Detection Of Landfill Leachate Seepage With Induced Polarization Method

Water is the source of life,the basis of production and ecology,and an important condition that human rely on to survive and develop.However,the safety and cleanliness of water resources are facing threats from all sides,one of which is landfill leachate.The precise detection of leachate pollution plume can provide an important basis for leachate pollution management and control,which is of great significance to water environmental protection and the promotion of ecological civilization.However,the traditional chemical sampling and analysis methods have limited accuracy range and may lead to vertical diffusion of pollutants during the drilling process.To address the above problems,in this paper,we use the induced polarization method as the main technical means,focusing on the effect of combined detection of leachate pollution plume by induced polarization method and water chemical analysis.The main research contents and results are as follows.(1)We improve the traditional induced polarization measurement method in the low resistivity leachate detection.The traditional single-cable induced polarization measurement device is susceptible to noise and the collected data are of poor quality.In this regard,a dualcable measurement method is adopted,in which the current cable is separated from the potential cable and non-polarizing electrodes are used in the potential cable to overcome the influence of electrode polarization and capacitive coupling and achieve high-quality data acquisition in the highly conductive subsurface environment.Meanwhile,the measurement protocol is improved,and the collected data can be directly imported into the software for processing,which improves the working efficiency.(2)Leachate contamination analysis was carried out based on 4 times groundwater chemistry data of 14 boreholes.Six contaminated boreholes were identified based on the contents of COD and ammonia nitrogen in each borehole.Comparing the major anion and cation compositions of groundwater samples from contaminated and uncontaminated boreholes,it was found that for the landfill site under investigation,the Cl-and Na+contents can be used as a good indicator of whether the groundwater is contaminated by the leachate plume.The linear regression fits of pore water conductivity with Cl-and Na+ concentrations in 14 boreholes then reflect that the concentrations of Cl-and Na+(especially Cl-)can be equally well characterized as pore water conductivity.When the groundwater conductivity in the borehole is greater than 500 mS/m,it means that the groundwater here is contaminated by the leachate plume.Based on the smooth fluctuation of chemical parameters in the contaminated borehole with time,it was judged that the sheet piles blocked the continuous contamination of the northern part of the landfill by the leachate plume.(3)The quality of the induced polarization data was verified and the cause of the high polarization rate anomaly was analyzed based on sand column experiments.The data quality of the induced polarization was demonstrated by the fit comparison of the chargeability data with the decay curve.Sand column experiments were conducted using soil samples collected in boreholes 13#and 14#.By analyzing the variation of conductivity and phase with frequency,it was determined that the abnormal high polarization effect in the inversion profile of the survey line A was attributed to the sheet piles adjacent to the survey line A.The differences in formation factors and surface conductivity calculated based on the sand column experiments and field data were within the tolerance range,thus further verifying the quality of the induced polarization data.(4)The combined use of water chemistry data analysis and 4 induced polarization line data successfully traced two leachate pollution plumes and inferred the location of the leachate pollution sources.Although the induced polarization effect in the inversion profile of survey line A is higher than expected,the relatively low chargeability region(<100 mV/V)still refines the high conductivity region(>600 mS/m)on the conductivity profile,and the circled leachate contamination plume is verified by the water chemistry data.Based on water chemistry data and the good correlation between leachate tank 1 and 2 and the location of the leachate contamination plum,it was inferred that the leachate contamination plume originated from the leakage of the leachate tanks.