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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. Remediation decisions favor technical data and technical solutions as the main means of determining remediation options, requiring significant investment and local capacity that are often not found in developing communities. Often these systems fail to account for the social aspects in environmental management and remediation. In contrast, new approaches in local knowledge-based solutions focus on pre-existing environmental management initiatives to establish objectives that are meaningful to the community itself. “Positive deviance” – or the idea that there are solutions already in communities that are successful at addressing challenges despite the barriers that a community faces – are often overlooked during project design and implementation. Identifying examples of positive deviance and working with community members who are well versed in local challenges, available resources, and local capacity presents opportunities for community members to establish project objectives and provides the foundation for future environmental management projects in the area. We present a case study of artisanal and small-scale gold mining (ASGM) in the Andes municipality, Antioquia, Colombia and local initiatives to overcome community-identified environmental pollutants. Through a series of semi-structured interviews, surveys, and site visits, we identified community perception of environmental pollutants, management techniques for mining waste, and grassroots initiatives that were locally developed to address them. Through key communication and interaction between innovators with identified positive deviance projects, technical experts, and other miners facing similar challenges, innovative projects that account for the social, political, and economic realities of a developing community can become widespread, leading to improved environmental and social conditions.

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 deri...

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 identified the need for a single forum (association) to allow artisanal and small-scale miners to represent their voice in front of government and large-scale mining operations and the need for a streamlined simple process for formalization that included mining, environment, health, safety, and employment considerations. A first step towards the single forum was taken with the creation of a social media outlet that allows participants to voice their concerns and share information. Future workshops are needed to cement the creation of the forum and provide specific recommendations for the streamlining of the formalization process.

Underground natural gas (NG) leaks pose an urgent safety threat, motivating ongoing efforts to improve leak detection methods. The objectives of this study were to investigate how realistic environ...

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 increased understanding of subsurface methane migration after gas release is required to support efficient leak response and effective use of available technologies. In this study, three field-scale experiments were performed at the Methane Emission Technology Evaluation Center in Colorado State University to investigate the effect of soil textural heterogeneity, soil moisture, and leak rate (0.5 and 0.85 kg/h) on methane migration caused by leaking pipelines. Subsurface methane concentrations, in addition to soil moisture and meteorological data, were collected over time. A previously validated numerical model was modified and used to understand the observed methane distribution behavior. Results of this study illustrate that the influence of soil texture, leak rate, and moisture on subsurface methane distribution is determined by the relative contribution of advection and diffusion and closely related to the distance to the leak source. Advection dominates gas transport within 1–1.5 m of the leak source, driving the migration of high concentration contours. Beyond this distance, diffusion dominates migration of lower concentration contours to the far-field. Although large leak rates initially result in faster and further gas migration, the leak rate has little influence on the diffusion dominated migration farther from the leak source. Soil moisture and texture complicate gas behavior with texture variations and elevated soil moisture conditions playing a dominant role in locally increasing methane concentrations. Scenarios highlight the importance of understanding the effects of soil moisture, texture, and leak rate on gas migration behavior in an attempt to unravel their contribution to the gas concentration within the soil environment.

Author(s): Shanujah, M; Deepagoda, TKKC; Karunarathna, AK; Nasvi, MCM; Shreedharan, V; Babu, GLS; Smits, KM; Oldenburg, CM | Abstract: 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 diffusivity (Dp/D0), soil-water characteristics (SWC), and particle size distribution in “soil-like” fractions of aged solid waste retrieved at 2.5–5nm depth from an old open dumpsite situated at Kurunegala, Sri Lanka. The “soil-like” fraction was proportioned into three groups based on particle size (0–4.75, 4.75–9.5, and 9.5–25nmm) to investigate the particle size effect on Dp/D0 and SWC. The simulated methane concentration profiles in different size groups were also examined using the transport simulator TOUGH2-EOS7CA based on the multiphase flow of multicomponent gas mixture (methane, water vapour and air) under dry and half-saturation conditions across a predefined temperature gradient. The results highlighted distinct two-region characteristics (i.e., inter-aggregate and intra-aggregate pore regions) in all three size fractions which could be adequately parameterized with existing and modified bimodal functions. We proposed a useful practical tool for estimating Dp/D0 for known mean particle size and volumetric water content in the absence of direct measurements. The results further revealed that Dp/D0 is particle-size dependent; however, Dp/D0 remained invariant across all size fractions at the volumetric water content of ∼0.22–0.25 cm3 cm−3. Numerical results further showed a pronounced effect of particle size and soil moisture on gas transport properties.

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 of emission point sources. However, quantitative estimation of underground leakage rates remains challenging, considering the complex nature of methane transport processes. We demonstrate a novel method for estimating underground leak rates based on controlled underground natural gas release experiments at the field scale. The proposed method is based on incorporation of easily measurable field parameters into a dimensionless concentration number, e , which considers soil and fluid characteristics. A series of field experiments was conducted to evaluate the relationship between the underground leakage rate and surface methane concentration data over varying soil and pipeline conditions. Peak surface methane concentrations increased with leakage rate, while surface concentrations consistently decreased exponentially with distance from the source. Deviations between the estimated and actual leakage rates ranged from 9% to 33%. A numerical modeling study was carried out by the TOUGH3 simulator to further evaluate how leak rate and subsurface methane transport processes affect the resulting methane surface profile. These findings show that the proposed leak rate estimation method may be useful for prioritizing leak repair, and warrant broader field-scale method validation studies. A method was developed to estimate fugitive emission rates from underground natural gas pipeline leaks. The method could be applied across a range of soil and surface covering conditions.

International audience

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 validate such models. Existing studies show numerical and experimental discrepancies in the evaporation behavior and soil water distribution in soils at various scales, driving us to revisit the key process representation in subsurface soil. Therefore, the goal of this work is to test different mathematical formulations used to estimate evaporation from bare soils to critically evaluate the model formulations, assumptions and surface boundary conditions. This comparison required the development of three numerical models at the REV scale that vary in their complexity in characterizing water flow and evaporation, using the same modeling platform. The performance of the models was evaluated by comparing with experimental data generated from a soil tank/boundary layer wind tunnel experimental apparatus equipped with a sensor network to continuously monitor water–temperature–humidity variables. A series of experiments were performed in which the soil tank was packed with different soil types. Results demonstrate that the approaches vary in their ability to capture different stages of evaporation and no one approach can be deemed most appropriate for every scenario. When a proper top boundary condition and space discretization are defined, the Richards equation-based models (Richards model and Richards vapor model) can generally capture the evaporation behaviors across the entire range of soil saturations, comparing well with the experimental data. The simulation results of the non-equilibrium two-component two-phase model which considers vapor transport as an independent process generally agree well with the observations in terms of evaporation behavior and soil water dynamics. Certain differences in simulation results can be observed between equilibrium and non-equilibrium approaches. Comparisons of the models and the boundary layer formulations highlight the need to revisit key assumptions that influence evaporation behavior, highlighting the need to further understand water and vapor transport processes in soil to improve model accuracy.

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 migration in soils while near†surface atmospheric boundary conditions (e.g. wind and temperature) affect off†site emissions across the soil†atmosphere interface. This study investigated the above†surface methane concentration boundary†layer development under different soil conditions (homogenous and layered) and atmospheric boundary controls (wind and temperature). A series of controlled bench†scale experiments was conducted using an open†loop boundary†layer wind tunnel interfaced with a porous media tank inside which a simulated methane point source was embedded to mimic a buried leaky pipeline. Results revealed pronounced effects of wind and, to a lesser extent, temperature on above†surface methane boundary†layer development. High atmospheric temperature contributed to the concentration boundary†layer build†up whereas high wind velocity caused erosion of the boundary layer. The boundary†layer methane concentration profiles were adequately simulated within an advection†diffusion modeling framework combined with a Navier†Stokes free flow domain by coupling free air flow, heat flow and flow of a multicomponent gas mixture. Simulations further implied that the Fickian diffusion approach may have limited applications when pronounced non†isothermal conditions prevail within the system. © 2017 Society of Chemical Industry and John Wiley & Sons, Ltd.

Meaningful model-based predictions of water quality and quantity are imperative for the designed footprint of managed aquifer recharge installations. A two-dimensional (2D) synthetic MAR system equipped with automated sensors (temperature, water pressure, conductivity, soil moisture, oxidation-reduction potential) and embedded water sampling ports was used to test and model fundamental subsurface processes during surface spreading managed aquifer recharge operations under controlled flow and redox conditions at the meso-scale. The fate and transport of contaminants in the variably saturated synthetic aquifer were simulated using the finite element analysis model, FEFLOW. In general, the model concurred with travel times derived from contaminant breakthrough curves at individual sensor locations throughout the 2D tank. However, discrepancies between measured and simulated trace organic chemical concentrations (i.e., carbamazepine, sulfamethoxazole, tris (2-chloroethyl) phosphate, trimethoprim) were observed. While the FEFLOW simulation of breakthrough curves captured overall shapes of trace organic chemical concentrations well, the model struggled with matching individual data points, although compound-specific attenuation parameters were used. Interestingly, despite steady-state operation, oxidation-reduction potential measurements indicated temporal disturbances in hydraulic properties in the saturated zone of the 2D tank that affected water quality.

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 approaches. A previously developed and verified coupled free flow and porous media flow model was extended by incorporating turbulent airflow through Reynolds‐averaged Navier–Stokes equations. The model explicitly describes the relevant physical processes and the key properties in the free flow, porous media, and at the interface, allowing for the analysis of coupled exchange fluxes. An experiment aiming to simultaneously collect the data of the boundary layer and soil evaporation in the area around the soil–atmosphere interface was conducted using a wind tunnel integrated with a soil tank. The turbulent boundary layer above the undulating soil surface was captured using high‐resolution hot‐wire anemometry, confirming the presence of recirculation zones in the undulating valleys and locally low evaporative flux. Experimental data were used to validate the extended model, and modeling results demonstrate that turbulent airflow enhances evaporation and shortens the duration of Stage I. The surface geometry significantly affects the local evaporative flux by influencing the vapor distribution, concentration gradient, and water availability at the soil surface, especially when recirculation zones form in the valleys. As a joint result of turbulence and surface undulations, the influence of wind speed on both the local and system‐level evaporation rate is restricted.

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 present several computational studies that demonstrate the ability of the numerical scheme.

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 studies linking soil aggregation, soil moisture variation, Dp/Do and N2O emissions are lacking. Using coarse (2–4 mm) and fine (

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 (SVAT) models to study the land surface energy balance, heat flux, and soil thermal regime under various climates and geographic regions. The selection of a STC scheme can result in large differences in temperature estimates in LSMs, sometimes masking the effects of climate change. Therefore, accurate selection of a STC scheme is critically important to LSM estimates. Although a number of STC schemes have been incorporated in various LSMs, no study has systematically evaluated their performance. Therefore, the objectives of this study were to review and evaluate STC schemes employed by LSMs by comparing (1) predicted and measured STCs and (2) modelled land surface temperature (LST) using the Community Land Model at three selected sites and the corresponding LST data from the moderate resolution imaging spectrometer (MODIS). In total, 24 STC schemes were collated from 38 mainstream LSMs, SVAT, and hydrological models. They were divided into three categories based on model types: one physically-based scheme, eight linear/non-linear regression schemes, and 13 normalized schemes. We also include two schemes that express STC as a function of matric potential (ψ, hereafter referred as λeff (ψ) schemes). The first three types of STC schemes were evaluated with a large compiled dataset consisting of 439 unfrozen and frozen measurements of λeff from 16 soils. The λeff (ψ) schemes were evaluated with simultaneously measured λeff (ψ) from eight soils from two separate or independent studies. Results showed that none of the STC schemes could be used to accurately predict λeff for all soil types. STC scheme performance largely depended on the size (number of samples) and characteristics (e.g., soil types) of the data used for comparison. Some STC schemes work well on certain types of soils, but care should be taken for larger scale applications. LSM simulated LST for 24 STC schemes varied when compared with MODIS LST. In general, the STC schemes performed better in medium- and coarse-textured soils than in fine-textured soils. However, large discrepancies were observed on the estimated LST using different STC schemes for medium and coarse-textured soils. We recommend that LSM modelers be mindful of the inherent bias in STC schemes on the surface temperature estimates and hence overall model predictions. Orchestrated efforts are urgently needed on the part of the soil science, hydrology, and climatology communities to develop a more extensive and systematic λeff database for development and evaluation of improved STC schemes for wider and more accurate applications.

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 organic chemical biodegradation potential in MAR systems under these conditions. A biologically active two-dimensional (2D) synthetic MAR system equipped with automated sensors (temperature, water pressure, conductivity, soil moisture, oxidation-reduction potential) and embedded water and soil sampling ports was used to test and model these important subsurface processes at the meso-scale. The fate and transport of the antiepileptic drug carbamazepine, the antibiotics sulfamethoxazole and trimethoprim, and the flame retardant tris (2-chloroethyl) phosphate were simulated using the finite element analysis model, FEFLOW. All of these compounds exhibit moderate to poor biodegradability in MAR systems. Within the operational MAR scenario tested, three episodic drying cycles spanning between 18 and 24 days were conducted over a period of 184 days. Notably, cessation of flow and partial dewatering of the 2D synthetic aquifer during dry cycles caused no measurable decrease in soil moisture content beyond the near-surface layer. The episodic flow introduction and dewatering cycles in turn had little impact on overall trace organic chemical biotransformation behavior and soil microbial community structure. However, spatial differences in oxidation-reduction potential and soil moisture were both identified as significant environmental predictors for microbial community structure in the 2D synthetic aquifer.

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 parameterizations. Two sets of simulations were performed. The first set investigates lateral variations in vertical fluxes, which emerge from both homogeneous and heterogeneous porous media, and their importance to capturing evaporation behavior. When evaporation decreases from parts of the heterogeneous soil surface, lateral flow and transport processes in the free flow and in the porous medium generate feedbacks that enhance evaporation from wet surface areas. In the second set of simulations, we assume that the vertical fluxes do not vary considerably in the simulation domain and represent the system using one-dimensional models which also consider dynamic forcing of the evaporation process, for example, due to diurnal variations in net radiation. Simulated evaporation fluxes subjected to dynamic forcing differed considerably between model concepts depending on how vapor transport in the air phase and the interaction at the interface between the free flow and porous medium were represented or parameterized. However, simulated cumulative evaporation losses from initially wet soil profiles were very similar between model concepts and mainly controlled by the desorptivity, Sevap, of the porous medium, which depends mainly on the liquid flow properties of the porous medium.

© 2016 Elsevier Ltd 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 subsurface soil conditions (e.g., soil heterogeneity and soil moisture) and are further affected by atmospheric conditions (e.g., wind and temperature). However, the transport and attenuation of methane under varying subsurface and atmospheric conditions are poorly understood, making it difficult to estimate leakage fluxes from methane concentration measurements at and above the soil surface. Based on a series of controlled bench-scale experiments using a large porous media tank interfaced with an open-return wind tunnel, this study investigated multiphase processes controlling migration of methane from a point source representing a buried pipeline leaking at fixed flow rate (kg/s) under various saturation and soil-texture conditions. In addition, potential effects of atmospheric boundary controls, wind (0.5 and 2.0 m s−1) and temperature (22 and 35 °C), were also examined. Results showed the distinct effects of soil heterogeneity and, to a varying degree, of soil moisture on surface methane concentrations. In addition, results also showed the pronounced effects of wind and, to a lesser degree, of temperature on surface methane concentrations in the presence of varying soil and moisture conditions. The observed subsurface methane profiles were simulated using the multiphase transport simulator TOUGH2-EOS7CA. Observed agreement between measured and simulated data demonstrates that for the conditions studied, multiphase migration of a multicomponent gas mixture (including methane) under density-dependent flow can be adequately represented with a Fickian advection-diffusion (or dispersion) model (ADM) framework. The dominant effect of saturation over the soil texture, could also be inferred from numerical characterization.

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 system can then be used to store renewable energy in the form of heat in the subsurface for later use. This method can be used for enhanced treatment of environmental pollutants for which temperature is considered a limiting factor. For instance, this system can be used at a wide variety of petroleum-related sites that are likely contaminated with hydrocarbons such as oil refineries and facilities with above- and underground storage tanks. In this paper, a case-study example was analyzed using a previously developed numerical model of heat transfer in unsaturated soil. Results demonstrate that coupling energy storage and thermally-enhanced bioremediation systems offer an efficient and sustainable way to achieve desired temperature&ndash, moisture distribution in soil that will ultimately enhance the microbial activity.

International audience; 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 coupled equations of mass conservation for two-phase flow in porous medium with single-phase flow in the free-flow domain under nonisothermal, nonequilibrium phase change conditions. In this model, the evaporation rate and soil surface temperature and relative humidity at the interface come directly from the integrated model output. To experimentally validate numerical results, we developed a unique test system consisting of a wind tunnel interfaced with a soil tank instrumented with a network of sensors to measure soil-water variables. Results demonstrated that, by using this coupling approach, it is possible to predict the different stages of the drying process with good accuracy. Increasing the wind speed increases the first stage evaporation rate and decreases the transition time between two evaporative stages (soil water flow to vapor diffusion controlled) at low velocity values; then, at high wind speeds the evaporation rate becomes less dependent on the wind speed. On the contrary, the impact of wind speed on second stage evaporation (diffusion-dominant stage) is not significant. We found that the thermal and solute dispersion in free-flow systems has a significant influence on drying processes from porous media and should be taken into account.