Contributions to predicting contaminant leaching from secondary materials used in roads

Slags, coal ashes, and other secondary materials can be used in road construction. Both traditional and secondary materials used in roads may contain contaminants that may leach and pollute the groundwater. The goal of this research was to further the understanding of leaching and transport of contaminants from pavement materials. Towards this goal, a new probabilistic framework was introduced which provided a structured guidance for selecting the appropriate model, incorporating uncertainty, variability, and expert opinion, and interpreting results for decision making. In addition to the framework, specific contributions were made in pavement and embankment hydrology and reactive transport, Bayesian statistics, and aqueous geochemistry of leaching. Contributions on water movement and reactive transport in highways included probabilistic prediction of leaching in an embankment, and scenario analyses of leaching and transport in pavements using HYDRUS2D, a contaminant fate and transport model. Water flow in a Minnesota highway embankment was replicated by Bayesian calibration of hydrological parameters against water content data. Extent of leaching of Cd from a coal fly ash was estimated. Two dimensional simulations of various scenarios showed that salts in the base layer of pavements are depleted within the first year whereas the metals may never reach the groundwater if the pavement is built on adsorbing soils. Aqueous concentrations immediately above the groundwater estimated for intact and damaged pavements can be used for regulators to determine the acceptability of various recycled materials. Contributions in the aqueous geochemistry of leaching included a new modeling approach for leaching of anions and cations from complex matrices such as weathered steel slag. The novelty of the method was its simultaneous inclusion of sorption and solubility controls for multiple analytes. The developed model showed that leaching of SO4, Cr, As, Si, Ca, Mg, and V were controlled by corresponding soluble solids. Leaching of Pb was controlled by Pb(VO4)3 solubility at low pHs and by surface precipitation reactions at high pHs. Leaching of Cd and Zn were controlled by surface complexation and surface precipitation, respectively

Probabilistic modeling of one dimensional water movement and leaching from highway embankments containing secondary materials

Predictive methods for contaminant release from virgin and secondary road construction materials are important for evaluating potential long-term soil and groundwater contamination from highways. The objective of this research was to describe the field hydrology in a highway embankment and to investigate leaching under unsaturated conditions by use of a contaminant fate and transport model. The HYDRUS2D code was used to solve the Richards equation and the advection–dispersion equation with retardation. Water flow in a Minnesota highway embankment was successfully modeled in one dimension for several rain events after Bayesian calibration of the hydraulic parameters against water content data at a point 0.32 m from the surface of the embankment. The hypothetical leaching of Cadmium from coal fly ash was probabilistically simulated in a scenario where the top 0.50 m of the embankment was replaced by coal fly ash. Simulation results were compared to the percolation equation method where the solubility is multiplied by the liquid-to-solid ratio to estimate total release. If a low solubility value is used for Cadmium, the release estimates obtained using the percolation/equilibrium model are close to those predicted from HYDRUS2D simulations (10–4–10–2 mg Cd/kg ash). If high solubility is used, the percolation equation over predicts the actual release (0.1–1.0 mg Cd/kg ash). At the 90th percentile of uncertainty, the 10-year liquid-to-solid ratio for the coal fly ash embankment was 9.48 L/kg, and the fraction of precipitation that infiltrated the coal fly ash embankment was 92%. Probabilistic modeling with HYDRUS2D appears to be a promising realistic approach to predicting field hydrology and subsequent leaching in embankments

RETRASO, a code for modeling reactive transport in saturated and unsaturated porous media

The code RETRASO (REactive TRAnsport of SOlutes) simulates reactive transport of dissolved and gaseous species in non-isothermal saturated or unsaturated problems. Possible chemical reactions include aqueous complexation (including redox reactions), sorption, precipitation-dissolution of minerals and gas dissolution. Various models for sorption of solutes on solids are available, from experimental relationships (linear KD, Freundlich and Langmuir isotherms) to cation exchange and surface complexation models (constant capacitance, diffuse layer and triple layer models). Precipitation-dissolution and aqueous complexation can be modelled in equilibrium or according to kinetic laws. For the numerical solution of the reactive transport equations it uses the Direct Substitution Approach. The use of the code is demonstrated by three examples. The first example models various sorption processes in a smectite barrier. The second example models a complex chemical system in a two dimensional cross-section. The last example models pyrite weathering in an unsaturated medium

Numerical modelling of the dynamics of chlorinated solvent pollution in aquifers and their remediation with engineered nano-particles: An integrated approach

[EN] The global water shortage is one of the main environmental concerns in the 21st century. The main source of drinking water is the groundwater that flows in the subsurface. The increased agriculture and industrial activities in the last few decades have been proven to be detrimental for groundwater. While these water resources are limited, the scarcity is further triggered by the loss of quality due to anthropogenic activities such as waste deposition and landfill leakage. Contaminants from the anthropogenic waste often migrates through the sub-surface and reach an underlying aquifer. The occurrence of these contaminants threatens the quality of water resources and often requires remediation efforts. Several in-situ and ex-situ remediation methodologies have been developed and tested in the last decades; recently, the use of Engineered Nano-Particles (ENPs) for in-situ contaminant degradation have gained a lot of interest in the field of groundwater remediation. These ENPs have been found to be effective due to their high reactive surface area, minimal disruption of the groundwater system and their aggressive contaminant degradation capabilities. However, the field scale implementation of this remediation technique is often challenging, as each polluted site require a custom design and strategy of remediation. The field scale remediation of groundwater using ENPs requires a lot of scientific investigation and technical resources, owing to complexity and the limited accessibility of the contamination- groundwater system. Therefore, it is necessary to develop a robust remediation strategy which includes laboratory scale and field scale studies as well as application of a numerical approach. The success in the remediation effort is often limited by lack of detailed understanding of the contaminant and hydrogeological properties of the aquifer. While, the information of contamination-aquifer dynamics can be studied at field, knowledge on the continuous and consistent contamination behavior on both temporal and spatial scale is often missing. The use of an integrated numerical model can be helpful for bridging the gap between the field studies and the relevant insights required for groundwater remediation

자연하천에서 물질 혼합해석을 위한 저장대에서의 정체시간분포 산정

학위논문(석사) -- 서울대학교대학원 : 공과대학 건설환경공학부, 2022.2. 서일원.자연하천에서 용존물질의 거동은 하천의 지형학적인 요인으로 형성된 저장대의 영향에 의해 흐름 영역의 특성만으로 해석될 수 없다. 이러한 저장대 효과를 분석하기 위해 지난 수십년동안 다양한 구조의 저장대 모형이 제시되어 왔다. 용존물질의 하류이송을 지체시키는 이러한 저장대의 영향을 고려하기 위해, 기존의 1차원 이송-분산 방정식을 바탕으로 다양한 형태의 저장대 모형이 개념적으로 제시되어 왔다. 이러한 모형의 타당성은 대부분 흐름영역에서 측정한 추적자의 농도-시간 곡선의 실측값으로부터 증명되어 왔다. 하지만, 흐름영역에서의 추적자 거동은 저장대의 영향보다 이송과 분산의 영향에 더욱 민감하기 때문에, 이는 저장대의 영향을 대표하기 어려우며, 저장대 모델링은 저장대의 영향의 실측값으로부터 검증되어야 한다. 하지만, 자연하천의 저장대는 그 형태가 다양하며 경계가 모호하기 때문에 실측값을 얻기 힘든 한계가 있다. 따라서, 본 연구에서는 이송, 분산의 영향과 저장대의 영향을 명시적으로 구분할 수 있는 모형을 제시하고, 역합성곱 기법을 적용하여 흐름영역에서 측정한 추적자의 거동으로부터 이송과 분산의 영향을 제외하여 저장대의 영향만을 측정할 수 있는 방법을 제시하였다. 측정한 저장대의 영향은 가장 대표적인 1차원 저장대 모형인 Transient Storage Model (TSM)의 모의 결과와 결정된 매개변수의 타당성을 검증하는데 활용되었다. 그 결과 TSM의 모의는 실제 하천의 저장대의 영향을 44%까지 과소평가하는 결과를 보였다. 또한, 자연하천에서 저장대가 수계 생물화학적 반응의 주요 영역이라는 점을 고려하여, 평가된 정체시간분포를 이용하여 여러 유기화학물질별 생화학적 반응에 의한 감쇠정도를 평가하는데 활용되었다.The solute propagation along stream flow cannot be interpreted only by hydrodynamic properties of surface flow due to the influence from surrounding storage zones of the stream. To analyze this unidentified storage effect, various transient storage models have been proposed for recent decades. The time dependent behavior of solute within the storage zone was often modeled a conceptualized retention time function added to conventional advection-dispersion equation. The validity of these models has been predominantly demonstrated with tracer breakthrough curves measured in surface flow. However, the storage effect is less responsible for the breakthrough curve behavior than in-stream flow dynamics. For model validation purpose, tracer behavior only within storage zones should be investigated. The present study is aimed at quantifying the time-dependent storage effect, herein termed the net retention time distribution (NRTD), from tracer measurements at the flow zone using a deconvolution technique with filtering in the Fourier domain. The results showed that the deconvolved NRTDs successively represented the temporal behavior of the tracer in the storage zones without significant distortion in the observed breakthrough curves. Using the estimates of NRTD, we evaluated the validity of first-order mass transfer and its parameters of the transient storage model (TSM), which is the most widely-used storage zone model. The simulation results of the parameter-optimized TSM underestimated the inherent storage effect by as much as an average 44 %. It is also noteworthy that the larger net retention time scale the channel has, the larger discrepancy the TSM’s exponential retention time function could yield.LIST OF FIGURES LIST OF TABLES LIST OF SYMBOLS LIST OF ABBREVIATIONS CHAPTER I. INTRODUCTION 1 1.1 Motivation 1 1.2 Problem Statement 3 II. THEORETICAL BACKGROUNDS 8 2.1 One-dimensional solute transport modeling 8 2.2 Conceptualization of storage mechanism 13 2.3 Determination of TSM parameters 23 2.4 Summary of literatural review 26 III. MATERIALS AND METHODS 27 3.1 Tracer experiments in a stream 27 3.1.1 Site description 27 3.1.2 Tracer Measurement 30 3.1.3 Preprocessing for Breakthrough Curves 31 3.2 Development of algorithm for storage effect quantification 32 3.2.1 Concept of residence time distribution 33 3.2.2 Convolutional Decomposition Equation (CDE) 34 3.2.3 Deconvolution technique with BTCs 39 3.2.4 Data stabilization for deconvolution 43 3.2.5 Parameter estimation 47 3.3 Net retention time distribution in TSM 52 3.4 Biodegradation of chemicals in streams 56 IV. RESULTS AND DISCUSSIONS 59 4.1 Tracer behavior in a stream 59 4.2 Net retention time distribution 66 V. APPLICATION 70 5.1 Evaluation of TSM simulation 70 5.2 Prediction of biodegradation of chemicals 78 IV. CONCLUSIONS 82 REFERENCES 85석

Simulation of Mobility and Retention of Selected Engineered Nanoparticles Beneath Landfills

Engineered Nanoparticles (ENPs) have generated significant public and scientific excitement due to their unique physical, chemical, and electrical properties which has led to their application in a wide variety of industries. Landfills are a likely disposal site for ENPs at the end of their useful life, either encapsulated in a product as discrete nanoparticles or in nanoparticle agglomerates. Most countries and jurisdictions have landfill design regulations to provide an effective impermeable barrier between a landfill and soil/groundwater, however, landfills are still of concern due to the potential threat to groundwater resources. This study assesses the fate of selected ENPs (multi-walled carbon nanotubes, single-walled carbon nanotubes, nC60, and Quantum dots) beneath a representative landfill using a two-dimensional finite element model that solves modified colloid filtration theory. Simulation conditions were representative of conditions present in landfill systems (e.g., porous media as fine as silt to clay and a natural groundwater flow). Findings suggest that site blocking function is an important factor governing ENP mobility. These findings suggest that properly designed and constructed landfills will be able to significantly limit ENP transport to the environment for extended periods of time (i.e., 100 years)

Modeling Virus Transport and Removal during Storage and Recovery in Heterogeneous Aquifers

A quantitative understanding of virus removal during aquifer storage and recovery (ASR) in physically and geochemically heterogeneous aquifers is needed to accurately assess human health risks from viral infections. A two-dimensional axisymmetric numerical model incorporating processes of virus attachment, detachment, and inactivation in aqueous and solid phases was developed to systematically evaluate the virus removal performance of ASR schemes. Physical heterogeneity was considered as either layered or randomly distributed hydraulic conductivities (with selected variance and horizontal correlation length). Geochemical heterogeneity in the aquifer was accounted for using Colloid Filtration Theory to predict the spatial distribution of attachment rate coefficient. Simulation results demonstrate that the combined effects of aquifer physical heterogeneity and spatial variability of attachment rate resulted in higher virus concentrations in the recovered water at the ASR well (i.e. reduced virus removal). While the sticking efficiency of viruses to aquifer sediments was found to significantly influence virus concentration in the recovered water, the solid phase inactivation under realistic field conditions combined with the duration of storage phase had a predominant influence on the overall virus removal. The relative importance of physical heterogeneity increased under physicochemical conditions that reduced virus removal (e.g. lower value of sticking efficiency or solid phase inactivation rate). This study provides valuable insight on site selection of ASR projects and an approach to optimize ASR operational parameters (e.g. storage time) for virus removal and to minimize costs associated with post-recovery treatment

Remediation actions by a risk assessment approach: a case study of mercury contamination

The risk assessment procedure for identifying the remediation actions which may be adopted at a mercury contaminated site, when the plants are upgraded in the future, is proposed. The potentially active exposure/migration pathways in the future arrangement of the area will be due to Hg contaminated subsoil as a primary source (vapor inhalation and groundwater leaching) and to groundwater as a possible secondary source (transport to the point of compliance). The data of mercury concentration in the soil were acquired through environmental monitoring campaigns, and were processed to establish the three-dimensional distribution of contamination in subsoil, to locate sources and to define their geometrical and chemical characteristics. Speciation tests of mercury in the soil indicated that the most abundant species present were poorly leachable under the site-specific environmental conditions, confirming the coefficient distribution value obtained by the leaching tests. Analytical and numerical fate and transport modeling tools were used to locate digging zones in the contaminated subsoil, so as to reduce the possible groundwater contaminant loading and to avoid the down-gradient exceeding the concentration limit according to regulations. Remediation actions additional to civil works were required, which consists of soil digging within one contamination source, for about 22,200 m3 of soil. In order to evaluate the Hazard Index (HI) for human receptors due to Hg vapor inhalation, the air concentration of volatile mercury at the exposure point was estimated, based on direct measurements carried out at the site. Simulation gave HI values below 1 for all tested scenarios, suggesting that public health is protected without any additional actions to the already scheduled plant upgrading and digging for groundwater protection

Predictive Modeling of Organic Pollutant Leaching and Transport Behavior at the Lysimeter and Field Scales

Soil and groundwater pollution has become a global issue since the advent of industrialization and mechanized agriculture. Some contaminants such as PAHs may persist in the subsurface for decades and centuries. In a bid to address these issues, protection of groundwater must be based on the quantification of potential threats to pollution at the subsurface which is often inaccessible. Risk assessment of groundwater pollution may however be strongly supported by applying process-based simulation models, which turn out to be particularly helpful with regard to long-term predictions, which cannot be undertaken by experiments. Such reliable predictions, however, can only be achieved if the used modeling tool is known to be applicable. The aim of this work was threefold. First, a source strength function was developed to describe the leaching behavior of point source organic contaminants and thereby acting as a time-dependent upper boundary condition for transport models. For general application of these functions dimensionless numbers known as Damköhler numbers were used to characterize the reaction of the pollutants with the solid matrix. Two functions were derived and have been incorporated into an Excel worksheet to act as a practical aid in the quantification of leaching behavior of organic contaminant in seepage water prognoses. Second, the process based model tool SMART, which is well validated for laboratory scale data, was applied to lysimeter scale data from two research centres, FZJ (Jülich) and GSF (München) for long term predictions. Results from pure forward model runs show a fairly good correlation with the measured data. Finally, the derived source term functions in combination with the SMART model were used to assess groundwater vulnerability beneath a typical landfill at Kwabenya in Ghana. The predicted breakthrough time after leaking from the landfill was more than 200 years considering the operational time of the facility (30 years). Considering contaminant degradation, the landfill would therefore not cause groundwater pollution under the simulated scenarios and the SMART model can be used to establish waste acceptance criteria for organic contaminants in the landfill at KwabenyaSeit dem Beginn der Industrialisierung und der mechanisierten Landwirtschaft wurde die Boden- und Grundwasserverschmutzung zu einem weltweiten Problem. Einige Schadstoffe wie z. B. PAK können für Jahrzehnte oder Jahrhunderte im Untergrund bestehen. Um diese Probleme behandeln zu können, muss der Schutz des Grundwassers basierend auf der Quantifizierung potentieller Gefährdungen des zumeist unzugänglichen Untergrundes erfolgen. Risikoabschätzungen von Grundwasserverschmutzungen können jedoch durch die Anwendung prozess-basierter Simulationsmodelle erheblich unterstützt werden, die sich besonders im Hinblick auf Langzeitvorhersagen als hilfreich erweisen und nicht experimentell ermittelbar sind. Derart zuverlässige Vorhersagen können jedoch nur erhalten werden, wenn das verwendete Modellierwerkzeug als anwendbar bekannt ist. Das Ziel dieser Arbeit bestand aus drei Teilen. Erstens wurde eine Quellstärke-funktion entwickelt, die das Ausbreitungsverhalten organischer Schadstoffe aus einer Punktquelle beschreibt und dadurch als zeitabhängige obere Randbedingung bei Transportmodellen dienen kann. Im Hinblick auf die allgemeine Anwendbarkeit dieser Funktion werden als Damköhler-Zahlen bekannte, dimensionslose Zahlen verwendet, um die Reaktion von Schadstoffen mit Feststoffen zu charakterisieren. Zwei Funktionen wurden abgeleitet und in ein Excel-Arbeitsblatt eingefügt, das ein praktisches Hilfsmittel bei der Quantifizierung des Freisetzungsverhaltens organischer Schadstoffe im Rahmen der Sickerwasserprognose darstellt. Der zweite Teil dieser Arbeit beinhaltet die Anwendung des prozessbasierten und mittels Laborexperimenten validierten Modellwerkzeugs SMART für Langzeitprognosen auf der Lysimeterskala anhand von Daten zweier Forschungszentren, FZJ (Jülich) und GSF (München). Ergebnisse reiner Vorwärtsmodellierungsläufe zeigten gute Übereinstimmungen mit den gemessenen Daten. Im dritten Teil wurden die erhaltenen Quellstärkefunktionen in Kombination mit dem SMART-Modell eingesetzt, um das Grundwassergefährdungspotential unter einer typischen Deponie in Kwabenya, Ghana, einzuschätzen. Die vorhergesagten Durchbruchszeiten nach einer Leckage in der Deponie betragen über 200 Jahre bei einer Betriebszeit von 30 Jahren. Unter Berücksichtigung des Schadstoffabbaus verursacht die Deponie somit keine Grundwasserverunreinigung im Rahmen der simulierten Szenarien und das SMART-Modell kann verwendet werden, um Schadstoffgrenzwerte für organische Schadstoffe in der Deponie in Kwabenya festzulegen