Contaminant Concentration Profiles Research Articles

Two-dimensional migration characteristics of contaminant through composite liner with arbitrarily distributed defects

Previous studies indicate that liner defects can significantly accelerate contaminant migration in landfill, shortening the migration time by orders of magnitude. Although the effect of defects upon contaminant migration and barrier capacity of liner system has been investigated based on several theoretical models, they are always limited to one-dimensional scopes. Here a two-dimensional (2-D) model was established for contaminant transport through composite liner to the soil layer, with geomembrane (GM) defects arbitrarily distributed along the horizontal direction, and then Laplace transform, Fourier transform, and boundary transform method were utilized to derive its semi-analytical solution, which was verified by experimental data and numerical results. The obtained solution can take nonuniformly distributed defects into account and demonstrates the 2-D contaminant concentration and flux profiles in the spatiotemporal domain. Computational results of the solution are employed to illustrate the roles of material coefficients and modeling sizes upon the variations of contaminant concentration and flux. Results support that contaminant migration is expedited by the GM defect in landfill, and geosynthetics clay liner can reduce the pollution level caused by GM failure. Moreover, the contaminant flux will not be significantly influenced by the defect positions, which, however, leads to non-negligible impact on concentration profiles.

Appraisal of groundwater contamination from surface spills of fluids associated with hydraulic fracturing operations

Contaminated groundwater is a priority issue on the environmental agendas of developed countries. Therefore, there is an obvious need to develop instruments and decision-making mechanisms that allow the estimation of the risk to human health due to the presence of contaminants in soils and groundwater, in a fast and reliable manner. Thus, this study aims to assess whether the spilling of hydraulic fracturing fluids prior to injection has a potential risk to groundwater quality in the Kern County Sub-basin, California, by identifying the hydrological factors and solute transport characteristics that control these risks while taking into consideration the temperature rises due to climate change. The approach uses the concept of the groundwater pollution risk based on comparing the concentration of pollutants within the water table by using a predetermined permissible level. The current average annual temperature and that by the end of the 21st century was used to estimate the diffusion of benzene through three types of soil by using HYDRUS-1D software. The software was used to predict the contaminant concentration profile of benzene in the water table with special reference to the impact of surface temperatures. The results showed that an expected rise of the surface temperature by 4.3 °C led to an increase in the concentration of benzene by 2.3 μg/l in sandy loam soil, 6.8 μg/l in silt loam soil, and finally, 2.6 μg/l in loam soil. The results show that climate change can substantially affect soil properties and their chemical constituents, which then play a major role in absorbing pollutants.

Molecular characterization of microbial communities in a peat-rich aquifer system contaminated with chlorinated aliphatic compounds.

In an aquifer-aquitard system in the subsoil of the city of Ferrara (Emilia-Romagna region, northern Italy) highly contaminated with chlorinated aliphatic toxic organics such as trichloroethylene (TCE) and tetrachloroethylene (PCE), a strong microbial-dependent dechlorination activity takes place during migration of contaminants through shallow organic-rich layers with peat intercalations. The in situ microbial degradation of chlorinated ethenes, formerly inferredby the utilization of contaminant concentration profiles and Compound-Specific Isotope Analysis (CSIA), was here assessed using Illumina sequencing of V4 hypervariable region of 16S rRNA gene and by clone library analysis of dehalogenase metabolic genes. Taxon-specific investigation of the microbial communities catalyzing the chlorination process revealed the presence of not only dehalogenating genera such as Dehalococcoides and Dehalobacter but also of numerous other groups of non-dehalogenating bacteria and archaea thriving on diverse metabolisms such as hydrolysis and fermentation of complex organic matter, acidogenesis, acetogenesis, and methanogenesis, which can indirectly support the reductive dechlorination process. Besides, the diversity of genes encoding some reductive dehalogenases was also analyzed. Geochemical and 16S rRNA and RDH gene analyses, as a whole, provided insights into the microbial community complexity and the distribution of potential dechlorinators. Based on the data obtained, a possible network of metabolic interactions has been hypothesized to obtain an effective reductive dechlorination process.

Measuring anthropogenic impacts on an industrialised coastal marine area using chemical and textural signatures in sediments: A case study of Augusta Harbour (Sicily, Italy)

From the early 1950s until the late 1970s, Augusta Bay (Sicily, Italy) served as a major European (petro) chemical hub. It thereafter began a progressive decline as several crude oil refining and industrial plants closed due to the transfer of production cycles to other sites around the globe. As a result of the rapid and relatively uncontrolled post-WWII development of the site, several environmental studies identified significant contamination in sediments around the southernmost sector of the bay. The pollution was mainly due to barium (Ba) and mercury (Hg), attributable to the former chlor-alkali plant (1958–2003), and polychlorobiphenyls (PCBs) and hexachlorobenzene (HCB). The present study focuses on understanding the broad legacy of pollution across the whole harbour by systematically analysing 10 sediment cores collected in 2008 for contaminant concentration profiles of Hg, Ba, PCBs, HCB and grain-size variations. Pre-industrial environmental geochemical background conditions were identified using data from the deeper parts of cores. The results show that contamination has affected the entire harbour area to varying degrees, and this has allowed identifying contamination transfer, based on decreasing concentrations and related depths in the sediment cores from the southernmost sector to the central and northern area. A recent finding by the current researchers is that the construction of the dam/breakwater in the early 1960s, that largely coincided with the start of industrial inputs, led to the trapping of fine terrestrial sediment inside the harbour, particularly in the central and northern area. This trapped sediment provides a granulometric time marker in those cores. The presence of highly contaminated sediments inside the harbour represents a significant future liability unless remedial action is applied to remove the worst of the polluted sediment.

Tracing indoor contaminant release location based on local mean residual-life-time of air

Even in case ventilation system is operating in optimal fashion, indoor air quality could be varied depending on the indoor contaminant release occasions. Thus, accurate and rapid identification of contaminant source locations in indoor environment is critical for occupants’ health as well as building safety and integrity. This study presented a novel method to locate indoor contaminant source using local mean residual-life-time (LMR). Based on the theoretical definition of LMR, a characteristic quantitative relationship between the LMR at source location and the contaminant concentration profile of a room was derived and assessed through two stages of studies: experimental and numerical explorations. In the experiments, by changing contaminant release location under limited condition, the LMR at the source location and the contaminant concentration profile of a test chamber were measured. Then, the outcomes were examined to verify whether the derived equation was established in the chamber. Computational Fluid Dynamics (CFD) technique was also used to make up for the experimental limitations. CFD simulations were carried out to analyze the validity of the equation in response to different release locations of the contaminant in a more complex physical environment by obtaining high-resolution information. Both experimental and numerical results showed that the presented equation was well established and could be used to locate indoor contaminant source even in non-ideal situation or in complicated spaces.

Impact of Partition Curtains on Temperature and Contaminant Concentration Profiles in a Displacement Ventilated Four-bed Hospital Ward

Impact of Partition Curtains on Temperature and Contaminant Concentration Profiles in a Displacement Ventilated Four-bed Hospital Ward

Displacement ventilation with radiant panel for hospital wards: Measurement and prediction of the temperature and contaminant concentration profiles

Displacement ventilation (DV) is known to provide high air quality and ventilation efficiency. With DV, a contaminant interface is formed in a room, and the air quality in the occupant zone below the contaminant interface height can be kept clean. This paper proposes a DV system to solve the serious odor problem in hospital wards. A vertical radiant panel that can be controlled individually is suggested as a complementary heating system. In order to study the influence of the panel on the displacement ventilated room, the temperature and contaminant concentration profiles were examined under different panel conditions: the distance between the panel and bed, height of the panel, surface temperature of the panel, and supply airflow rate. When the radiant panel was heated, it created a stronger plume than the human body, which produced contaminated air. When there was space between the radiant panel and bed, the contaminated air was locked up before reaching the ceiling. Personal exposure of a standing person was also investigated because the contaminated interface is generally lower than the breathing zone of a standing person with DV. The zonal model and improved zonal model were validated by a comparison of their results with the measured contaminant concentrations.

A course delivery method by using a software to predict contaminant migration through a soil layer

AbstractThe authors propose a course delivery method for the contaminant transport through a saturated soil layer to explain contamination of soils in the Environmental Geotechnology course. In civil and environmental engineering education, analytical simulation models help students to understand the processes. MATLAB©‐based simulation method is proposed in this paper, to enhance learning of students of contaminant migration phenomena, and the simulation program is written by the students within the course based on an existing analytical solution for two‐dimensional transport of contaminants in a saturated soil layer. Students use systematic, step‐by‐step problem solving approach while identifying, formulating and solving the contaminant migration problem. The program is written for pulse source and includes advective and dispersive transport as well as sorption and the simulation is used to obtain the profiles of contaminant concentration as a function of distance from the source and time for a steady groundwater velocity. It is shown that the contaminant concentration profiles obtained by simulation demonstrate the processes involved, by this way, the software tool integrates with the rest of the course content. It was seen by the author that, almost all of the students, who are taking Environmental Geotechnology course, could write matlab codes for contaminant migration if guided properly by the instructor/assistant. In this regard, it seems important to conduct studies which will allow students to increase their matlab programming practice. Also the use of the computer simulation encourages the students to ask “what if” questions and to carry out parametric studies and to learn by “discovery.”

Oscillations in soil bacterial redox reactions

Spatial oscillations in soil contaminant concentration profiles are sometimes observed, but rarely commented on, or are attributed to noisy data. In this paper we consider a possible mechanism for the occurrence of oscillatory reactant profiles within contaminant plumes. The bioremediative reactions which occur are effected by bacteria, whose rôle is normally conceived of as being passive. Here we argue that competition, for example between heterotrophic and fermentative bacteria, can occur in the form of an activator–inhibitor system, thus promoting oscillations. We describe a simple model for the competition between two such microbial populations, and we show that in normal oligotrophic groundwater conditions, oscillatory behaviour is easily obtained. When such competition occurs in a dispersive porous medium, travelling waves can be generated, which provide a possible explanation for the observed soil column oscillations.

A numerical investigation of oxygen concentration dependence on biodegradation rate laws in vapor intrusion.

In subsurface vapor intrusion, aerobic biodegradation has been considered as a major environmental factor that determines the soil gas concentration attenuation factors for contaminants such as petroleum hydrocarbons. The site investigation has shown that oxygen can play an important role in this biodegradation rate, and this paper explores the influence of oxygen concentration on biodegradation reactions included in vapor intrusion (VI) models. Two different three dimensional (3-D) numerical models of vapor intrusion were explored for their sensitivity to the form of the biodegradation rate law. A second order biodegradation rate law, explicitly including oxygen concentration dependence, was introduced into one model. The results indicate that the aerobic/anoxic interface depth is determined by the ratio of contaminant source vapor to atmospheric oxygen concentration, and that the contaminant concentration profile in the aerobic zone was significantly influenced by the choice of rate law.

Ground Water-Surface Water Interface (GWSWI) Modeling: Recent Advances and Future Challenges

Ground water-surface water interface (GWSWI) represents the interconnection of ground water and surface water in the hydrologic continuum. Interactions between these two water masses result in unique gradients and/or transitions of contaminant concentration profiles, biological populations, chemistry, flow, mixing characteristics, redox potential, dissolved oxygen, organic content, and thermal properties across GWSWI. In addition, many unique biogeochemical processes occur in this zone that can have significant impact on the fate and transport of contaminants across the GWSWI. Prediction of the distribution and concentrations of contaminants across the GWSWI is challenging, but is essential for evaluating human health and environmental risk, including remedial alternatives at contaminated sites. The objective of this paper is to review and assess existing modeling capabilities to recognize (a) the need for development of new modeling tools, (b) knowledge gaps, and (c) challenges required to address contaminant transport within GWSWI. Currently, the most important needs for future model development are, (a) linkage between ground water and surface water models; (b) integration of process-level models within the framework of large-scale models; and (c) understanding ground water-surface water interactions within a spatial and temporal framework.

STUDY ON INFLUENCE OF PARTITION CURTAIN IN SICKROOM WITH DISPLACEMENT VENTILATION

Most sickrooms in Japan have four beds, and there is the odor problem from patients or diapers. In this study, we propose to use the displacement ventilation as a means of obtaining high indoor air quality in sickrooms. The purpose of the study is intended to examine the validity of this system. In the previous study, temperature and contaminant concentration profile in a displacement-ventilated room were figured out. But, the actual sickroom has a partition curtain to keep patient's privacy and it is expected that the curtain has great influence on the temperature and contaminant concentration profile. This paper shows the experiment results and CFD analysis results to examine the effect of partition curtain in the displacement-ventilated room. Then the experiment results are compared with the calculated results by the zonal model.

Coupled Consolidation and Contaminant Transport in Compressible Porous Media

This paper presents an experimental and numerical investigation of coupled consolidation and contaminant transport in compressible porous media. Numerical simulations were performed using the CST2 computational model, in which a dual-Lagrangian framework is used to separately follow the motions of fluid and solid phases during consolidation. Diffusion and large strain consolidation-induced transport tests were conducted on composite specimens of kaolinite slurry consisting of an upper uncontaminated layer and a lower layer contaminated with potassium bromide. Assessment of the importance of the consolidation process on solute transport is based on measured and simulated solute breakthrough curves and final contaminant concentration profiles. CST2 simulations closely match the experimental data for three different loading conditions. Diffusion and consolidation-induced advection made important contributions to solute transport and mass outflow in this study. Additional simulations indicate that consolidation-induced contaminant transport may also be affected by specimen boundary drainage and initial concentration conditions.

A-16 置換換気を用いた病室の空調に関する研究(その2)カーテンと給排気口の位置関係が病室内の温度・汚染物濃度分布に与える影響(学術研究)

A-16 置換換気を用いた病室の空調に関する研究(その2)カーテンと給排気口の位置関係が病室内の温度・汚染物濃度分布に与える影響(学術研究)

Numerical Modeling of Contaminant Transport with Spatially-Dependent Dispersion and Non-Linear Chemical Reaction

A one-dimensional advective-dispersive contaminant transport model with scale-dependent dispersion coefficient in the presence of a nonlinear chemical reaction of arbitrary order is considered. Two types of variations of the dispersion coefficient with the downstream distance are considered. The first type assumes that the dispersivity increases as a polynomial function with distance while the other assumes an exponentiallyincreasing function. Since the general problem is nonlinear and possesses no analytical solutions, a numerical solution based on an efficient implicit iterative tri-diagonal finitedifference method is obtained. Comparisons with previously published analytical and numerical solutions for special cases of the main transport equation are performed and found to be in excellent agreement. A parametric study of all physical parameters is conducted and the results are presented graphically to illustrate interesting features of the solutions. It is found that the chemical reaction order and rate coefficient have significant effects on the contaminant concentration profiles. Furthermore, the scale-dependent polynomial type dispersion coefficient is predicted to obtain significant changes in the contaminant concentration at all dimensionless time stages compared with the constant dispersion case. However, relatively smaller changes in the concentration level are predicted for the exponentially-increasing dispersion coefficient.

Use of Plume Mapping Data to Estimate Chlorinated Solvent Mass Loss

AbstractResults from a plume mapping study from November 2000 through February 2001 in the sand‐and‐gravel surficial aquifer at Dover Air Force Base, Delaware, were used to assess the occurrence and extent of chlorinated solvent mass loss by calculating mass fluxes across two transverse cross sections and by observing changes in concentration ratios and mole fractions along a longitudinal cross section through the core of the plume. The plume mapping investigation was conducted to determine the spatial distribution of chlorinated solvents migrating from former waste disposal sites. Vertical contaminant concentration profiles were obtained with a direct‐push drill rig and multilevel piezometers. These samples were supplemented with additional ground water samples collected with a minipiezometer from the bed of a perennial stream downgradient of the source areas. Results from the field program show that the plume, consisting mainly of tetrachloroethylene (PCE), trichloroethene (TCE), and cis‐1,2‐dichloroethene (cis‐1,2‐DCE), was approximately 670 m in length and 120 m in width, extended across much of the 9‐ to 18‐m thickness of the surficial aquifer, and discharged to the stream in some areas. The analyses of the plume mapping data show that losses of the parent compounds, PCE and TCE, were negligible downgradient of the source. In contrast, losses of cis‐1,2‐DCE, a daughter compound, were observed in this plume. These losses very likely resulted from biodegradation, but the specific reaction mechanism could not be identified. This study demonstrates that plume mapping data can be used to estimate the occurrence and extent of chlorinated solvent mass loss from biodegradation and assess the effectiveness of natural attenuation as a remedial measure.

Extended bioremediation of PAH/PCP contaminated soils from the POPILE wood treatment facility

A study was conducted using two pilot-scale land-treatment units (LTUs) to evaluate the efficacy of different cultivation and maintenance schedules during bioremediation of contaminated soil from a wood treatment facility using landfarming technology. The soil contained high concentrations of polycyclic aromatic hydrocarbons (PAHs, ∼13 000 ppm) as well as of pentachlorophenol (PCP, ∼1500 ppm). An initial 6-month intensive-treatment phase was followed by 24 months of less-intensive treatment. During the first phase, traditional landfarming practice of regular cultivation was compared with a gas-phase composition based cultivation strategy, and both the landfarming units were intensively monitored and maintained with respect to moisture control and delivery of nutrients. The two strategies resulted in similar contaminant concentration profiles with time during this phase, although different microbial populations developed in the two-landfarming units. The second (less-intensive) treatment phase involved no moisture control and nutrient delivery beyond the initial adjustments, and compared natural attenuation (no cultivation) with quarterly cultivation of soil. Both the strategies showed similar behavior again. GC/MS analysis of the soil samples showed PAH removal including four-ring homologues. Leachability tests at zero time and after 6 and 22 months of operation showed significant reductions in leaching of PCP and low molecular weight PAHs. Extended treatment resulted in some leaching of high molecular weight PAHs. Significant biological activity was demonstrated, even at the high contaminant concentrations. Phospholipid ester-linked fatty acid (PLFA) analysis showed an increase in biomass and a divergence in community composition in soils depending on the treatment conducted.

Contribution des réseaux de neurones artificiels (RNA) à la caractérisation des pollutions de sol. Exemples des pollutions en hydrocarbures aromatiques polycycliques (HAP)

We develop the ANNs (Artificial Neural Networks) method to explore contaminant concentration profiles observed in soils of polluted sites. ANNs are particularly efficient in simultaneous analysis of numerous parameters and in identification of complex relations involving field data. Applying the ANN models on a PAH (Polycyclic Aromatic Hydrocarbon) database, we extracted the most characteristic components of known contaminations and applied it to identify the source type of similar polluted sites. The performed tests prove the generalisation capability of the selected ANN model. To cite this article: A. Dan et al., C. R. Geoscience 334 (2002) 957–965. L'analyse exploratoire de données environnementales utilise fréquemment des outils statistiques. Cet article présente l'applicabilité des réseaux de neurones artificiels (RNA) à l'étude des pollutions des sols par les hydrocarbures aromatiques polycycliques (HAP). Les RNA mettent en évidence des relations entre la distribution en polluants observée dans des prélèvements de sol et le type d'activité industrielle génératrice. Ces modèles facilitent, par exemple, l'identification des substances chimiques caractéristiques des pollutions observées sur les sites d'anciennes cokeries et usines à gaz. Pour citer cet article : A. Dan et al., C. R. Geoscience 334 (2002) 957–965.

GROUNDWATER CONTAMINATION DOWNSTREAM OF A CONTAMINANT PENETRATION SITE. II. HORIZONTAL PENETRATION OF THE CONTAMINANT PLUME

ABSTRACT Part I of this study (Rubin, H.; Buddemeier, R.W. Groundwater Contamination Downstream of a Contaminant Penetration Site Part 1: Extension–Expansion of the Contaminant Plume. J. of Environmental Science and Health Part A (in press).) addressed cases, in which a comparatively thin contaminated region represented by boundary layers (BLs) developed within the freshwater aquifer close to contaminant penetration site. However, at some distance downstream from the penetration site, the top of the contaminant plume reaches the top or bottom of the aquifer. This is the location of the “attachment point,” which comprises the entrance cross section of the domain evaluated by the present part of the study. It is shown that downstream from the entrance cross section, a set of two BLs develop in the aquifer, termed inner and outer BLs. It is assumed that the evaluated domain, in which the contaminant distribution gradually becomes uniform, can be divided into two sections, designated: (a) the restructuring section, and (b) the establishment section. In the restructuring section, the vertical concentration gradient leads to expansion of the inner BL at the expense of the outer BL, and there is almost no transfer of contaminant mass between the two layers. In the establishment section, each of the BLs occupies half of the aquifer thickness, and the vertical concentration gradient leads to transfer of contaminant mass from the inner to the outer BL. By use of BL approximations, changes of salinity distribution in the aquifer are calculated and evaluated. The establishment section ends at the uniformity point, downstream from which the contaminant concentration profile is practically uniform. The length of the restructuring section, as well as that of the establishment section, is approximately proportional to the aquifer thickness squared, and is inversely proportional to the transverse dispersivity. The study provides a convenient set of definitions and terminology that are helpful in visualizing the gradual development of uniform contaminant concentration distribution in an aquifer subject to contaminant plume penetration. The method developed in this study can be applied to a variety of problems associated with groundwater quality, such as initial evaluation of field data, design of field data collection, the identification of appropriate boundary conditions for numerical models, selection of appropriate numerical modeling approaches, interpretation and evaluation of field monitoring results, etc.

GROUNDWATER CONTAMINATION DOWNSTREAM OF A CONTAMINANT PENETRATION SITE. I. EXTENSION–EXPANSION OF THE CONTAMINANT PLUME

ABSTRACT This study concerns the possible use of boundary layer (BL) approach for the analysis and evaluation of contaminant transport in groundwater due to contaminant penetration into the groundwater aquifer through a site of limited size. The contaminant penetration may occur through either the upper (surface) or lower (bedrock) boundary of the aquifer. Two general cases of contaminant penetration mechanisms are considered: (1) the contaminant is transferred through an interface between a contaminating and freshwater fluid phases, and (2) the contaminant arrives at groundwater by leakage and percolation. For the purpose of BL evaluation the contaminant plume is divided into three different sections: (1) the penetration section, (2) the extension–expansion section, and (3) the spearhead section. In each section a different BL method approach yields simple analytical expressions for the description of the contaminant plume migration and contaminant transport. Previous studies of the BL method can be directly applied to the evaluation of contaminant transport at the contaminant penetration section. The present study extends those studies and concerns the contaminant transport in the two other sections, which are located downstream of the penetration section. This study shows that the contaminant concentration profiles in sections 1 and 2 incorporate two BLs: (1) an inner BL adjacent to the aquifer bottom or surface boundary, and (2) an outer BL, which develops above or below the inner one. The method developed in the present study has been applied to practical issues concerning salinity penetration into groundwater in south central Kansas.