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Vadose Zone (vadose + zone)

Distribution by Scientific Domains

Engineering	65%
Earth and Environmental Science	20%
Life Sciences	10%

Selected Abstracts

Estimating Persistent Mass Flux of Volatile Contaminants from the Vadose Zone to Ground Water

GROUND WATER MONITORING & REMEDIATION, Issue 2 2009
M.J. Truex
Contaminants may persist for long time periods within low permeability portions of the vadose zone where they cannot be effectively treated and are a potential continuing source of contamination to ground water. Setting appropriate vadose zone remediation goals typically requires evaluating these persistent sources in terms of their impact on meeting ground water remediation goals. Estimating the impact on ground water can be challenging at sites with low aqueous recharge rates where vapor-phase movement is the dominant transport process in the vadose zone. Existing one-dimensional approaches for simulating transport of volatile contaminants in the vadose zone are considered and compared to a new flux-continuity-based assessment of vapor-phase contaminant movement from the vadose zone to the ground water. The flux-continuity-based assessment demonstrates that the ability of the ground water to move contaminant away from the water table controls the vapor-phase mass flux from the vadose zone across the water table. Limitations of these approaches are then discussed with respect to the required assumptions and the need to incorporate three-dimensional processes when evaluating vapor-phase transport from the vadose zone to the ground water. The carbon tetrachloride plume at the U.S. Department of Energy Hanford Site is used as the example site where persistent vadose zone contamination needs to be considered in the context of ground water remediation. [source]

An In Situ Device to Measure Oxygen in the Vadose Zone and in Ground Water: Laboratory Testing and Field Evaluation

GROUND WATER MONITORING & REMEDIATION, Issue 2 2008
Bradley M Patterson
Oxygen probes developed to measure in situ oxygen concentrations in gaseous and aqueous environments were evaluated in laboratory tests and during long-term field evaluation trials at contaminated sites. The oxygen probes were shown to have a linear calibration and to be accurate compared to conventional dissolved oxygen electrodes and gas chromatography, both of which require labor-intensive sample collection and processing. The probes, once calibrated, required no maintenance or recalibration for up to a period of 7 years in low-oxygen environments, demonstrating long-term stability. Times to achieve 90% of the stabilized concentration (t90) after a step change in aqueous oxygen concentration were 100,120 min in laboratory experiments and up to 180 min in field experiments, which is adequate for monitoring subsurface changes. Field application data demonstrated that the oxygen probes could monitor oxygen concentrations in hydrocarbon-contaminated ground water to a depth of 20 m below the water table or in pyritic vadose zones over extended periods. During bioremediation field trials, oxygen monitoring enabled estimation of oxygen utilization rates by microorganisms and hydrocarbon biodegradation rates. Also, probes were able to monitor the development of ground water desaturation during air sparging trials, enabling the automated assessment of the distribution of injected air. [source]

Presence and distribution of wastewater-derived pharmaceuticals in soil irrigated with reclaimed water

ENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 2 2006
Chad A. Kinney
Abstract Three sites in the Front Range of Colorado, USA, were monitored from May through September 2003 to assess the presence and distribution of pharmaceuticals in soil irrigated with reclaimed water derived from urban wastewater. Soil cores were collected monthly, and 19 pharmaceuticals, all of which were detected during the present study, were measured in 5-cm increments of the 30-cm cores. Samples of reclaimed water were analyzed three times during the study to assess the input of pharmaceuticals. Samples collected before the onset of irrigation in 2003 contained numerous pharmaceuticals, likely resulting from the previous year's irrigation. Several of the selected pharmaceuticals increased in total soil concentration at one or more of the sites. The four most commonly detected pharmaceuticals were erythromycin, carbamazepine, fluoxetine, and diphenhydramine. Typical concentrations of the individual pharmaceuticals observed were low (0.02,15 ,g/kg dry soil). The existence of subsurface maximum concentrations and detectable concentrations at the lowest sampled soil depth might indicate interactions of soil components with pharmaceuticals during leaching through the vadose zone. Nevertheless, the present study demonstrates that reclaimed-water irrigation results in soil pharmaceutical concentrations that vary through the irrigation season and that some compounds persist for months after irrigation. [source]

A model describing the interactions between anaerobic microbiology and geochemistry in a soil amended with glucose and nitrate

EUROPEAN JOURNAL OF SOIL SCIENCE, Issue 1 2004
F. Dassonville
Summary Under anaerobic conditions, microbes closely interact with geochemical reactions and can have an impact on the soil, the deep vadose zone, the underlying aquifer and the atmosphere. We have designed a model combining anaerobic microbial activities with geochemical reactions in the soil, and assessed it in batch experiments. The model describes the dynamics of six functional microbial communities, their decomposition after death, and the catabolism of carbohydrates through denitrification, dissimilatory NH4+ production, Fe(III) reduction, fermentation, acetogenesis, and SO42, reduction. It was combined with a model that thermodynamically describes acid,base, reduction,oxidation and complexation reactions in solution, and kinetic precipitation and dissolution. Batch incubations were done on a Calcic Cambisol, either without amendment, or after supplying (i) glucose or (ii) glucose and NO3,. Gases, mineral cations and anions, glucose, fatty acids and alcohols were measured during incubation. Net production of CO2 was similar for both glucose treatments, about 40 times larger than in the control. For the glucose treatments, the main microbial activities were fermentation, acetogenic transformation of ethanol, and oxidation of H2. When the soil was enriched with NO3,, no H2 was produced, and microbial activities were rapidly inhibited by NO2,. The model shows these trends as well as geochemical characteristics including pH and reduction,oxidation potential. [source]

Mass fractal dimension of soil macropores using computed tomography: from the box-counting to the cube-counting algorithm

EUROPEAN JOURNAL OF SOIL SCIENCE, Issue 3 2003
J.S. Perret
Summary Transport phenomena in porous media depend strongly on three-dimensional pore structures. Macropore networks enable water and solute to move preferentially through the vadose zone. A complete representation of their geometry is important for understanding soil behaviour such as preferential flow. Once we know the geometrical, topological and scaling attributes of preferential flow paths, we can begin computer simulations of water movement in the soil. The box-counting method is used in three dimensions (i.e. cube-counting algorithm) to characterize the mass fractal dimension of macropore networks using X-ray computed tomography (CT) matrices. We developed an algorithm to investigate the mass fractal dimension in three dimensions and to see how it compares with the co-dimensions obtained using the box-counting technique in two dimensions. For that purpose, macropore networks in four large undisturbed soil columns (850 mm × 77 mm diameter) were quantified and visualized, in both two and three dimensions, using X-ray CT. We observed an increasing trend between the fractal dimension and macroporosity for the four columns. Moreover, similar natural logarithm functions were obtained for the four cores by a least squares fit through plots of mass fractal dimension against macroporosity. [source]

Groundwater biodiversity patterns in the Lessinian Massif of northern Italy

FRESHWATER BIOLOGY, Issue 4 2009
DIANA M. P. GALASSI
Summary 1. The distribution patterns of stygobiotic invertebrates were examined with a stratified sampling design at 197 sites selected among four hydrogeographic basins in the Lessinian Massif (northern Italy). The sites were approximately evenly distributed among four hydrogeological zones: unsaturated and saturated zone of karstic aquifers, and hyporheic and saturated zone of porous aquifers. 2. Outlying Mean Index (OMI) analysis which assesses deviation of habitat conditions from reference conditions, was used to evaluate the importance of 14 selected environmental variables in shaping groundwater biodiversity patterns in the region (total of 89 stygobiotic species). The measured variables explained 80% of the variability in the data set. 3. Sampling sites were distributed along the environmental gradients defined by OMI analysis. Significant differences were detected between karstic and porous site, as well as among sites located in the four hydrogeological zones. Differences among the four hydrogeographic basins were not observed. 4. Ordination of stygobiotic species along the environmental gradients was best explained by historical variables (mainly Würmian glaciation and age of the underlying geological formation), while variables related to hydrogeology (mainly pH, calcium concentration and habitat fragmentation) influenced species distributions in the hydrogeological zones. An Environmental Integrity Index and nitrate concentration were significantly correlated with altitude, but appeared not to play a significant role in determining stygobiotic biodiversity patterns at the regional scale. 5. Results of the OMI analysis were highly significant for all taxa, suggesting that stygobiotic species are sensitive to the environmental factors studied. Thirty-five species showed high habitat specialisation (OMI index > 10). These species were usually rare and endemic to the Lessinian Massif. Most of them were found in a single hydrogeological zone. 6. Quaternary glaciations appear not to have lowered stygobiotic species richness in the Lessinian Massif. This may be because of the marginal location of the region with respect to the Würmian glacier limit and because of extensive networks of fractures in the vadose zone of the karst, which may have allowed stygobionts to move deep down in the aquifers to seek refuge during surface freezing and to recolonise ancestral habitats after the glaciers retreated. [source]

Estimating Persistent Mass Flux of Volatile Contaminants from the Vadose Zone to Ground Water

Treatment of a Chromate-Contaminated Soil Site by in situ Gaseous Reduction

GROUND WATER MONITORING & REMEDIATION, Issue 1 2007
E.C Thornton
A proof-of-concept field test for the treatment of hexavalent chromium in the vadose zone using in situ gaseous reduction was successfully completed by the U.S. Department of Energy and U.S. Department of Defense in a joint demonstration conducted at White Sands Missile Range, New Mexico. The test involved injecting hydrogen sulfide, diluted in air, into contaminated vadose zone sediment to reduce Cr(VI) to Cr(III). The gaseous mixture was injected directly into the contaminated sediment through a central injection well and vacuum extracted through the flow field with six boreholes at the site periphery over a 76-d period. Comparison of soil samples taken before and after the test indicated 70% of the total mass of hexavalent chromium originally present at the site was reduced and immobilized. The zone of highest contamination was nearly completely treated, with average Cr(VI) concentrations decreasing in this interval from an average of 8.1 mg/kg before treatment to 1.1 mg/kg after treatment. Treatment was best in higher permeability clean gypsum sands and less effective in zones containing greater amounts of silt and clay and a slightly higher iron content. All hexavalent chromium concentrations measured in the posttest samples, however, were well below the remedial goal and regulatory limit of 30 mg/kg. In addition, the field test demonstrated that vadose zone treatment of contamination can be safely conducted using diluted hydrogen sulfide gas mixtures. Ongoing development of the technology is being directed toward addressing the limitations of gaseous treatment arising from variations in sediment permeability and iron content and assessing the relationship between hydrogen sulfide consumption and reaction kinetics. [source]

Vapor Intrusion in Homes over Gasoline-Contaminated Ground Water in Stafford, New Jersey

GROUND WATER MONITORING & REMEDIATION, Issue 1 2006
Paul F. Sanders
The potential for chemical vapor intrusion from contaminated ground water to the interior of homes was investigated at a site with a leaking underground gasoline storage tank in Stafford Township, New Jersey. This location exhibited conditions favorable to vapor intrusion, with sand soil and a water table depth of 3.3 m. Concentrations of volatile organic chemicals in the ground water were as high as 82 mg/L for total benzene, toluene, ethylbenzene, and xylene (BTEX) and up to 590 mg/L for methyl- t -butyl ether (MTBE). Soil vapor samples at multiple depths were taken adjacent to several homes. Inside the homes, air samples were taken on the main floor, in the basement, and under the foundation slab. Despite high ground water concentrations, only one home had measurable impacts to indoor air quality attributable to some of the ground water contaminants. In this house, the BTEX chemicals were not detected in the basement, indicating a lack of indoor air impacts from the ground water for these chemicals. Oxygen measurements suggested that degradation attenuated these chemicals as they diffused through the vadose zone. However, MTBE, 2,2,4-trimethylpentane (isooctane), and cyclohexane were found in the indoor air. The first two of these chemicals served as gasoline-specific tracers and indicated that vapor intrusion was occurring. Attenuation factors (the ratio of the indoor air concentration to a source soil vapor concentration) for the BTEX chemicals between the ground water and the indoor air were <1 × 10,5, and for MTBE was 1.2 × 10,5. Attenuation factors between the deep-soil vapor and the basement air were as follows: BTEX compounds, <1 × 10,5; MTBE, 2.2 × 10,5; 2,2,4-trimethylpentane, 3.6 × 10,4; and cyclohexane, 1.2 × 10,4. Attenuation factors between the subslab vapor and the basement air were 7 to 8 × 10,3. [source]

Simultaneous estimation of diffusive Volatile Organic Compound (VOC) fluxes and Non-Aqueous Phase Liquid (NAPL) saturation in the vadose zone

GROUND WATER MONITORING & REMEDIATION, Issue 2 2005
David Werner
Soil-gas monitoring is a widely used tool to observe the migration of volatile organic compounds (VOCs) at contaminated sites. By combining this technique with natural gradient tracer methods, diffusive contaminant fluxes can be measured in situ, and non,aqueous phase liquid (NAPL) can be detected and roughly quantified. This work describes the new approach and its application at a field site in Denmark with an emplaced NAPL contamination. Soil-gas probes with a low dead volume were installed at 1-m depths in the sandy vadose zone, and a small volume of gas containing conservative and partitioning tracers was injected. Soil-gas samples were withdrawn subsequently during 1 to 4 h and analyzed simultaneously for VOCs and tracers. Tracers detected the NAPL reliably, and the combined data allowed for a close delineation of the source zone. The calculated NAPL saturation deviated by up to a factor of 3 from the analyses of soil cores. Better agreement was found by taking the NAPL composition into consideration, which is, however, generally unknown at the actual field sites. In addition, the tracers were also used to estimate effective diffusion coefficients in situ, which varied by a factor of 2 between various locations. From these data, diffusive contaminant vapor fluxes were quantified without additional laboratory experiments or the use of empirical relationships. The new approach yields a better site investigation with a few additional measurements. [source]

Tracing solute infiltration using a combined method of dye tracer test and electrical resistivity tomography in an undisturbed forest soil profile

HYDROLOGICAL PROCESSES, Issue 21 2010
Jae Gon Kim
Abstract An accurate prediction of solute infiltration in a soil profile is important in the area of environmental science, groundwater and civil engineering. We examined the infiltration pattern and monitored the infiltration process using a combined method of dye tracer test and electrical resistivity tomography (ERT) in an undisturbed field soil (1 m × 1 m). A homogeneous matrix flow was observed in the surface soil (A horizon), but a preferential flow along macropores and residual rock structure was the dominant infiltration pattern in the subsurface soil. Saturated interflow along the slopping boundaries of A and C1 horizons and of an upper sandy layer and a lower thin clay layer in the C horizon was also observed. The result of ERT showed that matrix flow started first in A horizon and then the infiltration was followed by the preferential flows along the sloping interfaces and macropores. The ERT did not show as much detail as the dye-stained image for the preferential flow. However, the area with the higher staining density where preferential flow was dominant showed a relatively lower electrical resistivity. The result of this study indicates that ERT can be applied for the monitoring of solute transportation in the vadose zone. Copyright © 2010 John Wiley & Sons, Ltd. [source]

Thermal influence of urban groundwater recharge from stormwater infiltration basins

HYDROLOGICAL PROCESSES, Issue 12 2009
Arnaud Foulquier
Abstract Groundwater warming below cities has become a major environmental issue; but the effect of distinct local anthropogenic sources of heat on urban groundwater temperature distributions is still poorly documented. Our study addressed the local effect of stormwater infiltration on the thermal regime of urban groundwater by examining differences in water temperature beneath stormwater infiltration basins (SIB) and reference sites fed exclusively by direct infiltration of rainwater at the land surface. Stormwater infiltration dramatically increased the thermal amplitude of groundwater at event and season scales. Temperature variation at the scale of rainfall events reached 3 °C and was controlled by the interaction between runoff amount and difference in temperature between stormwater and groundwater. The annual amplitude of groundwater temperature was on average nine times higher below SIB (range: 0·9,8·6 °C) than at reference sites (range: 0,1·2 °C) and increased with catchment area of SIB. Elevated summer temperature of infiltrating stormwater (up to 21 °C) decreased oxygen solubility and stimulated microbial respiration in the soil and vadose zone, thereby lowering dissolved oxygen (DO) concentration in groundwater. The net effect of infiltration on average groundwater temperature depended upon the seasonal distribution of rainfall: groundwater below large SIB warmed up (+0·4 °C) when rainfall occurred predominantly during warm seasons. The thermal effect of stormwater infiltration strongly attenuated with increasing depth below the groundwater table indicating advective heat transport was restricted to the uppermost layers of groundwater. Moreover, excessive groundwater temperature variation at event and season scales can be attenuated by reducing the size of catchment areas drained by SIB and by promoting source control drainage systems. Copyright © 2009 John Wiley & Sons, Ltd. [source]

Hydrological behaviour and modelling of a volcanic tropical cultivated catchment

HYDROLOGICAL PROCESSES, Issue 22 2008
Jean-Baptiste Charlier
Abstract The hydrological behaviour of the cultivated Féfé catchment (17·8 ha) on the tropical volcanic island of Guadeloupe was studied to identify flow paths, to quantify water fluxes, and finally, to build a lumped model to simulate discharge and piezometer levels. The approach combined two steps, an experimental step and a modelling step, which covered two time scales, the annual and the storm event scale. The hydrological measurements were conducted over 2 years. The Féfé catchment is characterized by heavy rainfall (4229 mm year,1) on permeable Andosols; the results showed that underground flow paths involved two overlapping aquifers, and that the annual water balance in 2003 was shared among outflows of the deep aquifer (42%), evapotranspiration (31%), and streamflow (27%). On the event scale, the surface runoff coefficient ranges between 6·2% and 24·4% depending on antecedent dry or wet moisture conditions. Hortonian overland flow predominated over subsurface and saturation overland flow processes. Recharge of the shallow aquifer is mainly governed by a constant infiltration capacity of the Andosols with depth in the vadose zone. Outflows of this shallow aquifer were the baseflow of the main stream and the recharge of the deep aquifer. Volcanic deposits at Féfé promoted the underground flow path, and cultivated areas seemed to explain the high stormflow values relative to other tropical small catchments under rain forest. A conceptual lumped model integrating runoff, infiltration, evapotranspiration, and fluctuations of the two overlapping aquifers was developed. The model has six parameters and was calibrated and validated on the hydrograph at the outlet and on the two piezometers of the shallow and the deep aquifers. The results show fair to good agreement between measured and simulated variables, and consequently, the model was consistent with the main hydrological processes observed from experimental results in wet conditions. Copyright © 2008 John Wiley & Sons, Ltd. [source]

Simulating soil-water movement under a hedgerow surrounding a bottomland reveals the importance of transpiration in water balance

HYDROLOGICAL PROCESSES, Issue 5 2008
Z. Thomas
Abstract The objective of this study was to quantify components of the water balance related to root-water uptake in the soil below a hedgerow. At this local scale, a two-dimensional (2D) flow domain in the x,z plane 6 m long and 1·55 m deep was considered. An attempt was made to estimate transpiration using a simulation model. The SWMS-2D model was modified and used to simulate temporally and spatially heterogeneous boundary conditions. A function with a variable spatial distribution of root-water uptake was considered, and model calibration was performed by adjusting this root-water uptake distribution. Observed data from a previous field study were compared against model predictions. During the validation step, satisfactory agreement was obtained, as the difference between observed and modelled pressure head values was less than 50 cm for 80% of the study data. Hedge transpiration capacity is a significant component of soil-water balance in the summer, when predicted transpiration reaches about 5·6 mm day,1. One of the most important findings is that hedge transpiration is nearly twice that of a forest canopy. In addition, soil-water content is significantly different whether downslope or upslope depending on the root-water uptake. The high transpiration rate was mainly due to the presence of a shallow water table below the hedgerow trees. Soil-water content was not a limiting factor for transpiration in this context, as it could be in one with a much deeper water table. Hedgerow tree transpiration exerts a strong impact not only on water content within the vadose zone but also on the water-table profile along the transect. Results obtained at the local scale reveal that the global impact of hedges at the catchment scale has been underestimated in the past. Transpiration rate exerts a major influence on water balance at both the seasonal and annual scales for watersheds with a dense network of hedgerows. Copyright © 2007 John Wiley & Sons, Ltd. [source]

A probabilistic investigation of infiltration in the vadose zone: proposal for a new formula of infiltration rate

HYDROLOGICAL PROCESSES, Issue 21 2007
Erick Carlier
Abstract The infiltration rate in the unsaturated zone is analysed from a probabilistic point of view. It is shown that the empirical formulas of Horton and Kostiakov, without apparent physical basis, are explained in a probabilistic approach. Horton's formula reflects a Markovian process contrary to Kostiakov's formula. This approach made it possible to explain why Kostiakov's formula is more powerful than that of Horton. A new equation of infiltration is proposed. The three formulas were compared, for four types of soil, with the model of van Genuchten based on the Richards equation. Copyright © 2006 John Wiley & Sons, Ltd. [source]

Unusual preservation of crustaceans and microbial colonies in a vadose zone, northwest Morocco

LETHAIA, Issue 1 2003
MICHAEL J. DUANE
Exceptional fossil preservation is observed in self-sealing microcavities in limestones where lichens, cyanobacteria and fungi together entombed themselves and organic walled microfossils, crustaceans and their eggs. Preservation has been enabled by calcite coating, lining and impregnation of the exoskeleton of the crustaceans, which had a high original calcium content and acted as a nucleus for precipitation. The good preservation was facilitated by the microcavities, the surrounding limestone, the seasonality and rapidity of precipitation, the microbial colonies living on the specimens, and the fluxing of vadose waters through the karst. The microbes and the crustaceans probably became trapped by the very high rate of calcite precipitation promoted within the cavities. Entrapment in mucous-secreting mats of cyanobacteria and fungi preceded the destruction of some of the soft parts of the crustaceans. By the time the mats and the incorporated biota were sealed into the cavities in the limestone, the mucosic mats and their bacterial communities had mediated production of a range of calcite cements promoting preservation of the refractory tissues. This process has important implications for cementation studies in arid zones (and especially in the Martian subsurface), since a range of microbes are involved in progressive biomineralization leading to fossilization within a perched, vadose karst. [source]

A rain water infiltration model with unilateral boundary condition: qualitative analysis and numerical simulations

MATHEMATICAL METHODS IN THE APPLIED SCIENCES, Issue 17 2006
I. Borsi
Abstract We present a rigorous mathematical treatment of a model describing rain water infiltration through the vadose zone in case of runoff of the excess water. The main feature of the mathematical problem emerging from the model lies on the boundary condition on the ground surface which is in the form of a unilateral constraint. Existence and uniqueness of a weak solution is proved under general assumptions. We present also the results of a numerical study comparing the proposed model with other models which approach in a different way the rain water infiltration problem. Copyright © 2006 John Wiley & Sons, Ltd. [source]

Ordovician Carbonate Reservoir Bed Characteristics and Reservoir-Forming Conditions in the Lungudong Region of the Tarim Basin

ACTA GEOLOGICA SINICA (ENGLISH EDITION), Issue 5 2010
WANG Weili
Abstract: Basic characteristics of Ordovician carbonate reservoir beds in the Lungudong region of northeastern part of the Tarim Basin are described in detail and the reservoir-forming conditions of oil and gas are preliminarily discussed in this paper by collecting and sorting out a large amount of data. The carbonate reservoir beds are mainly developed in open-platform and platform marginal facies; the reservoir beds have large changes in and low average values of physical property; the main type is fractured reservoir beds with the fracture-porous type second. The reservoir bed development is chiefly controlled by the distribution of sedimentary facies, tectonic activity and karstification. Whereas the accumulation and distribution of hydrocarbons in the region are controlled by an advantageous structural location, a good reservoir-caprock combination and a favorable transporting system, with the distribution characterized by zones horizontally and belts vertically, the oil and gas are mainly concentrated in areas with structural uplift, densely developed fractures, and surface karst, a vertical vadose zone, and a horizontal undercurrent belt of palaeokarst. [source]