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  • 1.
    Bottacin-Busolin, Andrea
    et al.
    Univ Padua, Dept Hydraul Maritime Environm & Geotech Engn.
    Marion, Andrea
    Univ Padua, Dept Hydraul Maritime Environm & Geotech Engn.
    Combined role of advective pumping and mechanical dispersion on time scales of bed form-induced hyporheic exchange2010In: Water resources research, ISSN 0043-1397, E-ISSN 1944-7973, Vol. 46, p. W08518-Article in journal (Refereed)
    Abstract [en]

    This study analyzes the effect of advective pumping and pore scale dispersion on bed form-induced hyporheic exchange. Advection and dispersion play a competitive role in the exchange dynamics between the porous medium and the overlying stream: Advective fluxes first lead solutes deep into the bed and then back to the stream water, whereas dispersive fluxes favor the transfer of solutes deep into the bed leading to a permanent mass retention. The combined effect of advective exchange and dispersive fluxes produces complexity in the shape of the tails of the residence time distributions (RTDs), which follow at various stages of the process either a power law or an exponential decay. The seepage velocity induced by the stream gradient and, in case of a moving bed, the celerity of the translating bed forms limit the thickness of the advective hyporheic zone, inducing the RTDs to decrease rapidly at late time. This rapid decay can be preceded by a temporal region where the probability density functions (pdf's) tend to be inversely proportional to the square of time, and is followed by a region dominated by dispersion where the pdf's tend to be inversely proportional to the 3/2 power of time. The process shows distinct temporal ranges identified here by appropriate dimensionless parameters. Because of this complex exchange dynamics, models considering pure advection in the porous medium can significantly underestimate solute transfer at long time scales, whereas purely diffusive models of hyporheic exchange appear inadequate to represent the physical processes at an intermediate stage.

  • 2.
    Bottacin-Busolin, Andrea
    et al.
    Univ Padua, Dept Hydraul Maritime Environm & Geotech Engn.
    Tait, Simon
    Univ Bradford, Sch Engn Design & Technol.
    Marion, Andrea
    Univ Padua, Dept Hydraul Maritime Environm & Geotech Engn.
    Chegini, Amir
    Univ Guilan, Dept Civil Engn, Fac Engn.
    Tregnaghi, Matteo
    Univ Padua, Dept Hydraul Maritime Environm & Geotech Engn.
    Probabilistic description of grain resistance from simultaneous flow field and grain motion measurements2008In: Water resources research, ISSN 0043-1397, E-ISSN 1944-7973, Vol. 44, no 9, p. W09419-Article in journal (Refereed)
    Abstract [en]

    Experiments were carried out using a mobile gravel bed placed in a tilting flume with a modified particle image velocimetry (PIV) system. Individual grain movements were surveyed using data from time series of images. Near-bed velocity flow field measurements were made simultaneously above the same area of the sediment surface by applying cross-correlation techniques to the collected plan view images. Statistics of grain motions were collected through a semiautomatic procedure. Significant changes in the flow field were observed in the proximity of the entrained or deposited particles. A strong correlation is shown between the changes in the local streamwise and lateral velocity and the movement of the grains. The theory of Grass is revisited and developed based on the experimental results. The probability distribution of individual grain resistance has been derived from the statistics of the near-bed velocity field and of the entrainment risk.

  • 3.
    Cheng, Hua
    et al.
    KTH, Superseded Departments, Land and Water Resources Engineering.
    Cvetkovic, Vladimir
    KTH, Superseded Departments, Land and Water Resources Engineering.
    Hydrodynamic control of tracer retention in heterogeneous rock fractures2003In: Water resources research, ISSN 0043-1397, E-ISSN 1944-7973, Vol. 39, no 5, p. 1130-1139Article in journal (Refereed)
    Abstract [en]

    We investigate the statistical properties of a Lagrangian random variable beta[T/L], which has been shown to quantify hydrodynamic impact on retention [Cvetkovic et al., 1999], using Monte Carlo simulations of flow and transport in a single fracture. The "local cubic law'' of water flow is generalized to a power law Qsimilar tob(n), where Q is the flow rate, b is the half aperture, and nless than or equal to3. Simulations of flow and particle transport are carried out assuming "local cubic law'' (n=3) and "local quadratic law'' (n=2), and for two typical flow configurations: uniform flow and radially converging flow. We find that beta is related to tau as betasimilar totau(m), where m is dependent on the power n and the configuration of flow and transport. Simulation results for uniform flow indicate that betasimilar totau(n/n-1) for a small source section; as the source section increases, we have the convergence to betasimilar totau. For radially converging flow, we find betasimilar totau for a small source section and a convergence to beta=const for an increasing source section. Simulation results for both flow configurations are consistent with the results for a homogeneous fracture. The results for a homogeneous fracture provide reasonable bounds for simulated beta. The correlation between beta and Q is relatively weak for all cases studied.

  • 4.
    Cvetkovic, Vladimir
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Water Resources Engineering.
    A general memory function for modeling mass transfer in groundwater transport2012In: Water resources research, ISSN 0043-1397, E-ISSN 1944-7973, Vol. 48, p. W04528-Article in journal (Refereed)
    Abstract [en]

    A power-law extension of the gamma distribution is proposed as a general memory function for capturing rate limitations of retention in groundwater transport. Using moments, we show how the new memory function can be reduced to most other forms available in the literature, exactly or approximately. The proposed formulation is suitable for field scale or laboratory scale transport modeling. Rate limitation effects are illustrated for solute transport by considering the fractional mass release over a given transport scale. The equilibrium and no-retention cases set bounds for contaminant attenuation, between which the impact of rate limitations is clearly exposed.

  • 5.
    Cvetkovic, Vladimir
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Land and Water Resources Engineering.
    How accurate is predictive modeling of groundwater transport?: A case study of advection, macrodispersion, and diffusive mass transfer at the Forsmark site (Sweden)2013In: Water resources research, ISSN 0043-1397, E-ISSN 1944-7973, Vol. 49, no 9, p. 5317-5327Article in journal (Refereed)
    Abstract [en]

    We study predictive modeling of groundwater transport that accounts for three mechanisms: mean advection, macrodispersion, and mass transfer. A general methodology is presented and applied to a series of nonsorbing tracer tests along multiple pathways on scales ranging from ca. 70 to 300 m, in a highly heterogeneous aquifer at Forsmark (Sweden). The mean water residence time cannot be predicted well using a simple water balance model. Longitudinal macrodispersivity (L) (L) and a mass transfer parameter group (1/root T) are extrapolated from the control tracer experiments, to yield accurate predictions of tracer discharge, once the mean water residence time is constrained. A relatively simple modeling framework based on Fickian macrodispersion and diffusion seems to be adequate for reproducing the tracer discharge in this complex and highly heterogeneous porous media.

  • 6.
    Cvetkovic, Vladimir
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Water Resources Engineering.
    Significance of fracture rim zone heterogeneity for tracer transport in crystalline rock2010In: Water resources research, ISSN 0043-1397, E-ISSN 1944-7973, Vol. 46, no 3, p. W03504-Article in journal (Refereed)
    Abstract [en]

    Conducting fractures of crystalline rock are typically altered over long periods of time. The fracture rim zone, a result of these alterations, will as a rule have different physical and chemical properties from the unaltered ("fresh'') rock, depending on various microscopic and macroscopic factors of the alterations. In this paper, we study the impact of rim zone heterogeneity, exemplified by a decreasing porosity trend as inferred from the Aspo Hard Rock Laboratory site (Sweden), on short- and long-term tracer transport. Our main finding is that this particular rim zone structure will have a dominant effect on transport of moderately to strongly sorbing tracers on experimental time scales and a notable effect on application time scales. The findings of this work lend further support to the interpretation of the relatively strong retention reported by Cvetkovic et al. The fracture rim zone porosity structure may provide an additional safety margin for sorbing radionuclides in crystalline rock at sites where fracture alteration is prevalent.

  • 7.
    Cvetkovic, Vladimir
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Resources, Energy and Infrastructure.
    Statistical Formulation of Generalized Tracer Retention in Fractured Rock2017In: Water resources research, ISSN 0043-1397, E-ISSN 1944-7973, Vol. 53, no 11, p. 8736-8759Article in journal (Refereed)
    Abstract [en]

    We study tracer retention in fractured rock by combing Lagrangian and time domain random walk frameworks, as well as a statistical representation of the retention process. Mass transfer is quantified by the retention time distribution that follows from a Lagrangian coupling between advective transport and mass exchange processes, applicable for advection-dominated transport. A unifying parametrization is presented for generalized diffusion using two rates denoted by k(1) and k(2) where k(1) is a forward rate and k(2) a reverse rate, plus an exponent as an additional parameter. For the Fickian diffusion model, k(1) and k(2) are related to measurable retention properties of the fracture-matrix by the method of moments, whereas for the non-Fickian case dimensional analysis is used. The derived retention time distributions are exemplified for interpreting tracer tests as well as for predictive modeling of expected tracer breakthrough. We show that non-Fickian effects can be notable when transport is upscaled based on a non-Fickian interpretation of a tracer test for which deviations from Fickianity are relatively small. The statistical representation of retention clearly shows the significance of the forward rate k(1) which depends on the active specific surface area and is the most difficult parameter to characterize in the field.

  • 8.
    Cvetkovic, Vladimir
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Water Resources Engineering.
    Tracer attenuation in groundwater2011In: Water resources research, ISSN 0043-1397, E-ISSN 1944-7973, Vol. 47, no 12, p. W12541-Article in journal (Refereed)
    Abstract [en]

    The self-purifying capacity of aquifers strongly depends on the attenuation of waterborne contaminants, i.e.,irreversible loss of contaminant mass on a given scale as a result of coupled transport and transformation processes. A general formulation of tracer attenuation in groundwater is presented. Basic sensitivities of attenuation to macrodispersion and retention are illustrated for a few typical retention mechanisms. Tracer recovery is suggested as an experimental proxy for attenuation. Unique experimental data of tracer recovery in crystalline rock compare favorably with the theoretical model that is based on diffusion-controlled retention. Non-Fickian hydrodynamic transport has potentially a large impact on field-scale attenuation of dissolved contaminants.

  • 9.
    Cvetkovic, Vladimir
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Water Resources Engineering.
    Carstens, Christoffer
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Water Resources Engineering.
    Selroos, Jan-Olof
    Destouni, Georgia
    Water and solute transport along hydrological pathways2012In: Water resources research, ISSN 0043-1397, E-ISSN 1944-7973, Vol. 48, no 6, p. W06537-Article in journal (Refereed)
    Abstract [en]

    A Lagrangian framework for material transport along hydrological pathways is presented and consequences of statistically stationary space-time flow velocity variations on advective transport are investigated. The two specific questions addressed in this work are: How do temporal fluctuations affect forward and backward water travel time distributions when combined with spatial variability? and Can mass transfer processes be quantified using conditional probabilities in spatially and temporally variable flow? Space-time trajectories are studied for generic conditions of flow, with fully ergodic or only spatially ergodic velocity. It is shown that forward and backward distributions of advective water travel time coincide for statistically stationary space-time variations. Temporal variability alters the statistical structure of the Lagrangian velocity fluctuations. Once this is accounted for, integration of the memory function with the travel time distribution is applicable for quantifying retention. Further work is needed to better understand the statistical structure of space-time velocity variability in hydrological transport, as well as its impact on tracer retention and attenuation.

  • 10.
    Cvetkovic, Vladimir
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Water Resources Engineering.
    Cheng, H.
    Byegard, J.
    Winberg, A.
    Tullborg, E. -L
    Widestrand, H.
    Transport and retention from single to multiple fractures in crystalline rock at Aspo (Sweden): 1. Evaluation of tracer test results and sensitivity analysis2010In: Water resources research, ISSN 0043-1397, E-ISSN 1944-7973, Vol. 46, p. W05505-Article in journal (Refereed)
    Abstract [en]

    We evaluate the breakthrough curves obtained within a comprehensive experimental program for investigating the retention properties of crystalline rock, referred to as Tracer Retention Understanding Experiments (TRUE). The tracer tests were conducted at the Aspo Hard Rock Laboratory (Sweden) in two phases jointly referred to as TRUE Block Scale (TBS); the TBS tests comprise a total of 17 breakthrough curves with nonsorbing and a range of sorbing tracers. The Euclidian length scales are between 10 and 30 m, compared to 5 m for the earlier tests TRUE-1. The unlimited diffusion model is consistent with measured breakthrough curves and is adopted here for evaluation. The model has four independent parameters, two of which are related to advection and dispersion, one which is related to diffusion-sorption, and one which is related to surface sorption; the individual retention parameters or properties cannot be inferred from breakthrough curves alone and require additional constraints. The mean water residence times for the TBS tests are in the range 15-250 h, whereas the coefficient of variation of the water residence times is in the range 0.4-0.6. A consistent trend is found in the calibrated retention parameters with the sorption affinities of the tracers involved. Using Bode sensitivity functions, it is shown that sensitivity increases for the retention parameter with increasing sorption affinity; for nonsorbing tracers, diffusion and hydrodynamic dispersion are shown to "compete," exhibiting similar effects; hence, their estimates are uncertain. The analysis presented here exposes a few fundamental limitations and sensitivities when evaluating diffusion-controlled retention in the subsurface; it is general and applicable to any site with comparable tracer test data. In part 2, it will be shown how discrete fracture network simulations based on the hydrostructural information available can be used for further constraining individual retention parameters, in particular, the active specific surface area (s(f)) and the rock matrix porosity (theta).

  • 11.
    Cvetkovic, Vladimir
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Water Resources Engineering.
    Cheng, Hua
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Water Resources Engineering.
    Evaluation of single-well injection-withdrawal tests in Swedish crystalline rock using the Lagrangian travel time approach2011In: Water resources research, ISSN 0043-1397, E-ISSN 1944-7973, Vol. 47, p. W02527-Article in journal (Refereed)
    Abstract [en]

    A series of 10 single-well injection-withdrawal (SWIW) tests are evaluated with two tracers each: uranine and cesium (Cs). An evaluation tool for SWIW tests in crystalline rock is presented on the basis of the Lagrangian travel time approach, whereby probabilities of tracer particle residence times are computed for key stages of the test cycle. Calibration results for three transport parameters and each breakthrough curve are presented. We show that estimates of the controlling retention parameter group psi [1/root T] are robust for Cs but highly uncertain for uranine. The estimated retention for Cs is larger for the Laxemar-Simpevarp site compared to the Forsmark site. Deviations from the -3/2 asymptotic breakthrough curve slope observed in a few of the tests at Forsmark are possibly due to a thin fracture coating that has been identified in mineralogical studies at some locations of the site.

  • 12.
    Cvetkovic, Vladimir
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Water Resources Engineering.
    Cheng, Hua
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering.
    Sorbing tracer experiments in a crystalline rock fracture at Aspo (Sweden): 3. Effect of microscale heterogeneity2008In: Water resources research, ISSN 0043-1397, E-ISSN 1944-7973, Vol. 44, no 12Article in journal (Refereed)
    Abstract [en]

    We study the impact of microscale (10(-3) -10(-2) m) heterogeneity in material and structural properties on sorbing tracer transport in a single crystalline fracture of the TRUE-1 tests (mesoscale, 5 m) at Aspo (Sweden). The analysis is based on the microscale characterization results as presented in part 1 of this series. Our main objective in this last part of the series is to provide an independent interpretation (or "prediction'') of the effective parameters as estimated from calibration in part 2 by combining the data presented in part 1 with analytical and numerical transport modeling. We show here that the independent information from microscopic characterization can be used for "predicting'' the effective diffusion time t(d) reasonably well; a discrepancy is to be expected given the uncertainties of microscale retention properties, in particular of the sorption coefficient.

  • 13.
    Cvetkovic, Vladimir
    et al.
    KTH, Superseded Departments, Land and Water Resources Engineering.
    Cheng, Hua
    KTH, Superseded Departments, Land and Water Resources Engineering.
    Wen, X. -H.
    Analysis of nonlinear effects on tracer migration in heterogeneous aquifers using Lagrangian travel time approach1996In: Water resources research, ISSN 0043-1397, E-ISSN 1944-7973, Vol. 32, no 6, p. 1671-1680Article in journal (Refereed)
    Abstract [en]

    Advective transport in a heterogeneous two-dimensional aquifer is simulated and quantified by the statistical moments of tracer travel time and transverse displacement. These moments depend on the statistics of the Lagrangian velocity given as a function of space rather than time. A comparison is made with first-order results that appear to be robust for log transmissivity variance at least up to 1. Lagrangian statistics for travel time clearly expose a few essential features of nonlinear transport: nonstationary distribution and the increasing integral scale of the Lagrangian velocity. These reflect the tendency of streamlines to concentrate into relatively few flow paths ('preferential flow') for increasing log transmissivity variance. Two simple empirical relationships are identified that in combination with first-order results for the flow capture the main features of nonlinear transport. The proposed methodology can readily be generalized for analyzing advective transport under more complex flow conditions and for establishing relatively simple analytical models for estimating solute mass flux in heterogeneous aquifers.

  • 14.
    Cvetkovic, Vladimir
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Water Resources Engineering.
    Cheng, Hua
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering.
    Widestrand, H.
    Byegard, J.
    Winberg, A.
    Andersson, P.
    Sorbing tracer experiments in a crystalline rock fracture at Aspo (Sweden): 2. Transport model and effective parameter estimation2007In: Water resources research, ISSN 0043-1397, E-ISSN 1944-7973, Vol. 43, no 11Article in journal (Refereed)
    Abstract [en]

    [1] Transport and retention of sorbing tracers in a single, altered crystalline rock fracture on a 5 m scale is investigated. We evaluate the results of a comprehensive field study ( referred to as Tracer Retention Understanding Experiments, first phase ( TRUE- 1)), at a 400 m depth of the Aspo Hard Rock Laboratory ( Sweden). A total of 16 breakthrough curves are analyzed, from three test configurations using six radioactive tracers with a broad range of sorption properties. A transport- retention model is proposed, and its applicability is assessed based on available data. We find that the conventional model with an asymptotic power law slope of - 3/ 2 ( one- dimensional diffusion into an unlimited rock matrix) is a reasonable approximation for the conditions of the TRUE- 1 tests. Retention in the altered rock of the rim zone appears to be significantly stronger than implied by retention properties inferred from generic ( unaltered) rock samples. The effective physical parameters which control retention ( matrix porosity and retention aperture) are comparable for all three test configurations. The most plausible in situ ( rim zone) porosity is in the range 1% - 2%, which constrains the effective retention aperture to the range 0.2 - 0.7 mm. For all sorbing tracers the estimated in situ sorption coefficient appears to be larger by at least a factor of 10, compared to the value inferred from through- diffusion tests using unaltered rock samples.

  • 15.
    Cvetkovic, Vladimir
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Land and Water Resources Engineering.
    Fiori, Aldo
    Dagan, Gedeon
    Solute transport in aquifers of arbitrary variability: A time-domain random walk formulation2014In: Water resources research, ISSN 0043-1397, E-ISSN 1944-7973, Vol. 50, no 7, p. 5759-5773Article in journal (Refereed)
    Abstract [en]

    Solute transport in three-dimensional aquifers, with spatially varying hydraulic conductivity of arbitrary point distribution is investigated. The basis of our study is a multiindicator model (MIM) representation of the heterogeneity, combined with a self-consistent approximation for groundwater flow and particle transport. A time-domain random walk (TDRW) approach is presented for computing the expected mass arrival along the longitudinal transport direction that is simple and honors the hydrodynamics of flow for any variability. Using hydraulic conductivity measurements at the MADE site and the MIM, it is shown that the travel time distribution for large variability, cannot be well reproduced by the common distributions used for modeling hydrological transport, such as the log-normal distribution, or the inverse-Gaussian distribution. The proposed TDRW approach directly relates to the Lagrangian trajectory formulation and is appropriate for applications where occurrence of negative flow velocities is small. These results open new possibilities for modeling solute transport in aquifers of arbitrary variability by the time-domain random walk that can readily account for a wide range of mass transfer reactions.

  • 16.
    Cvetkovic, Vladimir
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering.
    Frampton, Andrew
    Solute transport and retention in three-dimensional fracture networks2012In: Water resources research, ISSN 0043-1397, E-ISSN 1944-7973, Vol. 48, p. W02509-Article in journal (Refereed)
    Abstract [en]

    Resolving the hydrodynamic control of retention is an important step in predictive modeling of transport of sorbing tracers in fractured rock. The statistics of the transport resistance parameter beta [T/L] and the related effective active specific surface area s(f) [1/L] are studied in a crystalline rock volume on a 100 m scale. Groundwater flow and advective transport are based on generic boundary conditions and realistic discrete fracture networks inferred from the Laxemar site, southeast Sweden. The overall statistics of beta are consistent with statistics of the water residence time tau; the moments of beta vary linearly with distance, at least up to 100 m. The correlation between log tau and log beta is predominantly linear, however, there is significant dispersion; the parameter s(f) strongly depends on the assumed hydraulic law (theoretical cubic or empirical quadratic). Fast and slow trajectories/segments in the network determine the shape of the beta distribution that cannot be reproduced by infinitely divisible model over the entire range; the low value range and median can be reproduced reasonably well with the tempered one-sided stable density using the exponent in the range 0.35-0.7. The low percentiles of the beta distribution seems to converge to a Fickian type of behavior from a 50 to 100 m scale.

  • 17.
    Cvetkovic, Vladimir
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering.
    Frampton, Andrew
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering.
    Transport and retention from single to multiple fractures in crystalline rock at Äspö (Sweden): 2. Fracture network simulations and generic retention model.2010In: Water resources research, ISSN 0043-1397, E-ISSN 1944-7973Article in journal (Refereed)
    Abstract [en]

    Hydrogeologic characterization of crystalline rock formations on the field scale is important for many applications but still presents a multitude of challenges [Neuman, 2005]. In this work we use comprehensive hydro-structural information and present a detailed simulation study of flow and advective transport in a discrete fracture network (DFN) that replicates the TRUE Block Scale rock volume at the Äspö Hard Rock Laboratory (Sweden). Simulated water residence time τ and hydrodynamic retention parameter β are used as independent constraints for estimating material retention properties as presented in part 1 of this series [Cvetkovic et al., 2009] whereas simulated mean water residence times are compared with observed values. We find that the DFN simulations reproduce water residence times reasonably well, indicating that the characterization data are sufficient and that the DFN model does capture dominant features of the flow paths analyzed. The empirical quadratic law that relates aperture and transmissivity seems to better reproduce calibrated mean water residence times than the theoretical cubic law, for the five flow paths. The active specific surface area (β/τ) [1/L] as inferred from simulations, is used for defining a generic retention model for the dominant rock type (”Äspö diorite”) that matches fairly well the entire range of calibrated retention parameters of the TRUE tests. The combination of Part 1 and this work provide a general, comprehensive methodology for evaluating tracer test results in crystalline rock where a comparable amount of information is available; critical to this methodology is that tracer tests are carried out using tracers with sufficiently different sorption affinities (of factor 10 to 100).

  • 18.
    Cvetkovic, Vladimir
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Land and Water Resources Engineering.
    Gotovac, Hrvoje
    Flow-dependence of matrix diffusion in highly heterogeneous rock fractures2013In: Water resources research, ISSN 0043-1397, E-ISSN 1944-7973, Vol. 49, no 11, p. 7587-7597Article in journal (Refereed)
    Abstract [en]

    Diffusive mass transfer in rock fractures is strongly affected by fluid flow in addition to material properties. The flow-dependence of matrix diffusion is quantified by a random variable ("transport resistance'') denoted as beta [T/L] and computed from the flow field by following advection trajectories. The numerical methodology for simulating fluid flow is mesh-free, using Fup basis functions. A generic statistical model is used for the transmissivity field, featuring three correlation structures: (i) highly connected non-multiGaussian; (ii) poorly connected (or disconnected) non-multi-Gaussian; and (iii) multi-Gaussian. The moments of beta are shown to be linear with distance, irrespective of the structure, after approximately 10 integral scales of ln T. Percentiles of beta are found to be linear with the mean beta when considering all three structures. Taking advantage of this property, a potentially useful relationship is presented between beta percentiles and the fracture mean water residence time that integrates all structures with high variability; it can be used in discrete fracture network simulations where T statistical data on individual fractures are not available.

  • 19.
    Cvetkovic, Vladimir
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Land and Water Resources Engineering.
    Gotovac, Hrvoje
    On the upscaling of chemical transport in fractured rock2014In: Water resources research, ISSN 0043-1397, E-ISSN 1944-7973, Vol. 50, no 7, p. 5797-5816Article in journal (Refereed)
    Abstract [en]

    The impact of flow heterogeneity on chemical transport from single to multiple fractures is investigated. The emphasis is on the dynamic nature of the specific surface area (SSA) due to heterogeneity of the flow, relative to a purely geometrical definition. The flow-dependent SSA is interpreted probabilistically, following inert tracer particles along individual fractures. Upscaling to a fracture network is proposed as a time domain random walk based on the statistics of SSA for single fractures. Statistics of SSA are investigated for three correlation structures of transmissivity: multi-Gaussian and two non-multi-Gaussian. The mean of SSA stabilizes after similar to 20 fractures at different values depending on whether the cubic or quadratic hydraulic law is assumed. The results are tested against comprehensive DFN simulations based on site-specific data but also against direct estimates from a wider range of tracer tests. The proposed time domain random walk methodology sets bounds for SSA in a 75% confidence interval as similar to 1800 1/m and 27,000 1/m, with a median of 14,000 1/m; these values capture reasonably well both the DFN simulation and tracer test SSA data. Presented results may be particularly relevant when quantifying uncertainty of reactive transport modeling in fractured rock.

  • 20.
    Cvetkovic, Vladimir
    et al.
    KTH, Superseded Departments, Land and Water Resources Engineering.
    Painter, S.
    Outters, N.
    Selroos, J. O.
    Stochastic simulation of radionuclide migration in discretely fractured rock near the Aspo Hard Rock Laboratory2004In: Water resources research, ISSN 0043-1397, E-ISSN 1944-7973, Vol. 40, no 2, p. W02404-Article in journal (Refereed)
    Abstract [en]

    We study the migration of sorbing tracers through crystalline rock by combining relatively simple transport measures with particle tracking in a discrete fracture network. The rock volume is on a 100 m scale and is a replica of a thoroughly characterized site at the Aspo Hard Rock Laboratory, Sweden. Flow is driven by generic boundary conditions consistent with the natural gradient in the region. The emphasis is on the global effect of fracture-to-fracture hydraulic variability where individual fractures are assumed to be of uniform aperture. The transport measures are conditioned on two random variables: the water residence time (tau) and a parameter which quantifies the hydrodynamic control of retention (beta). Results are illustrated for two radionuclides: technetium (strongly sorbing) and strontium (weakly sorbing). It is found that the assumption of streamline routing or full mixing at fracture intersections has comparatively little impact on transport. The choice of the cubic or quadratic hydraulic law (i.e., relation between transmissivity and aperture) strongly affects water residence times but has little impact on average transport since it does not affect the statistics of beta. If the statistics of beta are known, then the distribution of water residence time (tau) is of little importance for transport. We assess the applicability of a linearized model beta = tau/b(ret) using two different approaches to estimate the effective retention'' aperture 2b(ret): from transmissivity data and from fracture density and flow porosity data. Under some conditions, these conventional estimates may provide acceptable representation of transport. The results stress the need for further studies on upscaling of tau, beta distributions as well as on estimating effective parameters for hydraulic control of retention.

  • 21.
    Cvetkovic, Vladimir
    et al.
    KTH, Superseded Departments, Land and Water Resources Engineering.
    Painter, S.
    Turner, D.
    Pickett, D.
    Bertetti, P.
    Parameter and model sensitivities for colloid-facilitated radionuclide transport on the field scale2004In: Water resources research, ISSN 0043-1397, E-ISSN 1944-7973, Vol. 40, no 6Article in journal (Refereed)
    Abstract [en]

    We investigate the potential effects of inorganic colloids on radionuclide transport in groundwater using generic sensitivity studies and an example based on the alluvial aquifer near Yucca Mountain, Nevada. Our emphasis is on kinetically controlled sorption of radionuclides on mobile and immobile colloids. Three kinetic sorption models are considered for the sensitivity analysis: bilinear, Langmuir, and linear. Plutonium is assumed to be injected into the Yucca Mountain alluvial aquifer at a constant rate and follows a random stream tube to a monitoring boundary. The linear sorption model provides a reasonable upper bound on colloid-facilitated plutonium transport for the site-specific conditions. In the absence of colloid filtration and retardation, colloids enhance the plutonium discharge by a large factor over the situation without colloids. Exchange of plutonium between solution and reversibly attached colloids makes colloid retardation relatively ineffective at reducing colloid-facilitated transport except when the retardation factor is large. Irreversible removal of colloids (filtration) is more effective than retardation at reducing colloid-facilitated transport. For fixed filtration rate the degree of attenuation depends sensitively and nonmonotonically on the rate of plutonium desorption from colloids. These results emphasize the need for accurate measurements of rates of desorption from colloids as well as in situ studies of filtration of naturally occurring colloids.

  • 22. de Barros, F. P. J.
    et al.
    Bellin, A.
    Cvetkovic, Vladimir
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Land and Water Resources Engineering.
    Dagan, G.
    Fiori, A.
    Aquifer heterogeneity controls on adverse human health effects and the concept of the hazard attenuation factor2016In: Water resources research, ISSN 0043-1397, E-ISSN 1944-7973, Vol. 52, no 8, p. 5911-5922Article in journal (Refereed)
    Abstract [en]

    We analyze the probability distribution of the hazard attenuation factor for a noncarcinogenic reactive compound captured by a well in heterogeneous porous formations. The hazard attenuation factor is defined as the ratio between the hazard index HI at a detection well and at the source. Heterogeneity of the aquifer is represented through the multi-indicator model (a collection of blocks of independent permeability) while flow and transport are solved by the means of the self-consistent approach that is able to deal with any degree of heterogeneity. Due to formation heterogeneity, HI is a random variable and similar for hazard attenuation index. The latter can be fully characterized by its cumulative distribution function (CDF), which in turn can be related to the statistics of the travel time of solute particles, from the source to the detection well. The approach is applied to the case of a solute which undergoes decay and a well with a screen much smaller than the correlation scale of hydraulic conductivity. The results show that the probability of exceeding a given acceptable threshold of the hazard index is significantly affected by the level of heterogeneity comparable to the one observed for the MADE site, and the distance between the source and the well.

  • 23.
    Destouni, Georgia
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering.
    Prieto, Carmen
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering.
    Quantifying hydrological and tidal influences on groundwater discharges into coastal waters2005In: Water resources research, ISSN 0043-1397, E-ISSN 1944-7973, Vol. 41, no 12, p. W12427-Article in journal (Refereed)
    Abstract [en]

    [1] In coastal aquifers the dynamic mixing zone between intruding seawater and fresh groundwater constitutes a zone of salinity transition that may supply brackish groundwater along with chemical tracers and nutrients to coastal waters. Tidal influence has been proposed as a possible mechanism for enhancement of recirculated seawater, total submarine groundwater discharge (SGD), and associated tracer loading through salinity transition zones into coastal waters. We show that tidal oscillation may, for relatively low SGD cases, considerably increase the average recirculated seawater component of total SGD relative to nontidal conditions. High SGD cases, however, are dominated by and require large fresh groundwater flow components also under tidal conditions; this result is obtained from a wide range of different groundwater simulation scenarios and is supported by direct comparison with field data from different reported high-SGD sites in the world. For cases with hydrologically limited fresh groundwater flow directly into the sea we propose that observed excessive coastal loading of groundwater-derived tracers may be the result of large groundwater flow and transport into unmonitored coastal stream reaches, in addition to SGD.

  • 24. Fiori, A.
    et al.
    Bellin, A.
    Cvetkovic, Vladimir
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering.
    de Barros, F. P. J.
    Dagan, G.
    Stochastic modeling of solute transport in aquifers: From heterogeneity characterization to risk analysis2015In: Water resources research, ISSN 0043-1397, E-ISSN 1944-7973, Vol. 51, no 8, p. 6622-6648Article in journal (Refereed)
    Abstract [en]

    The article presents a few recent developments advanced by the authors in a few key areas of stochastic modeling of solute transport in heterogeneous aquifers. First, a brief review of the Lagrangian approach to modeling plumes longitudinal mass distribution and temporal (the breakthrough curve) mass arrival, is presented. Subsequently, transport in highly heterogeneous aquifers is analyzed by using a recently developed predictive model. It relates the non-Gaussian BTC to the permeability univariate pdf and integral scale, with application to the MADE field observations. Next, the approach is extended to transport of reactive solute, combinnig the effects of the random velocity field and multirate mass transfer on the BTC, with application to mass attenuation. The following topic is modeling of the local concentration field as affected by mixing and dilution due to pore scale dispersion. The results are applied to the analysis of concentration measurements at the Cape Cod field experiment. The last section incorporates the results of the preceding ones in health risk assessment by analyzing the impact of concentration prediction on risk uncertainty. It is illustrated by assessing the effect of identification of macrodispersivity from field characterization and transport modeling, upon the probability of health risk.

  • 25. Fiori, A.
    et al.
    Berglund, S.
    Cvetkovic, Vladimir
    KTH, Superseded Departments, Land and Water Resources Engineering.
    Dagan, G.
    A first-order analysis of solute flux statistics in aquifers: The combined effect of pore-scale dispersion, sampling, and linear sorption kinetics2002In: Water resources research, ISSN 0043-1397, E-ISSN 1944-7973, Vol. 38, no 8Article in journal (Refereed)
    Abstract [en]

    [1] We consider steady groundwater flow of uniform mean in aquifers of random, spatially variable, hydraulic conductivity. Analytical expressions for the statistical moments of mass fluxes of sorbing solutes in presence of pore-scale dispersion are derived, where the reactive solutes undergo first-order sorption kinetics. The developments which lead to the analytical formulation of the solute flux are rigorous in the first-order analysis framework, and results obtained are valid for weakly heterogeneous formations. The methodology is exemplified for a two-dimensional aquifer, assuming that the source is of small transverse extent compared to the heterogeneity length scales. The examples show that pore-scale dispersion has a relatively small effect on the mean point flux, whereas the point flux variance shows much larger sensitivity to pore-scale dispersion. The variance first decreases as the reaction rate departs from the nonreactive limit, but for equilibrium reactions it is of the same order as for nonreactive solutes. The effect of averaging the solute flux over a finite sampling area is also investigated. It is found that for the expected area-averaged flux the mixing effect induced by sampling tends to supersede that caused by pore-scale dispersion. On the contrary, pore-scale dispersion may have a strong effect on the flux variance also when sampling effects are taken into account.

  • 26. Fiori, A.
    et al.
    Cvetkovic, Vladimir
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering.
    Dagan, G.
    Attinger, S.
    Bellin, A.
    Dietrich, P.
    Zech, A.
    Teutsch, G.
    Debates—Stochastic subsurface hydrology from theory to practice: The relevance of stochastic subsurface hydrology to practical problems of contaminant transport and remediation. What is characterization and stochastic theory good for?2016In: Water resources research, ISSN 0043-1397, E-ISSN 1944-7973, Vol. 52, no 12, p. 9228-9234Article in journal (Refereed)
    Abstract [en]

    The emergence of stochastic subsurface hydrology stemmed from the realization that the random spatial variability of aquifer properties has a profound impact on solute transport. The last four decades witnessed a tremendous expansion of the discipline, many fundamental processes and principal mechanisms being identified. However, the research findings have not impacted significantly the application in practice, for several reasons which are discussed. The paper discusses the current status of stochastic subsurface hydrology, the relevance of the scientific results for applications and it also provides a perspective to a few possible future directions. In particular, we discuss how the transfer of knowledge can be facilitated by identifying clear goals for characterization and modeling application, relying on recent recent advances in research in these areas.

  • 27. Fiori, A.
    et al.
    Zarlenga, A.
    Gotovac, H.
    Jankovic, I.
    Volpi, E.
    Cvetkovic, Vladimir
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering.
    Dagan, G.
    Advective transport in heterogeneous aquifers: Are proxy models predictive?2015In: Water resources research, ISSN 0043-1397, E-ISSN 1944-7973, Vol. 51, no 12, p. 9577-9594Article in journal (Refereed)
    Abstract [en]

    We examine the prediction capability of two approximate models (Multi-Rate Mass Transfer (MRMT) and Continuous Time Random Walk (CTRW)) of non-Fickian transport, by comparison with accurate 2-D and 3-D numerical simulations. Both nonlocal in time approaches circumvent the need to solve the flow and transport equations by using proxy models to advection, providing the breakthrough curves (BTC) at control planes at any x, depending on a vector of five unknown parameters. Although underlain by different mechanisms, the two models have an identical structure in the Laplace Transform domain and have the Markovian property of independent transitions. We show that also the numerical BTCs enjoy the Markovian property. Following the procedure recommended in the literature, along a practitioner perspective, we first calibrate the parameters values by a best fit with the numerical BTC at a control plane at x(1), close to the injection plane, and subsequently use it for prediction at further control planes for a few values of sigma(2)(gamma) <= 8. Due to a similar structure and Markovian property, the two methods perform equally well in matching the numerical BTC. The identified parameters are generally not unique, making their identification somewhat arbitrary. The inverse Gaussian model and the recently developed Multi-Indicator Model (MIM), which does not require any fitting as it relates the BTC to the permeability structure, are also discussed. The application of the proxy models for prediction requires carrying out transport field tests of large plumes for a long duration.

  • 28. Fiori, Aldo
    et al.
    Boso, Francesca
    de Barros, Felipe P. J.
    De Bartolo, Samuele
    Frampton, Andrew
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering (moved 20130630), Water, Sewage and Waste technology.
    Severino, Gerardo
    Suweis, Samir
    Dagan, Gedeon
    An indirect assessment on the impact of connectivity of conductivity classes upon longitudinal asymptotic macrodispersivity2010In: Water resources research, ISSN 0043-1397, E-ISSN 1944-7973, Vol. 46, p. W08601-Article in journal (Refereed)
    Abstract [en]

    Solute transport takes place in heterogeneous porous formations, with the log conductivity, Y = ln K, modeled as a stationary random space function of given univariate normal probability density function (pdf) with mean < Y >, variance sigma(2)(Y), and integral scale I-Y. For weak heterogeneity, the above mentioned quantities completely define the first-order approximation of the longitudinal macrodispersivity sigma(L) = sigma I-2(Y)Y. However, in highly heterogeneous formations, nonlinear effects which depend on the multipoint joint pdf of Y, impact alpha(L). Most of the past numerical simulations assumed a multivariate normal distribution (MVN) of Y values. The main aim of this study is to investigate the impact of deviations from the MVN structure upon alpha(L). This is achieved by using the concept of spatial correlations of different Y classes, the latter being defined as the space domain where Y falls in the generic interval [Y,Y + Delta Y]. The latter is characterized by a length scale lambda(Y), reflecting the degree of connectivity of the domain (the concept is similar to the indicator variograms). We consider both "symmetrical" and "non-symmetrical" structures, for which lambda(Y') = lambda(-Y') (similar to the MVN), and lambda(Y') not equal lambda(-Y'), respectively, where Y' = Y - < Y >. For example, large Y zones may have high spatial correlation, while low Y zones are poorly correlated, or vice versa. The impact of lambda(Y) on alpha(L) is investigated by adopting a structure model which has been used in the past in order to investigate flow and transport in highly heterogeneous media. It is found that the increased correlation in the low conductive zones with respect to the high ones generally leads to a significant increase in alpha(L), for the same global I-Y. The finding is explained by the solute retention occurring in low Y zones, which has a larger effect on solute spreading than high Y zones. Conversely, alpha(L) decreases when the high conductivity zones are more correlated than the low Y ones. Dispersivity is less affected by the shape of lambda(Y) for symmetrical distributions. It is found that the range of validity of the first-order dispersivity, i.e., alpha(L) = I-Y sigma(2)(Y), narrows down for non-symmetrical structures.

  • 29. Fiori, Aldo
    et al.
    Jankovic, Igor
    Dagan, Gedeon
    Cvetkovic, Vladimir
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Water Resources Engineering.
    Ergodic transport through aquifers of non-Gaussian log conductivity distribution and occurrence of anomalous behavior2007In: Water resources research, ISSN 0043-1397, E-ISSN 1944-7973, Vol. 43, no 9Article in journal (Refereed)
    Abstract [en]

    Three-dimensional advective transport of passive solutes through isotropic porous formations of stationary non- Gaussian log conductivity distributions is investigated by using an approximate semianalytical model, which is compared with accurate numerical simulations. The study is a continuation of our previous works in which formation heterogeneity is modeled using spherical nonoverlapping inclusions and an approximate analytical model was developed. Flow is solved for average uniform velocity, and transport of an ergodic plume is quantified by mass flux ( traveltime distribution) at a control plane. The analytical model uses a self- consistent argument, and it is based on the solution for an isolated inclusion submerged in homogeneous background matrix of effective conductivity. As demonstrated in the past, this analytical model accurately predicted the entire distributions of traveltimes in formations of Gaussian log conductivity distributions, as validated by numerical simulations. The present study ( 1) extends the results to formations of non- Gaussian log conductivity structures ( the subordination model), ( 2) extends the approximate analytical model to cubical blocks that tessellate the entire domain, ( 3) identifies a condition in conductivity distribution, at the tail of low values, that renders transport anomalous with macrodispersivity growing without bounds, and ( 4) provides links of our work to continuous time random walk ( CTRW) methodology, as applied to subsurface transport. It is found that a class of CTRW solutions proposed in the past cannot be based on solution of flow in formations with conductivity distribution of finite integral scale.

  • 30. Fiori, Aldo
    et al.
    Zarlenga, Antonio
    Gotovac, Hrvoje
    Jankovic, Igor
    Volpi, Elena
    Cvetkovic, Vladimir
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Land and Water Resources Engineering.
    Dagan, Gedeon
    Reply to comment by S. P. Neuman on "Advective transport in heterogeneous aquifers: Are proxy models predictive?''2016In: Water resources research, ISSN 0043-1397, E-ISSN 1944-7973, Vol. 52, no 7, p. 5703-5704Article in journal (Refereed)
    Abstract [en]

    In this Reply we further comment on the main assumptions and the results of our recent manuscript "Advective transport in heterogeneous aquifers: Are proxy models predictive?''

  • 31.
    Frampton, Andrew
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering.
    Cvetkovic, Vladimir
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering.
    Numerical and analytical modelling of advective travel times in realistic three-dimensional fracture networks2011In: Water resources research, ISSN 0043-1397, E-ISSN 1944-7973, Vol. 47, no W02506, p. 16pp-Article in journal (Refereed)
    Abstract [en]

    Travel time distributions obtained from advective transport in multiple realisations of realistic discrete fracture network simulations are analysed using the truncated one-sided stable distribution, which has previously been shown to generalise both the advection-dispersion solution as well as one-sided stable distributions. Using this model it is shown that the Fickian assumption inherent in the advection-dispersion equation generally fails, despite that the first two moments of travel time essentially scale linearly with distance. It is also observed that the equally probable realisations drawn from the ensemble can produce a wide range of behaviour under the current configuration, such that Fickian conditions are almost obtained in some cases for increasing scales. Based on a small-scale calibration against particle breakthrough, the model is then shown to successfully predict limiting bounds of transport for a one order of magnitude increase in scale. Correlation in particle velocity is explicitly shown to be significant for scales close to the characteristic Lagrangian segment length. The network configuration is obtained from extensive site characterisation data at the Laxemar region in Sweden, and represents a block scale domain of reasonably sparse background fractures.

  • 32.
    Frampton, Andrew
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering.
    Cvetkovic, Vladimir
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering.
    Upscaling particle transport in discrete fracture networks: 1. Nonreactive tracers2007In: Water resources research, ISSN 0043-1397, E-ISSN 1944-7973, Vol. 43, no 10, p. W10428-Article in journal (Refereed)
    Abstract [en]

    We study tracer transport through discrete fracture networks and develop a methodology for upscaling particle breakthrough curves on the basis of fracture segment data. Our prime interest is to model the early arrival and peak of tracer breakthrough curves, i.e., to capture the bulk of the tracer mass arrival. This study is based on two-dimensional discrete fracture network simulations, combined with a truncated one-sided stable distribution as a model for upscaling particle transitions. Results indicate that this model can accurately capture the bulk mass and peak of the breakthrough distributions for an upscaled distance of at least 1 order of magnitude in terms of transport scale, which for our simulations is about 2 orders of magnitude greater than the mean fracture segment scale. We also introduce an accurate mapping algorithm for transforming Eulerian into Lagrangian flow statistics, without a priori knowledge of network connectivity.

  • 33.
    Frampton, Andrew
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering.
    Cvetkovic, Vladimir
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering.
    Upscaling particle transport in discrete fracture networks:  2. Reactive tracers2007In: Water resources research, ISSN 0043-1397, E-ISSN 1944-7973, Vol. 43, no 10, p. W10429-Article in journal (Refereed)
    Abstract [en]

    We study sorbing tracer transport through discrete fracture networks using astochastic Lagrangian framework, combined with the methodology for upscalingparticle breakthrough curves developed in the first part of this article series.Results indicate that this procedure can accurately predict expected normalizedtracer discharge for an upscaled distance of 1 order of magnitude in terms oftransport scale, which for our simulations is about 2 orders of magnitudegreater than the mean fracture segment scale. Specifically, we show theimportance of retaining the correlation between the water residence time τ andthe hydrodynamic control of retention β in order to make accurate tracerdischarge predictions. Also, we show that the extreme tails of τ and β distributions have essentially no impact on tracer discharge. These results areillustrated using the unlimited diffusion model, and for two hypotheticaltracers with properties designed to capture the behavior of many commonlyoccurring natural radionuclides.

  • 34.
    Frampton, Andrew
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Water Resources Engineering.
    Vladimir, Cvetkovic
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Water Resources Engineering.
    Inference of field scale fracture transmissivities in crystalline rock using flow log measurements2010In: Water resources research, ISSN 0043-1397, E-ISSN 1944-7973, Vol. 46, no 11, p. W11502-Article in journal (Refereed)
    Abstract [en]

    Characterization of transmissivity for crystalline rock is conducted through simulation by conditioning against borehole flow rates obtained from high-resolution, in situ field measurements during extraction pumping. Full three-dimensional discrete fracture network simulations are carried out according to specifications obtained from site characterization data in a stochastic Monte Carlo setting. A novel method of conditioning is thereby introduced and applied using nonparametric comparison tests, which provide quantifiable measures of accuracy enabling evaluation of simulated results against field measurements. The assumption of a constitutive relationship ( perfect correlation) between fracture size and transmissivity is adopted. The method is evaluated against both single and multiple realizations, various domain size, and fracture length configurations and shown to be robust for the cases considered. When the introduced method of conditioning is applied, transmissivity parameterization can be inferred to a narrow range with a quantifiable accuracy in terms of a probability value. Results indicate that elementary interpretation of transmissivity based on homogenization of a porous medium will generally underestimate transmissivity. Further implications on advective transport for natural flow conditions are briefly evaluated, indicating advective breakthrough times can be overestimated up to a factor of about 10 in the median.

  • 35.
    Gotovac, Hrvoje
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering.
    Cvetkovic, Vladimir
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering.
    Andricevic, Roko
    Flow and travel time statistics in highly heterogeneous porous media2009In: Water resources research, ISSN 0043-1397, E-ISSN 1944-7973, Vol. 45, no W07402Article in journal (Refereed)
    Abstract [en]

    In this paper we present flow and travel time ensemble statistics based on a new simulation methodology, the adaptive Fup Monte Carlo method (AFMCM). As a benchmark case, we considered two-dimensional steady flow in a rectangular domain characterized by multi-Gaussian heterogeneity structure with an isotropic exponential correlation and lnK variance sigma(2)(Y) up to 8. Advective transport is investigated using the travel time framework where Lagrangian variables (e. g., velocity, transverse displacement, or travel time) depend on space rather than on time. We find that Eulerian and Lagrangian velocity distributions diverge for increasing lnK variance due to enhanced channeling. Transverse displacement is a nonnormal for all sigma(2)(Y) and control planes close to the injection area, but after xI(Y) = 20 was found to be nearly normal even for high sigma(2)(Y). Travel time distribution deviates from the Fickian model for large lnK variance and exhibits increasing skewness and a power law tail for large lnK variance, the slope of which decreases for increasing distance from the source; no anomalous features are found. Second moment of advective transport is analyzed with respect to the covariance of two Lagrangian velocity variables: slowness and slope which are directly related to the travel time and transverse displacement variance, which are subsequently related to the longitudinal and transverse dispersion. We provide simple estimators for the Eulerian velocity variance, travel time variance, slowness, and longitudinal dispersivity as a practical contribution of this analysis. Both two-parameter models considered (the advection-dispersion equation and the lognormal model) provide relatively poor representations of the initial part of the travel time probability density function in highly heterogeneous porous media. We identify the need for further theoretical and experimental scrutiny of early arrival times, and the need for computing higher-order moments for a more accurate characterization of the travel time probability density function. A brief discussion is presented on the challenges and extensions for which AFMCM is suggested as a suitable approach.

  • 36.
    Gotovac, Hrvoje
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering.
    Cvetkovic, Vladimir
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering.
    Andricevic, Roko
    Significance of higher order moments to the completecharacterization of the travel time pdf in heterogeneous porous media using the maximum entropyprinciple2010In: Water resources research, ISSN 0043-1397, E-ISSN 1944-7973, Vol. 46, no W05502Article in journal (Refereed)
    Abstract [en]

    The travel time formulation of advective transport in heterogeneous porous media is of interest both conceptually, e. g., for incorporating retention processes, and in applications where typically the travel time peak, early, and late arrivals of contaminants are of major concern in a regulatory or remediation context. Furthermore, the travel time moments are of interest for quantifying uncertainty in advective transport of tracers released from point sources in heterogeneous aquifers. In view of this interest, the travel time distribution has been studied in the literature; however, the link to the hydraulic conductivity statistics has been typically restricted to the first two moments. Here we investigate the influence of higher travel time moments on the travel time probability density function (pdf) in heterogeneous porous media combining Monte Carlo simulations with the maximum entropy principle. The Monte Carlo experimental pdf is obtained by the adaptive Fup Monte Carlo method (AFMCM) for advective transport characterized by a multi-Gaussian structure with exponential covariance considering two injection modes (in-flux and resident) and lnK variance up to 8. A maximum entropy (MaxEnt) algorithm based on Fup basis functions is used for the complete characterization of the travel time pdf. All travel time moments become linear with distance. Initial nonlinearity is found mainly for the resident injection mode, which exhibits a strong nonlinearity within first 5I(Y) for high heterogeneity. For the resident injection mode, the form of variance and all higher moments changes from the familiar concave form predicted by the first-order theory to a convex form; for the in-flux mode, linearity is preserved even for high heterogeneity. The number of moments sufficient for a complete characterization of the travel time pdf mainly depends on the heterogeneity level. Mean and variance completely describe travel time pdf for low and mild heterogeneity, skewness is dominant for lnK variance around 4, while kurtosis and fifth moment are required for lnK variance higher than 4. Including skewness seems sufficient for describing the peak and late arrivals. Linearity of travel time moments enables the prediction of asymptotic behavior of the travel time pdf which in the limit converges to a symmetric distribution and Fickian transport. However, higher-order travel time moments may be important for most practical purposes and in particular for advective transport in highly heterogeneous porous media for a long distance from the source.

  • 37. Gupta, A.
    et al.
    Cvetkovic, Vladimir
    KTH, Superseded Departments, Land and Water Resources Engineering.
    Material transport from different sources in a network of streams through a catchment2002In: Water resources research, ISSN 0043-1397, E-ISSN 1944-7973, Vol. 38, no 7Article in journal (Refereed)
    Abstract [en]

    [1] A probabilistic model for material transport in a stream network is developed based on geomorphology of the subcatchment and water transit time distribution. A tracer may be a point source or a source distributed over the entire catchment. The tracer particles are transported by advection through streams of different order and also diffuse and react chemically with the sediments lying at the bottom of the streams. Stochastic analysis of travel time is complicated by microscopic exchange processes, which act to retain the tracer in the surrounding medium. These include kinetically controlled exchange with the storage zones, diffusion into the bed sediment, and linear equilibrium sorption. In addition, degradation delays the downstream tracer movement. The sensitivity analysis indicates that for 50% mass arrival the mean arrival time is increased by 3 times for a change in mass transfer parameter, chi*, by 10 times. This increase is further pronounced for higher mass arrivals and higher chi*. The results on a specific application example show that a mere doubling of the uncertain value of diffusive mass transfer rate in the bed sediment reduces the probability that 25% of solute mass arrives at the outlet by approximate to90%. The high sensitivity of the probability of the solute mass arrival at the outlet to the uncertain diffusive mass transfer rate implies uncertainty also in predictions of the solute transport process. Thus it can be concluded that the correct estimation of mass transfer rate in the bed sediments within a catchment plays an important role in field-scale estimation of transport parameters.

  • 38. Gupta, A.
    et al.
    Cvetkovic, Vladimir
    KTH, Superseded Departments, Land and Water Resources Engineering.
    Temporal moment analysis of tracer discharge in streams: Combined effect of physicochemical mass transfer and morphology2000In: Water resources research, ISSN 0043-1397, E-ISSN 1944-7973, Vol. 36, no 10, p. 2985-2997Article in journal (Refereed)
    Abstract [en]

    In environmental applications it is often of interest to predict the rates at which contaminant mass is discharged at a given cross section of streams and rivers. We present a Lagrangian methodology for evaluating tracer discharge (mass per unit time) at specified control cross sections (CCS) of streams. The key transport processes included in the analysis are advection, degradation/decay, and kinetically controlled mass transfer in storage zones and in bed sediment. The transport in the bed sediment is described as a diffusion process, where the tracer may sorb onto the sediment. We have derived a general solution for tracer discharge in the Laplace domain wherefrom temporal moments are computed. The derived solutions may account for deterministic changes in morphological characteristics along stretches of streams. The results are illustrated for zeroth and first two moments where we show the combined effect of advection, degradation, physicochemical mass transfer, and morphology. For illustrative purposes, we assume morphology to change downstream following power laws suggested by Langbein [1947] and Leopold and Maddock [1953]. The moments depend nonlinearly on the downstream distance, following power laws that reflect the power laws for the hydraulic geometry. We define two main dimensionless parameters, namely, kinetic storage parameter alpha* and bed parameter M, that control the amount of tracer mass eventually discharged at any given CCS. For M approximate to greater than or equal to 0.3 the most dominant mechanism that controls the amount of ultimately discharged tracer mass is the exchange with the bed sediment. Once estimated from field data for stretches of specified streams, the dimensionless parameters can be used in the derived expressions for predictive purposes.

  • 39. Hassan, A. E.
    et al.
    Andricevic, R.
    Cvetkovic, Vladimir
    KTH, Superseded Departments, Land and Water Resources Engineering.
    Evaluation of analytical solute discharge moments using numerical modeling in absolute and relative dispersion frameworks2002In: Water resources research, ISSN 0043-1397, E-ISSN 1944-7973, Vol. 38, no 2Article in journal (Refereed)
    Abstract [en]

    Two-dimensional numerical simulations are used to validate the analytical solutions for the solute discharge moments. In addition to the analysis of classical absolute dispersion we also consider relative dispersion whereby plume meandering (deviation from mean flow path caused by velocity variations at scales larger than plume size) is removed. The numerical simulations are used within a Monte Carlo framework to assess the accuracy and robustness of the analytical predictions of the solute discharge moments (mean and variance). Results show that the analytical predictions deviate from the numerical simulations as the log conductivity variance increases. Deviation occurs for the mean as well as the variance of the solute discharge. The absolute dispersion formulation, however, shows better agreement with the numerical simulations than does the relative dispersion for strong heterogeneity and vice versa for small variability. The relative dispersion results, however, depend on the prediction of the ensemble mean of the plume arrival time, which differs between simulations and analytical solution. Using the first-order analytical estimate for this parameter leads to a much better agreement between the numerical and the analytical results for solute discharge moments in the relative dispersion case.

  • 40. Jaime Gomez-Hernandez, J.
    et al.
    Butler, James. J.
    Fiori, Aldo
    Bolster, Diogo
    Cvetkovic, Vladimir
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Land and Water Resources Engineering.
    Dagan, Gedeon
    Hyndman, David
    Introduction to special section on Modeling highly heterogeneous aquifers: Lessons learned in the last 30 years from the MADE experiments and others INTRODUCTION2017In: Water resources research, ISSN 0043-1397, E-ISSN 1944-7973, Vol. 53, no 4, p. 2581-2584Article in journal (Refereed)
  • 41.
    Juston, John M.
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering.
    DeBusk, Thomas A.
    Evidence and implications of the background phosphorus concentration of submerged aquatic vegetation wetlands in Stormwater Treatment Areas for Everglades restoration2011In: Water resources research, ISSN 0043-1397, E-ISSN 1944-7973, Vol. 47, p. W01511-Article in journal (Refereed)
    Abstract [en]

    The limits of phosphorus (P) removal from the 18,120 ha Stormwater Treatment Areas (STAs) for Everglades restoration depend largely on the performance of submerged aquatic vegetation (SAV) wetlands, as SAV treatment cells now provide final stage treatment for 85% of the STA project. A long-term internal P profile in STA-2 cell 3 (STA2C3), one of the longest-running and best performing SAV cells, demonstrated no further net removal in the back quarter of the cell once total P (TP) levels approached 15 mu g L-1. Inflow-outflow performance data from STA2C3 were analyzed at monthly and annual scales and were pooled with data from an additional eight STA SAV treatment cells. The pooled data allowed inference of background TP concentrations in SAV treatment cells using existing Bayesian methods. Results showed a central tendency of 16 mu g L-1(13 - 17, 90% bounds), insensitivity to P loads less than similar to 1.7 g m(-2) yr(-1), and interannual variability outside these bounds. Internal data from the STA2C3 profile provided validation. Background P concentrations of 7 and 6 mu g L-1 were identified for dissolved organic and particulate P fractions in the data pool, respectively, again similar to values in the STA2C3 gradient. Existing simulation modeling approaches for STA evaluations were identified as ineffective at or near background TP concentrations. Instead, we use an empirical and probabilistic approach based on full-scale data from STAs that produces annual risk of exceedance statistics and is easy to update. The current analysis suggests tangible risks for exceeding proposed annual discharge criteria from the STAs in the range of 16-20 mu g L-1.

  • 42. Larsson, Martin
    et al.
    Oden, Magnus
    Niemi, Auli
    Neretnieks, Ivars
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Engineering.
    Tsang, Chin-Fu
    A new approach to account for fracture aperture variability when modeling solute transport in fracture networks2013In: Water resources research, ISSN 0043-1397, E-ISSN 1944-7973, Vol. 49, no 4, p. 2241-2252Article in journal (Refereed)
    Abstract [en]

    A simple yet effective method is presented to include the effects of fracture aperture variability into the modeling of solute transport in fracture networks with matrix diffusion and linear sorption. Variable apertures cause different degrees of flow channeling, which in turn influence the contact area available for these retarding processes. Our approach is based on the concept of specific flow-wetted surface (sFWS), which is the fraction of the contact area over the total fracture surface area. Larsson et al. (2012) studied the relationship between sFWS and the standard deviation sigma ln K of the conductivity distribution over the fracture plane. Here an approach is presented to incorporate this into a fracture network model. With this model, solute transport through fracture networks is then analyzed. The cases of S=0 and S=1 correspond to those of no matrix diffusion and full matrix diffusion, respectively. In between, a sFWS breakpoint value can be defined, above which the median solute arrival time is proportional to the square of sFWS. For values below the critical sFWS (more channeled cases), the change is much slower, converging to that of no matrix diffusion. Results also indicate that details of assigning sFWS values for individual fractures in a network are not crucial; results of tracer transport are essentially identical to a case where all fractures have the mean sigma ln K (or corresponding mean sFWS) value. This is obviously due to the averaging effect of the network.

  • 43.
    Lindgren, Georg
    et al.
    KTH, Superseded Departments, Land and Water Resources Engineering.
    Destouni, Georgia
    Miller, Adrienne
    Solute transport through the integrated groundwater-stream system of a catchment2004In: Water resources research, ISSN 0043-1397, E-ISSN 1944-7973, Vol. 40, no 3, p. W03511-Article in journal (Refereed)
    Abstract [en]

    We present a coupled groundwater-stream model of catchment-scale solute transport, using a Lagrangian stochastic advective-sorptive travel time approach. We consider distributed solute input over an entire catchment and investigate the resulting stream solute breakthrough, subject to the possible solute spreading mechanisms: (1) variable groundwater advection and solute mass transfer between mobile and immobile groundwater zones and (2) in-stream advection, mixing, and solute mass transfer between stream water and hyporheic zone. Among these mechanisms we show that fractal solute spreading over a wide timescale range is, for realistic parameter values, obtained in the stream only for the condition combination of both variable solute advection and solute mass transfer in the groundwater, with mean groundwater advection to mass transfer rate ratio that falls within a certain value range and with only a small fraction of solute input mass following fast overland and/or storm soil water flow to the stream

  • 44. Magnusson, Jan
    et al.
    Gustafsson, David
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering. Swedish Meteorological and Hydrological Institute, Sweden .
    Hüsler, Fabia
    Jonas, Tobias
    Assimilation of point SWE data into a distributed snow cover model comparing two contrasting methods2014In: Water resources research, ISSN 0043-1397, E-ISSN 1944-7973, Vol. 50, no 10, p. 7816-7835Article in journal (Refereed)
    Abstract [en]

    In alpine and high-latitude regions, water resource decision making often requires large-scale estimates of snow amounts and melt rates. Such estimates are available through distributed snow models which in some situations can be improved by assimilation of remote sensing observations. However, in regions with frequent cloud cover, complex topography, or large snow amounts satellite observations may feature information of limited quality. In this study, we examine whether assimilation of snow water equivalent (SWE) data from ground observations can improve model simulations in a region largely lacking reliable remote sensing observations. We combine the model output with the point data using three-dimensional sequential data assimilation methods, the ensemble Kalman filter, and statistical interpolation. The filter performance was assessed by comparing the simulation results against observed SWE and snow-covered fraction. We find that a method which assimilates fluxes (snowfall and melt rates computed from SWE) showed higher model performance than a control simulation not utilizing the filter algorithms. However, an alternative approach for updating the model results using the SWE data directly did not show a significantly higher performance than the control simulation. The results show that three-dimensional data assimilation methods can be useful for transferring information from point snow observations to the distributed snow model.

    Key Points

    • Evaluating methods for assimilating snow observations into distributed models
    • Assimilation can improve model skill also at locations without observations
    • Assimilation of fluxes appears more successful than assimilation of states
  • 45.
    Mahmoudzadeh, Batoul
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Engineering.
    Liu, Longcheng
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Engineering.
    Moreno, Luis
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Engineering.
    Neretnieks, Ivars
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Engineering.
    Solute transport in fractured rocks with stagnant water zone and rock matrix composed of different geological layers-Model development and simulations2013In: Water resources research, ISSN 0043-1397, E-ISSN 1944-7973, Vol. 49, no 3, p. 1709-1727Article in journal (Refereed)
    Abstract [en]

    A model is developed to describe solute transport and retention in fractured rocks. It accounts for the fact that solutes can not only diffuse directly from the flowing channel into the adjacent rock matrix composed of different geological layers but also at first diffuse into the stagnant water zone occupied in part of the fracture and then from there into the rock matrix adjacent to it. In spite of the complexities of the system, it is shown that the analytical solution to the Laplace-transformed concentration at the outlet of the flowing channel is a product of two exponential functions, and it can be easily extended to describe solute transport through channels in heterogeneous fractured media consisting of an arbitrary number of rock units with piecewise constant geological properties. More importantly, by numerical inversion of the Laplace-transformed solution, the simulations made in this study help to gain insights into the relative significance and the different contributions of the rock matrix and the stagnant water zone in retarding solute transport in fractured rocks. It is found that, in addition to the intact wall rock adjacent to the flowing channel, the stagnant water zone and the rock matrix adjacent to it may also lead to a considerable retardation of solute in cases with a narrow channel.

  • 46.
    Marion, Andrea
    et al.
    Univ Padua, Dept Hydraul Maritime Environm & Geotechn Engn.
    Packman, Aaron
    Northwestern Univ, Dept Civil & Environm Engn, Evanston.
    Zaramella, Mattia
    Univ Padua, Dept Hydraul Maritime Environm & Geotechn Engn.
    Bottacin-Busolin, Andrea
    Univ Padua, Dept Hydraul Maritime Environm & Geotechn Engn.
    Hyporheic flows in stratified beds2008In: Water resources research, ISSN 0043-1397, E-ISSN 1944-7973, Vol. 44, no 9, p. W09433-Article in journal (Refereed)
    Abstract [en]

    Surface-subsurface exchange fluxes are receiving increasing interest because of their importance in the fate of contaminants, nutrients, and other ecologically relevant substances in a variety of aquatic systems. Solutions have previously been developed for pore water flows induced by geometrical irregularities such as bed forms for the cases of homogeneous sediment beds and idealized heterogeneous beds, but these solutions have not accounted for the fact that streambed sediments are subject to sorting processes that often produce well-defined subsurface structures. Sediments at the streambed surface are often coarser than the underlying material because of size-selective sediment transport, producing relatively thin armor layers. Episodic erosional and depositional processes also create thick layers of different composition within the porous medium, forming stratified beds. A series of experiments were conducted to observe conservative solute transport in armored and stratified beds. An analytical solution was developed for advective exchange with stratified beds and provides appropriate scaling of the physical variables that control exchange flows. The results show that armor layers are too thin to significantly alter the advective pumping process but provide significant solute storage at short time scales. Stratified beds with layers of significant thickness favor development of horizontal flow paths within the bed and change the rate of solute transfer across the stream-subsurface interface compared to homogeneous beds.

  • 47.
    Marion, Andrea
    et al.
    Univ Padua, Dept Hydraul Maritime Environm & Geotech Engn.
    Zaramella, Mattia
    Univ Padua, Dept Hydraul Maritime Environm & Geotech Engn.
    Bottacin-Busolin, Andrea
    Univ Padua, Dept Hydraul Maritime Environm & Geotech Engn.
    Solute transport in rivers with multiple storage zones: The STIR model2008In: Water resources research, ISSN 0043-1397, E-ISSN 1944-7973, Vol. 44, no 10, p. W10406-Article in journal (Refereed)
    Abstract [en]

    Solute transport in rivers is controlled by surface hydrodynamics and by mass exchanges between the surface stream and distinct retention zones. This paper presents a residence time model for stream transport of solutes, Solute Transport in Rivers (STIR), that accounts for the effect of the stream-subsurface interactions on river mixing. A stochastic approach is used to derive a relation between the in-stream solute concentration and the residence time distributions (RTDs) in different retention domains. Particular forms of the RTD are suggested for the temporary storage within surface dead zones and for bed form-induced hyporheic exchange. This approach is advantageous for at least two reasons. The first advantage is that exchange parameters can generally be expressed as functions of physical quantities that can be reasonably estimated or directly measured. This gives the model predictive capabilities, and the results can be generalized to conditions different from those directly observed in field experiments. The second reason is that individual exchange processes are represented separately by appropriate residence time distributions, making the model flexible and modular, capable of incorporating the effects of a variety of exchange processes and chemical reactions in a detailed way. The capability of the model is illustrated with an example and with an application to a field case. Analogies and differences with other established models are also discussed.

  • 48.
    Molin, Staffan
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Water Resources Engineering.
    Cvetkovic, Vladimir
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Water Resources Engineering.
    Microbial risk assessment in heterogeneous aquifers: 1. Pathogen transport2010In: Water resources research, ISSN 0043-1397, E-ISSN 1944-7973, Vol. 46, p. W05518-Article in journal (Refereed)
    Abstract [en]

    Pathogen transport in heterogeneous aquifers is investigated for microbial risk assessment. A point source with time-dependent input of pathogens is assumed, exemplified as a simple on-site sanitation installation, intermingled with water supply wells. Any pathogen transmission pathway (realization) to the receptor from a postulated infection hazard is viewed as a random event, with the hydraulic conductivity varying spatially. For aquifers where VAR[lnK] < 1 and the integral scale is finite, we provide relatively simple semianalytical expressions for pathogen transport that incorporate the colloid filtration theory. We test a wide range of Damkohler numbers in order to assess the significance of rate limitations on the aquifer barrier function. Even slow immobile inactivation may notably affect the retention of pathogens. Analytical estimators for microbial peak discharge are evaluated and are shown to be applicable using parameters representative of rotavirus and Hepatitis A with input of 10-20 days duration.

  • 49.
    Molin, Staffan
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Water Resources Engineering.
    Cvetkovic, Vladimir
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Water Resources Engineering.
    Stenstrom, T. A.
    Microbial risk assessment in heterogeneous aquifers: 2. Infection risk sensitivity2010In: Water resources research, ISSN 0043-1397, E-ISSN 1944-7973, Vol. 46, p. W05519-Article in journal (Refereed)
    Abstract [en]

    The entire chain of events of human disease transmitted through contaminated water, from pathogen introduction into the source (E. coli, rotavirus, and Hepatitis A), pathogen migration through the aquifer pathway, to ingestion via a supply well, and finally, the potential infection in the human host, is investigated. The health risk calculations are based on a relevant hazardous event with safe setback distances estimated by considering the infection risk from peak exposure in compliance with an acceptable level defined by a regulatory agency. A site-specific hypothetical scenario is illustrated for an aquifer with similar characteristics as the Cape Cod site, Massachusetts (United States). Relatively large variation of safe distances for the three index pathogens is found; individually, none of the index pathogens could predict the safe distance under the wide range of conditions investigated. It is shown that colloid filtration theory (CFT) with spatially variable attachment-detachment rates yields significantly different results from the effective CFT model (i.e., assuming spatially constant parameters).

  • 50.
    Morén, Ida
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Hydraulic Engineering.
    Wörman, Anders
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Hydraulic Engineering.
    Riml, Joakim
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Hydraulic Engineering.
    Design of Remediation Actions for Nutrient Mitigation in the Hyporheic Zone2017In: Water resources research, ISSN 0043-1397, E-ISSN 1944-7973, Vol. 53, no 11, p. 8872-8899Article in journal (Refereed)
    Abstract [en]

    Although hyporheic exchange has been shown to be of great importance for the overall water quality of streams, it is rarely considered quantitatively in stream remediation projects. A main driver of hyporheic exchange is the hydraulic head fluctuation along the streambed, which can be enhanced by modifications of the streambed topography. Here we present an analytical 2-D spectral subsurface flow model to estimate the hyporheic exchange associated with streambed topographies over a wide range of spatial scales; a model that was validated using tracer-test-results and measurements of hydraulic conductivity. Specifically, engineered steps in the stream were shown to induce a larger hyporheic exchange velocity and shorter hyporheic residence times compared to the observed topography in Tullstorps Brook, Sweden. Hyporheic properties were used to parameterize a longitudinal transport model that accounted for reactions in terms of first-order decay and instantaneous adsorption. Theoretical analyses of the mitigation effect for nitrate due to denitrification in the hyporheic zone show that there is a Damkohler number of the hyporheic zone, associated with several different stream geomorphologies, that optimizes nitrate mass removal on stream reach scale. This optimum can be limited by the available hydraulic head gradient given by the slope of the stream and the geological constraints of the streambed. The model illustrates the complex interactions between design strategies for nutrient mitigation, hyporheic flow patterns, and stream biogeochemistry and highlights the importance to diagnose a stream prior remediation, specifically to evaluate if remediation targets are transport or reaction controlled.

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