Kathleen m Smits

Southern Methodist University | SMU

Abstract Soil gas diffusivity (Dp/Do, gas diffusion coefficients in soil and in free air, respectively) and its relation to soil moisture is of great importance for describing and quantifying essential provisional and regulatory functions associated with terrestrial ecosystems such as soil aeration and greenhouse gas (GHG) emissions. Because gas mi...

Soil density plays an important role in regulating the migration of greenhouse gases from terrestrial soils to the atmosphere. Soil moisture is one of the main soil physical controls determining the fate and transport of gases in soils. This study investigated the transport of methane (CH4) originating from a simulated CH4 source within a variably...

Soil-gas diffusivity and its variation with soil moisture plays a fundamental role in diffusion controlled migration of climate-impact gases from different terrestrial agroecosystems including cultivated soils and managed pasture systems. The wide contrast in soil texture and structure (e.g., density, soil aggregation) in agriculture topsoils (0-10...

Underground natural gas (NG) pipeline leakage can result in methane (CH4) buildup and migration through the soil. What is not well understood in such scenarios is how the soil conditions affect the gas migration behavior, particularly in regard to the relative contributions of specific soil properties such as soil moisture content. The objective of...

Methane (CH4) leakage from natural gas (NG) pipelines poses an environmental, safety, and economic threat to the public. While previous leak detection and quantification studies focus on the aboveground infrastructure, the analysis of underground NG pipeline leak scenarios is scarce. Furthermore, no data from controlled release experiments have bee...

The 2015 Paris agreement aims to cut greenhouse gas emissions and keep global temperature rise below 2 °C above pre-industrial levels. Reducing CH4 emissions from leaking pipelines presents a relatively achievable objective. While walking and driving surveys are commonly used to detect leaks, the detection probability (DP) is poorly characterized....

Recent technological advances in methane detection have improved leak detection and repair. However, current methods to reliably measure methane concentrations rely on expensive instruments or demand significant labor input. There is interest in using affordable methane sensors that are responsive to ppmv level changes in methane concentrations in...

Technical advancements in mine tailings recycling have led to the production of construction products such as bricks, cement, road pavers, and mortars in artisanal and small-scale mining (ASM) communities. Although such efforts show promise, the environmental, health, and social implications of such practices are often overlooked by stakeholders in...

Grazed pastures can be introduced as a dominant source of nitrous oxide (N2O), a high potent greenhouse gas. Although past studies have examined N2O emissions in relation to soil physical properties, linking emissions with soil gas diffusivity (Dp/Do) and its dependency on soil physical properties and soil moisture are lacking. This study to empiri...

Grazed pastures can be introduced as a dominant source of nitrous oxide (N2O), a high potent greenhouse gas. Although past studies have examined N2O emissions in relation to soil physical properties, linking emissions with soil gas diffusivity (Dp/Do) and its dependency on soil physical properties and soil moisture are lacking. This study to empiri...

Leaks in natural gas distribution networks are often initially detected by odor and then localized during operators' walking surveys. The size of the enhancement detected and the leak's proximity to infrastructure are used to determine leak severity of the leak and how quickly it is repaired. Methane (CH4) enhancements on the surface above the leak...

La colaboración internacional en proyectos humanitarios es cada vez más una parte importante de la educación de los ingenieros en su formación básica de pregrado, en especial cuando se trata de involucrar y retener a las mujeres en los programas de ingeniería. Sin embargo, estos proyectos frecuentemente están restringidos por limitaciones presupues...

Environmental remediation of polluted sites in developing communities often faces difficulties due to the misalignment of project objectives with the needs and interests of local communities, establishment of unrealistic expectations for the outcome of the project, and failure to account for the available resources in the community itself. Remediat...

Pollution remediation decisions in developing communities are often made with limited technical data and stakeholder engagement. Local knowledge of contamination is oftentimes neglected, resulting in efforts that fail to align with community objectives. In this work, we propose a new approach for incorporating local knowledge on contamination into...

With the increased use of natural gas, safety and environmental concerns from underground leaking natural gas pipelines are becoming more widespread. What is not well understood in leakage incidents is how the soil conditions affect gas migration behavior, making it difficult to estimate the gas distribution. To shed light on these concerns, an inc...

Accurately predicting bare‐soil evaporation requires the proper characterization of the near‐surface atmospheric conditions. These conditions, dependent on factors such as surface microtopography and wind velocity, vary greatly and therefore require high‐resolution datasets to be fully incorporated into evaporation models. These factors are oftenti...

Methane (CH4) transport in soil is primarily affected by soil physical conditions such as soil-texture and soil-structure, soil-moisture, soil-gas diffusivity, permeability and soil-temperature. Aggregated soils have distinct soil structure with two pore regions characteristics (i.e., inter-aggregate and intra-aggregate regions) and therefore show...

Rapid response to underground natural gas leaks could mitigate methane emissions and reduce risks to the environment, human health and safety. Identification of large, potentially hazardous leaks could have environmental and safety benefits, including improved prioritization of response efforts and enhanced understanding of relative climate impacts...

Effective thermal conductivity of soils (λeff) is a critical parameter for agriculture, environment science, and engineering. Functions to estimate λeff from readily available soil properties, known as soil thermal conductivity (STC) schemes, are needed by land-surface models (LSMs), hydrological models, and soil-vegetation-atmosphere transfer (SVA...

Environmental risk mitigation strategies employed in developing communities to address mercury pollution from artisanal and small-scale gold mining (ASGM) have largely failed to meet community needs, resulting in their abandonment. In contrast, the water and wastewater treatment sector has gained more traction, introducing sustainable and community...

Grazed pastures rich in nitrogen (N) from ruminant urine and fertilizer inputs are significant sources of nitrous oxide (N2O), a highly potent greenhouse gas. Diffusion-controlled emission of N2O from pasture systems can be described by soil-gas diffusivity (Dp/Do), and its dependency on soil physical properties and soil moisture dynamics. But stud...

We investigate the influence of near-surface wind conditions on subsurface gas transport and on soil-atmosphere gas exchange for gases of different density. Results of a sand tank experiment are supported by a numerical investigation with a fully coupled porous medium-free flow model, which accounts for wind turbulence. The experiment consists of a...

Evaporation from undulating soil surfaces is rarely studied due to limited modeling theory and inadequate experimental data linking dynamic soil and atmospheric interactions. The goal of this paper is to provide exploratory insights into evaporation behavior from undulating soil surfaces under turbulent conditions through numerical and experimental...

Open dumps constitute a major source of greenhouse gases (GHGs), predominantly methane and carbon dioxide, in developing countries. In an aged dump, typical waste composition is dominated by the “soil-like” fraction of which physical, hydraulic and gas transport characteristics markedly affect GHG emissions. This study characterized soil-gas diffus...

In developing countries, remediation projects are predominantly implemented in areas with imminent risks due to human exposure routes. Projects experience challenges due to funding constraints derived from the history of legacy pollution and informal livelihood occupations in addition to political and economic instability and weak regulatory struct...

Grazed pastures and cultivated fields are significant sources of greenhouse gas (GHG) emissions, in particular N2O emissions derived from fertilizer deposition and animal excreta. Net surface emissions rely on subsurface gas transfer controlled mainly by diffusion, expressed as the soil-gas diffusivity (Dp/Do). The value of Dp/Do is a function of s...

Understanding the effect of the top soil layer on surface evaporation and water distribution is critical to modeling hydrological systems. However, the dependency of near‐surface soil moisture and fluxes on layering characteristics remains unclear. To address this uncertainty, we investigate how the arrangement of soil horizons affects the evaporat...

Using a creative capacity building (CCB) framework, co-design workshops among artisanal and small-scale gold miners, government officials, NGO representatives, and academics can provide an effective mechanism to identify pressing needs and desires of miners and operators towards formalization. As recently implemented in Peru, one of these workshops...

Aggregated porous media are widely used as plant growth substrates due to its inherent structural properties and their distinctive mass transport characteristics. Soil-gas diffusivity (Dp/Do; where Dp and Do are gas diffusion coefficients for a given gas in porous medium and free air, respectively) characterizes the ability of the media to facilita...

Aggregated porous media are widely used as plant growth substrates due to its inherent structural properties and their distinctive mass transport characteristics. Soil-gas diffusivity (Dp/Do; where Dp and Do are gas diffusion coefficients for a given gas in porous medium and free air, respectively) characterizes the ability of the media to facilita...

Oscillating cycles of dewatering (termed drying) and rewetting during managed aquifer recharge (MAR) are used to maintain infiltration rates and could also exert an influence on subsurface microbial structure and respiratory processes. Despite this practice, little knowledge is available about changes to microbial community structure and trace orga...

Soil water evaporation plays a critical role in mass and energy exchanges across the land–atmosphere interface. Although much is known about this process, there is no agreement on the best modeling approaches to determine soil water evaporation due to the complexity of the numerical modeling scenarios and lack of experimental data available to vali...

Underground natural gas (NG) leaks pose an urgent safety threat, motivating ongoing efforts to improve leak detection methods. The objective of this study was to investigate how realistic environmental conditions affect methane concentration distributions near leaking underground NG distribution pipelines, and ultimately to inform protocols for lea...

The macroscale roughness of the soil surface has significant influences on the mass/energy interactions between the subsurface and the atmosphere during evaporation. However, most previous works only consider evaporation behavior from flat surfaces. Based on experimental and numerical approaches, the goal of this work is to provide a framework for...

This paper presents a novel method to couple an environmental bioremediation system with a subsurface renewable energy storage system. This method involves treating unsaturated contaminated soil using in-situ thermally enhanced bioremediation; the thermal system is powered by renewable energy. After remediation goals are achieved, the thermal syste...

Although siting of thermal energy storage systems in the vadose zone may be beneficial due to the low thermal conductivity of unsaturated soils, water phase change and vapor diffusion in soils surrounding geothermal heat exchangers may play important roles in both the heat injection and retention processes that are not considered in established des...

Characterization of differently-textured porous materials, as well as different volumetric porous media mixtures, in relation to mass and heat transport is vital for many engineering and research applications. Functional relations describing physical properties (e.g., grain-size distribution, total porosity), thermal and gas diffusion properties of...

Aquifers show troubling signs of irreversible depletion as climate change, population growth, and urbanization lead to reduced natural recharge rates and overuse. One strategy to sustain the groundwater supply is to recharge aquifers artificially with reclaimed water or stormwater via managed aquifer recharge and recovery (MAR) systems. Unfortunate...

Mitigation of atmospheric emission of methane from leaky underground infrastructure is important for controlling the global anthropogenic greenhouse gas burden. Overexposure to methane may also cause occupational health problems in indoor/outdoor environments at the local scale. Subsurface soil conditions (e.g., soil heterogeneity) affect methane m...

Meaningful model-based predictions of water quality and quantity are imperative for the designed footprint of MAR installations. A two-dimensional (2D) synthetic managed aquifer recharge system equipped with automated sensors (temperature, water pressure, conductivity, soil moisture, oxidation reduction potential) and embedded water sampling ports...

Evaporation is an important component of the soil water balance. It is composed of water flow and transport processes in a porous medium that are coupled with heat fluxes and free air flow. This work provides a comprehensive review of model concepts used in different research fields to describe evaporation. Concepts range from nonisothermal two-pha...

In an accompanying paper, we presented an overview of a wide variety of modeling concepts, varying in complexity, used to describe evaporation from soil. Using theoretical analyses, we explained the simplifications and parameterizations in the different approaches. In this paper, we numerically evaluate the consequences of these simplifications and...

A major concern resulting from the increased use and production of natural gas has been how to mitigate fugitive greenhouse gas emissions (predominantly methane) from natural gas infrastructure (e.g., leaky shallow pipelines). Subsurface migration and atmospheric loading of methane from pipeline leakage is controlled by source configurations and su...

In this study, we numerically and experimentally evaluated heat transfer in soils under unsaturated conditions in the context of simulating a laboratory- scale, three-dimensional soil-borehole thermal energy storage (SBTES) system. Most previous studies assumed that soil thermal and hydraulic properties are constant and that heat transfer in soil o...

The interactions between turbulent free flow and flow in a porous medium are of key interest in different fields, e.g., meteorology, agriculture, building physics, and aerospace engineering. Properly understanding the strongly coupled exchange processes between the two domains is crucial to describing these interactions. In (Mosthaf et al. in Water...

An understanding of soil thermal conductivity after a wildfire or controlled burn is important to land management and post-fire recovery efforts. Although soil thermal conductivity has been well studied for non-fire heated soils, comprehensive data that evaluate the long-term effect of extreme heating from a fire on the soil thermal conductivity ar...

A soil's grain-size distribution affects its physical and hydraulic properties; however, little is known about its effect on soil thermal properties. To better understand how grain-size distribution affects soil thermal properties, specifically the effective thermal conductivity, a set of laboratory experiments was performed using binary mixtures o...

We introduce a mathematical model for the description of non-isothermal compressible flow of gas mixtures in heterogeneous porous media and we derive an efficient semi-implicit time-stepping numerical scheme for the solution of the governing equations. We experimentally estimate the order of convergence of the scheme in spatial variables and we pre...

Detailed characterization of partially saturated porous media is important for understanding and predicting vadose zone transport processes. While basic properties (e.g., particle- and pore-size distributions and soil-water retention) are, in general, essential prerequisites for characterizing most porous media transport properties, key transport p...

In-situ bioremediation, a widely applied treatment technology for source zones contaminated with dense non-aqueous phase liquids (DNAPLs), has proven economical and reasonably efficient for long-term management of contaminated sites. Successful application of this remedial technology, however, requires an understanding of the complex interaction of...

Evaporation and condensation in bare soils govern water and energy fluxes between the land and atmosphere. Phase change between liquid water and water vapor is commonly evaluated in soil hydrology using an assumption of instantaneous phase change (i.e., chemical equilibrium). Past experimental studies have shown that finite volatilization and conde...

Evaporation is directly influenced by the interactions between the atmosphere, land surface and soil subsurface. This work aims to experimentally study evaporation under various surface boundary conditions to improve our current understanding and characterization of this multiphase phenomenon as well as to validate numerical heat and mass transfer...

Numerical simulation of hydrogeologic systems requires parameters characterizing fundamental physical, chemical and biological processes as model inputs. These processes at a very fundamental level occur within the inter-granular pore spaces of the porous medium. In the traditional applications in hydrogeology, the smallest scale where continuum fo...

The mixing of different sized soil particles is known to affect soil properties such as density, porosity, hydraulic conductivity, and soil water retention. To better understand how the mixing controls soil water retention characteristics, a set of laboratory experiments was performed using binary mixtures of coarse and fine particles with seven di...

The generation of vapor-phase contaminant plumes within the vadose zone is of interest for contaminated site management. Therefore, it is important to understand vapor sources such as non-aqueous-phase liquids (NAPLs) and processes that govern their volatilization. The distribution of NAPL, gas, and water phases within a source zone is expected to...

Thermal conductivity of unsaturated soil depends on soil water content and soil type. A transient water release and imbibition method (TRIM) is modified to include measurement of the thermal conductivity function (TCF) in conjunction with concurrent measurement of the soil water retention curve (SWRC) and hydraulic conductivity function (HCF). Two...

Thermal properties of unsaturated soils have not been widely investigated, despite their wide range of engineering implications. The volumetric fraction of each component (air, water and soil) and the particle size distribution are key factors in determining the thermal properties of unsaturated soils. A Transient water Release and Imbibition Metho...

In an effort to develop methods based on integrating the subsurface to the atmospheric boundary layer to estimate evaporation, we developed a model based on the coupling of Navier-Stokes free flow and Darcy flow in porous medium. The model was tested using experimental data to study the effect of wind speed on evaporation. The model consists of the...

A combined heat-pulse and sensible heat balance method can be used to determine evaporation using temperature measurements and thermal property estimations. The objective of this study was to investigate the applicability of the combined heat-pulse and sensible heat balance method by comparing laboratory experimental data to both an analytical and...

Evaporation from bare soil is a key component of the hydrologic cycle and the process primarily responsible for governing water and energy exchanges between the land and atmosphere. Despite its importance, there is still a great deal of uncertainty associated with our current understanding of this complex multiphase phenomenon. A common approach wh...

Due to the dynamic nature of the shallow subsurface, knowledge of soil thermal properties across a wide range of soil moisture and temperature conditions is necessary to accurately describe heat transport in many settings. Soil thermal properties are difficult to measure at high temperatures, however, due to the lack of suitable measurement devices...