An analysis of field data for evidence of anaerobic degradation of PAH and BTEX plumes at manufactured gas plant sites

Field data (including geology, hydrogeology, soil chemistry, groundwater chemistry, and aquifer characteristics) were analyzed at eight MGP sites located in the New Jersey Coastal Plain. These data were used to calculate biodegradation rate constants, which were then compared with laboratory microcosm data and published values. Isopleths were drawn from the field data to indicate the dominant biodegradation mechanisms at each of the sites, and stoichiometric calculations were used to determine the total capacity of the electron acceptors present to degrade the plume contaminants. In examining these data, the protocol described by the Air Force Center for Environmental Excellence (AFCEE) was used. The results of this study showed that at most of the sites, first-order decay constants calculated from field data were generally greater than values reported for the same contaminants at fuel sites. Furthermore, the total capacity of electron acceptors at five of the sites could account for only about a third of the contaminant mass, although at the other three sites there appeared to be sufficient electron acceptors for complete plume attenuation. For most sites, at the plume periphery, aerobic degradation played a major role. However, within the plume, the dominant mechanisms were nitrate, iron, and sulphate reduction. These findings were corroborated in the microcosm studies conducted for two of the sites, which indicated the importance of sulfate reduction in groundwater collected within the plume. The rate constant calculated for benzene from one of the microcosms was about the same order of magnitude as the constant calculated from field data. However, the rate constant calculated for naphthalene in the other microcosm from a different site was up to two orders of magnitude greater than the field data indicated

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

Modeling Transport of Non Aqueous Wastes in Unsaturated Soils.

In evaluating risks associated with chemical spills on the ground surface or leaks from underground storage tanks, it is required to know the extent and degree of contamination in the subsurface. In many cases pure organics are spilled and due to their low miscibility with water they remain pure or concentrated for some distance or time from the source. This dissertation is aimed at developing a model of the multiphase (air, water, organic) migration processes. The particular focus is on modeling organic infiltration in the unsaturated zone where the transport is largely vertical. Sand-column experiments using a variety of immiscible and miscible organics indicated that the organic infiltration front after a \u27spill\u27 was sharp and that little residual water was displaced by an infiltrating immiscible organic. Based upon these assumptions, the multiphase transport problem was essentially modeled as a single phase infiltration under the influence of gravity and capillary forces. The resulting model describing organic phase infiltration rate contained two parameters, an effective medium permeability and an effective capillary suction at the wetting front. For the case of a fully infiltrated organic, an effective capillary suction at the drainage front was also required. The boundary element method (BEM) is used to solve the governing quasi-steady differential equations. Good agreement between the experimental data and the model was observed taking the effective medium permeability equal to the saturated flow permeability and using measured values of the capillary suction parameters. Many groundwater contamination incidents begin with the release of an essentially immiscible fluid into the subsurface environment. Once in the subsurface, an immiscible fluid participates in a complex pattern of transport processes. For immiscible fluids that are commonly found in contaminated groundwater environments the interphase mass transfer between the nonaqueous liquid phase and the aqueous phase is an important process. A model capable of exploring the effect of interphase mass transfer on in-situ extraction is also presented

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

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

A Narrative Review of Groundwater and Soil Pollution

In accordance with the migration and transformation laws of pollutants in soil and groundwater, the research progress of chemical fertilizers, pesticides, and sewage irrigation is reviewed systematically from three perspectives: the topsoil layer, the underground aquifer, and the unsaturated zone. The results of the study of migration and transformation in various water layers and unsaturated soils illuminate the current research's problems and future directions

A Comparison of Remediation Priorities Developed by the Defense Priority Model, the Relative Risk Evaluation Method, and a Quantitative Risk Assessment Approach

The Superfund, established by the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) of 1980, seriously underestimated both the number of severely contaminated sites and the associated cleanup cost. The magnitude of projected cleanup costs, coupled with shrinking federal budgets, necessitated the development and use of risk-based prioritization models among some federal agencies. Among these tools, the DOD prioritization models are meant to give priority to sites posing the greatest threat to human health. Their failure to properly rank sites could incorrectly shift the focus from those that pose substantial risk to sites of lesser risk. The DOD site ranking models addressed in this study are the Relative Risk Evaluation Method (RREM), and its predecessor, the Defense Priority Model (DPM). RREM\u27s site evaluation approach uses a quantitative assessment of contaminants and a qualitative assessment of both pathways and receptors to group sites into a low, medium, or high risk category. The RREM has been criticized as relying too much upon qualitative factors that could, perhaps, create inconsistencies between users of the model. The DPM, not used after 1993, used a combination of quantitative and qualitative approximations to calculate pathway subscores combined to provide an overall site score from 0 to 100. One criticism is that some of DPM\u27s models appear theoretically weak. The problem is that these two DOD approaches for prioritizing sites for remediation have not been validated. The research objective was as an initial validation effort for the RREM and the DPM models by comparing their rankings of a sample of contaminated sites against those of a rigorous, quantitative risk assessment model

Subsurface radioactive gas transport and release studies using the UTEX model

textUnderground nuclear explosions (UNEs) produce anthropogenic isotopes that provide the only definitive means by which to determine whether a nuclear explosion has taken place. Verification of a suspected test under the Comprehensive Nuclear-Test-Ban Treaty (CTBT) includes both on-site and atmospheric sampling of specific noble gas radioisotopes for analysis of origin. It is well-established that the processes of subsurface transport can affect the rate at which such gases will reach the surface. However, the relative abundance of anthropogenic isotopes reaching the surface following transport is currently assumed to rely solely on their direct fission yield, decay rate, and their production from precursor decay, making no account for the influence of transport processes on isotopic ratios. The Underground Transport of Environmental Xenon (UTEX) model has been developed to examine the possible effects of subsurface transport on radioxenon isotopic ratios as well as to consider a number of on-site inspection-related applications. In this work, background on the UTEX model's development, evolution and vetting is presented. This is followed by the characterization and analysis of a number of applications of the model for consideration of CTBT-relevant scenarios. Specifically, the UTEX model's capability to analyze CTBT on-site inspection concept of operations is demonstrated. This is accomplished through an examination of generalized UNE source terms, geological stratigraphy, UNE impact on local geology, natural soil-gas radionuclide backgrounds, atmospheric infiltration, and sampling methodology. It is shown that the processes driving noble gas transport through geological media can significantly skew the ratios of key radioxenon isotopes that are used to help verify whether or not a well-contained underground test has taken place. This result emphasizes the need for a broader understanding of radionuclide signatures used for CTBT verification purposes and the mechanisms that can alter them.Mechanical Engineerin