Diagnostics of Oil Pollution Zones by Electro-Physical Method

The article presents the rationale and development of electro physical methods of control of the degree of soils pollution with petroleum products. The ranges of variation for the parameters of the pore space structure and wettability for the Kuzbass conditions are determined by inverse calculations on the basis of experimental data. The theoretical dependences are shown which allow us to assess the degree of soil pollution with oil products according to the results of longitudinal and areal electrical sounding. The study confirms the possibility of rapid prediction of the degree of soil contamination by measuring its electrical resistance. The database has been compiled for interpretation of the results of experimental sounding when monitoring the changes in the degree of contamination. The use of the express forecast of numerical values of the contamination factor was studied.


Introduction
One of the most dangerous soil pollutants are petroleum products: lubricants and liquid fuel [1,2].The relevance of the problem of cleaning soils from oil pollution in mining industry (coal surface and underground mines, ore mines) due to large amounts of fuel consumption by road and rail transport, and lubricants in the operation of mining equipment, and technical oils in electric power plants.The refined petroleum products contain toxic watersoluble fractions [3,4], also, gasoline, and especially motor oils contain up to 20% of additives, solvents, heavy metals.One liter of used oil may contaminate one million liters of water, not more than 60% of their volume being regenerated One of the effective methods for managing the soil properties, especially of low permeability (filtration coefficient K f < 10-8 m/s), is the method of electrochemical treatment [5,6], its main impact on the contaminated soil being the electrical destruction of ecotoxicants and the electroosmotic displacement of the diluted pollutant in the area of mechanical removal (pumping).Experimental and theoretical bases of the electrochemical method were developed for the solution of problems of technical reclamation (drainage) and for stabilizing the unstable waterlogged soils.The criteria for the rational use of this method are determined: the ratio of the coefficients of electroosmotic activity and filtration K e /K f > 10 7 and electrical resistance (SER specific electrical resistivity) ρ < 8 Ohm•m.
Direct and indirect methods are applied to control the processes of cleaning of soils from pollution.Direct methods [7][8][9] (infrared spectrophotometry, ultraviolet luminescence, gas and gas-liquid chromatography) require sophisticated equipment, significant duration of the analysis and extraction of soil samples, the measurement error can reach 40-50%.

Materials and methods
Diagnosis and ongoing monitoring of soil condition, properties and physico-chemical processes in the area of electrical treatment can be provided by geophysical methods that are effective supplement to geotechnical investigations.Very promising for the study of contaminated soils are electrical and electromagnetic methods [10] based on the measurement of electric fields, because oil and petroleum products exhibit pronounced dielectric properties and therefore they are electrically contrasting.
To control the degree of soil pollution with oil products, it is advisable to use the dependence of electrical resistivity of the three-phase medium on porosity, moisture and electrical resistivity of the pore filler that is used in electrical prospecting and includes structural-textural empirical parameters [11,12]: where m is porosity (pore cavitation); W -coefficient of the saturation space of the pores and cracks; ρ в -electrical resistivity of the solution, filling pore space, Ohm⋅m; К n , α, β, γare empirical parameters that depend on the structural and textural features of the studied soils; К n -is the parameter that takes into account the surface conductivity of clay microlayer on the surface of the pores; α -is the parameter depending on the type of geological deposits; β is the parameter determined by the structure of the pore space (mainly by tortuosity of the channels); γ -parameter that depends on the wettability of surface pores by the solution.
The ranges of variation of the parameters of the pore space structure β = 1.3-2.2 and wettability γ = 1.8-3.3should be taken for conditions of Kuzbass on the results of the inverse calculations based on experimental data; and electrical resistivity of the pore filler is calculated by the formula of harmonic weighted average for the two-component media [13]: where ρ в , ρ н , ρ э -electrical resistivity of, respectively, weighted, oil and electrolyte, Ohm⋅m; V н ,V э -volume fraction in the solution, respectively of the oil and electrolyte.Theoretical dependence ( 1) and ( 2) basically allow us to assess the degree of soil pollution with oil products according to the results of single measurements, longitudinal and areal electrical sounding [14].
To further analyze the process of electrochemical treatment of contaminated soils, it is necessary to have information about the electrophysical properties of natural aqueous solutions and liquids containing contaminants or saturated soils.Experimental studies of electrical properties of electrolyte solutions, containing oil-products, with the measurements at permanent and variable electric current.
Figure 1 shows the measurement results of the electrical resistivity ρ э of the NaCl solution depending on the salt concentration in solution and the a. c. frequency, and Figure 2 shows the same dependence of the specific electrical resistance ρ н of motor oil and gasoline.It follows from these data that all petroleum products are electrically quite contrasting, because their electrical resistivity is by at least 3 orders of magnitude higher than electrical resistivity of natural water solutions.The given of experimen value [15].e of saturation s equal to the r pore fluid.By g expression: il of oil pollu s of sounding When using l feeding elect trodes-injecto electrodes for utant, the coef olume of oil c ion of equatio  The contr tivity ρ к alon sumption or t The main termination o before and af For Expr design depen studies: linea for a known contaminant the contamin tive resistivit

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