STUDY ON THE MECHANISMS OF POLLUTANTS ON SOIL AND GROUNDWATER

从第一例VOCs污染地下水算起，已经过去了20年。目前，土壤和地下水污染的调查与修复方法和技术已发展成熟。众所周知，VOCs在土壤和地下水中的迁移主要受水文地质条件的控制。本文通过室内实验、蒸渗仪实验和现场实验三个尺度对VOCs在土壤和地下水中的迁移机理进行了研究。1室内实验结果污染源周围的抽水、曝气、入渗等引起的地下水位变化影响了非水污染物在地下的分布。可见，地下水位的变化可以通过改变水、空气和它们之间的平衡，使TCE和苯移动。在地下水位上升过程中，TCE体保持静止，而苯体则趋向于一起运动，并可能被水拦截而滞留在饱和带中。饱和带中滞留的TCE和苯在地下水位变化的情况下，都可能改变其形态，而不会向上移动。因此，DNAPL比LNAPL更容易被水捕获。另一方面，在地下水位下降过程中，TCE体由扁条状变为长条状，进入压力增大，而苯只是横向扩散，扩大了其分布范围。2.蒸渗仪试验结果降雨过程中，入渗水通常会将TCE溶解水和TCE气体向下推。这说明TCE可以通过溶解的方式随入渗水迁移，TEC气体可以通过封闭孔隙和压缩非饱和带中的气体向下迁移。3.现场试验结果VOCs可以改变土壤的导水率。结果表明，水体和挥发性有机物在水体中的分布变得非常复杂，这必然影响到污染物的去除效果。

20 years has passed since the first case of groundwater pollution caused by VOCs. By now, there were many methods and technologies developed for soil and groundwater pollution investigation as well as remediations. As well known, movements of VOCs in soil and goundwater are mostly controlled by hydrogeological conditions. In this research, we investigated mechanisms of VOCs migrations in soil and groundwater in three scales: indoor experiment, lysimeter experiment and in site experiment.1 Results of indoor experimentsThe underground distributions of NAPLs are effected by the water table changes due to pumping, air sparging, infiltration etc. around the pollution sources. It is clear that variations of water table can make TCE and benzene movable by changing balances among water, air and them. During the water table moves up, TCE body keeps still and benzene body tends to move together and may be intercepted by water and trapped in saturated zone. Both of trapped TCE and benzene in saturated zone may change its shape, and never move up in spite of variations of the water table. Therefore, DNAPLs are trapped by water more easily than LNAPLs. On the other hand, during the water table moves down, TCE body changes its shape from flat to long bar and increase its entry pressure, but benzene only spreads laterally to expand its distribution area.2.Results of lysimeter experimentsGenerally, infiltrating water can push both TCE-dissolved-water and TCE gas downward during rain events. It means that TCE can move with infiltraing water by dissolution and TEC gas can move down through the soil due to sealing porous pores and compressing gases in the unsaturated zone during the events.3.Results of in site experimentsVOCs can change the hydraulic conductivities of soil. As a results, distributions of both water and VOCs became very complicated, which must effect on the remediation efficiency.