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Transient hydraulic tomography (THT) is a robust method of aquifer characterization to estimate the spatial distributions (or tomograms) of both hydraulic conductivity ( K ) and specific storage ( S s ). However, the highly-parameterized nature of the geostatistical inversion approach renders it computationally intensive for large-scale investigations. In addition, geostatistics-based THT may produce overly smooth tomograms when head data used to constrain the inversion is limited. Therefore, alternative model conceptualizations for THT need to be examined. To investigate this, we simultaneously calibrated different groundwater models with varying parameterizations and zonations using two cases of different pumping and monitoring data densities from a laboratory sandbox. Specifically, one effective parameter model, four geology-based zonation models with varying accuracy and resolution, and five geostatistical models with different prior information are calibrated. Model performance is quantitatively assessed by examining the calibration and validation results. Our study reveals that highly parameterized geostatistical models perform the best among the models compared, while the zonation model with excellent knowledge of stratigraphy also yields comparable results. When few pumping tests with sparse monitoring intervals are available, the incorporation of accurate or simplified geological information into geostatistical models reveals more details in heterogeneity and yields more robust validation results. However, results deteriorate when inaccurate geological information are incorporated. Finally, our study reveals that transient inversions are necessary to obtain reliable K and S s estimates for making accurate predictions of transient drawdown events. [ABSTRACT FROM AUTHOR]

• HPT surveys at a site with K spanning nearly-seven orders of magnitude. • HPT reveals both sharp and gradual changes in K values across layer boundaries. • Integration of HPT-inverted K into HT yields better matches with permeameter K. • HPT K can help HT refine layer boundaries and capture intralayer K variability. Hydraulic profiling tool (HPT) and hydraulic tomography (HT) have been developed as promising techniques for the high-resolution characterization of surficial aquifer systems. HPT surveys can be rapidly conducted at a resolution of 1.5-cm, but provide only one-dimensional vertical profiles and require site-specific formulae to relate HPT measurements to K. Geostatistics-based HT can estimate three-dimensional distributions of hydraulic parameters, but may fail to provide detailed information and can be smooth when pumping/observation data density is sparse and usually are constrained to the area enclosed by the pumping and observation network. In this study, HPT and HT surveys were conducted at the North Campus Research Site (NCRS) in Waterloo, Ontario, Canada to characterize a glaciofluvial multi-aquifer-aquitard system with permeameter K values spanning nearly seven orders of magnitude. We first performed the geostatistical analysis of K values derived from 11 HPT surveys using the power-law model developed for the NCRS by Zhao and Illman (2022b). Then, the benefits of incorporating HPT K profiles into HT were evaluated for the reconstruction of hydraulic parameter fields. Results showed that the arithmetic mean of 11 HPT K profiles was nearly one order of magnitude higher than that of the 544 permeameter test K measurements. The K fields interpolated by ordinary kriging captured the vertical alternating layering patterns of aquifer and aquitard layers, while they over-predicted the values by nearly one order of magnitude than permeameter K for the top part of the aquifer system. By incorporating the kriged K values as prior means for the geostatistics-based HT, improvements were found in capturing spatial heterogeneity of K fields for areas both inside and outside the well cluster and in drawdown predictions than the inversion case using only pressure head data. The inclusion of vertical variation information of K derived from HPT into HT was also helpful in refining the vertical locations of estimated layer boundaries and introducing intralayer variation patterns of K for both aquifer and aquitard layers. This study demonstrates the potential ability of HT and HPT and advocates the joint use of both techniques for the characterization of subsurface heterogeneity at highly heterogeneous sites such as the NCRS. [ABSTRACT FROM AUTHOR]

• A calibrated perfect-geological model yields better flow and transport predictions. • With HT-inverted K fields, the ADE can reasonably simulate tracer plumes and BTCs. • Fusing geology into geostatistics-based HT reveals inter- and intra-layer K changes. • High-resolution K fields with geological features reproduce plume fingering vividly. Hydraulic tomography (HT) has been developed over the last two decades to image subsurface heterogeneity at high resolution that is critically important to robust solute transport predictions. In this study, HT based on two concepts (i.e., geological zonation and geostatistical inversion models) was utilized to characterize the K distribution of a laboratory sandbox aquifer at different parameter resolutions. We compared the estimated K fields for predicting independent pumping tests and solute transport using the classical advection–dispersion equation (ADE). The impact of using geological zonation models of varying accuracy for HT analyses was investigated. Results revealed that, when being calibrated to datasets from multiple pumping tests, geological zonation models that faithfully represented the true stratigraphy predicted groundwater flow satisfactorily. The deterministic K field of the calibrated reliable geological zonation models satisfactorily reproduced the preferential migration path of the observed tracer plume, and the breakthrough curves (BTCs) at sampling ports. With further resolving the inter- and intra-layer heterogeneity, the reconstructed K fields by HT better predicted both migrating plumes and BTCs for two conservative tracer tests. The estimated dispersivity values for ADE only resulted in slight improvements in the fitting between observed and simulated solute tracer data. It also demonstrated the need of integrating reliable geological information into the geostatistical inversion approach to reproduce geological structures in K fields. Our study suggested the proper consideration of geological zonation between boreholes during field implementation of HT to yield improved solute transport results. [ABSTRACT FROM AUTHOR]

• Inverse modeling approach proposed to invert cm-scale K from HPT surveys. • Based on inverted K , a new power-law model was developed for HPT surveys at NCRS. • The site-specific model predicted K values that correspond well with permeameter K. • Integrating HPT-inverted K into SSHT better defined sharp boundaries of a K field. Direct-push based hydraulic profiling tool (HPT) and geostatistically-based hydraulic tomography (HT) are two promising techniques for the high-resolution estimation of hydraulic conductivity (K) for unconsolidated sediments. Although HPT surveys could be conducted rapidly, relating the 1.5-cm resolution injection logging profiles to K always involve the upscaling of centimeter-scale measurements to coarser intervals for the development of site-specific formulae. On the other hand, K fields reconstructed by HT could be smooth when pumping test data are sparse. In this study, an inverse modeling approach was firstly utilized to estimate K values directly from HPT survey data for the glaciofluvial deposits at the North Campus Research Site (NCRS) in Waterloo, Ontario, Canada. A site-specific power-law relationship was generated for the NCRS to relate HPT profiles to the vertical distributions of K. Then, the proposed inverse modeling approach was evaluated with a two-dimensional synthetic aquifer under controlled conditions, and the estimated K profiles from inverse analysis of synthetic HPT surveys were incorporated into the steady-state HT. Results of the field study showed that K estimates from the developed formula corresponded better with K values from permeameter tests, than those estimated from the empirical model of McCall and Christy (2010) for HPT surveys. Moreover, through synthetic experiments, we demonstrated that integration of K values inverted from HPT into steady-state HT analyses yielded K tomograms that were significantly better than the geostatistical inversion results relying on pumping test data alone. Overall, this study highlights the need in developing site-specific formulae for the HPT and the joint implementation of HPT and HT techniques for the more cost-effective high-resolution characterization of subsurface heterogeneity. [ABSTRACT FROM AUTHOR]

• HPT pressure logs (P c) can be rapidly collected in unconsolidated deposits. • P c data provide information on sharp and gradually-varying layer boundaries. • Integrating HPT-derived hydrostratigraphy and HT yields a K field with sharp boundaries. • HPT K estimates require additional evaluations for highly heterogeneous deposits. Hydraulic tomography (HT) has been developed as a robust technique in characterizing subsurface heterogeneity over the last two decades. Hydraulic conductivity (K) and specific storage (S s) estimated by geostatistically-based HT inversion approaches are typically smooth and lack geological features when observation data density is sparse. Although integrating geological information can be helpful in adding structural features into parameter fields, costly efforts are required to obtain borehole logging through conventional coring and sampling. Also, identification of geological features such as layer boundaries from sampled materials can be a subjective process. In this study, corrected pressure (P c) logs collected during hydraulic profiling tool (HPT) surveys are utilized to derive the local hydrostratigraphic layers of the glaciofluvial deposit at the North Campus Research Site (NCRS) in Waterloo, Ontario, Canada. Site-specific geological models representing aquifer and aquitard layers are developed and calibrated to drawdown data of multiple pumping tests. Results show that estimated K fields correctly reflect the variation features of permeameter-estimated K profiles, as well as the spatial distribution of high and low K sediments. The calibrated geological models performed better than the geostatistically-based inversion approach in predicting independent pumping tests used for model validation. Moreover, by including K estimates of geological models as prior means, the estimated K fields reveal both intra- and interlayer heterogeneity, and the performances of drawdown prediction are further improved for the geostatistical inversion approach. Overall, our study suggests that, integration of stratigraphic information derived from HPT P c logs is useful for HT to capture the sharp boundaries in K fields, especially when the pumping test data is sparse. [ABSTRACT FROM AUTHOR]

• THT analysis treating S s to be homogeneous yields less accurate results. • S s heterogeneity should be considered in THT for improved mapping of K and S s fields. • Reliable geological data helps THT to improve not only K , but also S s estimates. Over the last two decades, various studies on Transient Hydraulic Tomography (THT) have shown that it is an effective approach to characterize subsurface heterogeneity. Typically, high-resolution hydraulic conductivity (K) distributions were recovered, while the spatial variability of specific storage (S s) was found to be smooth. In some studies, S s heterogeneity has been intentionally ignored due to the belief that S s is less variable than K. Therefore, one may question the importance of considering S s heterogeneity during THT and its impact on the reliability of estimated hydraulic parameters. To investigate these issues, three modeling approaches (i.e., effective parameters, geological, and geostatistics-based) were used to obtain K and S s estimates of varying spatial resolutions. The reliability of K and S s estimates were evaluated by comparing their drawdown prediction performances. The values of using different prior K and S s information for THT analyses were investigated. Our results revealed that: (1) the K distribution estimated from the geostatistics-based steady-state HT analysis accurately predicted the late time drawdowns, while further improvements in transient drawdowns were obtained only after jointly treating the S s field as heterogeneous; (2) S s heterogeneity should be considered in addition to K for THT inversions, even when the estimated S s field is smooth; and (3) using K and S s estimates from the calibrated geological model as initial mean distributions for the geostatistical inversion approach were helpful in capturing both interlayer and intralayer heterogeneity of K and S s. These findings suggested that S s heterogeneity should be properly considered during the implementation of THT. [ABSTRACT FROM AUTHOR]

The concept of chaotic advection is a novel approach that has the potential to overcome some of the challenges associated with mixing of reagents that commonly occur when injection based in situ treatment techniques are used. The rotated potential mixing (RPM) flow system is one configuration which has been theorized to achieve chaotic advection in porous media, and enhance reagent mixing by periodically re-oriented dipole pumping at a series of radial wells. Prior to field implementation of chaotic advection, the selection of an RPM flow protocol will likely require a numerical model that can adequately represent groundwater flow within the zone of interest. As expected, the hydraulic conductivity (K) field is the most critical input requirement for the selected groundwater flow model. Hydraulic tomography (HT) is an innovative characterization approach that has shown potential to provide information on a K field. In this investigation, we explored whether the same well system required to invoke chaotic advection can also be applied in a HT analysis, and evaluated the use of the generated K tomogram for the selection of RPM flow parameters that can enhance reagent mixing. A series of dipole pumping tests were conducted within an area of interest as defined by the limits of the circular network of eight injection/extraction wells used to invoke chaotic advection. Hydraulic head data collected from independent dipole pumping tests were used in an inverse model to perform steady-state hydraulic tomography (SSHT) analysis to generate a K tomogram. Both the K tomogram and an effective parameter approach (i.e., a single K value assigned across the entire spatial domain as determined by single well pumping and slug tests) produced estimates of hydraulic head that closely resembled those observed due to the relative homogeneous nature of the aquifer and the small spatial scale of the area of interest. In contrast, particle tracking results showed that incorporating a heterogeneous K field significantly enhanced the spatial distribution of particle trajectories indicative of reagent mixing. These findings support the hypothesis that the same well system used to invoke chaotic advection can be combined with SSHT analysis as a viable site characterization tool for delineating the spatial variability of K. Incorporating this K tomogram in a groundwater flow model with a particle tracking engine can be used as a design tool to aid in the selection of a site-specific RPM flow protocol to achieve enhanced reagent mixing. • The same well system for chaotic advection can be combined with K tomography to delineate the K field of a TTZ. • Use of a K tomogram led to enhanced spatial distribution of particle trajectories compared to a homogeneous K. • A design tool to aid in the selection of chaotic advection system parameters. [ABSTRACT FROM AUTHOR]