Feasibility Study On In-situ Monitoring Of Heavy Metal Contaminated Soil Based On Conductance Principle

With the development of China’s economy,the treatment of urban soil pollution has also received attention.Defining the pollution situation of polluted sites is the initial link and the most important link in the treatment of contaminated sites.However,the traditional drilling sampling combined with the indoor chemical analysis method has the problems of long time and high cost.Therefore,a special technology for in-situ and rapid pollution site identification of contaminated sites is developed,which makes it easy to delineate the scope of contaminated sites and discriminate pollution levels,which becomes an important prerequisite for the rehabilitation and redevelopment of contaminated sites.In this paper,based on the principle of conductance,the constitutive relationship between soil heavy metal pollutant content,heavy metal type,water content,composite heavy metals and heavy metal contaminated soil samples is constructed,and the feasibility of in-situ identification is explored.Then it is applied to heavy metal pollution in soil.The osmotic migration transformation model test of the material to study the timeliness in the application process.The research results can provide theoretical basis and data support for the identification of pollution characteristics of contaminated sites.The research results are as follows:The Archie’s law is satisfied between the soil conductivity of the saturated sand and the pore water conductivity,and the fitting effect is good.The Campbell type formula can be used to convert the soil conductivity under different temperature conditions to room temperature to solve the ambient temperature.Impact.Under the single pollution condition,the content of heavy metal pollutants in sand,silt and cohesive soil has a quadratic function relationship with the soil conductivity value.Under the condition of multiple heavy metal mixed pollution,the soil conductivity is low.The sum of the electrical conductivities of various heavy metals when present alone,that is,the "additiveness" between a plurality of heavy metals;when the content of Ni2+ and Cr6+ having a strong conductivity reaches about 0.5%(that is,the soil is in a highly polluted state),The conductivity of soil tends to be stable with the increase of heavy metal content.The model of osmotic migration and transformation of heavy metal pollutants confirmed that the conductivity method can be used to monitor the changes of soil heavy metal pollution,and can reflect the pollution degree in a timely and effective manner.Theresults of soil conductivity values are consistent with the PVC column test.The seepage of heavy metal pollutants in the soil conforms to Darcy’s law and is proportional to the hydraulic gradient,and the percolation rate decreases with the decrease of the hydraulic gradient.The type of pollutants has little effect on the migration of pollutants.The permeation rate is proportional to the porosity,contaminant concentration,and initial moisture content.As the precipitation progresses,heavy metals in the soil are discharged as the pore water flows.As the number of precipitation increases,the peak conductivity of the soil decreases.It also indicates a decrease in heavy metal content,heavy metal contaminants migrate downwards,and gradually discharge the soil.The conductivity method can effectively predict the degree of soil pollution.When conducting in-situ on-site monitoring,the conductivity meter can directly obtain the soil conductivity and water content parameters,and establish the ratio of soil conductivity to water content,and The pollution degree discrimination table is compared to realize the prediction of the degree of soil pollution.Before the measurement,it is recommended to carry out the investigation and determination of the pollution source and soil type to improve the accuracy of the determination of the pollution level.