Investigation On The Migration Process Of Emerging Contaminants (PFOA) Based On Electric Resistivity Tomography

The environmental and health risks of perfluorooctanoic acid(PFOA)are of increasing concern and have become a current research hotspot in environmental hydrogeology.Among the methods to monitor the migration of contaminants in aquifers,electric resistivity tomography(ERT)is widely used in the field of groundwater environmental research as a fast and nondestructive means to produce accurate and rapid results.In this paper,we investigate the contaminant transport monitoring of PFOA based on resistivity imaging technology by setting up solution concentration and sand resistivity correction experiments,PFOA migration experiments in a one-dimensional sand column model,and PFOA migration experiments in a two-dimensional model.The experimental results are as follows:(1)It is clear that PFOA pollutants have electrical properties similar to KBr,and the correction equation in the form of power function of pollutant concentration and sand resistivity is obtained.Using the obtained correction equation for fitting analysis,the correlation coefficient R~2 was 0.9930 in coarse sandy soil,0.9521 in medium sandy media and 0.9816 in fine sandy soil,all of which had good correlation.It indicates that a more stable and feasible mapping relationship can be established for the correction equation of solution concentration and sand resistivity in the form of power function in sandy soil media with different grain sizes.(2)The error analysis was performed by comparing the results of indoor physical experiments with the Hydrus-1D simulation results.The root mean square error RMSE is 0.144 in the one-dimensional coarse sand column model,0.158 in the medium sand model,and 0.193 in the fine sand model,and the degree of error is small in all three grain sizes of sandy soils.It shows that the contaminant concentration penetration curves calculated by monitoring sand resistivity data can respond to the migration of PFOA in sandy soils,which verifies the feasibility of using the resistivity method to respond to the migration process and concentration changes of PFOA in a sandy medium.(3)By monitoring the migration and distribution of PFOA in the two-dimensional sand tank model by ERT,visual monitoring of the extent and degree of PFOA contamination in sandy soil media was achieved.Horizontally,the migration velocities of PFOA contaminated area in coarse sand,medium sand and fine sand media were0.075 m/h,0.060 m/h and 0.055 m/h,respectively;vertically,the PFOA contaminated area in coarse sand media had reached the bottom of the sand tank at 1 h of infiltration,the contaminated area in medium sand media had infiltrated to the bottom of the sand tank at 180 min,and the contaminated area in fine sand media was always in the The contaminated area in the fine sand media was always in the upper part of the sand tank for migration behavior.From the contamination range and diffusion rate,it can be seen that ERT is sensitive to the migration and diffusion behavior of PFOA,which clearly reflects the migration path and distribution range of PFOA contaminated area in porous media;the relative resistivity degree of the media monitored by ERT in different grain size sand tanks is different.The relative resistivity values of PFOA contaminated area in coarse sand,medium sand and fine sand media are 150Ω·m,70Ω·m and 30Ω·m respectively,and the range of contaminated area is more accurate according to the needs.The experimental results confirm that ERT is effective and feasible for visualizing and monitoring the migration and distribution processes of PFOA contaminants in the groundwater environment.In this paper,an in situ,non-destructive and visualized monitoring method is used to study the migration process of PFOA contaminants in groundwater environment,which is of high practical application to delineate the extent and degree of PFOA contamination in groundwater environment.