Method for remote monitoring of the degree of soil pollution by electrically contrasting ecotoxicants

Abstract

FIELD: geoelectric exploration.SUBSTANCE: used to monitor the degree of soil contamination with electrically contrasting ecotoxicants. Supply (A, B) and receiving (M, N) electrodes in the form of four-electrode microprobe sensors (4) immersed in the ground are placed according to the depth and area of the controlled zone (3). The electrodes are connected via a multi-channel cable (5) to the data collection and processing system. The data collection and processing system includes a switch (6), a controller (7), a processor (10), and a GSM transmitter (11) with an antenna (12). The true specific electrical resistance at the point where the sensors are installed is periodically measured. Based on the results of comparing the measured value with the previously obtained one, two-dimensional maps of the distribution of the coefficient of soil pollution by ecotoxicants are constructed.EFFECT: increasing the accuracy of monitoring results.1 cl, 1 dwg

Description

[0001] The invention relates to geoelectric exploration and can be used in monitoring the processes of contamination of soils in the near-surface zone with electrically contrasting ecotoxicants using methods based on the propagation of electric current.

[0002] Devices and methods for monitoring the formation of hazardous zones with anomalous electrical conductivity in rock masses (soils) are known in geoelectrical exploration. For example, a sensor for recording fatigue cracks is known, ensuring the determination of the coordinates of the initiation and development direction of cracks on an outcrop of a rock mass (see A.S. No. 932210 C1 (RU) IKI G01D 7 / 16, priority 03.10.1980). The device comprises a system of parallel conductors made of calibrated wire, arranged mutually perpendicular to each other, the electrical resistance of which is set to increase, as well as communication lines arranged non-parallel to the conductors. Thus, the system of conductors and communication lines is a superficially distributed sensor. When a crack forms on the outcrop, the corresponding conductor glued to it ruptures, and the electrical resistance of the circuit changes, the value of which is used to determine the coordinates of the incipient cracks and the rate of their development.The disadvantages of this device are as follows: low accuracy, since only cracks in the outcrop are recorded; labor-intensive preparation of the sensor and the need for precise calibration of the conductors.

[0003] A method for assessing the condition of mine workings roofs (see A.S. No. 1252488 C1 (RU) IKI E 21C 39 / 00, priority dated 11.12.1981) significantly eliminates the deficiencies of the analog. According to this method, clamp-on or adhesive sensors are installed on the roof of the mine workings, connected by wire to an instrumentation unit. This unit is connected to the sensors in pairs in a specific sequence, by rows and between them, measures the electrical resistance and stores it. An increase in the measured value is used to determine the location of any delamination cracks that have formed.

[0004] This method is less labor-intensive, as the sensors used are of a simplified design and do not require precise calibration. However, the monitoring accuracy is insufficient, as the measurements do not provide information on the depth of the delamination cracks or their opening.

[0005] A more advanced method of geoelectric exploration for predicting areas of heterogeneous coal seam roofs (see patent No. 2021506 C1 (RU), IPC E 21C 39 / 00, priority dated 11.12.1991) is based on the application of electrical sounding. A four-electrode setup is used, with the first current and first measuring electrodes grounded at the side of the first working, the second current electrode extended to infinity, and the second measuring electrode grounded in the opposite working of the seam at a specified pitch. The monitoring results in isoline maps of the main roof thickness in electrical resistivity units. This method is more informative, as it provides a two-dimensional forecast of the studied zone; however, it does not provide for automated and remote monitoring.

[0006] A more advanced method for monitoring the physical condition of the geological environment is based on the use of a group sounding method using a three-electrode setup with paired electrodes that act as both feeder and receiver ground electrodes (see patent No. 2650084 C2 (RU), IPC G01V 3 / 04, priority dated December 31, 2015). The implementation scheme of the method includes an area of ​​fixed measuring lines, the electrodes of which are connected via a switch to a generator and a measuring device. Data processing is performed by a computer using the ZOND software system. This universal method provides an automated mode for the inspection of hydraulic structures and undermining mining facilities with data transmission via the Internet. This method eliminates most of the disadvantages of the analogs discussed above.Its main drawback is that it relies on electrical sounding from the earth's surface followed by computer inversion of sounding databases (solving inverse electrical exploration problems). To date, software for interpreting soundings of multilayered media with vertical, horizontal, and inclined boundaries has been insufficiently accurate. In particular, the results of multi-electrode sounding (electrical tomography) are most significantly influenced by the physical state of the upper surface layer, which is subject to intense climatic influences: rainfall moistens it, leading to a sharp (severalfold) decrease in the specific electrical resistance (SER) of the soil; drought and moisture evaporation increase SER by the same amount; at subzero temperatures and when the soil freezes, sounding becomes virtually impossible due to the low electrical conductivity of ice.

[0007] The most advanced method currently available for monitoring a diaphragm made of bored clay-cement piles in an earth dam is the electrical resistivity tomography method (see patent No. 2678535 C1 (RU), IPC E02B 7 / 06, E02B 3 / 16, G01N 27 / 00, priority dated 06.02.2012). The method involves installing supply and receiving electrodes directly into the body of the monitored object (the diaphragm of the earth dam) along a profile with the required step to a depth of 0.25 m to eliminate the undesirable effect of the surface layer, connecting them via a multi-core cable to a data collection and processing unit, periodic tomographic probing with the construction of a two-dimensional pattern of the electrical resistivity distribution and its comparison with the previously obtained one. The method ensures monitoring of the formation of high-filtration zones in the diaphragm when the electrical resistivity deviation is more than 10-15%.

[0008] This invention partially eliminates the main drawbacks of similar technologies: sensors (electrodes) are installed throughout the entire monitored object at a spacing that ensures the required monitoring detail; immersion of the electrodes to a depth of more than 0.25 m reduces the influence of the surface layer; the method provides automated and remote monitoring modes.

[0009] We choose this method as a prototype.

[0010] The disadvantages of the prototype are as follows.

[0011] 1. When installing electrodes on the ground surface and using the electrical resistivity tomography method, the entire monitoring zone is not covered. Since the two-dimensional resistivity distribution map (electrotomogram) is trapezoidal with a 25-30° slope on the sides, up to 30% of the object's volume remains unmonitored.

[0012] 2. Insufficient accuracy of electrical sounding inversion (transition from effective to true resistivity) remains when studying multi-layer geological sections with vertical and inclined boundaries.

[0013] The operations of the method adopted as a prototype can be used to solve other similar technological problems, in particular, for environmental monitoring of the processes of contamination of near-surface zones of soils with electrically contrasting ecotoxicants.

[0014] The aim of the invention is to increase the accuracy of remote monitoring of the degree of soil contamination by electrically contrasting ecotoxicants.

[0015] The stated objective is achieved by the fact that in the known method, which includes installing supply and receiving electrodes in the body of the monitored object, connecting them via a multi-channel cable to the data collection and processing system, periodically determining the resistivity and comparing it with previously obtained values, the supply and receiving electrodes are installed in the form of four-electrode microprobe sensors immersed in the ground according to the depth and area of ​​the monitored object, the data collection and processing system includes a switch, a controller, a processor and a GSM transmitter with an antenna, the true resistivity is periodically measured at the point of installation of the sensors, and based on the results of comparing this value with the previously obtained one, two-dimensional maps of the distribution of the coefficient of soil pollution with an ecotoxicant are constructed, transmitted via a cellular network to the operator.

[0016] The figure shows a functional diagram of the method for remote monitoring of the degree of soil contamination with electrically contrasting ecotoxicants. The diagram shows the following functional elements of the claimed method: earth's surface 1; impermeable layer of the soil massif 2; geocontrol zone 3; submersible four-electrode microprobe sensors 4; multichannel cable 5; switch 6; controller 7; measuring device 8; analog-to-digital converter (ADC) 9; processor 10; GSM transmitter 11; antenna 12.

[0017] The sequence of operations for the claimed method is as follows. Based on the results of engineering-geological, geophysical, and environmental surveys and an analysis of the technological characteristics of the production enterprise, the geometric parameters of geocontrol zone 3 are determined, located at a depth interval from the earth's surface 1 to the boundary of the aquifer 2. Within the geocontrol zone 3, AMNB 4 submersible four-electrode microprobe sensors (A, B - supply electrodes, M, N - receiving electrodes) are installed in depth and in the plan, while the installation pitch of the AMNB 4 submersible four-electrode microprobe sensors is selected depending on the required monitoring detail. The immersion four-electrode microprobe sensors AMNB 4 are connected by a multi-core cable 5 to the switch 6, which connects electrode A and B to the supply circuit, and M and N to the receiving circuit of the measuring device 8, which determines the true resistivity at the point of installation of the immersion four-electrode microprobe sensors 4.Controller 7 controls the operation of elements 6 and 8, setting the frequency of measurement cycles and the connection order of the submersible four-electrode microprobe sensors 4. ADC 10 converts the analog resistivity value into digital code, and processor 10 generates output information on two-dimensional maps of the distribution of the soil contamination coefficient with the ecotoxicant in the form of tables or contour fields. Transmitter 11, via antenna 12, transmits the generated information via the cellular network in GSM format.

[0018] The described method provides a fundamentally higher level of accuracy in monitoring the processes of change in the physical state of soils due to the transition from the method of electrical resistivity tomographic sounding from the earth's surface to measurements of the true resistivity of the soil using submersible four-electrode microprobe sensors, which makes it possible to completely eliminate the influence of the error of computer inversion of the results of electrical resistivity tomography when switching from effective resistivity to true resistivity, regardless of the complexity of the geological structure of the studied massif.

[0019] High-precision electrophysical monitoring allows not only to monitor the location and size of the zone contaminated with ecotoxicants but also to assess changes in the degree of contamination. An experimental and analytical framework for the proposed method has been developed and is described below.

[0020] The main physical premise of the proposed method is that a significant portion of the most dangerous environmental pollutants exhibit abnormal electrical conductivity. Thus, all petroleum products (oils, diesel fuel, gasoline) used in automobile, rail, and air transport exhibit pronounced dielectric properties. The resistivity of these liquids varies in the range of 10 11 -10 12 Ohm⋅m, while for natural mineral solutions this range is 10-100 Ohm⋅m. Concentrated solutions of alkalis, acids, and metal salts, on the contrary, have abnormally low resistivity of 0.1-1.0 Ohm⋅m.

[0021] The resistivity of a water-saturated rock, which is a three-phase medium, is determined using the classical empirical relationship (see Prostove S.M. Electrical stabilization of soils. - Tomsk: Tomsk University Press, 2011. - Pp. 83-84):

[0022]

[0023] where m is porosity (pore voidage); W is the coefficient of moisture saturation of the pore and crack space; ρ в - Resistivity of the solution filling the pore space, Ohm⋅m; β, γ - empirical parameters depending on the structural and textural features of the soils (rocks) being studied; β - parameter determined by the structure of the pore space (mainly by the tortuosity of the channels); γ - parameter depending on the wettability of the pore surface by the solution.

[0024] Parameter β depends on the structure of the pore space and for compacted cohesionless soils varies in the range of β=1.3-2.2; parameter γ is determined by the degree of wettability of the surface of the solid phase and varies in the range of γ=1.8-3.5.

[0025] From equation (1) it follows that when the soil pores are filled with oil product, a positive anomaly ρ is formed, and when contaminated with an inorganic electrolyte, a negative anomaly is formed.

[0026] To estimate the pollutant content in the pore fluid, it is advisable to use the theoretical dependence of the harmonic weighted average for a two-component medium, which allows one to calculate the desired value with high reliability:

[0027]

[0028] where ρ в , ρ н ρ п - resistivity of the weighted average, oil product and natural moisture, respectively, Ohm⋅m; V н , V п - the volume of oil product and natural moisture in the solution, respectively.

[0029] Theoretical dependencies (1) and (2) fundamentally allow us to assess the degree of soil contamination with oil products.

[0030] To quantitatively assess the degree of pollutant saturation, a soil contamination coefficient k was introduced, equal to the ratio of the volume of oil product contained in the soil pores to the total volume of pore fluid. By transforming equations (1) and (2), the following expressions can be obtained:

[0031]

[0032] where V н - the volume of filling of mountains with oil products;

[0033]

[0034] where k is the pollution coefficient.

[0035] Theoretical dependencies (3) and (4) allow us to estimate the degree of soil contamination with oil products based on the results of monitoring the resistivity ρ using the declared method.

[0036] In a more accessible version, the change in the degree of soil contamination with oil products can be approximately estimated using an empirical relationship

[0037]

[0038] where k(t) is the current value of k at time t; k o - initial value determined by a direct laboratory method; - statistical dependence determined based on the results of preliminary laboratory or field experiments; ρ and ρ o - respectively, the current and initial values ​​of ρ.

[0039] Similarly, the degree of soil contamination with toxic inorganic electrolytes can be assessed.

[0040] The above allows us to consider that the above-stated objective of the invention has been achieved.

Claims

A method for remotely monitoring the degree of soil contamination with electrically contrasting ecotoxicants, which includes installing supply and receiving electrodes in the body of the monitored object, connecting them via a multi-channel cable to a data collection and processing system, periodically determining the resistivity and comparing it with previously obtained values, characterized in that the supply and receiving electrodes are installed in the form of four-electrode microprobe sensors immersed in the soil according to the depth and area of ​​the monitored object, the data collection and processing system includes a switch, a controller, a processor and a GSM transmitter with an antenna, the true resistivity is periodically measured at the point of installation of the sensors, and based on the results of comparing this value with the previously obtained one, two-dimensional maps of the distribution of the coefficient of soil contamination with an ecotoxicant are constructed, transmitted via a cellular network to the operator.

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