Underground Contamination Research Articles

Borehole Water Supply in Enugu Metropolis: Water Quality Comparative Study of Sources from 9th Mile and Emene, Enugu State, Nigeria

Abstract: Water quality study presents status of water for domestic, irrigation, industrial and other uses. Indiscriminate and wasteful water consumption, improper waste disposal practices, and underground contamination have led to deterioration and pollution of water quality. This study was aimed at determining water quality status using parameters in borehole water. Samples from two different towns; Ngwo and Enene, Enugu East. Sampling locations 1(6o 28’24.7”N 7o 34’49.2”E) and 2(6o 27’36”N 7 o 36’46”E) are situated within Nike East Local Government (precisely Emene) while sample 3(6o 25’52.8”N 7o 25’10.6”E), 4(6o 25’55.3”N 7o 24’22.8”E) and 5(6o 25’50.4”N 7o 26’08.5”E) are within Enugu Ngwo (9thMile Corner). The parameters analyzed include; Electrical conductivity, Turbidity, pH, TDS, TSS, SS, Calcium, Magnesium, and Total Hardness, using laboratory standard methods of analysis. The data provided by this investigation shows that the water samples from Enugu Ngwo only is more acidic outside the recommended level. Other qualities of all the parameters are all measurable for both locations. Based on these findings, recommendations were presented for the purpose of improving water quality and sustainable assess in Enugu Metropolis and beyond.

Contamination vulnerability assessment of the Bambuí karst aquifer, in the Terra Ronca region - Goiás, Brazil

Karstic environments are characterized as areas of intense rock dissolution, which allows the generation of several typical features, such as sinkholes, resurgences, caves, and dolines. The spatial distribution of these features is of great importance to identify the contamination vulnerability of karst aquifers and serve as a basis for the application of assessment methods. This study aimed to identify and classify the areas vulnerable to underground contamination in the karstic region of the Terra Ronca State Park (PETeR) and its surroundings. The method chosen was the COP, which assesses the physical conditions of the environment (relief, lithology, soils, precipitation, karst features, and vegetation) to determine the areas naturally vulnerable to contamination. The analyses were performed in a GIS environment. The results indicated five categories of areas vulnerable to groundwater contamination: Very High to High (3.14%), Moderate (16.21%), and Low to Very Low (80.62%). The Terra Ronca State Park was the analysis unit with the highest vulnerability in the region (9.91%), due to the concentration of karstic features in the area. The acquired results aim to help in the underground water resources conservation as well as the speleological patrimony.

3D Near-surface Velocity Model Building by Integrating Surface, Borehole Seismic, and Well-logging Data in a Small-scale Testbed

This study aims to build a 3D velocity model for investigating and evaluating underground contaminants flowing through groundwater pathways. To accomplish this goal, we performed seismic exploration at a test site with fractured rock layers within a depth of 100 m. The acquired seismic data was then used to construct a three-dimensional (3D) P-wave velocity model of the test site. Although comprehensive geophysical exploration may be useful for investigating the near-surface structure, this paper focuses only on constructing a P-wave velocity model using the seismic method. The primary information of the model consists of extracted velocities from a two-dimensional surface, borehole first-arrival traveltime tomography results, and full waveform sonic log data. Since the test site has the spatial restriction of the survey line, we intended to improve the geological structure analysis results using various quantitative and qualitative analysis methods. First, to increase the reliability of velocity information, we performed a traveltime analysis on the zero vertical interval (ZVI) gather from the borehole seismic data. Then, we identified the qualitative information of the fracture zone's location by analyzing the amplitude variation of the ZVI gather. Moreover, we extracted structural information using the common reflection point gather from the borehole seismic data to supplement the obtained lithological information. However, the information for constructing a 3D P-wave velocity model was still insufficient due to the spatial constraints of the survey line and the limited depth of the borehole seismic survey. We filled this gap using the radial basis function interpolation method. We could verify the completed 3D P-wave velocity model by comparing it with core log data. Overall, the integrated interpretation of the final velocity model and the analysis results could provide a probable pathway that indicates hydraulic connectivity.

Capacitive Resistivity Method Applied to the Environmental Diagnosis and Management of Contaminated Area of Gas Station

This article presents a case study of fuel underground contamination where the geophysical method was applied to support for decision making regarding environmental management activities. The application of geophysical methods that measure electrical resistivity in the study of contaminated areas and their correlations with organic contaminants are discussed, in addition to the presentation of theoretical and practical aspects of Capacitive Resistivity (CR) method. The importance of this work is based on the evaluation of the potential for identification of free phase of organic contaminant by the capacitive method and the assessment of the effectiveness of the remediation implemented through the geophysical data obtained. The method applied was able to identify the highest electrical resistivities related to fuel in the subsurface and indicated the inefficiency of the current remediation by the inadequate positioning of the extraction wells and the inaccuracies in the monitoring of underground contamination and allowed the proposition of recommendations related to management of the case based on geophysical information. From results, it is concluded that the Capacitive Resistivity method can be applied in similar cases of leaks in gas stations to diagnose contamination and to guide the adoption of more appropriate actions of environmental management.

Evaluating the impact of a cemetery on groundwater by multivariate analysis.

Water analyses in conjunction with hydrological and geotechnical investigations were carried out to assess the potential for groundwater contamination from the decomposition of buried human bodies. Water samples were collected from 2007 to 2018 in three monitoring wells built within the cemetery area. Water quality was evaluated based on the determination of 25 analytical parameters (20 physical-chemical and 5 microbiological). Laboratory data reported by the local sewage water company for water collected in household cisterns located outside the cemetery area were also evaluated. Multivariate analysis showed a similar pattern between iron content, turbidity, and rainfall data collected at the rainfall station closest to the study area. This behavior is a direct consequence of soil leaching (oxisol). The physical characterization of the soil of the unsaturated area above the aquifer indicates that the absorption of body waste by the soil is favored, preventing surface contaminants from reaching the aquifer. This work also found that the water samples collected outside the cemetery area do not comply with the Brazilian limits for drinking water. In conclusion, water samples collected from monitoring wells located within the cemetery area have little to none impact on both subsurface and underground contamination.

Detecting vinyl chloride by phytoscreening in the shallow critical zone at sites with potential human exposure

Chlorinated ethene (CE) contaminants are widespread in groundwater, and the occurrence of vinyl chloride (VC), among others, is a well-known issue due to its mobility, persistence, and carcinogenicity. Human exposure to VC may occur through inhalation after soil vapor intrusion into buildings at sites with shallow underground contamination. Soil vapor intrusion risk is traditionally assessed through indoor air and sub-slab sampling (direct evidence) or soil gas and groundwater surveys (indirect evidence). Phytoscreening (sampling and analysis of tree trunk matrices) was proven as a cost-effective alternative technique to indirectly detect shallow underground contamination by higher chlorinated ethenes and subsequent vapor intrusion risk. However, the technique has appeared barely capable to screen for the lower chlorinated VC, likely due to its fugacity and aerobic bio-degradability, with only one literature record to date showing successful detection in trees. We applied phytoscreening at two sites with severe CE contamination nearby residential buildings caused by illegal dumping of chlorinated pitches from petrochemical productions. The two sites show variable amounts of VC in the shallow groundwater (1e2 to 1e4 μg/L), posing potential sanitary risk issues. Former soil gas surveys did not detect VC in the vadose zone. At both sites, we sampled trunk micro-cores and trunk gas from poplar trees close to contaminated piezometers in different seasons. VC was detected in several instances, disproving the shared literature assumption of the inefficacy of phytoscreening towards this compound. Factors influencing the detectability of VC and other CEs in trees were analyzed through linear regressions. Two different conceptual models were proposed to explain the effective uptake of VC by trees at the two sites, i.e., direct uptake of contaminated groundwater at the first site and uptake of VC from an anoxic vadose zone at the second site. In planta reductive dechlorination of CEs is not expected based on current literature knowledge. Thus, the detection of VC in trunks would indicate its occurrence in the shallow underground, suggesting higher screening effectiveness of phytoscreening compared to soil gas; this has implications for indirect vapor intrusion risk assessment.

Identifying Suitable Areas for Plantation of Organic Products Using GIS and AHP

Organic farming is a technique, which involves cultivation of plants in natural ways. In Malaysia, because the organic food industry is still small-scale, over 60% of organic foods are still imported and it is not possible for the availability and output of organic goods to meet the local demand and need. This study was intended to utilize the GIS and AHP technique to identify suitable areas for organic farming in Sabak Bernam, Malaysia. The study was conducted based on the objectives where criteria for organic farming were identified through background research. Pair-wise comparison (PWCM) method using questionnaires answered by experts were used to determine the weights for each of the parameters used. For this study, seven (7) criteria were considered. The criteria were then weighted according to importance and those weighted criteria were combined to produce a suitability map. A site suitability model was built using the Modelbuilder tool in Arcmap. The model used the AHP and Weighted Overlay basis which provides promising result for the analysis of finding suitable sites for organic farming. Results obtained showed that the majority of land within the Sabak Bernam district is suitable to carry out organic cultivation where the land is far from road networks, contains high organic matter content, gentle slopes with flat aspects low elevation and less than 10 meters from drainages. While land deemed not suitable involves land in dense urban area. This simultaneously means that the land is too close to road networks where underground contamination is a major possibility.

Characteristics of sedimentary environment since Quaternary in northern Jianghan Basin, China: Reconstruction of paleoenvironments

Reconstruction of sedimentary evolution plays a significant role in the investigation of natural groundwater contamination and stratigraphic mineral resources. In this paper, the variation in sedimentary characteristics and sedimentary evolution were studied by lithology, chronology and organic matter with the high-resolution grain size parameters of boreholes for Quaternary in northern Jianghan Basin. Following more traditional plotting of grain size parameters and summary statistics, visual categorization and analysis of grain size frequency distribution curves provided an effective measure for the identification of sedimentary facies. Combining with the Fisher model, new and highly efficient discriminant formulas were established, and tested for the validity. Additionally, the sedimentary evolution process and the provenance of different sedimentary facies were identified with the help of organic matter and δ13Corg data, provided geological information to explore the natural contamination of reducing arsenic ions and excessive nitrate in strata. The identification results suggest that fluvial and lacustrine sediments are dominant in the area, and the regional sedimentary environment is uniform and not affected by the transgression. The analysis results of grain size with organic matter parameters are consistent for discriminating sedimentary facies, which verified the rationality of grain size analysis and confirmed the use of organic matter content to be effective in identifying the process of fluvial and lacustrine sediments. Based on the chronological results of Optically Stimulated Luminescence dating and sedimentary facies determination, the sedimentary evolutionary process was deduced during the Quaternary for the study area. This research has important significance for the division and correlation of Quaternary borehole strata, underground contamination study, as well as environmental planning and protection.

Evaluation of the contamination of the soil and water of an open dump in the Amazon Region, Brazil

The emergence of cities and the ongoing growth of urban areas have contributed to an overwhelming increase in negative environmental impacts. A major concern is the impact caused by the inadequate disposal of municipal solid waste in open dumps without proper regulation or planning. The negative impacts caused by the inadequate disposal of solid waste include the contamination of groundwater and soils, the proliferation of disease vectors, and odoriferous and visual pollution. One specific problem generated by the disposal of solid waste is the decomposition of the organic matter found in this waste, which generates leachates. These highly soluble substances can percolate through the soil and penetrate bodies of superficial water or the water table. The present study was based on the integration of geophysical data with physicochemical, hydrochemical, and microbiological analyses, as well as the analysis of heavy metal concentrations in water and leachate samples. Contamination was confirmed and may be associated with the leachate produced by the solid waste deposited inadequately at the study site. The results provide insights into important public health and safety issues, and should alert local authorities with regard to the environmental impacts caused by underground contamination in the Amazon town of Mocajuba (Brazil).

Advances in Nanoscale Study of Organomineral Complexes of Termite Mounds and Associated Soils: A Systematic Review

Termite mounds are replete with natural nanoparticles, and they vary in physicochemical, geochemical, mineralogical, and biological properties from the adjoining soils. Although termite mounds have wide ecological and environmental roles including soil formation, faunal and vegetation growth and diversity, organic matter decomposition, geochemical exploration, water survey, treatment of underground contamination, thermoregulation, gas exchange, and global climate change, their nanoscale structures made by the associated organomineral complexes are still poorly understood because of technical limitations. In this review, we highlight the ecological and environmental significance of termite mounds and the documented techniques that have been successfully used to study nanostructure of termite mounds, namely, midinfrared spectroscopy (MIRS), photogrammetry and cross-sectional image analysis, a combination of transmission electron microscopy (TEM) and pyrolysis field ionization mass spectrometry (Py-FIMS), scanning transmission X-ray microscopy (STXM) using synchrotron radiation in conjunction with near-edge X-ray absorption fine structure (NEXAFS) spectroscopy, and high-resolution magic angle spinning nuclear magnetic resonance (HR-MAS NMR) for further appraisals. There is a need to continually develop and integrate nanotechnology with the routine classical soil analysis methods to improve our understanding of the functional mechanisms of nanostructure of termite mounds that are responsible for specific properties. In view of the numerous roles termite mounds play in the environments, agriculture, and engineering, there is no better time to channel much research into understanding how they function at nanoscale.

Management by risk of water sources contamination from soil by herbicide 2,4-D

The possibility of management by risk of surface and underground water sources contamination from soil by herbicide 2,4-D by active coals application was estimated. Active coals absorb the herbicide which is in the soil and its migration in water sources prevent. The effect of sorption by active coals has been established on the content of herbicide in a liquid phase of soil presented by capillary and gravitational moisture.

Fluid dynamic modeling of multiphase flow in heterogeneous porous media with matrix, fracture, and skin

Underground contaminants such as non-aqueous phase liquids (NAPLs) or volatile organic compounds (VOCs) threaten public safety and health. The presence of fractures or regions of high permeability significantly limits the recovery due to the contrast in the capillary pressures of the low- and high-permeability regions. We previously proposed a methodology to improve the recovery of liquids upon gas injection process from a porous system with a percolating network of fractures. This methodology uses a high capillary pressure skin at the production well and controls the injection pressure below a threshold value for the breakthrough. In this paper, a mixed finite element method is employed to model the gas-water drainage process in a porous medium containing, matrix, fracture, and skin. An additional mixed-layer is also used to account for the mixing of the solid particles at the boundaries between the matrix, fracture, and skin. The mathematical model for immiscible gas-water displacement in the heterogeneous porous medium is implemented in COMSOL Multiphysics®. The model successfully captures the dynamics of the injection pressure and fluid recovery with and without gravitational effects. The model is developed to predict the injection pressure corresponding to gas breakthrough. By injecting the gas phase at a pressure below this threshold value, the gas breakthrough can be significantly postponed. During this delayed time, more liquid recovery is expected. The model is verified with experiments using a constant injection rate scheme. We also study the optimal operation by considering recovery factor and process time as the variables, in horizontal gas injection case. Without the use of high capillary pressure skin and pressure control scheme, the ultimate recovery from porous medium is limited to that from the fracture only, (approximately 9% pore volume or PV). Using the skin and pressure control, the model predicts the recovery values to be increased by one order of magnitude, which is in agreement with the experimental data. The computational fluid dynamic (CFD) model can be used for process control and optimization to achieve optimal recovery conditions in remediation and enhanced oil recovery (EOR).

EXPERIMENTATION AND INDIRECT METHODS APPLIED TO INVESTIGATE THE CONTAMINATED AREAS

O presente artigo tem por objetivo principal apresentar as diferentes metodologias geofísicas, suas definições, características e potencialidades, exemplificando quais seriam os mais adequados métodos para cada tipo de situação envolvida na investigação da contaminação subterrânea. No desenvolvimento do texto, é abordada a temática de áreas contaminadas e suas fontes de contaminação, os termos conceituais da metodologia geofísica, o histórico no Brasil dos estudos ambientais para investigação da qualidade do solo e água subterrânea, o enquadramento da Geofísica Ambiental no Gerenciamento de Áreas Contaminadas e apontamentos quanto às normas de referência nacionais e internacionais sobre a aplicação dos métodos geofísicos em estudos de contaminação subterrânea. Além disso, são apresentados os aspectos teóricos em que se fundamentam os métodos geofísicos aplicados aos estudos ambientais, bem como exemplos de aplicação e que se constituem em casos onde a metodologia foi empregada com sucesso e contribuiu de forma relevante para o diagnóstico ambiental dos locais investigados. A relevância deste tipo de divulgação, além do aspecto de apresentação dos métodos geofísicos e de sua importância para diferentes profissionais da área ambiental, também traduz a necessidade de atualização dos textos técnicos sobre o tema, haja vista que o Manual de Áreas Contaminadas da CETESB, que é a referência principal que congrega os métodos aqui descritos, já completa quase duas décadas de sua publicação e, atualmente, não está disponível para consultas. Ao final deste artigo técnico, são apresentadas tabelas orientativas quanto à aplicação dos métodos geofísicos para a detecção de contaminação por diversos tipos de contaminantes, e referente à influência do material geológico local e relativa às características, potencialidades e limitações dos métodos geofísicos aqui abordados.

Space Charge and Electric Field Analysis on Contaminated XLPE Insulator

<p>Nowadays, XLPE cable has been widely used because it has better resistance than other cables. XLPE insulation has unique features including a high dielectric strength and high insulation resistance. A lot of researches based on hardware and software have been conducted to prove the effectiveness of XLPE cable such as AC and DC applications and Space Charge Distribution measurement under HVDC at High Temperature. This research focused on analysis of space charge and electric field on XLPE cable with effect of non-uniform contamination layer by using Quickfield Software. Non-uniform contaminations have been applied along XLPE cable using Arsenic Tribromide (AsBr3), Boron Bromide (BBr3), Ethylene Dichloride (CH2C1), Formic Acid (CH1O2), Formamide (CH3NO) and Alcohol element. Presence of these contamination elements represent of underground contamination. The size and layer of the contamination were non-uniform type. From the results, it is shown that lower dielectric constant of contamination will affect more on charge of XLPE insulation. As a conclusion, it can be seen lower dielectric constant value of contamination element greatly affecting the performance of XLPE insulation. Furthermore, size of contamination also influences the content of charge in contamination where the bigger the contamination size, the more charge contained in the contamination.</p>

Tebuthiuron leaching in three Brazilian soils as affected by soil pH

Underground contamination water by herbicides depends on the interactions between their molecules with physical and chemical soil characteristics and climatic conditions. Studies with columns can estimate the leaching potential of herbicides in soils. This study aimed to determine the effect of soil pH on tebuthiuron leaching, and capacity of bioindicators to detect tebuthiuron residues in three Brazilian soils. Cucumber plants (Cucumis sativus) were more negatively affected when grown in soils with lower amounts of organic matter and clay, and in these soils, the tebuthiuron levels reached greater depths in the column. There was a positive correlation between tebuthiuron concentration and cucumber intoxication, and a negative correlation between tebuthiuron concentration and dry matter cucumber in all soils. The tebuthiuron leached up to 50 cm depth even in soils with higher organic matter and clay content. The increasing of soil pH can affect the leaching of nonionic herbicides, and liming practice may elevate the environmental contamination risk by tebuthiuron. The bioindicator method using Cucumis sativus is viable and can be recommended to detect tebuthiuron concentrations above 0.2 mg kg−1.

Rheological Properties of Aqueous Colloidal Silica Suspensions Related to Amendment Delivery for Subsurface Remediation

Abstract Colloidal silica (fumed silica) suspensions tested as carriers for remedial amendment delivery in subsurface contaminant remediation and as media for underground contamination containment. Rheological behavior of the silica suspensions under subsurface environment is not well documented while this knowledge is essential for the preparation and field injection of the suspensions. This contribution is focused on rheological characteristics of colloidal silica suspensions under various environmental conditions relevant to remedial amendment delivery for subsurface remediation. Influence of silica particle concentration, water source, ionic strength, pH, aging, amendment type and concentration, and subsurface sediment on rheological behavior of silica suspensions was evaluated. This work is the first attempt to relate the rheology of aqueous silica suspension to subsurface injection and amendment emplacement. Impact of remedial amendment and subsurface sediment is reported for the first time. Additio...

Ground Penetrating Radar as a Contextual Sensor for Multi-Sensor Radiological Characterisation.

Radioactive sources exist in environments or contexts that influence how they are detected and localised. For instance, the context of a moving source is different from a stationary source because of the effects of motion. The need to incorporate this contextual information in the radiation detection and localisation process has necessitated the integration of radiological and contextual sensors. The benefits of the successful integration of both types of sensors is well known and widely reported in fields such as medical imaging. However, the integration of both types of sensors has also led to innovative solutions to challenges in characterising radioactive sources in non-medical applications. This paper presents a review of such recent applications. It also identifies that these applications mostly use visual sensors as contextual sensors for characterising radiation sources. However, visual sensors cannot retrieve contextual information about radioactive wastes located in opaque environments encountered at nuclear sites, e.g., underground contamination. Consequently, this paper also examines ground-penetrating radar (GPR) as a contextual sensor for characterising this category of wastes and proposes several ways of integrating data from GPR and radiological sensors. Finally, it demonstrates combined GPR and radiation imaging for three-dimensional localisation of contamination in underground pipes using radiation transport and GPR simulations.

Contaminations at the derma of Gaia: a case study in environmental geology

Crucial problems of natural resource conservation in Gaia are related to industrial, agricultural and urban pollutions of its atmosphere, water bodies and upper crust; today, one of the main human concerns is how to survive and to manage the environmental changes caused by widespread disasters related to improper disposal of large industrial and urban waste. During the last decade, we have developed hydro-bio-geological methods to quantitatively describe the soil and water contamination within a 4.0 km2 area, including two landfill deposits and a tannery industry of Alagoinhas city, Bahia state, Brazil. Geological reconnaissance works, and a detailed geophysical survey consisting of 59 Schlumberger resistivity and time-domain induced polarization soundings, were conducted around this urban–industrial disposal area to detect and delineate the 3-D extent of an underground contamination plume. These indirect results pointed out the presence of a strong electrical conductive anomaly within the aquifer, resulting from invasive fluids from the landfills, and from the surface disposal lagoons from the tannery. Complimentarily, permanent multi-electrode logging arrays were installed on three monitoring wells, constructed with thin rings copper electrodes of 1.0 cm width, externally mounted at 0.5-m distance interval, on the entire length of the rigid PVC well casings and filter sections of such wells. In each well, the ring electrodes are accessed in different electrode combinations at the ground surface, through electrical insulated multi-cables. Repeated apparent resistivity and chargeability logs were obtained for these wells using normal electrode arrays. Such measurements were also used to characterize the plume extent and to estimate changes in water chemistry below the water table and throughout the upper vadose section of the Marizal-Sao Sebastiao aquifer system. Chemical analyses of water samples, collected at available wells and along the neighboring Sauipe River, have shown drastic changes in the total dissolved solids, major cations and anions contents, total chromium and other heavy metals, inorganic macro-components, biochemical oxygen demand, chemical oxygen demand, nutrients and bacterial content. This work has conclusively shown that the subsurface is severely contaminated by liquids generated from these three surface sources. In addition, the monitoring technique using jointly electrical soundings and multi-electrode wells is an efficient and low-cost complement for an environmental evaluation of extensive aquifers.

Remote Real Time Monitoring for Underground Contamination in Mongolia Using Electrical Impedance Tomography

Mongolia’s abundant natural resources have driven much recent economic development and with it the need for an underground contamination monitoring system. For instance, the fast growth of the mining industry coincides with underground contamination caused by petrol, copper tailings, mercury, etc. These contaminants are highly electrically conductive, and can therefore be assessed by electrical impedance tomography (EIT). This non-destructive and inexpensive method can visualize the conductivity distribution of a target area, and is suited for use in Mongolia. A number of electrodes are placed on the ground surface to induce currents and to measure the resulting voltages. We introduce a new electrode configuration, and use the local projective conductivity image method to monitor the near-surface area. Additionally, conventional EIT is used to monitor areas deeper underground. The collected voltage data can be used for both algorithms–separate measurements are not required–allowing near real-time monitoring for underground contamination.

Numerical simulation of air ventilation in super-large underground developments

Recent advancements in engineering technology have enabled the construction of super-large underground engineering projects in China. Currently, the ventilation requirements and standards of normal-size underground spaces are used for super-large underground excavating engineering projects in China. For example, the minimum air velocity of 0.15m/s is the standard velocity for normal-size underground spaces; however, this value is also used as the required air velocity for diluting underground contaminants in super-large underground developments. This paper aims to examine the minimum ventilation requirements for super-large underground developments (S>100m2). A three-dimensional computational domain representing a full-scale underground space has been developed. The pertinent parameters such as dust concentration, smoke density, oxygen concentration and air temperature have been simulated. The results show that at some specific underground conditions, the ventilation air velocity of 0.15m/s is sufficient to control the dust level, provide required oxygen concentration and maintain the air temperature at acceptable levels during development; however, it is not sufficient to bring the CO concentration below an acceptable safe limit. This must be considered by the ventilation system designers of super-large underground developments.