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1.
Screening level models are now commonly used to estimate vapor intrusion for subsurface volatile organic compounds (VQCs). Significant uncertainty is associated with processes and models and, to date, there has been only limited field-based evaluation of models for this pathway. To address these limitations, a comprehensive evaluation of the Johnson and Ettinger (J&E) model is provided through sensitivity analysis, comparisons of model-predicted to measured vapor intrusion for 11 petroleum hydrocarbon and chlorinated solvent sites, and review of radon and flux chamber studies. Significant intrusion was measured at five of 12 sites with measured vapor attenuation ratios (αm's) (indoor air/source vapor) ranging from ∼1 × 10−6 to 1 × 10−4. Higher attenuation ratios were measured for studies using radon, inert tracers, and flux chambers; however, these ratios are conservative owing to boundary conditions and tracer properties that are different than those at most VOC-contaminated sites. Reasonable predictions were obtained using the J&E model with comparisons indicating that model-predicted vapor attenuation ratios (αp's) were on the same order, or less than the αm's. For several sites, the αm were approximately two orders of magnitude less than the αp's indicating that the J&E model is conservative in these cases. The model comparisons highlight the importance in using appropriate input parameters for the J&E model. The regulatory implications associated with use of the J&E model to derive screening criteria are also discussed.  相似文献   

2.
Azimuth-dependent AVO in reservoirs containing non-orthogonal fracture sets   总被引：1，自引：0，他引：1  
Azimuthal anisotropy in rocks can result from the presence of one or more sets of partially aligned fractures with orientations determined by the stress history of the rock. The symmetry of a rock with horizontal bedding that contains two or more non-orthogonal sets of vertical fractures may be approximated as monoclinic with a horizontal plane of mirror symmetry. For offsets that are small compared with the depth of the reflector, the azimuthal variation in P-wave AVO gradient for such a medium varies with azimuth as     where φ is the azimuth measured with respect to the fast polarization direction for a vertically polarized shear wave. φ 2 depends on both the normal compliance B N and the shear compliance B T of the fractures and may differ from zero if B N B T varies significantly between fracture sets. If B N B T is the same for all fractures,     and the principal axes of the azimuthal variation in P-wave AVO for fixed offset are determined by the polarization directions of a vertically propagating shear wave. At larger offsets, terms in     and     are required to describe the azimuthal variation in AVO accurately. φ 4 and φ 6 also depend on B N B T. For gas-filled open fractures     but a lower value of B N B T may result from the presence of a fluid with non-zero bulk modulus.  相似文献   

3.
The Guelph Permeameter (GP) method for simultaneous, in situ measurement in the vadose zone of field-saturated hydraulic conductivity (KfS), sorptivity (S) and the conductivity-pressure head relationship [K(Ψ)] is described and discussed.
The method involves measuring the steady-state liquid recharge, Q, necessary to maintain a constant depth of water, H, in an uncased, cylindrical well of radius, a, finished above the water table. An "in-hole" Mariotte bottle device is used to maintain H and to measure Q.
Step-by-step procedures with example calculations are given for obtaining KfS, S and K( Ψ ). Techniques for assessing the results are also given.
Although detailed field verification of the GP method is still incomplete, the studies conducted so far are quite encouraging.
Theoretical and practical advantages afforded by the GP method make it a desirable and cost-effective means for in situ measurement of Kfs, S and K( Ψ ), which are three of the most important parameters governing the flow of water and other wetting liquids in the vadose zone.  相似文献   

4.
Screening level models are now commonly used to estimate vapor intrusion for subsurface volatile organic compounds (VOCs). Significant uncertainty is associated with processes and models and, to date, there has been only limited field-based evaluation of models for this pathway. To address these limitations, a comprehensive evaluation of the Johnson and Ettinger (J&E) model is provided through sensitivity analysis, comparisons of model-predicted to measured vapor intrusion for 11 petroleum hydrocarbon and chlorinated solvent sites, and review of radon and flux chamber studies. Significant intrusion was measured at five of 12 sites with measured vapor attenuation ratios (αm's) (indoor air/source vapor) ranging from ∼1 × 10−6 to 1 × 10−4. Higher attenuation ratios were measured for studies using radon, inert tracers, and flux chambers; however, these ratios are conservative owing to boundary conditions and tracer properties that are different than those at most VOC-contaminated sites. Reasonable predictions were obtained using the J&E model with comparisons indicating that model-predicted vapor attenuation ratios (αp's) were on the same order, or less than the αm's. For several sites, the (m were approximately two orders of magnitude less than the a 's indicating that the J&E model is conservative in these cases. The model comparisons highlight the importance in using appropriate input parameters for the J&E model. The regulatory implications associated with use of the J&E model to derive screening criteria are also discussed.  相似文献   

5.
The one-dimensional pressure head profile above a fixed water-table was studied for different steady infiltration rates. As shown in previous studies, when the infiltration rate (qin) is less than the soil saturated hydraulic conductivity (Ks), this profile can be divided into two parts: (1) from the water-table surface (z0) to an elevation zγ, the pressure head varies from 0 to a value hγ such as K(hγ)=−qin; (2) above the elevation zγ the pressure head is constant and equal to hγ. Above the water-table the zone where the pressure head is variable has been called ‘transition zone’. Its height is shown to be highly variable and to depend on soil properties as well as on the infiltration rate. This transition zone is not the ‘capillary fringe’ as defined by Gillham (Gillham R.W., 1984. The capillary fringe and its effect on water-table response. J. Hydrol. 67, 307–324). Numerical experiments performed with HYDRUS-2D® for the case of a water-table drained by parallel ditches have shown that the height of the transition zone is similar in the one-dimensional profile and in the two-dimensional system as long as the local slope of the water-table is small. This result is important since in a two-dimensional system, the transition zone is the place where all the horizontal component of the unsaturated flow occurs. The ratio of the horizontal component of the unsaturated flow vs the total horizontal flow in both the unsaturated and saturated zones has been computed. For a given soil, this ratio decreases as the infiltration rate increases; for a given infiltration rate, the soil with the thinnest transition zone transfers the largest amount of water above the water-table.  相似文献   

6.
An important quantity in groundwater protection is the residence time of water in an aquifer. It relates to both the travel time of a pollutant to arrive at a well and the time span required for self-purification of a polluted aquifer after removal of pollutant inputs. Time scales for aquifers can be gained from artificial tracer experiments or from environmental tracer data, the latter offering the only realistic alternative if time scales of years or decades have to be taken into account.

Different tracers show different time scales due to their different transport mechanisms especially in the unsaturated zone. While solute tracers are moved advectively with the seepage water, gas tracers pass the unsaturated zone diffusively through the air phase. Depending on the properties of the unsaturated zone (hydraulic properties, thickness) this difference in behavior can be used to separate the subsurface transport process into the unsaturated and the saturated parts.

In a field study in Germany, SF6 and 3H were used as environmental tracers. Both have a relatively well-known input function. Interpretation of data from observation wells by a box model approach led to spatially and temporally varying residence times. This was an indication that the influence of the unsaturated zone could not be neglected. While the gas tracer SF6 shows only residence times in the saturated zone, the tracer 3H reflects the whole travel time of water including both the unsaturated and saturated zones. Using a one-dimensional plug-flow model for the unsaturated zone combined with a detailed two-dimensional flow and transport model for the saturated zone leads to a holistic and consistent interpretation of the measured tracer concentrations. The observed pattern of old water under thick loess cover and younger water under areas where the fractured basalt aquifer crops out is reproduced after adjusting only two parameters: the effective porosity of the saturated aquifer and the product of field capacity and thickness of the unsaturated zone. While the effective porosity of the saturated zone is adjusted by means of the SF6 data, the field capacity of the loess layer is adjusted by means of the 3H observations. The thickness of the unsaturated zone is deduced from geological and pedological maps. All flow data are obtained from a calibrated flow model, which is based on geological data, observed heads and pumping tests only.

The transport model for the saturated zone was calibrated by fitting the porosity by means of gaseous tracer concentrations (SF6). The combined saturated–unsaturated zone model was then calibrated by fitting the field capacity of the unsaturated zone by means of 3H concentrations. With this model it was possible to verify the observed NO3 concentrations at the drinking water wells and to develop predictions for their future development under various scenarios of fertilizer input reduction in specific areas.  相似文献   


7.
A second occurrence of chrome-rich clinopyroxene has been discovered as inclusions in orthopyroxene in orthopyroxenite from Maowu, the Dabie Mountains, Central China. The average formula for chrome-rich clinopyroxene can be expressed as (Na0.39Ca0.54)0.93(Mg0.57Fe2+0.06Fe3+0.01Cr0.24Al0.15)1.03Si2.02O6, with a maximum amount of kosmochlor component of 28.52 mol%. The unit cell parameters obtained from a single-crystal are a  = 9.614 Å, b  = 8.800 Å, c =  5.240 Å, β = 106.59°, space group C2 / c . The indices of refraction are α = 1.697, β = 1.704, γ = 1.726. Chrome-rich clinopyroxene, which coexists with chromite, chromian rutile and chromian pyrope, crystallized at a temperature of 1025 °C and very high pressure, and therefore represents a mantle relic. Together with the appearance of low-pressure inclusion mineral assemblage and the estimation of physical–chemical conditions for matrix minerals, the Maowu eclogite–ultramafic complex is considered to be formed during ultrahigh-pressure metamorphism from the mantle-derived protolith.  相似文献   

8.
A direct aqueous injection capillary gas chromatography/flame ionization (GC/FID) procedure for the analysis of petroleum-contaminated water was developed and applied to seven water samples saturated with different petroleum products. Separation of C1 to C4 alcohols, C6 to C9 monoaromatics, MTBE, phenol, aniline, and other compounds, and the detection of BTEX compounds at concentrations at or below their maximum contaminant levels (MCLs) is reported. Among the test compounds analyzed, the only pair found to coelute were 1-butanol and benzene. A method for confirmation of alcohols and polar compounds in the presence of dissolved petroleum hydrocarbons was also evaluated. In this case, water samples were analyzed before and after purging. Polar compounds were found to be significant components of the water soluble fractions of commercial petroleum products.  相似文献   

9.
Abstract Rocks from Karaginsky accretionary prism (Karaginsky Island, Bering Sea) yield both prefolding (close to original) and postfolding magnetic vectors. The prefolding vectors suggest that the Maastrichtian–Paleocene volcanic–terrigenous sequences of Karaginsky Island formed at approximately 40°N to 50°N ( n = 45, D G = 325, I G = 57, K G = 6, α95G = 8, F G = 15.06, D S = 332, I S = 63, K S = 20, α95S = 4.5, F S = 0.3297, F cr = 2.64) and were not originally part of either Eurasia ( F = 19, Δ F = 6.5) or North America ( F = 17, Δ F = 4.4). The geologic blocks rotated insignificantly counterclockwise about the horizontal plane, suggesting that the structure of Karaginsky Island arose without major strike-slip motions. Analysis of secondary magnetizations (for example, n = 28, D G = 311, I G = − 50, K G = 9, α95G = 8.7, F G = 2.44; D S = 293, I S = − 41, K S = 5, α95S = 11, F S = 12.04, F cr = 2.65) reveals that the development of this framework involved at least two stages of deformation. During the second stage the sequences must have been tilted to west-northwest and northwest directions at 45–65°. This agrees with the northwest vergence of the structure of Karaginsky Island.  相似文献   

10.
Infiltration systems are widely used as an effective urban stormwater control measure. Most design methods and models roughly approximate the complex physical flow processes in these systems using empirical equations and fixed infiltration rates to calculate emptying times from full. Sophisticated variably saturated flow models are available, but rarely applied owing to their complexity. This paper describes the development and testing of an integrated one‐dimensional model of flow through the porous storage of a typical infiltration system and surrounding soils. The model accounts for the depth in the storage, surrounding soil moisture conditions and the interaction between the storage and surrounding soil. It is a front‐tracking model that innovatively combines a soil‐moisture‐based solution of Richard's equation for unsaturated flow with piston flow through a saturated zone as well as a reservoir equation for flow through a porous storage. This allows the use of a simple non‐iterative numerical solution that can handle ponded infiltration into dry soils. The model is more rigorous than approximate stormwater infiltration system models and could therefore be valuable in everyday practice. A range of test cases commonly used to test soil water flow models for infiltration in unsaturated conditions, drainage from saturation and infiltration under ponded conditions were used to test the model along with an experiment with variable depth in a porous storage over saturated conditions. Results show that the model produces a good fit to the observed data, analytical solutions and Hydrus. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

11.
The area surrounding the Colorado Department of Transportation Materials Testing Laboratory in Denver was the subject of intense investigation, involving the collection of thousands of ground water, soil-gas, and indoor air samples in order to investigate indoor air impacts associated with a subsurface release of chlorinated solvents. The preremediation portion of that data set is analyzed and reduced in this work to ground water–to-indoor air attenuation factors (αgw= the ratio of the measured indoor air concentration to the soil-gas concentration predicted to be in equilibrium with the local ground water concentration). The empirical αgw values for this site range from about 10−6 to 10−4 with an overall average of 3 × 10−5 (μg/L indoor air)/(μg/L soil gas). The analysis of this data set highlights the need for a thorough data review and data screening when using large data sets to derive empirical relationships between subsurface concentrations and indoor air. More specifically, it is necessary to identify those parts of the data that contain a strong vapor intrusion pathway signal, which generally will require concentrations well above reported detection levels combined with spatial or temporal correlation of subsurface and indoor concentrations.  相似文献   

12.
Air Channel Formation, Size, Spacing, and Tortuosity During Air Sparging   总被引：4，自引：0，他引：4  
Characterizing mass transfer during in situ air sparging requires knowledge of the size, shape, and interfacial area of air channels. These characteristics were determined by analysis of digital images of air channels passing through submerged glass beads having particle size in the sand range. Pore-scale channeling occurred in all cases. The analysis showed that the air channels were narrower, more tortuous, more closely spaced, and moved nearly vertically through the coarser media. In the finer media, air channels had larger diameter, were spaced further apart, and passed nearly horizontally through the media. The mean diameter of the channels varied between 2.8 and 8.1 mm, and the mean spacing varied between 8.3 and 19.4 mm. Estimates of the area of the air-water interface per unit volume of soil (a0), computed using data from the digital images and an assumed arrangement of channels, ranged from 0.02 to 0.2 mm2/mm3. Larger a0 were obtained for coarser media and uniformly graded media. These estimates of a0 compare well with published values for common packed-column materials and for unsaturated soils.  相似文献   

13.
Treatment of nitrogen in landfill leachate has received considerable attention recently because of the relatively low levels at which some nitrogen species (i.e., NH3) can be toxic to aquatic life forms. This study reports on the results of a three-year, pilot-scale field trial demonstrating the use of infiltration bed and nitrate barrier technology to achieve nitrogen removal in landfill leachate. The infiltration bed comprises an unsaturated sand layer overlying a saturated layer of waste cellulose solids (sawdust), which acts as a carbon source for heterotrophic denitrification. When loaded at a rate of 1 to 3 cm/day, the infiltration bed was successful at lowering leachate inorganic nitrogen (NH4++ NO3-) levels averaging 24.8 mg/L N by 89%, including 96% in the third year of operation. The surface water discharge criteria for un-ionized ammonia (NH3) were met on all occasions in the treated leachate during the second and third years of operation. Nitrogen attenuation is presumed to occur by a two-step process in which leachate NH4+ is first oxidized to NO3- in the unsaturated sand layer and then is converted to nitrogen gas (N2) by denitrification occurring in the underlying sawdust layer. Mass balance calculations suggest that the sawdust layer has sufficient carbon to allow denitrification to proceed for long periods (1.0 to 30 years) without replenishment. Because this technology is simple to construct and is relatively maintenance free, it should be attractive for use at smaller landfills where the installation of conventional treatment plants may not be feasible.  相似文献   

14.
Hydraulic properties of saturated and unsaturated stony soils were studied on a 3.35 m long column, 1.24 m in diameter, filled with alternating sand and boulder layers. The boulders averaged 6.2 × 15 × 20 cm in size and were laid down on their flat side. Tensiometers and a neutron probe access tube were placed in the column for measuring pressure heads and water contents, respectively. Saturated conditions were obtained by ponding the column. The resulting hydraulic conductivity K was 5.1 m/day. This value could also be calculated from the measured K for the sand alone on separate samples, using a simple equation that takes into account the void ratio of the sand alone and that of the boulder-sand mixture. Unsaturated K was determined by applying water at less than ponded infiltration rates. Resulting relations between the unsaturated K and water content or negative pressure head could also be estimated from the relation between unsaturated K and pressure head for the sand alone and the calculated saturated K of the boulder-sand mixture. The method of Millington and Quirk for calculating the relation between unsaturated K and water content also gave reasonable results. The dispersivity of the boulder-sand column was 18 times that of the sand alone. Pore velocity was accurately estimated as the Darcy velocity divided by the volumetric water content. Hydraulic properties of stony vadose zones are difficult to determine. This work shows that they can be estimated from K relations measured in the laboratory on samples of the soil between the rocks. Knowledge of hydraulic properties of vadose zones is important in predicting movement of water and pollutants to the underlying ground water.  相似文献   

15.
Tomohiro  Toki  Toshitaka  Gamo  Urumu  Tsunogai 《Island Arc》2006,15(3):285-291
Abstract   We collected free-gas and in situ fluid samples up to a depth of 200.6 m from the Sagara oil field, central Japan (34°44'N, 138°15'E), during the Sagara Drilling Program (SDP) and measured the concentrations and stable carbon isotopic compositions of CH4 and C2H6 in the samples. A combination of the CH4/C2H6 ratios with the carbon isotope ratios of methane indicates that the hydrocarbon gases are predominantly of thermogenic origin at all depths. The isotope signature of hydrocarbon gases of δ13      < δ13     suggests that these gases in the Sagara oil field are not generated by polymerization, but by the decomposition of organic materials.  相似文献   

16.
Abstract Deformation in the Sanbagawa Belt is characterized by ductile flow in an east-west direction sub-parallel to its length. The east-west flow (D1) caused large-scale recumbent folding of the metamorphic sequence in central Shikoku, which can explain the inverted thermal structure of this region. Chemical zoning of metamorphic minerals associated with D1 microstructures also suggest that the east-west flow developed under retrograde conditions. D1 is therefore related to exhumation rather than subduction processes. A variety of kinematic indicators show that during the east-west flow, deformation was partitioned into structurally continuous domains with opposed senses of shear. This suggests that bulk deformation was not simple shear but included a component of flattening.  相似文献   

17.
Measurements of CO2 fluxes from ground surface of the atmosphere (soil respiration) are needed to quantify biotic and abiotic reaction rates in unsaturated zones and to gain insight into the importance of these processes on global warming. The use of three techniques (dynamic closed chambers, static chambers, and gradient calculations) to determine soil respiration was assessed by measuring fluxes of microbially produced CO2 from an unsaturated mesocosm (2.4 m dia.×3.2 m thick) and two unsaturated minicosms (0.58 m dia.×1.2 m thick), one maintained at 18–23 °C (HT) and the other at 5 °C (LT). By injecting known and constant CO2 fluxes into the bottom of the HT minicosm and measuring the resulting fluxes, it was shown that the dynamic closed chamber (DCCS) technique yielded accurate measurements of fluxes over the range observed from natural unsaturated media. Over this same range, results showed that the concentration gradient method yielded reasonable estimates of fluxes but its accuracy was limited by uncertainties in both the concentration gradient and the gaseous diffusion coefficient in the soil atmosphere. The static chamber method underestimated the actual flux at higher CO2 fluxes and when adsorption times of >24 h were used.  相似文献   

18.
The goal of this study was the cleanup of residual solvents in the saturated zone using an in situ biochemical treatment. Perchloroethylene (PCE) was chosen as a model compound because it is the most commonly found organic ground water contaminant. A mixture of vitamin B12 with titanium citrate was pumped as the remedial solution through a column containing 100 μL of PCE residual. The rate of reaction was found to be first order with respect 10 the concentration of PCE and to the concentration of vitamin B2. At 10 ppm B12, more than 85 percent PCM was degraded to trichloroelhylene (TCE) and dichloroelhylene (DCE) in two hours. The presence of low to moderate concentrations of organic carbon had no significant effect on the reaction. Vitamin B12 reduced by titanium citrate was found lo be compatible with the survival of anaerobic bacteria. The four major advantages of the biochemical system over the use of anaerobic bacteria are that (1) the rate is faster: (2) there is no need for the careful balance of nutrients or the addition of an extraneous carbon source: (3) there is no restriction in the concentration range of the compound to be treated; and (4) the remedial solution is mobile, even in the presence of organic carbon.  相似文献   

19.
Electromigration is proposed as an in situ method for preconcentrating contaminants in ground water prior to pumping and treating. In earlier investigations by the senior author and co-workers, it was found that Cu in synthetic ground water migrated strongly to a Pt cathode and plated out as metallic copper. In the present study, carbon electrodes were inserted into a laboratory column of fine quartz sand that was saturated with a lower concentration of CuSO4 solution. A fixed potential of 2.5 V was applied, causing dissolved Cu and SO4 to accumulate strongly at the cathode and anode, respectively. Only minor plating-out of Cu took place on the carbon electrodes. In addition to the use of carbon electrodes, the present research also investigated the effects of a lower concentration of metal, accumulation of SO4 adjacent to the anodes, adsorption of Cu on the sand, and competition by moving ground water.
At an imposed voltage of 2.5 V and in the presence of 65 mg/L of dissolved Cu and 96 mg/L of SO4 (0.001 M CuSO4 solution), electrolysis of water caused large changes in the pH and speciation of the aqueous components, as well as precipitation of solid Cu-hydroxides. Significant retardation of Cu occurred in the presence of ground water flowing at an average intergranular velocity of 0.2 m/day, but only minor retardation at water velocities of 1.9 and 2.9 m/day.
Sulfate tends to migrate strongly to the anodes, suggesting that in situ electromigration may offer a useful new method for preconcentrating such highly soluble ions as SO4, NO3, and CI that are difficult to remove by conventional pump-and-treat methods. A number of potential problems exist that should be addressed in a field test.  相似文献   

20.
Non-unique solutions of inverse problems arise from a lack of information that satisfies necessary conditions for the problem to be well defined. This paper investigates these conditions for inverse modeling of water flow through multi-dimensional variably saturated porous media. It shows that in order to obtain a unique estimate of hydraulic parameters, along each streamline of the flow field (1) spatial and temporal head observations must be given; (2) the number of spatial and temporal head observations required should be greater or equal to the number of unknown parameters; (3) the flux boundary condition or the pumping rate of a well must be specified for the homogeneous case and both boundary flux and pumping rate are a must for the heterogeneous case; (4) head observations must encompass both saturated and unsaturated conditions, and the functional relationships for unsaturated hydraulic conductivity/pressure head and for the moisture retention should be given, and (5) the residual water content value also need to be specified a priori or water content measurements are needed for the estimation of the saturated water content.For field problems, these necessary conditions can be collected or estimated but likely involve uncertainty. While the problems become well defined and have unique solutions, the solutions likely will be uncertain. Because of this uncertainty, stochastic approaches are deemed to be appropriate for inverse problems as they are for forward problems to address uncertainty. Nevertheless, knowledge of these necessary conditions is critical to reduce uncertainty in both characterization of the vadose zone and the aquifer, and prediction of water flow and solute migration in the subsurface.  相似文献   

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