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Hongbin Zhan - One of the best experts on this subject based on the ideXlab platform.

  • new model of reactive transport in a single well push pull test with Aquitard effect and wellbore storage
    Hydrology and Earth System Sciences, 2020
    Co-Authors: Quanrong Wang, Hongbin Zhan, Junxia Wang, Wenguang Shi
    Abstract:

    Abstract. The model of single-well push–pull (SWPP) test has been widely used to investigate reactive radial dispersion in remediation or parameter estimation of in situ aquifers. Previous analytical solutions only focused on a completely isolated aquifer for the SWPP test, excluding any influence of Aquitards bounding the tested aquifer, and ignored the wellbore storage of the chaser and rest phases in the SWPP test. Such simplification might be questionable in field applications when test durations are relatively long because solute transport in or out of the bounding Aquitards is inevitable due to molecular diffusion and cross-formational advective transport. Here, a new SWPP model is developed in an aquifer–Aquitard system with wellbore storage, and the analytical solution in the Laplace domain is derived. Four phases of the test are included: the injection phase, the chaser phase, the rest phase and the extraction phase. As the permeability of the Aquitard is much smaller than the permeability of the aquifer, the flow is assumed to be perpendicular to the Aquitard; thus only vertical dispersive and advective transports are considered for the Aquitard. The validity of this treatment is tested against results grounded in numerical simulations. The global sensitivity analysis indicates that the results of the SWPP test are largely sensitive (i.e., influenced by) to the parameters of porosity and radial dispersion of the aquifer, whereas the influence of the Aquitard on results could not be ignored. In the injection phase, the larger radial dispersivity of the aquifer could result in the smaller values of breakthrough curves (BTCs), while there are greater BTC values in the chaser and rest phases. In the extraction phase, it could lead to the smaller peak values of BTCs. The new model of this study is a generalization of several previous studies, and it performs better than previous studies ignoring the Aquitard effect and wellbore storage for interpreting data of the field SWPP test reported by Yang et al. (2014).

  • New Model of Reactive Transport in Single-Well Injection-Withdrawal Test with Aquitard Effect
    Copernicus GmbH, 2020
    Co-Authors: Quanrong Wang, Wenguang Shi, Hongbin Zhan
    Abstract:

    Abstract. The model of single-well injection-withdrawal (SWIW) test has been widely used to investigate reactive radial dispersion in remediation or parameter estimation of the in situ aquifers. Previous analytical solutions only focused on a completely isolated aquifer for the SWIW test, excluding any influence of Aquitards bounding the tested aquifer. This simplification might be questionable in field applications when test durations are relatively long, because solute transport in or out of the bounding Aquitards is inevitable due to molecular diffusion and cross-formational advective transport. Here, a new SWIW model is developed in an aquifer-Aquitard system, and the analytical solution in the Laplace domain is derived. Four phases of the test are included: the injection phase, the chaser phase, the rest phase and the extraction phase. The Green's function method is employed for the solution in the extraction phase. As the permeability of Aquitard is much smaller than the permeability of the aquifer, the flow is assumed to be perpendicular to the Aquitard, thus only vertical dispersive and advective transports are considered for Aquitard. The validity of this treatment is tested by a numerical solution. The sensitivity analysis demonstrates that the influence of vertical flow velocity and porosity in the Aquitards, and radial dispersion of the aquifer is more sensitive to the SWIW test than other parameters. In the injection phase, the larger radial dispersivity of the aquifer could result in the smaller values of breakthrough curves (BTCs), while greater values of BTCs of the chaser and rest phases. In the extraction phase, it could lead to the smaller peak values of BTCs. The new model of this study performs better than previous studies excluding the Aquitard effect for interpreting data of the field SWIW test.

  • Aquitard horizontal dispersion on reactive solute transport in an aquifer Aquitard system
    Transport in Porous Media, 2016
    Co-Authors: Hongbin Zhan, Abolfazl Rezaei, Mohammad Zare
    Abstract:

    In this article, the effect of horizontal dispersion in an Aquitard (HDA) on reactive solute transport in an aquifer–Aquitard system is investigated. The governing equations in both the main aquifer and the Aquitard incorporate terms accounting for advection, horizontal and vertical dispersions, first-order irreversible decay and linear sorption. The analytical approach is developed by applying the Laplace transform along with cosine Fourier transforms. The Laplace domain solutions are inverted to the real-time domain solutions using the Stehfest algorithm. Generally, the results reveal that the role of HDA is generally not significant on solute transport. Nevertheless, its effect depends on the Aquitard/aquifer thickness ratio, the ratio of the Aquitard horizontal dispersion to the aquifer longitudinal dispersion, as well as Peclet numbers of both the aquifer and the Aquitard. At small Peclet numbers of the aquifer and/or large ratios of the Aquitard horizontal dispersion to the aquifer longitudinal dispersion and/or large Peclet numbers of the Aquitard, ignoring HDA may cause some moderate errors in concentration and stored mass within the Aquitard, especially at longer times. As a consequence, the error varies across the Aquitard width and depends on changes in slope of the vertical concentration profile there.

  • a new type curve method for estimating Aquitard hydraulic parameters in a multi layered aquifer system
    Journal of Hydrology, 2015
    Co-Authors: Chao Zhuang, Zhifang Zhou, Hongbin Zhan, Guangya Wang
    Abstract:

    Summary We propose a new type curve method for estimating the hydraulic conductivity ( K ) and the specific storage ( S s ) of an Aquitard in a multi-layered aquifer system. Theoretical type curves of rate of Aquitard compaction versus time are obtained through drawdown-time series in the Aquitard, under a condition that the drawdown history of the underlying aquifer can be approximated as piecewise linear segments (PLS), in each of which the drawdown shows a linear increase trend with time. Comparing with previous analytical solutions, which are limited by the assumption of a constant head in the overlying unconfined aquifer, the superposition principle can be called when water levels fluctuate with time in both upper and lower aquifers adjacent to the Aquitard. When applying the new PLS method to estimate K and S s values of an Aquitard, the starting point of drawdown history at adjacent aquifers should be determined at first. After that the drawdown history is approximated as PLS to obtain drawdown rate of change for each linear stage and turning points of drawdown history. The new PLS method is demonstrated at a field site in Changzhou City, Jiangsu Province of China. Estimated results show that K and S s are, respectively, 9.80 × 10 −10  m/s and 4.46 × 10 −4  m −1 for a thick Aquitard, and 2.34–3.50 × 10 −10  m/s and 2.28 × 10 −4  m −1 for a thin Aquitard. Estimated field K values, as well as S s values, through the new PLS method, are generally in accordance with the results obtained from the geologic method by Konikow and Neuzil (2007). They are also in agreements with the numerically calibrated results of Shi et al. (2008a) at the regional scale and the laboratory experimental values of in-situ soil samples collected by Geological Survey of Jiangsu Province of China.

  • on the Aquitard aquifer interface flow and the drawdown sensitivity with a partially penetrating pumping well in an anisotropic leaky confined aquifer
    Journal of Hydrology, 2015
    Co-Authors: Qinggao Feng, Hongbin Zhan
    Abstract:

    Summary A mathematical model for describing groundwater flow to a partially penetrating pumping well of a finite diameter in an anisotropic leaky confined aquifer is developed. The model accounts for the jointed effects of Aquitard storage, aquifer anisotropy, and wellbore storage by treating the Aquitard leakage as a boundary condition at the Aquitard–aquifer interface rather than a volumetric source/sink term in the governing equation, which has never developed before. A new semi-analytical solution for the model is obtained by the Laplace transform in conjunction with separation of variables. Specific attention was paid on the flow across the Aquitard–aquifer interface, which is of concern if Aquitard and aquifer have different pore water chemistry. Moreover, Laplace-domain and steady-state solutions are obtained to calculate the rate and volume of (total) leakage through the Aquitard–aquifer interface due to pump in a partially penetrating well, which is also useful for engineers to manager water resources. The sensitivity analyses for the drawdown illustrate that the drawdown is most sensitive to the well partial penetration. It is apparently sensitive to the aquifer anisotropic ratio over the entire time of pumping. It is moderately sensitive to the Aquitard/aquifer specific storage ratio at the intermediate times only. It is moderately sensitive to the Aquitard/aquifer vertical hydraulic conductivity ratio and the Aquitard/aquifer thickness ratio with the identical influence at late times.

Zhifang Zhou - One of the best experts on this subject based on the ideXlab platform.

  • parameter estimation of an overconsolidated Aquitard subjected to periodic hydraulic head variations within adjacent aquifers
    Journal of Hydrology, 2020
    Co-Authors: Zhifang Zhou, Zhi Dou, Chao Zhuang, Walter A Illman, Jinguo Wang
    Abstract:

    Abstract Extensometers provide long-term records of deformation over a depth interval of interest. An overconsolidated Aquitard usually undergoes elastic deformation if the hydraulic head within adjacent aquifers remains higher than the preconsolidation head within the Aquitard. The vertical hydraulic conductivity K v and elastic skeletal specific storage S ske are two critical parameters that control the deformation behavior of an overconsolidated Aquitard, and they could be interpreted from valuable extensometer data. An analytical solution for the elastic Aquitard deformation caused by periodic hydraulic head variations (PHHV) within adjacent aquifers is derived using the separation of variables method based on Euler’s formula. The phase difference in PHHV between adjacent aquifers is found to reduce the amplitude of periodic Aquitard deformation. Meanwhile, the phase difference is found to cause no influence on the growth pattern of the phase shift, which is between the periodic Aquitard deformation and PHHV, versus the period. A new parameter estimation method is further proposed to interpret Aquitard K v and S ske from periodic Aquitard deformation data. This new method yields robust K v and S ske estimates of a moderately thick Aquitard, whose deformation history has been recorded by an extensometer, located in Shanghai, China. The field study confirms that the phase difference in PHHV between the aquifers adjacent to the overconsolidated Aquitard of interest cannot be ignored.

  • geostatistical inverse modeling for the characterization of Aquitard heterogeneity using long term multi extensometer data
    Journal of Hydrology, 2019
    Co-Authors: Zhifang Zhou, Chao Zhuang, Walter A Illman, Jinguo Wang
    Abstract:

    Abstract The classical Aquitard drainage model COMPAC was used to simulate the deformation of a one-dimensional vertically heterogeneous Aquitard (i.e. Heter-COMPAC). By coupling Heter-COMPAC with the quasi-linear geostatistical inversion approach, the vertical heterogeneities of hydraulic conductivity ( K v ), elastic specific storage ( S ske ) and inelastic specific storage ( S skp ) fields could be characterized with the availability of long-term multi-extensometer data. The methodology was first tested through a group of ten synthetic cases with randomly generated K v , S ske and S skp fields. Results of the synthetic cases revealed that a geostatistical model could characterize the variability of Aquitard hydraulic parameter fields, and yields improved fits of simulated versus observed zone deformation than a geological model that treats each zone to be homogeneous. Subsequently, the methodology was applied to a research site situated in Changzhou city, Jiangsu Province, China, where long-term deformation behaviors of the strata within the aquifer-Aquitard system have been monitored. Vertical heterogeneities of K v , S ske and S skp fields of the investigated Aquitard at the site were characterized using the quasi-linear geostatistical approach. The correlation length of the three fields that yielded the best-quality fit was assessed to be approximately 50 m, and the fitting quality was slightly improved in comparison with that produced from calibrating a geological or zonation model. Through Monte Carlo analysis of Aquitard deformation utilizing the inversed parameters and corresponding uncertainties, the investigated Aquitard is estimated to have compacted −914.8 ± (42.6) mm before the rise in groundwater levels in adjoining aquifers.

  • Contaminant transport in a largely-deformed Aquitard affected by delayed drainage
    Journal of contaminant hydrology, 2019
    Co-Authors: Zhifang Zhou, Yunfeng Dai, Beibing Dai
    Abstract:

    Abstract This paper employed a one-dimensional large-deformation model in consideration of the coupling of mechanical consolidation and solute transport, to study the transport of contaminants in a largely-deformed Aquitard. An analytical solution has been derived to describe the drawdown variation in a largely-deformed Aquitard which is subjected to abrupt hydraulic head decline in adjacent confined aquifers. The pore water flux and void ratio variation were obtained on the basis of the analytical solution. The equation for transient contaminant flux was solved by the finite difference method. A hypothetical case study was done to explore the effect of consolidation on the contaminant transport in a largely-deformed Aquitard. The transit time of contaminant transport in the Aquitard is mainly determined by the hydraulic conductivity, thickness, partitioning coefficient, void ratio and effective diffusion coefficients of Aquitard, as well as the drawdown in the adjacent confined aquifer. The impact of delayed drainage on the contaminant transport in the largely-deformed Aquitard is mainly controlled by two factors: the transient water flow and the decrease of Aquitard thickness, in the process of Aquitard consolidation. The former increases the breakthrough time of contaminant transport in the Aquitard, and the latter gives rise to an opposite case with its effect decreasing with increasing contaminant partitioning coefficient for soil particles sorption. A larger deformation, which may be induced by a larger thickness, higher specific storativity of Aquitard or a larger drawdown of the adjacent confined aquifer, and a lower hydraulic conductivity of Aquitard cause a more significant impact of delayed drainage on the contaminant transport in an Aquitard.

  • Delayed Drainage of a Largely Deformed Aquitard due to Abrupt Water Head Decline in Adjacent Aquifer
    Geofluids, 2018
    Co-Authors: Zhaofeng Li, Mingyuan Li, Zhifang Zhou, Boran Zhang
    Abstract:

    A governing equation of drawdown was put forward to describe the one-dimensional large-strain consolidation behavior of an Aquitard without consideration of the creeping effect. An analytical solution was derived to characterize the drawdown variation in the Aquitard subjected to sudden hydraulic head decline in adjacent confined aquifer. The characteristics of the groundwater dynamics and water balance in the Aquitard have been analyzed based on the analytical solution. A comparison analysis of results has been made between the large-strain theory and the classical small-strain theory. The type-curve fitting method was used to determine the hydrogeological parameters, on the basis of the observed variations of Aquitard deformation with time. The analytical solution was thus validated by a comparison with the observed experimental results. It is found that the water drainage of Aquitard is obviously delayed in response to the water head decline in the adjacent aquifer. All delayed water release from the Aquitard terminates when the consolidation time reaches the value of . The Aquitard deformation predicted by the large-strain theory is less than that given by the small-strain theory, and the prediction discrepancy of these two theories increases with the increasing soil compressibility.

  • Contaminant transport in a small deformation Aquitard affected by the delayed drainage phenomenon
    Hydrological Processes, 2017
    Co-Authors: Zhifang Zhou, Yunfeng Dai, Yong Huang, Qiaona Guo, Cuiying Zhou
    Abstract:

    This paper presents a formulation accounting for the effect of Delayed Drainage Phenomenon (DDP) on the breakthrough of contaminant flux in an Aquitard, by considering the movement of soil particles, porosity variation, hydraulic head variation and transient flow during the consolidation. The water flow equation in an Aquitard was based on the Terzaghi's consolidation theory, and the contaminant transport equation was derived on the basis of the mass balance law. Two cases were used to illustrate the effect of DDP on the contaminant transport in an Aquitard of small deformation. It is found that the breakthrough time of contaminant in an Aquitard is very long, which is mainly ascribed to the low permeability of Aquitard and sorption of soil particles. It is also found that the increase of depletion, which is in general induced by the increase of thickness and specific storativity, and the decrease of hydraulic conductivity, enhance the impact of DDP on the contaminant transport in an Aquitard. A larger delay index (τ0) of DDP gives a greater Delay Breakthrough Time (DBT) of solute transport in an Aquitard, which controls the difference of the breakthrough time of contaminant transport in Aquitards with and without the occurrence of DDP. For the cases where advection plays a dominant role during the process of solute transport, τ0 is almost linearly correlated with DBT, and the ratio of DBT over the breakthrough time without consideration of DDP also approximately shows a linear relationship with the ratio of specific storativity to porosity, given a fixed drawdown in the adjacent aquifer with the sorption being ignored.

Chao Zhuang - One of the best experts on this subject based on the ideXlab platform.

  • parameter estimation of an overconsolidated Aquitard subjected to periodic hydraulic head variations within adjacent aquifers
    Journal of Hydrology, 2020
    Co-Authors: Zhifang Zhou, Zhi Dou, Chao Zhuang, Walter A Illman, Jinguo Wang
    Abstract:

    Abstract Extensometers provide long-term records of deformation over a depth interval of interest. An overconsolidated Aquitard usually undergoes elastic deformation if the hydraulic head within adjacent aquifers remains higher than the preconsolidation head within the Aquitard. The vertical hydraulic conductivity K v and elastic skeletal specific storage S ske are two critical parameters that control the deformation behavior of an overconsolidated Aquitard, and they could be interpreted from valuable extensometer data. An analytical solution for the elastic Aquitard deformation caused by periodic hydraulic head variations (PHHV) within adjacent aquifers is derived using the separation of variables method based on Euler’s formula. The phase difference in PHHV between adjacent aquifers is found to reduce the amplitude of periodic Aquitard deformation. Meanwhile, the phase difference is found to cause no influence on the growth pattern of the phase shift, which is between the periodic Aquitard deformation and PHHV, versus the period. A new parameter estimation method is further proposed to interpret Aquitard K v and S ske from periodic Aquitard deformation data. This new method yields robust K v and S ske estimates of a moderately thick Aquitard, whose deformation history has been recorded by an extensometer, located in Shanghai, China. The field study confirms that the phase difference in PHHV between the aquifers adjacent to the overconsolidated Aquitard of interest cannot be ignored.

  • geostatistical inverse modeling for the characterization of Aquitard heterogeneity using long term multi extensometer data
    Journal of Hydrology, 2019
    Co-Authors: Zhifang Zhou, Chao Zhuang, Walter A Illman, Jinguo Wang
    Abstract:

    Abstract The classical Aquitard drainage model COMPAC was used to simulate the deformation of a one-dimensional vertically heterogeneous Aquitard (i.e. Heter-COMPAC). By coupling Heter-COMPAC with the quasi-linear geostatistical inversion approach, the vertical heterogeneities of hydraulic conductivity ( K v ), elastic specific storage ( S ske ) and inelastic specific storage ( S skp ) fields could be characterized with the availability of long-term multi-extensometer data. The methodology was first tested through a group of ten synthetic cases with randomly generated K v , S ske and S skp fields. Results of the synthetic cases revealed that a geostatistical model could characterize the variability of Aquitard hydraulic parameter fields, and yields improved fits of simulated versus observed zone deformation than a geological model that treats each zone to be homogeneous. Subsequently, the methodology was applied to a research site situated in Changzhou city, Jiangsu Province, China, where long-term deformation behaviors of the strata within the aquifer-Aquitard system have been monitored. Vertical heterogeneities of K v , S ske and S skp fields of the investigated Aquitard at the site were characterized using the quasi-linear geostatistical approach. The correlation length of the three fields that yielded the best-quality fit was assessed to be approximately 50 m, and the fitting quality was slightly improved in comparison with that produced from calibrating a geological or zonation model. Through Monte Carlo analysis of Aquitard deformation utilizing the inversed parameters and corresponding uncertainties, the investigated Aquitard is estimated to have compacted −914.8 ± (42.6) mm before the rise in groundwater levels in adjoining aquifers.

  • a joint analytic method for estimating Aquitard hydraulic parameters
    Ground Water, 2017
    Co-Authors: Zhifang Zhou, Chao Zhuang, Walter A Illman
    Abstract:

    The vertical hydraulic conductivity (Kv ), elastic (Sske ), and inelastic (Sskv ) skeletal specific storage of Aquitards are three of the most critical parameters in land subsidence investigations. Two new analytic methods are proposed to estimate the three parameters. The first analytic method is based on a new concept of delay time ratio for estimating Kv and Sske of an Aquitard subject to long-term stable, cyclic hydraulic head changes at boundaries. The second analytic method estimates the Sskv of the Aquitard subject to linearly declining hydraulic heads at boundaries. Both methods are based on analytical solutions for flow within the Aquitard, and they are jointly employed to obtain the three parameter estimates. This joint analytic method is applied to estimate the Kv , Sske , and Sskv of a 34.54-m thick Aquitard for which the deformation progress has been recorded by an extensometer located in Shanghai, China. The estimated results are then calibrated by PEST (Doherty 2005), a parameter estimation code coupled with a one-dimensional Aquitard-drainage model. The Kv and Sske estimated by the joint analytic method are quite close to those estimated via inverse modeling and performed much better in simulating elastic deformation than the estimates obtained from the stress-strain diagram method of Ye and Xue (2005). The newly proposed joint analytic method is an effective tool that provides reasonable initial values for calibrating land subsidence models.

  • estimating hydraulic parameters of a heterogeneous Aquitard using long term multi extensometer and groundwater level data
    Hydrogeology Journal, 2017
    Co-Authors: Zhifang Zhou, Qiaona Guo, Chao Zhuang, Walter A Illman, Jinguo Wang
    Abstract:

    The classical Aquitard-drainage model COMPAC has been modified to simulate the compaction process of a heterogeneous Aquitard consisting of multiple sub-units (Multi-COMPAC). By coupling Multi-COMPAC with the parameter estimation code PEST++, the vertical hydraulic conductivity (K v) and elastic (S ske) and inelastic (S skp) skeletal specific-storage values of each sub-unit can be estimated using observed long-term multi-extensometer and groundwater level data. The approach was first tested through a synthetic case with known parameters. Results of the synthetic case revealed that it was possible to accurately estimate the three parameters for each sub-unit. Next, the methodology was applied to a field site located in Changzhou city, China. Based on the detailed stratigraphic information and extensometer data, the Aquitard of interest was subdivided into three sub-units. Parameters K v, S ske and S skp of each sub-unit were estimated simultaneously and then were compared with laboratory results and with bulk values and geologic data from previous studies, demonstrating the reliability of parameter estimates. Estimated S skp values ranged within the magnitude of 10−4 m−1, while K v ranged over 10−10–10−8 m/s, suggesting moderately high heterogeneity of the Aquitard. However, the elastic deformation of the third sub-unit, consisting of soft plastic silty clay, is masked by delayed drainage, and the inverse procedure leads to large uncertainty in the S ske estimate for this sub-unit.

  • a new type curve method for estimating Aquitard hydraulic parameters in a multi layered aquifer system
    Journal of Hydrology, 2015
    Co-Authors: Chao Zhuang, Zhifang Zhou, Hongbin Zhan, Guangya Wang
    Abstract:

    Summary We propose a new type curve method for estimating the hydraulic conductivity ( K ) and the specific storage ( S s ) of an Aquitard in a multi-layered aquifer system. Theoretical type curves of rate of Aquitard compaction versus time are obtained through drawdown-time series in the Aquitard, under a condition that the drawdown history of the underlying aquifer can be approximated as piecewise linear segments (PLS), in each of which the drawdown shows a linear increase trend with time. Comparing with previous analytical solutions, which are limited by the assumption of a constant head in the overlying unconfined aquifer, the superposition principle can be called when water levels fluctuate with time in both upper and lower aquifers adjacent to the Aquitard. When applying the new PLS method to estimate K and S s values of an Aquitard, the starting point of drawdown history at adjacent aquifers should be determined at first. After that the drawdown history is approximated as PLS to obtain drawdown rate of change for each linear stage and turning points of drawdown history. The new PLS method is demonstrated at a field site in Changzhou City, Jiangsu Province of China. Estimated results show that K and S s are, respectively, 9.80 × 10 −10  m/s and 4.46 × 10 −4  m −1 for a thick Aquitard, and 2.34–3.50 × 10 −10  m/s and 2.28 × 10 −4  m −1 for a thin Aquitard. Estimated field K values, as well as S s values, through the new PLS method, are generally in accordance with the results obtained from the geologic method by Konikow and Neuzil (2007). They are also in agreements with the numerically calibrated results of Shi et al. (2008a) at the regional scale and the laboratory experimental values of in-situ soil samples collected by Geological Survey of Jiangsu Province of China.

Leonard I Wassenaar - One of the best experts on this subject based on the ideXlab platform.

  • in situ experiment to determine advective diffusive controls on solute transport in a clay rich Aquitard
    Journal of Contaminant Hydrology, 2012
    Co-Authors: Lee S Barbour, Jim M Hendry, Leonard I Wassenaar
    Abstract:

    Abstract Solute transport in clay-rich Aquitards is characterized as molecular diffusion- or advection-dominated based on the Peclet number (Pe). However, few field-based measurements of the coefficient of molecular diffusion (De) exist, and none with a range of advection- or diffusion-dominated conditions in the same Aquitard. In this long-term field experiment, standing water in a recovering well was spiked with deuterium (2H), then water-level recovery and δ2H values were monitored as the well returned to static conditions over 1054 days. After a second 2H spike, water levels and δ2H values were monitored to day 1644 while under near static conditions. Modeling of the second spike was used to define the De of 2H as (3–4) × 10− 10 m2 s− 1 for an accessible porosity of 0.31. Reservoir concentrations from the initial spike were modeled to define the transition from advection- to diffusion-dominated transport. This occurred after 200 days, consistent with a transition in Pe from  1 when the length term is taken as the radial extent of the tracer plume (normalized concentration

  • controls on the long term downward transport of δ h of water in a regionally extensive two layered Aquitard system
    Water Resources Research, 2011
    Co-Authors: M J Hendry, S L Barbour, J Zettl, V L Chostner, Leonard I Wassenaar
    Abstract:

    [1] Seven high-resolution (0.3–0.6 m depth intervals), 1-D vertical profiles of the δ²H of pore water were collected across a 300 km2 study area in southern Saskatchewan, Canada, to define the vertical controls on solute transport in a >120 m thick, two-layered Aquitard system. The 1-D profiles were augmented with an existing δ²H profile collected from a previous study. The surficial Aquitard in the area consists of Quaternary deposits (either glacial till or lacustrine deposits; 13 to 128 m thick) underlain by an upper Cretaceous claystone Aquitard (80–110 m thick). The shape of the individual δ²H profiles and associated 1-D transport modeling suggest diffusion is the regionally dominant vertical transport mechanism across the Aquitards. The profile shape is controlled by the thickness of the Quaternary deposit and the δ²H value at the upper boundary, which coincides with the depth of the water table. The upper boundary δ²H value varies considerably across the area (−149‰ to −101‰), perhaps due to differences in local hydrological conditions (e.g., slope, aspect, infiltration) across the landscape. Modeling of all profiles shows the timing for till deposition and the timing of climate change during the Holocene are consistent across the area (∼30 ka and 7–10 ka before the present, respectively), corroborating other studies. This study provides insights into the hydrogeologic controls on solute transport in an Aquitard system and associated geologic and climatic changes for a prairie region over the past 30 ka, and improves our understanding of initial and time-dependent transport boundary conditions for the study of Aquitards.

  • origin and migration of dissolved organic carbon fractions in a clay rich Aquitard 14c and δ13c evidence
    Water Resources Research, 2005
    Co-Authors: M J Hendry, Leonard I Wassenaar
    Abstract:

    [1] The origin and long-term transport of dissolved organic carbon (DOC) and its high molecular weight (HMW) and low molecular weight (LMW) fractions were investigated in a clay-rich till Aquitard system. DOC concentrations decreased systematically with depth from 168 mg L−1 in the surficial fractured zone (1.2 m) to minimum values of 12–16 mg L−1 from 15 to 43 m depth in the nonfractured Aquitard. The HMW and LMW DOC fractions and their corresponding δ13C values also decreased systematically with depth. Numerical transport simulations of the downward migration of DOC from the soil zone into the Aquitard closely approximated field-measured values and show transport of DOC was controlled by diffusive mixing. The depth trends for HMW and LMW DOC fractions and δ13C support hypothesized transport via diffusion, as well as earlier findings that microbial respiration in this nonfractured Aquitard was negligible over the time period studied. The 14C content of the HMW DOC fraction decreased systematically with depth from 87 percent modern carbon (pmC) at 1.2 m to 13–15 pmC from 15 to 43 m depth. A simple model accounting for diffusive mixing and radioactive decay described the 14C profile in the Aquitard. Radiocarbon measurements, transport modeling, and δ13C data suggest DOC and its fractions were derived from two distinct end-members: soil organic carbon formed since the Holocene (∼10 ka B.P.) and DOC in connate pore water (∼15 ka B.P.).

  • characterizing the hydrogeology of a complex clay rich Aquitard system using detailed vertical profiles of the stable isotopes of water
    Journal of Hydrology, 2004
    Co-Authors: Jim M Hendry, Leonard I Wassenaar, C J Kelln, J Shaw
    Abstract:

    Abstract High-resolution 1D profiles of the stable isotopes of porewater (δ2H and δ18O) obtained by direct porewater-equilibration of core samples were used to identify hydrogeologic zones in a thick, complex, till Aquitard system in Saskatchewan, Canada. Detailed 1D isotope profiles revealed the presence of three distinct hydrogeological zones: an upper (5–10 m), an intermediate (10–30 m), and a lower (30–62.5 m) till zone. The upper hydrogeological zone was controlled by a sand layer having a high hydraulic conductivity (K). The lack of vertical variability in the stable isotope data in the intermediate zone suggested groundwater flow and solute transport was controlled by a system of interconnected vertical fractures and lateral sand layers. The curved shape of the isotope profile in the lower till zone suggested that solute transport in this zone was controlled mainly by molecular diffusion. We show that high-resolution vertical stable isotope profiles of porewater obtained from core samples and direct equilibration yield cost-effective and invaluable hydrogeologic information on groundwater flow in Aquitard systems that cannot be realistically obtained by construction of costly conventional piezometer bundles (i.e. δ2H and δ18O analyses of water samples and K determinations). Further, the direct equilibration approach overcomes the problem of piezometer leakage in low K Aquitards.

  • transport and geochemical controls on the distribution of solutes and stable isotopes in a thick clay rich till Aquitard canada
    Isotopes in Environmental and Health Studies, 2004
    Co-Authors: Jim M Hendry, Leonard I Wassenaar
    Abstract:

    A comprehensive understanding of the transport and geochemical processes controlling solutes in clay-rich Aquitard confining units is needed to accurately predict the long-term migration of contaminants into the subsurface. To this end, the geochemical and stable isotopic composition of porewaters in the upper 22 m of a thick, unoxidized and nonfractured clay-rich, till Aquitard (Sutherland Group) was examined in detail. The Aquitard is overlain by about 8 m of oxidized and fractured till (Floral Fm). Concentrations of TDS, SO4 2−, HCO3 −, Cl−, Na+, Mg2+, Ca2+ and porewater deuterium were greater in the Floral Fm and decreased with depth through the Aquitard. The elevated and seasonably variable solute concentrations in the oxidized Floral Fm were attributed to geochemical weathering and dynamic water movement through fractures. Good fits between measured δ2H, TDS, SO4 2−, Cl− and HCO3 − profiles through the Aquitard and simulated solute transport profiles were obtained by diffusion (without advection) wi...

Jiu Jimmy Jiao - One of the best experts on this subject based on the ideXlab platform.

  • abundance and diversity of aerobic anaerobic ammonia ammonium oxidizing microorganisms in an ammonium rich Aquitard in the pearl river delta of south china
    Microbial Ecology, 2018
    Co-Authors: Kwokho Lee, Ya Wang, Yongfeng Wang, Jiu Jimmy Jiao
    Abstract:

    Natural occurring groundwater with abnormally high ammonium concentrations was discovered in the aquifer-Aquitard system in the Pearl River Delta, South China. The community composition and abundance of aerobic/anaerobic ammonia/ammonium-oxidizing microorganisms (AOM) in the Aquitard were investigated in this study. The alpha subunit of ammonia monooxygenase gene (amoA) was used as the biomarker for the detection of aerobic ammonia-oxidizing archaea (AOA) and bacteria (AOB), and also partial 16S rRNA gene for Plantomycetes and anaerobic ammonium-oxidizing (anammox) bacteria. Phylogenetic analysis showed that AOA in this Aquitard were affiliated with those from water columns and wastewater treatment plants; and AOB were dominated by sequences among the Nitrosomonas marina/Nitrosomonas oligotropha lineage, which were affiliated with environmental sequences from coastal eutrophic bay and subtropical estuary. The richness and diversity of both AOA and AOB communities had very little variations with the depth. Candidatus Scalindua-related sequences dominated the anammox bacterial community. AOB amoA gene abundances were always higher than those of AOA at different depths in this Aquitard. The Pearson moment correlation analysis showed that AOA amoA gene abundance positively correlated with pH and ammonium concentration, whereas AOB amoA gene abundance negatively correlated with C/N ratio. This is the first report that highlights the presence with low diversity of AOM communities in natural Aquitard of rich ammonium.

  • chloride as tracer of solute transport in the aquifer Aquitard system in the pearl river delta china
    Hydrogeology Journal, 2016
    Co-Authors: Xingxing Kuang, Jiu Jimmy Jiao, Ya Wang
    Abstract:

    A 1D numerical model is constructed to investigate the impact of sedimentation and sea level changes on transport of Cl− in the aquifer–Aquitard system in the Pearl River Delta (PRD), China. The model simulates the evolution of the vertical Cl− concentration profiles during the Holocene. Sedimentation is modeled as a moving boundary problem. Chloride concentration profiles are reconstructed for nine boreholes, covering a wide area of the PRD, from northwest to southeast. Satisfactory agreement is obtained between simulated and measured Cl− concentration profiles. Diffusion solely is adequate to reproduce the vertical Cl− concentration profiles, which indicates that diffusion is the regionally dominant vertical transport mechanism across the Aquitards in the PRD. The estimated effective diffusion coefficients of the Aquitards range from 2.0 × 10–11 to 2.0 × 10–10 m2/s. The effective diffusion coefficients of the aquifers range from 3.0 × 10–11 to 4.0 × 10–10 m2/s. Advective transport tends to underestimate Cl− concentrations in the Aquitard and overestimate Cl− concentrations in the basal aquifer. The results of this study will help understand the mechanisms of solute transport in the PRD and other deltas with similar geological and hydrogeological characteristics.

  • investigation on bacterial community and diversity in the multilayer aquifer Aquitard system of the pearl river delta china
    Ecotoxicology, 2014
    Co-Authors: Kun Liu, Jiu Jimmy Jiao
    Abstract:

    Bacteria play an important role in groundwater chemistry. The groundwater resource in the Pearl River Delta (PRD) is responsible for 50 million people's water requirement. High amount of ammonium, arsenic and methane had been reported in groundwater of the PRD, which was considered as the result of intensive bacterial metabolism in the multilayer aquifer-Aquitard system. To investigate bacterial community in this system and its relation with groundwater chemistry, sediment and groundwater samples were taken from representative locations in the PRD at different lithological units. Bacterial 16S rRNA gene clone libraries were constructed for microbial identifications and community structures in different strata. Canonical correlation analysis between bacterial linages and environment variables (Cl(-), PO4(3-), SO4(2-), NH4(+)) showed that community structures were significantly modified by geological conditions. Higher bacterial diversity was observed in samples from the Holocene Aquitard M1 and aquifer T1, while in the older Aquitard M2 and basal aquifer T2, bacterial diversity was much lower. Chloroflexi, γ-proteobacteria and δ-proteobacteria were the dominant phyla in the Aquitard sediment. β-proteobacteria was the dominant phylum in sediment which was strongly influenced by fresh water. The results of this study demonstrated that bacterial community contains information of geological events such as sea transgression and deltaic evolution, and microbes in the Aquitards have great potential in dominating groundwater quality in aquifers.

  • contribution of the Aquitard to the regional groundwater hydrochemistry of the underlying confined aquifer in the pearl river delta china
    Science of The Total Environment, 2013
    Co-Authors: Ya Wang, Jiu Jimmy Jiao, John A Cherry, Chun Ming Lee
    Abstract:

    article i nfo Aquitards are capable of generating and preserving large amounts of chemicals. The release of the chemicals from the Aquitards poses a potential contamination risk to groundwater that may be used as a drinking water source. This work aimed to identify the contribution of hydrogeochemical processes in the Aquitards to groundwater hydrochemistry in the underlying confined basal aquifer by studying the coastal Quaternary aquifer-Aquitard system of the Pearl River Delta, China. The system was submerged by paleo-seawater in the early Holocene and mainly receives infiltration of precipitation at present, as indicated by investigations on stable isotopes (δ 2 H, δ 18 O), water chemistry (SO4 2� and Cl � ) and salinity. Significant correlations between total dissolved solids in the basal aquifer and the thickness of the overlying Aquitard further suggested the contribution of the Aquitard to the groundwater hydrochemistry in the aquifer. Significant correlations between the chloride concentrations in Aquitard porewater and that in groundwater in the aquifer, and between the thickness of the Aquitard and the chloride concentrations in groundwater indicated the strong influence of the Aquitard on the chloride in the aquifer. This is probably because the low-permeability Aquitard is capable of preserving the paleo-seawater in the aquifer and releasing the salinity from the Aquitard down to the aquifer via downward flow or diffusion. Isotopic and geochemical studies revealed that the Aquitard is also responsible for generating and preserving large amounts of naturally occurring ammonium. Analysis between the concentrations of ammonium in groundwater in the basal aquifer and the total available ammonium in Aquitard sediments suggested that the former is significantly controlled by the latter.

  • occurrence and geochemical behavior of arsenic in a coastal aquifer Aquitard system of the pearl river delta china
    Science of The Total Environment, 2012
    Co-Authors: Ya Wang, Jiu Jimmy Jiao, John A Cherry
    Abstract:

    Abstract Elevated concentrations of arsenic, up to 161 μg/L, have been identified in groundwater samples from the confined basal aquifer underlying the Aquitard of the Pearl River Delta (PRD). Both aquatic arsenic in pore water and solid arsenic in the sediments in the basal aquifer and Aquitard were identified. Arsenic speciation of groundwater in the basal aquifer was elucidated on a pH-Eh diagram. In the PRD, arsenic is enriched in groundwater having both low and high salinity, and arsenic enriched groundwater is devoid of dissolved oxygen, has negative Eh values, is slightly alkaline, and has abnormally high concentrations of ammonium and dissolved organic carbon, but low concentrations of nitrate and nitrite. Results of geochemical and hydrochemical analyses and sequential extraction analysis suggest that reductive dissolution of iron oxyhydroxide could be one of the important processes that mobilized solid arsenic. We speculate that mineralization of sedimentary organic matter could also contribute to aquatic arsenic. Scanning electron microscope analysis confirms that abundant authigenic pyrite is present in the sediments. Sulphate derived from paleo-seawater served as the important sulfur source for authigenic pyrite formation. Co-precipitation of arsenic with authigenic pyrite significantly controlled concentrations of aquatic arsenic in the coastal aquifer–Aquitard system.