STUDY ON THE MECHANISMS OF POLLUTANTS ON SOIL AND GROUNDWATER

从第一起VOCs污染地下水案例到现在，已经过去了20年。到目前为止，已经开发了许多土壤和地下水污染调查和修复的方法和技术。众所周知，土壤和地下水中挥发性有机化合物的运动主要受水文地质条件的控制。本研究通过室内实验、渗滤仪实验和现场实验三个尺度对土壤和地下水中挥发性有机化合物（VOCs）的迁移机理进行了研究室内实验结果：污染源周围因抽水、空气喷射、入渗等引起的地下水位变化，影响了NAPLs在地下的分布。很明显，地下水位的变化可以通过改变水、空气和它们之间的平衡而使三氯乙烯和苯移动。在地下水位上升过程中，TCE体保持不动，而苯体则趋向于一起移动，可能被水截留而困在饱和区。饱和区捕获的三氯乙烯和苯都可能改变其形状，尽管地下水位发生变化，但它们不会向上移动。因此，DNAPLs比LNAPLs更容易被水捕获。另一方面，在地下水位下降的过程中，TCE体由扁平变为长条状，进入压力增大，但苯只是横向扩散，扩大了其分布范围。总体而言，降雨过程中，入渗水可以将TCE溶解水和TCE气体向下推。这意味着在事件发生过程中，TCE可以通过溶蚀作用随着水的渗入而移动，TEC气体可以通过封闭孔隙和压缩非饱和区气体而向下移动。现场试验结果表明，挥发性有机化合物可以改变土壤的水力导率。因此，水体和VOCs的分布都变得非常复杂，这必然会影响修复效果。

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.