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1.
Estimates of contaminant fluxes from DNAPL sources as a function of time and DNAPL mass reduction are important to assess the long-term sustainability and costs of monitored natural attenuation and to determine the benefits of partial source removal. We investigate the accuracy of the upscaled mass transfer function (MTF) proposed by Parker and Park [Parker JC, Park E. Modeling field-scale dense nonaqueous phase liquid dissolution kinetics in heterogeneous aquifers. WRR 2004;40:W05109] to describe field-scale dissolved phase fluxes from DNAPL sources for a range of scenarios generated using high-resolution 3-D numerical simulations of DNAPL infiltration and long-term dissolved phase transport. The results indicate the upscaled MTF is capable of accurately describing field-scale DNAPL dissolution rates as a function of time. For finger-dominated source regions, an empirical mass depletion exponent in the MTF takes on values greater than one which results in predicted mass flux rates that decrease continuously with diminishing DNAPL mass over time. Lens-dominated regions exhibit depletion exponents less than one, which results in more step-function like mass flux versus time behavior. Mass fluxes from DNAPL sources exhibiting both lens- and finger-dominated subregions were less accurately described by the simple MTF, but were well described by a dual-continuum model of the same form for each subregion. The practicality of calibrating a dual-continuum model will likely depend on the feasibility of obtaining spatially resolved field measurements of contaminant fluxes or concentrations associated with the subregions using multilevel sampling or some other means.  相似文献   

2.
Simulation of biodegradation of chlorinated solvents in dense non-aqueous phase liquid (DNAPL) source zones requires a model that accounts for the complexity of processes involved and that is consistent with available laboratory studies. This paper describes such a comprehensive modeling framework that includes microbially mediated degradation processes, microbial population growth and decay, geochemical reactions, as well as interphase mass transfer processes such as DNAPL dissolution, gas formation and mineral precipitation/dissolution. All these processes can be in equilibrium or kinetically controlled. A batch modeling example was presented where the degradation of trichloroethene (TCE) and its byproducts and concomitant reactions (e.g., electron donor fermentation, sulfate reduction, pH buffering by calcite dissolution) were simulated. Local and global sensitivity analysis techniques were applied to delineate the dominant model parameters and processes. Sensitivity analysis indicated that accurate values for parameters related to dichloroethene (DCE) and vinyl chloride (VC) degradation (i.e., DCE and VC maximum utilization rates, yield due to DCE utilization, decay rate for DCE/VC dechlorinators) are important for prediction of the overall dechlorination time. These parameters influence the maximum growth rate of the DCE and VC dechlorinating microorganisms and, thus, the time required for a small initial population to reach a sufficient concentration to significantly affect the overall rate of dechlorination. Self-inhibition of chlorinated ethenes at high concentrations and natural buffering provided by the sediment were also shown to significantly influence the dechlorination time. Furthermore, the analysis indicated that the rates of the competing, nonchlorinated electron-accepting processes relative to the dechlorination kinetics also affect the overall dechlorination time. Results demonstrated that the model developed is a flexible research tool that is able to provide valuable insight into the fundamental processes and their complex interactions during bioremediation of chlorinated ethenes in DNAPL source zones.  相似文献   

3.
A two-dimensional numerical transport model is developed to determine the effect of aquifer anisotropy and heterogeneity on mass transfer from a dense nonaqueous phase liquid (DNAPL) pool. The appropriate steady state groundwater flow equation is solved implicitly whereas the equation describing the transport of a sorbing contaminant in a confined aquifer is solved by the alternating direction implicit method. Statistical anisotropy in the aquifer is introduced by two-dimensional, random log-normal hydraulic conductivity field realizations with different directional correlation lengths. Model simulations indicate that DNAPL pool dissolution is enhanced by increasing the mean log-transformed hydraulic conductivity, groundwater flow velocity, and/or anisotropy ratio. The variance of the log-transformed hydraulic conductivity distribution is shown to be inversely proportional to the average mass transfer coefficient.  相似文献   

4.
《Advances in water resources》2007,30(6-7):1618-1629
Residual dense non-aqueous liquids (NAPLs) in aquifers constitute a great challenge for groundwater cleanup. Active engineered treatment of regions that contain residual NAPLs is often required to shorten the long-term impact of NAPLs on groundwater quality. Enhanced residual NAPL cleanup can be achieved by promoting biodegradation of NAPL components in the aqueous phase, thereby increasing contaminant fluxes from the NAPL phase. Reaction-enhanced NAPL dissolution is often mathematically simulated under the assumption that lumped mass transfer coefficients, used to describe the dissolution behavior of the NAPL phase, are independent of the reactions. However, this assumption is not warranted because reactions occurring near the water–NAPL interface can reduce characteristic mass transfer lengths, which tend to enhance mass transfer over the no-reaction case.In this study, we mathematically investigated the connections between lumped mass transfer coefficients and reaction kinetics over an idealized residual NAPL domain. Since mass transfer is frequently a scale-dependent process, we also examined the influence of system extent on mass transfer coefficients. For our idealized domain with an assumed first-order decay reaction, the results show that lumped mass transfer coefficients depend on reaction kinetics and system scale. The mass transfer coefficient derived from the non-reactive case cannot properly represent the mass transfer process under the reactive conditions. When the advection time scale is long in comparison to the transverse dispersion time scale in the system, a fast reaction can increase significantly the lumped mass transfer coefficient. The mass transfer coefficient used for simulation was also found to be affected by the nature of the numerical scheme used.  相似文献   

5.
A model is presented for estimating vapor concentrations in buildings because of volatilization from soil contaminated by non- aqueous phase liquids (NAPL) or from dissolved contaminants in ground water. The model considers source depletion, diffusive- dispersive transport of the contaminant of concern (COC) and of oxygen and oxygen-limited COC biodecay. Diffusive-advective transport through foundations and vapor losses caused by foundation cross-flow are considered. Competitive oxygen use by various species is assumed to be proportional to the product of the average dissolved-phase species concentration and a biopreference factor. Laboratory and field data indicate the biopreference factor to be proportional to the organic carbon partition coefficient for the fuel hydrocarbons studied. Predicted indoor air concentrations were sensitive to soil type and subbase permeability. Lower concentrations were predicted for buildings with shallow foundations caused by flushing of contaminants by cross-flow. NAPL source depletion had a large impact on average exposure concentration. Barometric pumping had a minor effect on indoor air emissions for the conditions studied. Risk-based soil cleanup levels were much lower when biodecay was considered because of the existence of a threshold source concentration below which no emissions occur. Computed cleanup levels at NAPL-contaminated sites were strongly dependent on total petroleum hydrocarbon (TPH) content and COC soil concentration. The model was applied to two field sites with gasoline-contaminated ground water. Confidence limits of predicted indoor air concentrations spanned approximately two orders of magnitude considering uncertainty in model parameters. Measured contaminant concentrations in indoor air were within model-predicted confidence limits.  相似文献   

6.
Parameter estimation in nonlinear environmental problems   总被引：5，自引：4，他引：1  
Popular parameter estimation methods, including least squares, maximum likelihood, and maximum a posteriori (MAP), solve an optimization problem to obtain a central value (or best estimate) followed by an approximate evaluation of the spread (or covariance matrix). A different approach is the Monte Carlo (MC) method, and particularly Markov chain Monte Carlo (MCMC) methods, which allow sampling from the posterior distribution of the parameters. Though available for years, MC methods have only recently drawn wide attention as practical ways for solving challenging high-dimensional parameter estimation problems. They have a broader scope of applications than conventional methods and can be used to derive the full posterior pdf but can be computationally very intensive. This paper compares a number of different methods and presents improvements using as case study a nonlinear DNAPL source dissolution and solute transport model. This depth-integrated semi-analytical model approximates dissolution from the DNAPL source zone using nonlinear empirical equations with partially known parameters. It then calculates the DNAPL plume concentration in the aquifer by solving the advection-dispersion equation with a flux boundary. The comparison is among the classical MAP and some versions of computer-intensive Monte Carlo methods, including the Metropolis–Hastings (MH) method and the adaptive direction sampling (ADS) method.  相似文献   

7.
The influence of model dimensionality on predictions of mass recovery from dense non-aqueous phase liquid (DNAPL) source zones in nonuniform permeability fields was investigated using a modified version of the modular three-dimensional transport simulator (MT3DMS). Thirty-two initial two- (2D) and three-dimensional (3D) tetrachloroethene–DNAPL source zone architectures, taken from a recent modeling study, were used as initial conditions for this analysis. Commonly employed source zone metrics were analyzed to determine differences between 2D and 3D predictions: (i) down-gradient flux-averaged contaminant concentration, (ii) reductions in contaminant mass flux through a down-gradient boundary, (iii) source zone ganglia-to-pool (GTP) ratio, and (iv) time required to achieve a remediation objective. 3D flux-averaged contaminant concentrations were approximately 3.5 times lower than concentrations simulated in 2D. This difference was attributed to dilution of the contaminant concentrations down gradient of the source zone. Contaminant flux reduction predictions for a given mass recovery were generally 5% higher in 3D simulations than in 2D simulations. The GTP ratio declined over time as mass was recovered in both 2D and 3D simulations. Although the source longevity (i.e., time required to achieve 99.99% mass recovery) differed between individual 2D and 3D realizations, the mean source longevity for the 2D and 3D simulation ensembles was within 2%. 2D simulations tended to over-predict the time required to achieve lower mass recovery levels (e.g. 50% mass recovery) due to a smaller contaminated area exposed to uncontaminated water. These findings suggest that ensemble averages of 2D numerical simulations of DNAPL migration, entrapment, dissolution, and mass recovery in statistically homogenous, nonuniform media may provide reasonable approximations to average behavior obtained using simulations conducted in fully three-dimensional domains.  相似文献   

8.
《Advances in water resources》2004,27(11):1045-1059
Transient and steady-state analytical solutions are derived to investigate solute transport in a fractured porous medium consisting of evenly spaced, parallel discrete fractures. The solutions incorporate a finite width strip source, longitudinal and transverse dispersion in the fractures, source decay, aqueous phase decay, one-dimensional diffusion into the matrix, sorption to fracture walls, and sorption within the matrix. The solutions are derived using Laplace and Fourier transforms, and inverted by interchanging the order of integration and utilizing a numerical Laplace inversion algorithm. The solutions are verified for simplified cases by comparison to solutions derived by Batu [Batu V. A generalized two-dimensional analytical solution for hydrodynamic dispersion in bounded media with the first-type condition at the source. Wat Resour Res 1989;25(6):1125] and Sudicky and Frind [Sudicky EA, Frind EO. Contaminant transport in fractured porous media: analytical solutions for a system of parallel fractures. Wat Resour Res 1982;18(6):1634]. The application of the solutions to a fractured sandstone demonstrates that narrower source widths and larger values of transverse dispersivity both lead to lower downstream concentrations in the fractures and shorter steady-state plumes. The incorporation of aqueous phase decay and source concentration decay both lead to lower concentrations and shorter plumes, with even moderate amounts of decay significantly shortening the persistence of contamination.  相似文献   

9.
We investigate a special type of variability in response spectral amplification ratios computed from numerical “engineering” models for a soft soil site. The engineering models are defined by shallow soil layers over “engineering” bedrock with a shear-wave velocity over 600–700 m/s and the model is subjected to vertical propagating shear waves. The variability, perhaps unique in earthquake engineering, is a result of the “perfectly accurate” computational procedure. For example, an engineering soil site model, subjected to two rock site records or the two horizontal components of a rock site record, produces different response spectral amplification ratios. We use a large number of strong-motion records from “engineering” rock sites, with a reasonably balanced distribution with respect to magnitude and source distance, generated by subduction earthquakes in Japan, to investigate the nature of the variability. In order to avoid any approximation in removing the effect of soil nonlinear response, we use a simple model, a single horizontal soil layer over a bedrock, modelled as elastic. We then demonstrate that a similar type of variability observed in the one- or two-dimensional nonlinear soil models is caused by the nature of response spectral amplification ratios, not a direct result of soil nonlinear response. Examination of variability reveals that the average of response spectral amplification ratios systematically depends on both earthquake magnitude and source distance. We find that, at periods much longer than the site natural periods of the soil sites, the scatter of the amplification ratios decreases with increasing magnitude and source distance. These findings may have a potential impact in establishing design spectra for soft soil sites using strong-motion attenuation models or dynamic numerical modelling.  相似文献   

10.
A field demonstration was performed at Edwards Air Force Base to assess bioaugmentation for treatment of a well‐characterized tetrachloroethene (PCE) dense nonaqueous phase liquid (DNAPL) source area in fractured rock. Groundwater recirculation was employed to deliver remedial amendments, including bacteria, to facilitate reductive dechlorination and enhance DNAPL dissolution. An active treatment period of 9 months was followed by a 10‐month posttreatment rebound evaluation. Dechlorination daughter products were observed in both the shallow and deep fracture zones following treatment. In the shallow fracture zone, the calculated DNAPL mass removed was approximately equal to the DNAPL mass estimated using partitioning tracer testing, and no rebound in chlorinated ethenes or ethene was observed during the posttreatment period. A maximum DNAPL dissolution enhancement factor of 5 was observed in the shallow fracture zone. In the deep fracture zone, only approximately 45% of the DNAPL mass—as estimated via partitioning tracer testing—was removed and rebound in the total molar chlorinated ethenes + ethene was observed. The difference in behavior between the shallow and deep fracture zones was attributed to DNAPL architecture and the fracture flow field.  相似文献   

11.
The release of stored dissolved contaminants from low permeability zones contributes to plume persistence beyond the time when dense nonaqueous phase liquid (DNAPL) has completely dissolved. This is fundamental to successfully meeting acceptable low concentrations in groundwater that are driven by site‐specific cleanup goals. The study goals were to assess the role of DNAPL entrapment morphology on mass storage and plume longevity. As controlled field studies are not feasible, two‐dimensional (2D) test tanks were used to quantify the significance of mass loading processes from source dissolution and stored mass rebound. A simple two‐layer soil domain representing a high permeable formation sand overlying a zone of lower permeability sand was used in the tests. DNAPL mass depletion through dissolution was monitored via X‐ray photon attenuation, and effluent samples were used to monitor the plume. These data enabled analysis of the DNAPL distribution, the dissolved plume, and the dissolved phase distribution within the low permeability layer. Tests in an intermediate tank showed that mass storage contributes substantially to plume longevity. Detectable effluent concentrations persisted long after DNAPL depletion. The small tank results indicated that the DNAPL morphology influenced the flow field and caused distinctive transport mechanisms contributing to mass storage. Zones of high DNAPL saturation at the interface between the low and high permeability layers exhibited flow bypassing and diffusion dominated transport into the low permeability layer. In the absence of a highly saturated DNAPL zone near the soil interface the contaminant penetrated deeper into the low permeability layer caused by a combination of advection and diffusion.  相似文献   

12.
《Advances in water resources》2007,30(6-7):1547-1561
Recent laboratory experimental evidence has suggested that bioremediation may be an attractive management strategy for dense non-aqueous phase liquid (DNAPL) source-zones. In particular, metabolic reductive dechlorination has been shown to reduce aqueous phase chlorinated ethene contaminant concentrations and enhance DNAPL dissolution, reducing source longevity. Transitioning this technology from the laboratory to the field will be facilitated by tools capable of simulating bioenhanced dissolution. This work presents a mathematical model for metabolic reductive dechlorination in a macroscale two-phase (aqueous-organic) environment. The model is implemented through adaptation of an existing multi-phase compositional simulator, which has been modified to incorporate eight chemical components and four microbial populations: a fermentative population, two dechlorinating populations, and a competitor population (e.g., methanogens). Monod kinetics, modified to incorporate electron donor thresholds, electron acceptor competition, and competitor inhibition, are used to simulate microbial growth and component degradation. The developed model is numerically verified and demonstrated through comparisons with published column-scale dechlorination data. Dechlorination kinetics, electron donor concentrations, and DNAPL saturation and distribution are all found to affect the extent of dissolution enhancement, with enhancements ranging from 1.0 to ∼1.9. Comparison of simulation results with those from a simplified analytic modeling approach suggest that the analytical model may tend to over-predict dissolution enhancement and fail to account for the transient nature of dissolution enhancement, leading to significant (70%) under-prediction of source longevity.  相似文献   

13.
Analytical expressions for the exact 2 × 2 one-way propagator matrix of a plane S wave, propagating along the axis of spirality in the simple 1-D anisotropic simplified twisted crystal model, are presented. The analytical equations are useful in testing the applicability and accuracy of various approximate wavefield modelling methods, especially of the coupling ray theory and of its various quasi-isotropic approximations and various numerical implementations.In addition to the exact analytical solution of the elastodynamic equation in the simplified twisted crystal model, the analytical solutions of the equations of the four ray methods are given. The ray methods are (a) the coupling ray theory, (b) the coupling ray theory with the quasi-isotropic perturbation of travel times, (c) the anisotropic ray theory, (d) the isotropic ray theory. These four approximate solutions of the elastodynamic equation are roughly compared with the exact solution. Both the exact analytical solution and the analytical ray-theory solutions in the simplified twisted crystal model are also helpful in debugging computer codes for various approximate wavefield modelling methods, especially for the coupling ray theory.  相似文献   

14.
Hydraulic displacement is a mass removal technology suitable for stabilization of a dense, nonaqueous phase liquid (DNAPL) source zone, where stabilization is defined as reducing DNAPL saturations and reducing the risk of future pool mobilization. High resolution three-dimensional multiphase flow simulations incorporating a spatially correlated, heterogeneous porous medium illustrate that hydraulic displacement results in an increase in the amount of residual DNAPL present, which in turn results in increased solute concentrations in groundwater, an increase in the rate of DNAPL dissolution, and an increase in the solute mass flux. A higher percentage of DNAPL recovery is associated with higher initial DNAPL release volumes, lower density DNAPLs, more heterogeneous porous media, and increased drawdown of groundwater at extraction wells. The fact that higher rates of recovery are associated with more heterogeneous porous media stems from the fact that larger contrasts in permeability provide for a higher proportion of capillary barriers upon which DNAPL pooling and lateral migration can occur. Across all scenarios evaluated in this study, the ganglia-to-pool (GTP) ratio generally increased from approximately 0.1 to between approximately 0.3 and 0.7 depending on the type of DNAPL, the degree of heterogeneity, and the imposed hydraulic gradient. The volume of DNAPL recovered as a result of implementing hydraulic displacement ranged from between 9.4% and 45.2% of the initial release volume, with the largest percentage recovery associated with 1,1,1 trichloroethane, the least dense of the three DNAPLs considered.  相似文献   

15.
The Earth's mantle contains a mixture of primordial noble gases, in particular solar-type helium and neon, and radiogenic rare gases from long-lived U, 232Th, 40K and short-lived 129I, 244Pu. Rocks derived from deep mantle plume magmatism like on Hawaii or Iceland contain a higher proportion of primordial nuclides than rocks from the shallow upper mantle, e.g. mid ocean ridge basalts (MORBs). This is widely regarded as the key evidence for survival of a less degassed and more “primitive” reservoir within the lower mantle. We present an evaluation of noble gas composition showing the shallow mantle to have about five times more radiogenic (relative to primordial) isotopes than Hawaii/Iceland-type plume reservoirs, no matter if short- or long-lived decay systems are considered. This fundamental property suggests that both MORB and plume-type noble gases are mixtures of: (1) a homogeneous radiogenic component present throughout most of the mantle and (2) a uniform primordial noble gas component with very minor radiogenic ingrowth. This conclusion depends crucially on the observed excess of radiogenic Xe in plume-derived rocks, and is only valid if this Xe excess is inherent to the plume sources.Possible sources of the primordial component of mantle plume reservoirs—and possibly also the MORB mantle—could be mantle reservoirs that remained relatively isolated over most of Earth's history (“blobs”, a deep abyssal layer, or the D” layer), but these need a considerable concentration of primordial gases to compensate U, Th, K decay over 4.5 Ga. Earth's core is evaluated as an alternative viable source feeding primordial nuclides into mantle reservoirs: even low metal-silicate partitioning coefficients allow sufficient primordial noble gases to be incorporated into the early forming core, as the undifferentiated proto-Earth was initially gas-rich. Massive mantle degassing soon after core formation then provides the opposite concentration gradient that allows primordial noble gases reentering the mantle at the core-mantle boundary, probably via partial mantle melts. Another possible source of primordial noble gases in Earth's mantle are subducted sediments containing extraterrestrial dust with solar He and Ne, but this supply mechanism crucially depends on largely unconstrained parameters. The latter two scenarios do not require the preservation of a “primitive” mantle reservoir over 4.5 Ga, and can potentially better reconcile increasing geochemical evidence of recycled lithospheric components in mantle plumes and seismic evidence for whole mantle convection.  相似文献   

16.
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17.
The spontaneous expansion and mobilization of discontinuous gas above dense non-aqueous-phase liquid (DNAPL) pools can affect the aqueous-phase concentrations of the DNAPL constituents above the pool. The results of an intermediate-scale, two-dimensional flow cell experiment showed that the discontinuous gas flow produced by spontaneous expansion, driven by the partitioning of 1,1,1-TCA from the surface of a DNAPL pool, resulted in detectable aqueous-phase concentrations of 1,1,1-TCA well above the pool surface. In comparison to a conventional model for DNAPL pool dissolution in the absence of a discontinuous gas phase, these concentrations were greater than expected, and were present at greater than expected elevations. Additionally, this study showed that the discontinuous gas flow produced transient behavior in the aqueous-phase concentrations, where the elevated concentrations occurred as short-term, pulse-like events. These results suggest that the spontaneous expansion and mobilization of discontinuous gas in DNAPL source zones could lead to the misdiagnosis of source zone architecture using aqueous concentration data, and that the transient nature of the elevated concentrations could further complicate the difficult task of source zone characterization.  相似文献   

18.
At sites where a dense nonaqueous phase liquid (DNAPL) was spilled or released into the subsurface, estimates of the mass of DNAPL contained in the subsurface from core or monitoring well data, either in the nonaqueous or aqueous phase, can be highly uncertain because of the erratic distribution of the DNAPL due to geologic heterogeneity. In this paper, a multiphase compositional model is applied to simulate, in detail, the DNAPL saturations and aqueous-phase plume migration in a highly characterized, heterogeneous glaciofluvial aquifer, the permeability and porosity data of which were collected by researchers at the University of Tübingen, Germany. The DNAPL saturation distribution and the aqueous-phase contaminant mole fractions are then reconstructed by sampling the data from the forward simulation results using two alternate approaches, each with different degrees of sampling conditioning. To reconstruct the DNAPL source zone architecture, the aqueous-phase plume configuration, and the contaminant mass in each phase, one method employs the novel transition probability/Markov chain approach (TP/MC), while the other involves a traditional variogram analysis of the sampled data followed by ordinary kriging. The TP/MC method is typically used for facies and/or hydraulic conductivity reconstruction, but here we explore the applicability of the TP/MC method for the reconstruction of DNAPL source zones and aqueous-phase plumes. The reconstructed geometry of the DNAPL source zone, the dissolved contaminant plume, and the estimated mass in each phase are compared using the two different geostatistical modeling approaches and for various degrees of data sampling from the results of the forward simulation. It is demonstrated that the TP/MC modeling technique is robust and accurate and is a preferable alternative compared to ordinary kriging for the reconstruction of DNAPL saturation patterns and dissolved-phase contaminant plumes.  相似文献   

19.
This study presents a multiphase flow and multispecies reactive transport model for the simultaneous simulation of NAPL and groundwater flow, dissolution, and reactive transport with isotope fractionation, which can be used for better interpretation of NAPL-involved Compound Specific Isotope Analysis in 3D heterogeneous hydrogeologic systems. The model was verified for NAPL-aqueous phase equilibrium partitioning, aqueous phase multi-chain and multi-component reactive transport, and aqueous phase multi-component transport with isotope fractionation. Several illustrative examples are presented to investigate the effect of DNAPL spill rates, degradation rate constants, and enrichment factors on the temporal and spatial distribution of the isotope signatures of chlorinated aliphatic hydrocarbon groundwater plumes. The results clearly indicate that isotope signatures can be significantly different when considering multiphase flow within the source zone. A series of simulations indicate that degradation and isotope enrichment compete with dissolution to determine the isotope signatures in the source zone: isotope ratios remain the same as those of the source if dissolution dominates the reaction, while heavy isotopes are enriched in reactants along groundwater plume flow paths when degradation becomes dominant. It is also shown that NAPL composition can change from that of the injected source due to the partitioning of components between the aqueous and NAPL phases even when degradation is not allowed in NAPL phase. The three-dimensional simulation is presented to mechanistically illustrate the complexities in determining and interpreting the isotopic signatures with evolving DNAPL source architecture.  相似文献   

20.
Field investigations were carried out to determine the occurrence of tetrachloroethene (PCE) dense nonaqueous phase liquid (DNAPL), the source zone architecture and the aquitard integrity at a 30‐ to 50‐year old DNAPL release site. The DNAPL source zone is located in the clay till unit overlying a limestone aquifer. The DNAPL source zone architecture was investigated through a multiple‐lines‐of‐evidence approach using various characterization tools; the most favorable combination of tools for the DNAPL characterization was geophysical investigations, membrane interface probe, core subsampling with quantification of chlorinated solvents, hydrophobic dye test with Sudan IV, and Flexible Liner Underground Technologies (FLUTe) NAPL liners with activated carbon felt (FACT). While the occurrence of DNAPL was best determined by quantification of chlorinated solvents in soil samples supported by the hydrophobic dye tests (Sudan IV and NAPL FLUTe), the conceptual understanding of source zone architecture was greatly assisted by the indirect continuous characterization tools. Although mobile or high residual DNAPL (S t > 1%) only occurred in 11% of the source zone samples (intact cores), they comprised 86% of the total PCE mass. The dataset, and associated data analysis, supported vertical migration of DNAPL through fractures in the upper part of the clay till, horizontal migration along high permeability features around the redox boundary in the clay till, and to some extent vertical migration through the fractures in the reduced part of the clay till aquitard to the underlying limestone aquifer. The aquitard integrity to DNAPL migration was found to be compromised at a thickness of reduced clay till of less than 2 m.  相似文献   

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