基于保护地下水的北京市土壤通用筛选值推导

分别采用三相平衡耦合地下水稀释模型(以下称方法1)和SESOIL耦合地下水稀释模型(以下称方法2)对北京市不同水文地质条件(永定河山前冲洪积扇顶部区域、中上部区域和下部区域)下27种VOCs(挥发性有机污染物)、31种SVOCs(半挥发性有机污染物)、11种农药/PCBs(多氯联苯)及二英基于保护地下水的土壤通用筛选值进行推导. 结果表明,下部区域土壤通用筛选值最保守,顶部区域次之,中上部区域最宽松. 采用方法1推导的中上部区域土壤通用筛选值分别是顶部区域和下部区域的1.1~1.4、9.9~34.9倍,顶部区域土壤通用筛选值是下部的10.7~24.9倍；采用方法2推导的中上部区域土壤通用筛选值是下部区域的9.8~49.9倍. 对于有连续非饱和带弱水层的中上部区域及下部区域,方法2推导的结果较方法1宽松. 其中,PAHs(多环芳烃)、PCBs、二英、多数农药及酯类等高K_oc(有机碳-水分配系数)污染物均难以穿透清洁非饱和土壤进入地下水；而对于VOCs、酚类等低K_oc污染物,方法2推导的中上部区域土壤通用筛选值普遍是方法1的4.3~18.4倍,下部区域为方法1的3.0~24.6倍. 考虑到土壤通用筛选值应具有风险筛选功能及一定保守性,建议各种污染物以顶部区域方法1推导结果及中上部区域和下部区域方法2推导结果中最保守的值作为北京市基于保护地下水的土壤通用筛选值. 

Derivation of Soil Screening Values for Groundwater Protection in Beijing

Generic soil screening values for 27 kinds of VOCs (volatile organic compounds), 31 kinds of SVOCs (semi-volatile organic compounds), 11 kinds of pesticides, PCBs and dioxin were derived for groundwater protection according to different hydro-geological conditions in Beijing using two methods:three-phase equilibrium equation combined with groundwater dilution model (method 1) and SESOIL model combined with groundwater dilution model (method 2). The results revealed that the screening values for the downstream areas of the Yongding River alluvial-proluvial fan were the most conservative, followed by the values for the upstream and middle areas. The screening values derived with method 1 for the middle areas were 1.1-1.4 times and 9.9-34.9 times those for the upstream and downstream areas, respectively, while the values for the upstream areas were 10.7-24.9 times those for the downstream areas. For method 2, the values for the middle areas were 9.8-49.9 times those for the downstream areas. In addition, for the areas in the middle and downstream where continuous aquitard existed, the screening values derived by method 2 were more conservative than those derived by method 1. For PAHs, PCBs, dioxin, most pesticides and esters, whose K_oc (organ-water partition coefficients) were high, the results derived by method 2 indicated they would hardly penetrate the clean soil in the vadose zone, meaning less risk of groundwater contamination. For VOCs and phenols, whose K_oc were low, the values derived with method 2 were 4.3-18.4 times those derived by method 1 for the middle areas, and 3.0-24.6 times those for the downstream areas. Given the conservative nature of the generic screening levels and its risk screening function, the conservative values among screening levels derived for the upstream areas with method 1 and for the middle and downstream areas with method 2 were recommended as the generic screening values of Beijing to prevent groundwater contamination from soil pollution.