| Organic pollutants are highly toxic and persistent,and can cause serious pollution to soilwater system when they enter the near-surface environment,among which Light Non-Aqueous Phase Liquid(LNAPL)is the most difficult to cure.After entering the soil-water system,LNAPL migrates and accumulates under the action of gravity and capillary force,which seriously pollutes the soil and groundwater.In this paper,we adopt non-destructive High density Electrical Resistivity Tomography(ERT)to obtain real-time monitoring data through 2D and 3D physical models.The migration and enrichment characteristics of LNAPL in soil-water system under different experimental conditions were studied from the analysis of the spatio-temporal variation process and distribution characteristics of the comprehensive physical parameter resistivity.The main research results are as follows:(1)In the obtained resistivity image,the distribution and rich area of LNAPL in the soilwater system caused the increase of the resistivity value in the corresponding local area,showing a relatively high resistance value.The spatial and temporal distribution characteristics of high resistance region under different experimental conditions reflect the migration and accumulation characteristics of LNAPL in soil-water system.The spatial and temporal distribution characteristics of high resistance are mainly affected by hydrodynamic conditions,medium characteristics and other factors.(2)Under hydrodynamic conditions,LNAPL migration is affected by hydrodynamic and capillary forces,and it migrates horizontally around the axis where the injection point is located.The enrichment occurs at the injection point,and the rich area moves downstream with the flow of water.The upstream migration rate of LNAPL is 5.15cm/h,and the downstream migration rate is 2.42cm/h,and the upstream migration rate is higher than the downstream migration rate.This indicates that the anisotropy of clay varies greatly in the clay layer,resulting in the capillary action of different intensity,which makes the horizontal migration rate of LNAPL in the upstream and downstream directions different under the capillary action.(3)Under the condition of groundwater exploitation,a water level drop funnel is formed within a certain range,and the migration rate of LNAPL to the downstream increases from0.17cm/h to 1.47cm/h,and the migration rate to the upstream decreases from 0.78cm/h to0.09cm/h,and the increase range of the change rate reaches as far as 1.3m.This indicates that the hydrodynamics promotes the horizontal migration of LNAPL,and the migration speed is accelerated under the action of clay capillary.Meanwhile,the existence of pumping well will hinder the migration of LNAPL,and it will accumulate in the pumping well.(4)Under the condition of three-dimensional hydrodynamic test,LNAPL migrated from the injection point to both sides,mainly to the right of the injection point,and accumulated at the injection point and at the depth of 0.2m X=0.9m.The upstream migration of LNAPL was inhibited and downstream migration of LNAPL was promoted by the hydrodynamic effect.The injected LNAPL migrated to the bottom of aquifer,clay layer,upper and lower reaches of clay layer under the action of gravity,hydrodynamic force and capillary force,reached the lithologic mutation interface and produced accumulation,produced lateral migration at the accumulation,and less migration into clay layer. |
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