盐度对多孔介质中DNAPL运移和分布的影响

摘要

选用四氯乙烯(PCE)作为典型DNAPL污染物,以NaCl作为地下水中溶解盐代表,研究盐度对DNAPL在饱和多孔介质中运移和分布的影响.通过批次实验测定NaCl水溶液/石英砂/PCE三相体系下的接触角和界面张力,结果表明,PCE在石英砂表面的接触角随着水中NaCl浓度的增大而减小,而PCE和NaCl水溶液的界面张力随着NaCl浓度的增大而增大,尤其当氯化钠浓度较高时(＞0.1 mol/L),影响程度更为显著.在此基础上,采用透射光法监测不同介质情景下DNAPL在二维砂箱中的运移和分布,定量测定DNAPL在介质中的饱和度.实验结果表明,地下水盐度的增加将促进DNAPL的垂向入渗,减少被截留在运移路径上的DNAPL量,使得DNAPL运移路径及累积形成的池状DNAPL(pool)向水流方向偏移.在均质多孔介质和含有透镜体的非均质多孔介质中,随着盐度的增加,DNAPL在横向和垂向上的展布均呈现出增加趋势,导致污染源区变大,且介质中以离散状存在的DNAPL量明显增加.%In this work the effect of salinity on the migration and distribution of DNAPL in saturated porous media was investigated.Tetrachloroethylene (PCE) was selected as the representative DNAPL (Dense Non-aqueous Phase liquid),and sodium chloride (NaCl) was used as the typical dissolved salt in groundwater.Batch experiments were first conducted to measure the contact angles and interfacial tensions (IFTs) of the NaCl solutions/PCE/quartz system.The results show that the contact angles of PCE decrease and IFTs between PCE and NaCl solution increase with the increasing concentration of NaCl,and the effects are more obvious at high concentrations of NaCl (＞ 0.1 mol/L).Four 2-D flow cell experiments were then conducted,and the light transmission method was used to monitor the migration process of PCE and quantitatively measure the PCE saturation distribution in the porous media.The experimental results show that the increasing salinity in groundwater promotes the vertical migration of DNAPL,decreases the volumes of DNAPL entrapped along the migration path,and leads to the inclination of the migration path and pooled DNAPL towards the water flow direction.Moreover,in both homogeneous and heterogeneous (lenses) porous media,the horizontal and vertical spreading of DNAPL increases with the increasing salinity,resulting in a larger source-zone and the increasing PCE ganglia.