Study On The Electrical Resistivity Of Contaminated Soils

With the rapid socioeconomic progress, environmental pollution, such as land pollution has become a serious problem. The environment of the contaminated sites should be investigated before soil remediation and re-utilization. Therefore, an important research project is how to expediently determine the bound and level of pollution of these sites. The electrical conductivity of a soil is changed because of the change in composition and structure due to contaminations. DC resistivity, a geophysical method, can be used for detecting contaminated soil effectively. However, application of DC resistivity in contaminated soil investigation is at its starting stage and the detection results are still exploratory. There are some other factors other than contaminants simultaneously influence the in-situ measured electrical resistivity, which are difficult to be distinguished from the contaminants. This results in the interpretation uncertainty of DC resistivity method.Electrical resistivity of loess (Q3) contaminated by inorganic and organic solution was measured by simulation test in laboratory to study the effect of moisture content, contaminations and porosity on electrical resistivity. Test results showed that moisture content was the major factor responsible for the alteration of resistivity: electrical resistivity decreased with the increase in moisture content. Soluble salts such as NaCl,ZnCl2 in soil water, lead to electrical resistivity of soil decreased with the increase of contamination content. The electrical resistivity of soils contaminated by diesel oil was found to be increased. This can be explained by the fact that diesel oil affected the tortuosity of the conduction path. The smaller porosity is, the better continuity of pore solution and particles will be, thereby the conduction path will increase and the electrical resistivity decrease. But the porosity itself had little effect on electrical resistivity.Moisture content, contaminations, porosity and other factors interact each other and influence the electrical resistivity at the same time. The results showed that the resistivity was not significantly changed according to the contaminations content for the soils having higher water content. For soils contaminated by NaCl, the effect of moisture content on electrical resistivity decreased with the increase in NaCl content. Furthermore, porosity affected the electrical resistivity of soils more differently because of the difference in contaminants types. Porosity shows a less effect on resisitivity for the soil contaminated by NaCl and ZnCl2, but a more effect for the soil contaminated by diesel oil compared with the uncontaminated soils.Based on the experimental results and above analysis, the following revelations can be obtained:(1) Moisture content influences the resistivity so greatly that which can shade the effect of other factors. This means that the moisture content of soil should be estimated prior in the interpretation of site investigation. (2) If the soil has a high moisture content or an initial soil salinity, determination of the contamination is capable by the electrical resistivity, but it is practically difficult to estimate the contamination degree. (3) Additional attention should be paid to the effect of porosity on resisitivity when detection of organic contaminated soil is done.As a trial of laboratory research, field investigation of leachate contamination using DC resistivity was carried out at Fulongping landfill site, Lanzhou. The outline of the leachate feather, flow direction and depth, was detected from the resistivity results.