Optimization of multi-frequency electromagnetic surveying for investigating waste characteristics in an open dumpsite

Abstract

ABSTRACT Multi-frequency electromagnetic (EM) surveying is a type of frequency-domain electromagnetic (FDEM) survey, a new geophysical exploration approach used as a scanning tool to investigate waste characteristics within a final disposal site before electrical resistivity tomography (ERT) surveying. EM surveys provide information about shallow subsurface conditions; however, to date, no studies on waste bodies or waste characteristics in open dumpsites have assessed the optimal frequency for use in multi-frequency EM surveys. This research aims to determine the optimal frequency set for multi-frequency EM surveying for initial waste quality assessment in open dumpsites. These initial waste quality data are critical to assess the feasibility of open dump mining projects. First, a multi-frequency EM survey was performed in this study, which was measured at the exact electrode positions of the three ERT profiles. This FDEM survey used 15 frequencies ranging from 1,000–⁠15,000 Hz, which were grouped into frequency sets for inversion modeling of the electrical conductivity. Second, an ERT survey was carried out along all three profiles, each of which was around 144 m long. Subsequently, synthetic electrical resistivity data were generated by processing the electrical conductivity model. Data from each frequency set were then generated at the same depth, with interpolation techniques used to analyze the linear correlation between synthetic electrical resistivity and real electrical resistivity data and compare the Pearson’s correlation coefficient (R) values to determine the optimum frequency set for FDEM surveys in the open dumpsite. The results showed that the E4 frequency set, consisting of 5,000, 11,000, and 15,000 Hz values, typically had the highest positive correlations (R = 0.74–0.91) across all profiles and provided waste characteristics information close to the true conditions. Thus, these frequencies represent the optimal set for multi-frequency EM surveys for the primary assessment of waste characteristics in open dumpsites. Implications: Open dump mining (ODM) is now applied as a sustainable approach to combat improper waste disposal and reduce municipal solid waste (MSW) in the open dumpsite. To implement ODM for producing RDF, business developers must know the amount and composition of waste that can be converted into RDF before mining. This study used multi-frequency EM surveys with frequencies of 5,000, 11,000, and 15,000 Hz. This multi-frequency method effectively determined the waste composition and identified potential excavation points in the open dumpsite prior to ODM. This method can mitigate the limitations of traditional surveying, due to its improved mobility, lower time consumption, and reduced labor needs.