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  • 1
    Language: English
    In: Water Research, 01 May 2016, Vol.94, pp.120-127
    Description: Global warming and urbanization together with development of subsurface infrastructures (e.g. subways, shopping complexes, sewage systems, and Ground Source Heat Pump (GSHP) systems) will likely cause a rapid increase in the temperature of relatively shallow groundwater reservoirs (subsurface thermal pollution). However, potential effects of a subsurface temperature change on groundwater quality due to changed physical, chemical, and microbial processes have received little attention. We therefore investigated changes in 34 groundwater quality parameters during a 13-month enhanced-heating period, followed by 14 months of natural or enhanced cooling in a confined marine aquifer at around 17 m depth on the Saitama University campus, Japan. A full-scale GSHP test facility consisting of a 50 m deep U-tube for circulating the heat-carrying fluid and four monitoring wells at 1, 2, 5, and 10 m from the U-tube were installed, and groundwater quality was monitored every 1–2 weeks. Rapid changes in the groundwater level in the area, especially during the summer, prevented accurate analyses of temperature effects using a single-well time series. Instead, Dual-Well Analysis (DWA) was applied, comparing variations in subsurface temperature and groundwater chemical concentrations between the thermally-disturbed well and a non-affected reference well. Using the 1 m distant well (temperature increase up to 7 °C) and the 10 m distant well (non-temperature-affected), the DWA showed an approximately linear relationships for eight components (B, Si, Li, dissolved organic carbon (DOC), Mg , NH , Na , and K ) during the combined 27 months of heating and cooling, suggesting changes in concentration between 4% and 31% for a temperature change of 7 °C.
    Keywords: Subsurface Thermal Pollution ; Ground Source Heat Pump (Gshp) Systems ; Long-Term Heating and Cooling ; Confined Marine Aquifer ; Dual-Well Analysis (Dwa) ; Groundwater Quality ; Engineering
    ISSN: 0043-1354
    E-ISSN: 1879-2448
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  • 2
    Language: English
    In: Journal of Hazardous Materials, 2010, Vol.179(1), pp.573-580
    Description: Quantifying the spatial variability of factors affecting natural attenuation of hydrocarbons in the unsaturated zone is important to (i) performing a reliable risk assessment and (ii) evaluating the possibility for bioremediation of petroleum-polluted sites. Most studies to date have focused on the shallow unsaturated zone. Based on a data set comprising analysis of about 100 soil samples taken in a 16 m-deep unsaturated zone polluted with volatile petroleum compounds, we statistically and geostatistically analysed values of essential soil properties. The subsurface of the site was highly layered, resulting in an accumulation of pollution within coarse sandy lenses. Air-filled porosity, readily available phosphorous, and the first-order rate constant ( ) of benzene obtained from slurry biodegradation experiments were found to depend on geologic sample characterization ( 〈 0.05), while inorganic nitrogen was homogenously distributed across the soil stratigraphy. Semivariogram analysis showed a spatial continuity of 4–8.6 m in the vertical direction, while it was 2–5 times greater in the horizontal direction. Values of displayed strong spatial autocorrelation. Even so, the soil potential for biodegradation was highly variable, which from autoregressive state-space modeling was partly explained by changes in soil air-filled porosity and gravimetric water content. The results suggest considering biological heterogeneity when evaluating the fate of contaminants in the subsurface.
    Keywords: Biological Heterogeneity ; Petroleum Vapors ; Spatial Variability ; Semivariogram Analysis ; State-Space Modeling ; Engineering ; Law
    ISSN: 0304-3894
    E-ISSN: 1873-3336
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  • 3
    Language: English
    In: Soil Science Society of America journal, 2011, Vol.75(4), pp.1315-1329
    Description: Accurate predictions of the soil-gas diffusivity (Dp/Do, where Dp is the soil-gas diffusion coefficient and Do is the diffusion coefficient in free air) from easily measureable parameters like air-filled porosity (ε) and soil total porosity (ϕ) are valuable when predicting soil aeration and the emission of greenhouse gases and gaseous-phase contaminants from soils. Soil type (texture) and soil density (compaction) are two key factors controlling gas diffusivity in soils. We extended a recently presented density-corrected Dp(ε)/Do model by letting both model parameters (α and β) be interdependent and also functions of ϕ. The extension was based on literature measurements on Dutch and Danish soils ranging from sand to peat. The parameter α showed a promising linear relation to total porosity, while β also varied with α following a weak linear relation. The thus generalized density-corrected (GDC) model gave improved predictions of diffusivity across a wide range of soil types and density levels when tested against two independent data sets (total of 280 undisturbed soils or soil layers) representing Danish soil profile data (0–8 m below the ground surface) and performed better than existing models. The GDC model was further extended to describe two-region (bimodal) soils and could describe and predict Dp/Do well for both different soil aggregate size fractions and variably compacted volcanic ash soils. A possible use of the new GDC model is engineering applications such as the design of highly compacted landfill site caps. ; p. 1315-1329.
    Keywords: Data Collection ; Sand ; Soil Profiles ; Texture ; Landfills ; Prediction ; Engineering ; Soil Density ; Porosity ; Models ; Peat ; Greenhouse Gas Emissions ; Aeration ; Air ; Volcanic Ash Soils ; Diffusivity
    ISSN: 0361-5995
    E-ISSN: 14350661
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  • 4
    Language: English
    In: Journal of Geotechnical and Geoenvironmental Engineering, July, 2011, Vol.137(7), p.653(10)
    Description: Landfill sites have been implicated in greenhouse warming scenarios as a significant source of atmospheric methane. In this study, the effects of extreme compaction on the two main soil-gas transport parameters, the gas diffusion coefficient ([D.sub.p]) and the intrinsic air permeability ([k.sub.a]), and the cumulative methane oxidation rate in a landfill cover soil were investigated. Extremely compacted landfill cover soil exhibited negligible inactive soil-air contents for both [D.sub.p] and ka. In addition, greater [D.sub.p] and [k.sub.a] were observed as compared with normal compacted soils at the same soil-air content ([epsilon]), likely because of reduced water-blockage effects under extreme compaction. These phenomena are not included in existing predictive models for [D.sub.p]([epsilon]) and ka([epsilon]). On the basis of the measured data, new predictive models for [D.sub.p]([epsilon]) and ka([epsilon]) were developed with model parameters (representing air-filled pore connectivity and water-blockage effects) expressed as functions of dry density ([[rho].sub.b]). The developed [D.sub.p] ([epsilon]) and [k.sub.a] (e) models together with soil-water retention data for soils at normal and extreme compaction ([[rho].sub.b] = 1.44 and 1.85 g [cm.sup.-3]) implied that extremely compacted soils will exhibit lower [D.sub.p] and [k.sub.a] at natural field-water content (-100 cm [H.sub.2]O of soil-water matric potential) because of much lower soil-air content. Numerical simulations of methane gas transport, including a first-order methane oxidation rate, were performed for differently compacted soils by using the new predictive [D.sub.p]([epsilon]) model. Model results showed that compaction-induced difference in soil-air content at a given soil-water matric potential condition is likely the most important parameter governing methane oxidation rates in extremely compacted landfill cover soil. DOI: 10.1061/(ASCE)GT.1943-5606.0000459. CE Database subject headings: Landfills; Coverings; Gas; Parameters; Methane. Author keywords: Landfill final cover soil; Gas transport parameters; Compaction.
    Keywords: Atmospheric Carbon Dioxide -- Analysis ; Waste Management -- Analysis ; Methane -- Analysis ; Permeability -- Analysis ; Natural Gas Transmission -- Analysis
    ISSN: 1090-0241
    E-ISSN: 19435606
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  • 5
    Language: English
    In: Waste Management, 2011, Vol.31(12), pp.2464-2472
    Description: ► The effects of soil physical properties on gas transport parameters were investigated. ► Higher values of and exhibited in the ‘+gravel’ than the ‘−gravel’ fraction at same soil–air content ( ). ► Recent power law models for (WLR) and (RPL) were modified. ► Model parameters were linearly related to easily measurable dry bulk density ( ). Landfill sites are emerging in climate change scenarios as a significant source of greenhouse gases. The compacted final soil cover at landfill sites plays a vital role for the emission, fate and transport of landfill gases. This study investigated the effects of dry bulk density, , and particle size fraction on the main soil–gas transport parameters – soil–gas diffusivity ( / , ratio of gas diffusion coefficients in soil and free air) and air permeability ( ) – under variably-saturated moisture conditions. Soil samples were prepared by three different compaction methods (Standard and Modified Proctor compaction, and hand compaction) with resulting values ranging from 1.40 to 2.10 g cm . Results showed that and values for the ‘+gravel’ fraction (〈35 mm) became larger than for the ‘−gravel’ fraction (〈2 mm) under variably-saturated conditions for a given soil–air content ( ), likely due to enhanced gas diffusion and advection through less tortuous, large-pore networks. The effect of dry bulk density on and was most pronounced for the ‘+gravel’ fraction. Normalized ratios were introduced for all soil–gas parameters: (i) for gas diffusivity / , the ratio of measured to in total porosity ( ), (ii) for air permeability / , the ratio of measured to at 1235 kPa matric potential (=pF 4.1), and (iii) for soil–air content, the ratio of soil–air content ( ) to total porosity ( ) (air saturation). Based on the normalized parameters, predictive power-law models for ( / ) and ( / ) models were developed based on a single parameter (water blockage factor for and for ). The water blockage factors, and , were found to be linearly correlated to values, and the effects of dry bulk density on and for both ‘+gravel’ and ‘−gravel’ fractions were well accounted for by the new models.
    Keywords: Air Permeability ; Gas Diffusivity ; Dry Bulk Density ; Landfill Final Cover ; Engineering ; Chemistry
    ISSN: 0956-053X
    E-ISSN: 1879-2456
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  • 6
    Language: English
    In: Journal of Hazardous, Toxic, and Radioactive Waste, 10/2011, Vol.15(4), pp.275-284
    Description: Understanding colloid mobilization, transport, and deposition in the subsurface is a prerequisite for predicting colloid-facilitated transport of strongly adsorbing contaminants and further developing remedial activities. This study investigated the transport behavior of soil-colloids extracted from a red-yellow soil from Okinawa, Japan. Different concentrations of suspended-soil colloids (with diameter 〈1  μm) were applied, at different flow velocities and pH conditions, to 10-cm long water-saturated columns repacked with either Narita (mean diameter D50=0.64  mm) or Toyoura (mean diameter D50=0.21  mm) sands. The transport and retention of colloids were studied by analyzing colloid effluent breakthrough curves (BTCs), particle size distribution in the effluent, and colloid deposition profiles within the column. The results showed a significant influence of flow velocity: Low flow velocity caused tailing of colloid BTCs with higher reversible entrapment and release of colloids than high flow velocity. The finer Toyoura sand retained more colloids than the coarser Narita sand at low pH conditions. The deposition profile and particle size distribution of colloids in the Toyoura sand clearly indicated a depth-dependent straining mechanism. By fitting colloid transport models (one-site and two-site models) to the colloid effluent breakthrough curves, transport and deposition of colloids in Narita sand at low pH were best described by a one-site attachment-detachment model, whereas colloid transport and deposition in Toyoura sand at low pH were better captured by a two-site attachment, detachment, and straining model. The coupled effects of solution chemistry, colloid sizes, and medium surface properties have a dominating role in particle-particle and particle-collector interactions in colloid transport and deposition.
    Keywords: Technical Papers ; Engineering;
    ISSN: 2153-5493
    E-ISSN: 2153-5515
    Source: American Society of Civil Engineers (via CrossRef)
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  • 7
    Language: English
    In: Soils and Foundations, August 2016, Vol.56(4), pp.676-690
    Description: Mass transport in soils occurs through pore networks that are highly affected by basic physical properties such as the degree of compaction, and particle size and shape. In this study, micro-focus X-ray computed tomography (CT) was used to obtain information on the pore network structure at different compaction levels for repacked columns of sands and glass beads representing different size fractions and particle shapes. Mass transport parameters, including gas diffusion coefficient ( ) and air permeability ( ) at variably saturated conditions, were measured on the same columns using standard methods, and literature data on saturated hydraulic conductivity ( ) for the same materials were analyzed. A comparison of X-ray CT derived pore network structure and physical parameters showed that the round sands and glass beads exhibited larger pores, a higher pore coordination number, and a lower volumetric surface area than that of angular sands at the same particle size, resulting in higher as well as higher and under relatively dry conditions. The X-ray CT derived the mean pore diameter ( ), and the pore coordination number ( ) for each material correlated well with key gas transport properties such as percolation thresholds and pore network connectivity. A predictive model from wet to dry conditions based fully on X-ray CT derived parameters ( and ) was developed and showed good agreement with measured for both round and angular sands.
    Keywords: Micro-Focus X-Ray CT ; Pore Structure ; Mass Transport Parameters ; Engineering
    ISSN: 0038-0806
    Source: ScienceDirect Journals (Elsevier)
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  • 8
    Language: English
    In: Water, Air, & Soil Pollution, 2014, Vol.225(9), pp.1-13
    Description: Biochar, a by-product resulting from the pyrolysis of biomass, is considered to be an anthropogenic carbonaceous sorbent. Despite a worldwide increase in the application of biochar on agricultural fields to improve crop productivity over the past few decades, there have been few studies on their influences on the sorption of environmental contaminants. In a field-based study at two experimental sites in Denmark, we investigated the effect of birch wood-derived biochar ( Skogans kol ) on the sorption of phenanthrene in soils with different properties. The soil sorption coefficient, K d (L kg −1 ), of phenanthrene was measured on sandy loam and loamy sand soils which have received from zero up to 100 t ha −1 of biochar. Results show that birch wood biochar had a higher K d compared to soils. Furthermore, the application of birch wood biochar enhanced the sorption of phenanthrene in agricultural soils, and the enhancement effect increased with an increasing biochar application rate. Aging, repeated application, and higher clay content suppressed the biochar enhancement effect on the sorption of phenanthrene. Phenanthrene K d was found to be strongly and positively correlated with both total and non-complexed organic carbon, while negatively correlated with clay content. The results also revealed that biochar–mineral interactions play an important role in the sorption of phenanthrene in biochar-amended soil.
    Keywords: Phenanthrene ; Biochar ; Sorption ; Organic carbon
    ISSN: 0049-6979
    E-ISSN: 1573-2932
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  • 9
  • 10
    Language: English
    In: Journal of Environmental Engineering, 2017, Vol.143(7)
    Description: Transport of microbubbles and nanobubbles (MNBs) in porous media has drawn increasing attention as a promising technology for soil and groundwater remediation. Understanding the transport mechanisms of MNBs in soils is essential to optimize MNB-based remediation techniques. In this study, effects of flow rates and bubble gas species on transport characteristics of MNBs were investigated in columns packed with glass beads. Microbubbles and nanobubbles were created by either air or oxygen injection to the columns at different flow rates. All results showed marked entrapment of MNBs inside the columns and relatively higher retardation of MNBs with smaller bubble size. The entrapment was enhanced for air-based MNBs under lower flow rate. A convection-dispersion model including bubble attachment could well capture the obtained effluent curves for MNB transport at high flow conditions. For low flow conditions, a model including bubble attachment-detachment and straining terms best described the data. The fitted model parameters suggested that irreversible straining is an important deposition mechanism for MNB transport in porous media.
    Keywords: Groundwater – Environmental Aspects ; Microbubbles – Research ; Microbubbles – Usage ; Porous Materials – Research ; Soil Chemistry – Environmental Aspects
    ISSN: 0733-9372
    E-ISSN: 19437870
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