染概念模型来计算室内污染物浓度是偏离客观事实的,必须对现有模型进行修正。

Site investigation at an abandoned chemical plant site, which will be developed as residential area, showed that the site was contaminated by BTEX, including toluene, ethyl benzene and xylene. Those identified contaminants may pose health risk to future residents through vapor intrusion. As the site＇s stable groundwater table is 2.67 m below ground level（bgl）, and the basement ground is 3.66 m bgl, the site-generic vapor intrusion model recommended in T echnical Guidelines for Risk Assessment of Contaminated Sites, is not applicable to this specific site. A new vapor intrusion model was developed for the site that groundwater level is shallower than basement ground. The model, according to different intrusion patterns, includes air-leak conceptual model and water-leak conceptual model. The indoor concentration was calculated using both the new model and the site-generic model. The results indicated that the calculated concentration by the new model is more than 400 times higher than the result by the site-generic conceptual model. It is concluded for the site that groundwater level is shallower than basement ground, the site-generic conceptual model cannot be directly used and new model should be developed.