北京市东南郊再生水灌区地下水多环芳烃污染风险评估

为研究污染物随再生水进入地下环境后其迁移衰减情况及对地下水的潜在危害性,以Multi-cell模型为基础,结合污染物质量守恒、在水土中吸附再分配、生物降解等机理,针对地下水污染风险评估构建了计算污染物随水在土壤剖面的垂向迁移衰减一维模型,并以北京通州大兴再生水灌区为研究区域,以再生水中持久性有机污染物多环芳烃萘和菲为研究对象,根据当地钻孔资料及灌溉水水质、地下水水质资料,应用该模型进行试算。结果表明,经过多年连续灌溉后,通州大兴大部分地区进入潜水含水层的萘、菲浓度较低,整体污染风险较低,仅在通州区潞城镇等个别地区萘、菲浓度较高,应引起重视;由于大兴区整体包气带较厚,其污染风险低于通州区。土壤粘土层是萘、菲积累的主要层位,其吸附容量远大于细砂等粗颗粒介质,在土壤表层低环多环芳烃迁移性更强。应用这一模型,能够较为宏观地掌握通州大兴再生水灌区不同区域地下水中多环芳烃萘和菲的污染风险差异。

Groundwater PAHs Contamination Risk Assessment of Reclaimed Wastewater Irrigation Area,South-east Part of Beijing,China

In order to better understand the migration and attenuation of pollutants and its potential pollution risk to groundwater during the reclaimed wastewater irrigation,a model based on Multi-cell was developed,which combined with mass conservation,adsorption and re-distribution and biodegradation mechanism.This one-dimensional model was aimed at groundwater contaminants risk assessment which can calculate the attenuation of pollutants during the vertical migration through the soil profiles.This paper used the model to perform groundwater pollution risk assessment in Tongzhou,Daxing agriculture district,a typical reclaimed wastewater irrigation area in South-east of Beijing.During the calculation,two typical polycyclic aromatic hydrocarbons,naphthalene and phenanthrene were selected to represent the reclaimed wastewater pollutants,and local data of well drilling and quality of irrigation water and groundwater were used.Conclusions suggested that the concentration of naphthalene and phenanthrene migrating into aquifer of most part of Tongzhou,Daxing district after long-term of reclaimed wastewater irrigation was low except of Lucheng town in Tongzhou district;the groundwater vulnerability of Daxing district was better than Tongzhou district because of its thickness of vadose zone;the major accumulated layer of naphthalene and phenanthrene in soil was the clay layer,and its adsorption capacity was much higher than coarse sand;the migration capability of low molecular PAHs in the surface of soil was better.Through this assessment,the difference of groundwater contamination risk for naphthalene and phenanthrene could be identified,and this could help to better understand the risk of reclaimed wastewater irrigation in Tongzhou and Daxing.