The use of electrical resistivity tomography and borehole to characterize leachate distribution in Laogang landfill, China

Maximizing RDF recovery potential through the integration of electrical resistivity tomography and frequency-domain electromagnetic surveys for waste characterization in open dump mining

Open dumping is a widespread waste management technique used in developing countries. This approach is simple and economical but has numerous environmental and health impacts. Open dump mining (ODM) can reduce waste in both open and controlled dumpsites by converting waste into refuse-derived fuel (RDF) for energy generation; however, before ODM implementation, the waste's characteristics and composition must be assessed. Geophysical surveys are widely used to characterize waste. The electrical resistivity tomography (ERT) method is a particularly common technique for determining waste composition, but it has several limitations. Therefore, a frequency-domain electromagnetic (FDEM) survey was used in this study as a pre-screening tool to evaluate the waste composition and overcome the limitations of ERT surveys. This study aimed to determine the relationship between geophysical data types (i.e., ERT and FDEM) and the optimal waste composition for RDF production and assess the ability of FDEM surveys to identify areas with RDF recovery potential. This study combined ERT and FDEM surveys with waste sample analysis in old/new controlled dumpsites in Thailand. The quantitative and qualitative correlations between the geophysical data (i.e., resistivity, conductivity, waste composition, and moisture content (MC)) were then assessed using linear and multiple linear regression analysis. Integrating geophysical surveys was found to have the potential to locate optimal RDF recovery areas, with low conductivity (0-100 mS/m) and high resistivity (>55 Ω·m) characteristics associated with areas of high RDF content (>40 % by weight). An unexpected finding was that increased waste age resulted in increased resistivity and decreased conductivity. Additionally, the MC depended on factors affecting spatial variability (e.g., precipitation and biodegradation). Overall, this study demonstrates that integrating ERT and FDEM surveys is a suitable pre-screening tool to evaluate waste characteristics and composition, mitigate ERT survey limitations, and improve waste investigation before ODM.

Investigating the effect of waste age and soil covering on waste characteristics prior to landfill mining using an electrical resistivity tomography technique

This study analyzed the potential of landfill mining for refuse-derived fuel (RDF) production based on waste electrical resistivity, including the influence of waste age and soil cover. Electrical resistivity tomography (ERT) was used to determine the resistivity value of landfilled waste in four active and inactive zones, with two to four ERT survey lines collected per zone. Waste samples were collected for composition analysis. Linear and multivariate regression analyses were used to constrain the data correlation based on the waste's physical characteristics. An unexpected finding was that soil cover, rather than the waste's age, influenced the characteristics of the waste. To evaluate the RDF recovery potential, multivariate regression analysis showed a significant correlation between electrical resistivity, conductive materials, and moisture content. However, the obtained correlation between electrical resistivity and RDF fraction using linear regression analysis can be more conveniently used to evaluate RDF production potential in practice.

An overview of in situ testing and geophysical methods to investigate municipal solid waste landfills

Municipal solid waste (MSW) management is challenging as a whole. Global waste generation is expected to continue to increase in the coming years, and landfills are currently the primary destination. Therefore, the stability of these structures must be carefully evaluated to prevent failures and associated health and pollution risks, which implies the determination of waste properties using more reliable approaches. This paper presents a scoping review of field data from MSW landfills and outlines suggestions for future work. Studies published in the past twenty years were selected following a systematic search process in databases. Aspects discussed include (1) strength parameters and soil behavior type from in situ testing, (2) elastic moduli from seismic wave propagation, and (3) moisture content from geoelectrical measurements. Although the values of geotechnical parameters have varied due to waste heterogeneity and applied methods, the trends observed with depth and age could be compared. Research opportunities involve the spatial analysis of mechanical properties at a given site, seismic response of landfills with high organic content and saturation degree, interpretation of long-term resistivity monitoring, and combination of electrical properties to assess the degradation stages within the waste mass.

Experiment on monitoring leakage of landfill leachate by parallel potentiometric monitoring method

The accumulation of municipal solid waste (MSW) in landfills often becomes a serious pollution source of geological environment and groundwater. The geological environment is the carrier of the landfill, and also the main pollution object of the landfill. The main pollution modes of the landfill site to the surrounding geological environment are purging, flushing, leachate, etc. If the leachate leakage cannot be found and repaired in time, it will cause serious harm to the geological environment and groundwater. The cost of geological environment and groundwater sampling through borehole surveys is high. Therefore, monitoring the seepage path and migration law of leachate is of great significance for determining the pollution range of the landfill site. In this study, by adjusting the grids of different sizes and changing the flow rate of leachate, the monitoring of fluid migration of different types of leachate was strengthened. The results show that the parallel potential monitoring method can quickly reflect the location and number of leachate points and the migration law of leachate. It provides effective reference data for landfill leachate monitoring.

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

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.

Quantitative water content estimation in landfills through joint inversion of seismic refraction and electrical resistivity data considering surface conduction

The disposal of municipal solid waste (MSW) in landfills is the prevalent method of waste management at the global scale. However, the production of landfill gases due to the methanogenic fermentation of wet MSW is a possible threat to human health and accounts for a substantial contribution to the global greenhouse gas emissions. Accordingly, information regarding water content is critical as it is an important factor triggering methane production in MSW landfills. In this study, we propose a petrophysical joint inversion scheme to quantitatively solve for the water content (WC) in landfills based on seismic refraction as well as electrical resistivity data collected at two different frequencies. In this way, we also take into account the contribution of the surface conductivity to the observed electrical response, which is crucial for a reliable quantification of the WC. Our results reveal a high water content within the MSW unit (WC > 20%) for areas characterized by a strong polarization response (normalized chargeability > 5 M_n mS/m). Such areas can be related to an increased biogeochemical activity as evidenced by the detected methane production. We observe consistent estimates between the water content resolved through the proposed joint inversion scheme and values measured in waste samples with a median percentage error of 17%. Our study demonstrates the possibility to obtain reliable estimates for the WC in MSW landfills through the petrophysical joint inversion of seismic and electrical data when surface conductivity is explicitly considered.

Mapping the impact of a large municipal waste disposal area on surface water: 1993-2017, case of Laogang, Shanghai

In China, the impact of waste disposal facilities is always a cause of concern for the government and the public. Laogang Municipal Waste Disposal Area (LMDA), Shanghai, one of the largest municipal waste disposal areas in the world was selected as case in this study, and it was attempted to analyze the changes in the surface water quality, and map the impacted area by LMDA on surrounding streams from its operation period of 1993-2017. The results showed that, during the whole period, only biochemical oxygen demand (BOD₅) showed a continuous improvement with a percentage of 85.92%, however, chemical oxygen demand (COD_cr), ammonia (NH₄⁺-N) and total phosphorus (TP) significantly improved but BOD₅ slightly deteriorated began from 2013. Using spatial analysis tools and Kendall's concordance test, COD_cr and phenol at LMDA showed a significant impact on surrounding surface water; especially, the impacted area for COD_cr decreased from 106.30 km² to 22.86 km² from 1993 to 2017, which dropped from 4.3 to 0.9 times the area of LMDA. Surprisingly, NH₄⁺-N and TP at LMDA were affected by the surrounding streams, instead of having an impact on them. Interestingly, heavy metals and non-metals such as Hg, As, Zn, and Se in the surrounding streams were unlikely affected by LMDA. The driving forces for surface water quality improvement included the eco-remediation of closed unsanitary landfills, upgrade in waste shipping and terminals, operation of sanitary landfills and incineration plants for landfill diversion. Capsule: Impacted area of municipal waste disposal area is not so large.

Electrical resistivity methods to characterize the moisture content in Brazilian sanitary landfill

The moisture content of the municipal solid waste (MSW) is a physical characteristic that plays a fundamental role in the stability and settlement of landfills. However, this physical index is difficult to monitor within the mass of landfilled MSW because it undergoes great variation due, mainly, to the heterogeneity and biodegradation of the waste. Brazilian MSW generally has a large amount of organic matter, that when biodegraded, generates a considerable volume of gases and fluids, aggravated by climatic conditions, such as high rainfall and temperatures. Hence, the importance of obtaining and evaluating the distribution of moisture content in the MSW mass over time. Currently, the electrical resistivity properties have been presented as an interesting approach to obtain the moisture content in landfills indirectly. This study aimed to apply geoelectrical methods as a tool to obtain and evaluate the moisture content distribution in an experimental cell of a sanitary landfill using Archie's law, which correlates the volumetric moisture content and electrical resistivity. Moisture content values were obtained in laboratory tests with MSW samples collected in two vertical holes and electrical resistivity measurements by means of vertical electrical sounding. The moisture content and the resistivity values of the samples were used to calculate the parameters a and m of Archie's law. This allowed to convert the resistivity tomography to moisture content tomography. The good correlation achieved between the moisture content calculated by Archie's law and that obtained from samples indicates that the use of electrical resistivity methods is useful to assess and monitor quantitatively the moisture content in landfills using Archie's law.

Effects of surfactant injection position on the airflow pattern and contaminant removal efficiency of surfactant-enhanced air sparging

Surfactant-enhanced air sparging (SEAS) is an effective remediation technique for VOCs-contaminated soil. In this study, three types of tests are performed to investigate the effects of the surfactant injection position on the airflow pattern, contaminant removal efficiency, and airflow path control. The three tests are conventional air sparging (CAS), entire SEAS (ESEAS), where the surfactant is incorporated into the entire contaminated soil, and local SEAS (LSEAS), where the surfactant is injected locally at different positions. With increasing distance between the injection position and the central axis, the LSEAS test results approach the results measured in the CAS test. When the surfactant is injected directly at the central axis, a high contaminant removal rate of 89% is obtained, which is even higher than that obtained for the ESEAS test. As the injection position moves away from the central axis, the removal rate decreases. Furthermore, when the injection position is close to the sparging point, the surfactant can successfully control the airflow path. Based on the test results, a critical distance between the surfactant injection position and sparging point exists where high remediation efficiency can be achieved. This optimal surfactant injection position is specific to each contamination site.

Assessment of strength and leaching characteristics of heavy metal-contaminated soils solidified/stabilized by cement/fly ash

Solidification/stabilization technique has been widely adopted to remediate the heavy metal-contaminated sites. In the present work, the strength and leaching characteristics of the contaminated soils solidified/stabilized by cement/fly ash were systemically investigated. Electrical resistivity was also measured to establish empirical relationships for assessment of remediation efficacy. Tests results showed that the unconfined compressive strength increased and the leached ion concentration decreased with increasing curing time. In contrast, the unconfined compressive strength decreased and the leached ion concentration increased with increasing initial heavy metal ion concentration in the specimen. For the strength characteristic, the most notable detrimental effect was induced by Cr³⁺ and the least was induced by Pb²⁺. For the leaching characteristic, the trend was reversed. The electrical resistivity of the tested specimen increased significantly with increasing curing time and with decreasing initial ion concentration. The electrical resistivity of the Pb-contaminated specimen was higher than that of the Zn-contaminated specimen, which in turn was higher than that of the Cr-contaminated specimen. Empirical relationships between the strength, leaching characteristic, and electrical resistivity were established, which could be adopted to assess the remediation efficacy of heavy metal-contaminated soil solidified/stabilized by cement/fly ash.

Use of electrical resistivity tomography for detecting the distribution of leachate and gas in a large-scale MSW landfill cell

In this study, integrate electrical resistivity tomography (ERT) tests were carried out in a large-scale (5.0 × 4.0 × 7.5 m) MSW landfill cell to investigate the possibility of detecting perched leachate mounds, leachate level, and gas accumulation zones at wet landfills. The resistivity of both bulk waste and waste components at different moisture states were measured and the three-phase volumetric relationships of the waste pile were analyzed to better interpret the ERT test results in the large-scale cell. The following observations were given: (1) The relationship between resistivity and volumetric moisture content (VMC) of waste sample can be reasonably fitted by Archie's law. The resistivity of waste components at a saturated state was all lower than 21 Ω m. (2) A significant amount of void gas was entrapped in the underwater waste, being 30.4-34.8% of the whole waste pile in volume. (3) Low-resistivity zones (< 5.0 Ω m) were observed in the waste pile being fully drained under a gravity condition, which was believed to be related to a perched leachate. (4) The average VMC values of the waste layer below and above the leachate level were in the ranges of 46.5-53.1% and 28.1-41.3%, respectively. (5) Irregular variations of high-resistivity zones (> 40 Ω m) observed in the underwater waste were associated with the accumulation and dissipation of gas pressure. It was found that the "gas-breaking value" in the gas accumulation zone was up to 10.5 kPa greater than the pore liquid pressure in the stable methanogenesis stage. These findings shone a light on the possibility of using the ERT method as an efficient tool for mapping the gas/leachate distribution and improving operations at wet landfills.

Experimental investigation on the migration of leachate under flowing conditions through laboratory ERT

With an increase of service time of landfills, a great amount of old landfills begin to leak and the leachate impairs the surrounding environment severely. Defining the flow of leachate is significant to the monitoring and restoration of the landfill. Field tests and laboratory tests are often used to investigate the leachate flow. However, many uncontrollable factors may affect the accuracy of field tests, and the application of field test results is usually limited. At the same time, it is difficult to simulate and monitor the migration process of leachate in real time in laboratory. To address this problem, a new physical simulating device is created to simulate the leachate migration under flowing conditions, and improved ERT device is designed to monitor the migration in laboratory tests. The results show that the improved ERT could delineate the migration range well in laboratory tests, providing a new method to investigate the leachate migration in laboratory test and providing a reference to the application of ERT in field tests. The relative variation rate of resistivity could reduce the influence of background, and is very suitable for time-lapse ERT. In addition, the effect of flowing rate, leakage rate, and time on the leachate migration is also investigated. The results show that the horizontal migration rate increases with an increase of flowing rate. The leakage rate has a significant influence on the vertical migration, but has limited effect on the horizontal migration. The curvature of migration front increases with an increase of flowing rate and time.

Impacts of leachate of landfill on the groundwater hydrochemistry and size distributions and heavy metal components of colloids: a case study in NE China

Colloids associated with heavy metals are ubiquitous in contaminated groundwater; waste accumulation at imperfectly sealed landfills can produce large amounts of leachate with colloids and heavy metal contaminants, which can pollute the downstream groundwater. In this study, three sites in a landfill were sampled to reveal heavy metal particle size distributions and their chemical compositions. The > 220 nm particle sizes were the predominant size in the downstream groundwater, while the < 10 nm particle sizes were the predominant size in the upstream groundwater. Total Fe increased from 35.5 μg/L in the upstream groundwater to 107 μg/L in the downstream groundwater. This increase was attributed to the enhanced migration and accumulation of colloids in the aqueous phase. The elements and the colloid size distribution in the landfill indirectly reflected the composition and degradation of the waste. Colloids played a key role in distribution of both solid particles and aqueous contaminants in the landfill. The results of this study will contribute to the knowledge of the effect of different contaminants in the vicinity of landfills without appropriate sealing systems.