A Study Of Detecting Contaminated Soil Layers And Aquifers Using Resistivity Tomography Method

Electrical resistivity tomography (ERT) is a new detection method for subsurface contamination prospecting. Over the past decade, the ERT method is being applied in many field studys, and reveals rapid, non-destructive and effective features. However, as a indirect means, many theories and technologies are not solved, it limits greatly the application of this technolog .The paper, through detection technical system, electrical property of contaminated soil, interpretation of detection sections, detection methods of the contaminated soil and etc, systematically discusses the unsolved theoretical issues, key techniques and indistinct acquaintances about the contaminated water-bearing media detection using ERT method, and conducted special researches by using theoretical analysis, laboratory experiment, numerical simulation, field experiments and etc. The paper has obtained creative results on the detection section images reconstruction technique, electrical property theory of contaminateded soil, interpretation techniques of the detecting sectional abnormal, in- situ pollution monitoring techniques and etc.In this paper, The ERT system is build firstly according to the basic theory, implementation, data processing, and image reconstruction, and then, develop the Zhody inversion and improve the least-squares inversion algorithm for the 2D image reconstruction . Those research can provide better result detecting the contaminated area from 2D ERT section.Landfill leachate- contaminated soil samples and diesel -contaminated soil samples are tested . The test datum are used to study the law, main factors and electricial resistivity equation of soil contaminated by the soluble phase contamination or NAPL. The study results show that the electrical conductivity of the landfill leachate contaminated soil will increase, according to uncontaminated soil, and the magnitude will controlled by the clay content and the initial water content of soil; The decreasing of porous fluid, increasing of saturation, and the resistance caused by the suspended particles are the main effects of resistivity variation; For the first time, the Archie-type formula was put forward, which covered all the factors mentioned above.The variation of resistivity of disel-contaminated soil is complex. The resistivity variation is not only affected by clay content, but also by the control of soil moisture. The resistivity will increase for the oleophilic soil, otherwise decrease for the hydrophilic soil. In this paper, the impact of the moist of soil was first concerns in the study on resistivity character of LNAPL contaminated soil .Base on the typical structure of oil contaminated area ,landfill leachate contaminated area, and the typical dissolution process of contaminated area in aquifers , paper develop the original geo-electrical model of those contaminated areas , then got a series of 2D ERT sections measured by different arrays through forward calculation , the least-squares inversion and the D-ratio calculate technique are adopted to reconstruct the image. By analyzing the numerical calculation results, the 2-D image characters of three types of contaminated areas are determined. At the same time, the detection ability of different array and the contamination describing ability of the reconstructed image was outlined. The research shows that the measured images of different arrays can reflect the existence of the contaminated area, but it can't effectively reflect the spread of the contaminated area and the degree of pollution. Effective image reconstruction technique is the key to solve this problem, least-squares inversion technology and D- ratio method can get good results.In order to improve the ability of the in-situ real-time detection technique of the pollution leakage, the paper also introduces a kind of independent design of landfill site leakage 3D electric monitoring system . The tests analyzed the reflection ability of the system to the pollution diffusion of the landfill leachate in the unsaturated soil layers and aquifers and the repairing process. The study concludes the designed 3D electric monitoring system is characterized by clear principles, simplified layout, low cost, high intelligent degree and obvious applied results, which can realize whether the leakage of the fixed pollution sources occurs and the diffusion process of the underground liquid pollutants, as well as realize the monitoring an precaution of the pollution process.At last, a practical instance was applied in order to analyze the working flow, job contents and the implementation of the ERT method, and the detecting technology systems of ERT method was summarized.The research contents extend and develop the ERT method of detecting the underground pollution , and pushed the technology application from qualitative to quantitative.