Chromium-contaminated sites: migration characteristics and monitoring using dual-frequency IP method

Given that the migration process of chromium-contaminated sites is subjected to various uncertainties, it is difficult to investigate the migration characteristics and explore the monitoring process using experiments. Based on the basic law of groundwater flow and the migration mechanisms of pollutants, this study conducted a simulation analysis of the migration characteristics of static chromium contamination sources and the law of changes in the migration characteristics using the COMSOL software. Then, this study verified the reliability and accuracy of numerical forward simulations through physical simulation experiments on a static soil bin. Specifically, using the model of chromium contamination source migration as a basic model for geoelectric monitoring, as well as the intermediate gradient detection device and symmetrical quadrupole sounding device, this study performed numerical forward simulations to monitor the migration process of chromium-contaminated sites with the dual-frequency induced polarization (IP) method. Accordingly, it analyzed the effects of flat and undulating terrains, as well as the orientations of measurement points, on the monitoring effects. The findings are as follows: (1) Permeable beds with high permeability coefficients produce strong adsorption effects for areas with severe chromium contamination during chromium pollutant migration. Meanwhile, these layers can intensify the lateral spreading of polluted areas in a short time. (2) Intermediate gradient detection device outperforms sounding detection in terms of the correspondence between the peaks of apparent amplitude frequency and the IP anomalies of the troughs of apparent resistivity curves. (3) The contamination monitoring accuracy of symmetrical quadrupole sounding can be enhanced by deploying measurement points in the middle of projected edges of contaminated sites. (4) The presence of valleys may induce multiple peaks in the IP curves during intermediate gradient detection and symmetrical quadrupole sounding. (5) By arranging power supply electrodes on the mountain frontiers on both sides of the mountain peaks, areas with severe chromium contamination can be comprehensively pinpointed using the curves of both apparent amplitude frequency and apparent resistivity. These findings enrich the theory of the monitoring of heavy metal-contaminated sites of soils using the dual-frequency IP method and provide theoretical and technical guidance for real-time monitoring of the sites, thus holding positive significance for promoting ecological protection.