a reduced order successive linear estimator for geostatistical inversion and its application in hydraulic tomography national natural science foundation of china 51779179 51609173 51479144 51522904 crdf daa2 15 61224 1 tianjin normal university from the thousand talents plan of tianjin city special fund for public industry research from ministry of land and resources of china 201511047

resolution analysis of tomographic slug test head data two dimensional radial case hydraulic tomography inverse problems which are solved to estimate aquifer hydraulic properties between wells are known to be ill conditioned and a priori information is often added to regularize numerical inversion of head data because both head data and a priori information have effects on the inversed solution assessing the meaningful information contained in head data alone is required to ensure comprehensive interpretation of inverse solutions whether they are regularized or not this study thus aims to assess the amount of information contained in tomographic slug tests head data to resolve heterogeneity in kh kv kh and ss therefore a resolution analysis based on truncated singular value decomposition of the sensitivity matrix with a noise level representative of field measurements is applied using synthetic data reflecting a known littoral aquifer as an approximation of the hydraulic behavior of a real aquifer system synthetic tomographic experiments and associated sensitivity matrices are generated using a radial flow model accounting for wellbore storage to simulate slug tests in a plane encompassing a stressed well and an observation well although fine scale resolution of heterogeneities is limited by the diffusive nature of the groundwater flow equations inversion of tomographic slug tests head data holds the potential to uniquely resolve coarse scale heterogeneity in kh kv kh and ss as inscribed in the resolution matrix this implies that tomographic head data can provide key information on aquifer heterogeneity and anisotropy but that fine scale information must be supplied by a priori information to obtain finer details

a bayesian approach for inversion of hydraulic tomographic data 1 hydraulic tomography is a promising methodology that shows the potential to map subsurface hydraulic properties at an unprecedented level of detail by interpreting a suite of hydraulic tests in the present work we apply the hydraulic tomography concept to a multiple pulse multiple receiver mpmr cross well configuration which consists of two boreholes subdivided into intervals by packers a short pressure or flow pulse is applied sequentially to all the intervals and for each perturbation the transient heads are recorded at the remaining intervals the resulting tomograms are inverted within the bayesian framework by using the pilot point approach in addition to the values of the hydraulic conductivity at the pilot points we assume that the stochastic parameters of the spatial variability model the structural parameters are unknown using synthetic two dimensional and three dimensional examples we demonstrate the effectiveness of the mpmr configuration and the inversion procedure for characterizing the spatial variability of the hydraulic conductivity with limited or no prior information we observed that increasing the number of source points the locations at which the pulse is alternatively applied provides more details on the spatial variability and that the parameters of the hydrogeological model of spatial variability are inferred with an acceptable although variable level of accuracy in particular the theoretical variance of the log conductivity is estimated with large errors while the estimate of the anisotropic integral scales depends on the distance between the boreholes inversion preserves the overall spatial pattern of hydraulic conductivity although low conductivity values are less connected in the inferred than in the true conductivity fields

transient hydraulic tomography in a fractured dolostone laboratory rock block experiments 1 the accurate characterization of fractured geologic medium imaging of fracture patterns and their connectivity have been a challenge for decades recently hydraulic tomography has been proposed as a new method for imaging the hydraulic conductivity k and specific storage ss distributions of fractured geologic media while encouraging results have been obtained in the field the method has not been rigorously assessed in a controlled laboratory setting in this study we assess the performance of transient hydraulic tomography tht in a fractured dolomitic rock block the block is characterized through flow through tests and multiple pumping tests the pumping test data were then analyzed with the tht code of zhu and yeh 2005 to image the fracture patterns and their connectivity through the delineation of k and ss distributions or tomograms results show that the tht analysis of pumping tests yields high k and low ss zones that capture the fracture pattern and their connectivity quite well and those patterns become more vivid as additional pumping test data are added to the inverse model the performance of the estimated k and ss tomograms are then assessed by 1 comparing the tomograms obtained from synthetic to real data 2 comparing the tomograms from two different pumping configurations 3 comparing the estimated geometric mean of the hydraulic conductivity kg from the k tomogram to the effective hydraulic conductivity keff estimated from the flow through tests and 4 predicting five independent pumping tests not used in the construction of the k and ss tomograms the performance assessment of the k and ss tomograms reveals that tht is able to image high k and low ss zones that correspond to fracture locations in the fractured rock block and that the tomograms can be used to predict drawdowns from pumping tests not used in the construction of the tomograms with reasonable fidelity

storage change in a flat lying fracture during well tests 1 the volume of water released from storage per unit head drop per volume of an rev is a basic quantity in groundwater hydrology but the details of the process of storage change in the vicinity of a well are commonly overlooked we characterize storage change in a flat lying fracture or thin sedimentary bed through the apparent hydraulic compliance cf the change in aperture of the fracture or thickness of the layer per unit change in pressure the results of theoretical analyses and field measurements show that cf increases with time near the well during pumping but it drops suddenly and may become negative at the beginning of recovery during a well test profiles of cfincrease with radial distance from a well but they are marked by a sharp increase and a sharp decrease at the edge of the region affected by the wellbore pressure transient the conventional view in groundwater hydrology is that storage change at a point is proportional to the local change in pressure which requires that the hydraulic compliance is uniform and constant it appears that this conventional view is a simplification of a process that varies in both space and time and can even take on negative values this simplification may be a source of uncertainty when interpreting well tests and extensometer records or predicting long term well performance

river stage tomography a new approach for characterizing groundwater basins received 19 june 2008 revised 16 february 2009 accepted 12 march 2009 published 9 may 2009 1 data from tomographic surveys make an inverse problem better posed in comparison to the data from a single excitation source a tomographic survey provides different coverages and perspectives of subsurface heterogeneity nonfully redundant information of the subsurface fusion of these pieces of information expands and enhances the capability of a conventional survey provides cross validation of inverse solutions and constrains inherently ill posed field scale inverse problems basin scale tomography requires energy sources of great strengths spatially and temporally varying natural stimuli are ideal energy sources for this purpose in this study we explore the possibility of using river stage variations for basin scale subsurface tomographic surveys specifically we use numerical models to simulate groundwater level changes in response to temporal and spatial variations of the river stage in a hypothetical groundwater basin we then exploit the relation between temporal and spatial variations of well hydrographs and river stage to image subsurface heterogeneity of the basin results of the numerical exercises are encouraging and provide insights into the proposed river stage tomography using naturally recurrent stimuli such as river stage variations for characterizing groundwater basins could be the future of geohydrology however it calls for implementation of sensor networks that provide long term and spatially distributed monitoring of excitation as well as response signals on the land surface and in the subsurface

identification of groundwater basin shape and boundary using hydraulic tomography abstract shapes and boundary types of a groundwater basin play essential roles in the analysis of groundwater management and contaminant migration hydraulic tomography ht a recently developed new approach for high resolution characterization of aquifers is not only an inverse method but a logical strategy for collecting non redundant hydraulic information in this study ht was applied to synthetic 2 d aquifers to investigate its feasibility to map the irregular shapes and types of the aquifer boundaries we first used the forward model of vsaft2 to simulate hydraulic responses due to ht surveys in the aquifer with irregular geometry and predetermined constant head conditions at some boundaries and no flow conditions at others the simsle simultaneous successive linear estimator inverse model in vsaft2 was then used to interpret the simulated ht data to estimate the spatial distribution of hydraulic properties of the aquifer using a domain with a wrong geometry surrounded by boundaries of a constant head condition the inverse modeling experiment used steady state and transient states data from the ht forward simulations and it used the same monitoring network as in the aquifer with irregular geometry to assess the ability of ht for detecting types and shapes of the boundary as well as heterogeneity in the aquifer results of the experiment show that no flow boundaries which were incorrectly treated as constant head boundaries in inverse models were portrayed as low permeable zones of the aquifer near the boundaries overall the results show that ht could delineate not only the irregular shape of the aquifer in general but also heterogeneity in the aquifer improvements of the estimation with prior information of transmissivity and storage coefficient was also investigated the study shows that using homogeneous initial guess parameters resulted in a slightly better estimate than others moreover this study employs monte carlo simulations to ensure statistically meaningful conclusions

new experimental techniques for pneumatic tomographical determination of the flow and transport parameters of highly fractured porous rock samples abstract the investigation of flow and transport parameters in fractured porous material is difficult due to the high permeability contrast between the fracture networks and the porous material and due to the question of the scale dependency of the parameters determined here experimental methods and new experimental equipment are presented using a pneumatic technique for the experimental tomographical investigation of highly fractured bench scale porous sandstone samples the procedure allows a great deal of flexibility in the determination of the spatially variable flow and transport parameters and allows the question of scale to be addressed examples of the results gained from the application of these new techniques are given for both flow and transport parameter determination

aquifer heterogeneity characterization with oscillatory pumping sensitivity analysis and imaging potential 1 periodic pumping tests in which a fluid is extracted during half a period then reinjected have been used historically to estimate effective aquifer properties in this work we suggest a modified approach to periodic pumping test analysis in which one uses several periodic pumping signals of different frequencies as stimulation and responses are analyzed through inverse modeling using a steady periodic model formulation we refer to this strategy as multifrequency oscillatory hydraulic imaging oscillating pumping tests have several advantages that have been noted including no net water extraction during testing and robust signal measurement through signal processing through numerical experiments we demonstrate additional distinct advantages that multifrequency stimulations have including 1 drastically reduced computational cost through use of a steady periodic numerical model and 2 full utilization of the aquifer heterogeneity information provided by responses at different frequencies we first perform fully transient numerical modeling for heterogeneous aquifers and show that equivalent results are obtained using a faster steady periodic heterogeneous numerical model of the wave phasor the sensitivities of observed signal response to aquifer heterogeneities are derived using an adjoint state based approach which shows that different frequency stimulations provide complementary information finally we present an example 2 d application in which sinusoidal signals at multiple frequencies are used as a data source and are inverted to obtain estimates of aquifer heterogeneity these analyses show the different heterogeneity information that can be obtained from different stimulation frequencies and that data from several sinusoidal pumping tests can be rapidly inverted using the steady periodic framework

hydraulic partitioning tracer tomography for characterization of dense nonaqueous phase liquid source zones 1 a new technology hydraulic partitioning tracer tomography hptt is proposed to survey spatial distributions of hydraulic properties and dense nonaqueous phase liquids dnapls in the subsurface hptt is nothing more than a set of multiple hydraulic partitioning tracer tests and synthesis of all the tests to map the spatial distributions it involves injection of water at one borehole in a source zone to create a steady state forced gradient flow field then release of conservative partitioning tracers at the same borehole and monitoring heads and tracer breakthroughs at the others the same operation is repeated using different boreholes for the water and the tracer injections to analyze the head and tracer data obtained from the proposed tomographic survey a joint stochastic estimator was developed numerical experiments were then conducted to evaluate the effectiveness of hptt as well as the stochastic estimator results show that prior knowledge of hydraulic heterogeneity is critical for mapping the distribution of dnapls in addition the results suggest that the proposed hptt in conjunction with the stochastic estimator is potentially a viable tool for high resolution characterization of subsurface heterogeneity and contamination

estimation of fracture zone geometry from steady state hydraulic head data using iterative sequential cokriging the hydrogeology of fractured crystalline rock is often controlled by a few highly conductive features such as faults and or fractures zones accurate modeling of fluid flow and transport in these systems requires that the geometry of these conductive features be characterized explicitly a new method for estimating the geometry of these features is presented the method is an extension of the recently developed geostatistical technique of sequential cokriging in this extension the geometry of the fracture zone is iteratively updated until an update increases the discrepancy between the estimated and observed hydraulic heads results from two hypothetical examples demonstrate that the method can accurately estimate the geometry of highly conductive fracture zones

hydraulic tomography analog outcrop study combining travel time and steady shape inversion summary travel time and steady shape inversions are complementary methods for tomographic aquifer characterization in this work a combined procedure is presented that facilitates determination of spatial hydraulic conductivity and specific storage distributions in heterogeneous groundwater systems the procedure is applied to a highly heterogeneous sedimentary aquifer analog that is implemented as a two and three dimensional case study in a numerical flow model by interpreting the observations from multiple simulated short term pumping tests the main hydraulic features of the analog are successfully reconstructed the final results demonstrate the encouraging potential of the combined procedure for identifying the dominant structural elements and composition of sedimentary aquifers however limits derived from the test design of hydraulic travel time tomography in our synthetic case study prevented us from resolving small scale 10 cm in size variability of hydraulic conductivity with high discrepancies up to 5 orders of magnitude a better reconstruction of the aquifer hydraulic parameters is expected by utilizing a larger amount of measurements which involve more test and observation intervals although such a test design would be less feasible for field applications still this newly combined scheme is very attractive for an up scaled reconstruction on the sub meter scale for the present case study representative parameter values could be estimated in a computationally efficient way

improved predictions of saturated and unsaturated zone drawdowns in a heterogeneous unconfined aquifer via transient hydraulic tomography laboratory sandbox experiments summary interpretation of pumping tests in unconfined aquifers has largely been based on analytical solutions that disregard aquifer heterogeneity in this study we investigate whether the prediction of drawdown responses in a heterogeneous unconfined aquifer and the unsaturated zone above it with a variably saturated groundwater flow model can be improved by including information on hydraulic conductivity k and specific storage s s from transient hydraulic tomography tht we also investigate whether these predictions are affected by the use of unsaturated flow parameters estimated through laboratory hanging column experiments or calibration of in situ drainage curves to investigate these issues we designed and conducted laboratory sandbox experiments to characterize the saturated and unsaturated properties of a heterogeneous unconfined aquifer specifically we conducted pumping tests under fully saturated conditions and interpreted the drawdown responses by treating the medium to be either homogeneous or heterogeneous we then conducted another pumping test and allowed the water table to drop similar to a pumping test in an unconfined aquifer simulations conducted using a variably saturated flow model revealed 1 homogeneous parameters in the saturated and unsaturated zones have a difficult time predicting the responses of the heterogeneous unconfined aquifer 2 heterogeneous saturated hydraulic parameter distributions obtained via tht yielded significantly improved drawdown predictions in the saturated zone of the unconfined aquifer and 3 considering heterogeneity of unsaturated zone parameters produced a minor improvement in predictions in the unsaturated zone but not the saturated zone these results seem to support the finding by mao et al 2011 that spatial variability in the unsaturated zone plays a minor role in the formation of the s shape drawdown time curve observed during pumping in an unconfined aquifer

validation of hydraulic tomography in an unconfined aquifer a controlled sandbox study in this study we demonstrate the effectiveness of hydraulic tomography ht that considers variably saturated flow processes in mapping the heterogeneity of both the saturated and unsaturated zones in a laboratory unconfined aquifer the successive linear estimator sle developed by mao et al 2013c for interpreting ht in unconfined aquifers is utilized to obtain tomograms of hydraulic conductivity k specific storage ss and the unsaturated zone parameters pore size parameter and saturated water content s for the gardner russo s model the estimated tomograms are first evaluated by visually comparing them with stratigraphy visible in the sandbox results reveal that the ht analysis is able to accurately capture the location and extent of heterogeneity including high and low k layers within the saturated and unsaturated zones as well as reasonable distribution patterns of and s for the gardner russo s model we then validate the estimated tomograms through predictions of drawdown responses of pumping tests not used during the inverse modeling effort the strong agreement between simulated and observed drawdown curves obtained by pressure transducers and tensiometers demonstrates the robust performance of ht that considers variably saturated flow processes in unconfined aquifers and the unsaturated zone above it in addition compared to the case using the homogeneous assumption ht results as expected yield significantly better predictions of drawdowns in both the saturated and unsaturated zones this comparison further substantiates the unbiased and minimal variance of ht analysis with the sle algorithm

a comparison of deterministic and stochastic approaches for regional scale inverse modeling on the mar del plata aquifer summary inversion of the spatial variability of transmissivity t in groundwater models can be handled using either stochastic or deterministic i e geology based zonation approaches while stochastic methods predominate in scientific literature they have never been formally compared to deterministic approaches preferred by practitioners for regional aquifer models we use both approaches to model groundwater flow and solute transport in the mar del plata aquifer where seawater intrusion is a major threat to freshwater resources the relative performance of the two approaches is evaluated in terms of i model fits to head and concentration data available for nearly a century ii geological plausibility of the estimated t fields and iii their ability to predict transport we also address the impact of conditioning the estimated fields on t data coming from either pumping tests interpreted with the theis method or specific capacity values from step drawdown tests we find that stochastic models based upon conditional estimation and simulation techniques identify some of the geological features river deposit channels and low transmissivity regions associated to quartzite outcrops and yield better fits to calibration data than the much simpler geology based deterministic model which cannot properly address model structure uncertainty however the latter demonstrates much greater robustness for predicting sea water intrusion and for incorporating concentrations as calibration data we attribute the poor performance and underestimated uncertainty of the stochastic simulations to estimation bias introduced by model errors qualitative geological information is extremely rich in identifying large scale variability patterns which are identified by stochastic models only in data rich areas and should be explicitly included in the calibration process

derivation of site specific relationships between hydraulic parameters and p wave velocities based on hydraulic and seismic tomography derivation of site specific relationships between hydraulic parameters and p wave velocities based on hydraulic and seismic tomography brauchler r 1 doetsch j 1 2 dietrich p 3 sauter m 4 eth zurich department of earth sciences sonneggstrasse 5 8092 zurich switzerland now at earth sciences division lawrence berkeley national laboratory one cyclotron road berkeley ca 94720 ufz helmholtz centre for environmental research department monitoring and exploration technologies permoserstrasse 15 04318 leipzig germany geoscientific centre university of gottingen goldschmidtstrase 3 37077 gottingen germany

influence of heterogeneity on the interpretation of pumping test data in leaky aquifers 1 pumping tests are routinely interpreted from the analysis of drawdown data and their derivatives these interpretations result in a small number of apparent parameter values which lump the underlying heterogeneous structure of the aquifer key questions in such interpretations are 1 what is the physical meaning of those lumped parameters and 2 whether it is possible to infer some information about the spatial variability of the hydraulic parameters the system analyzed in this paper consists of an aquifer separated from a second recharging aquifer by means of an aquitard the natural log transforms of the transmissivity ln t and the vertical conductance of the aquitard ln c are modeled as two independent second order stationary spatial random functions srfs the monte carlo approach is used to simulate the time dependent drawdown at a suite of observation points for different values of the statistical parameters defining the srfs drawdown data at each observation point are independently used to estimate hydraulic parameters using three existing methods 1 the inflection point method 2 curve fitting and 3 the double inflection point method the resulting estimated parameters are shown to be space dependent and vary with the interpretation method since each method gives different emphasis to different parts of the time drawdown data moreover the heterogeneity in the pumped aquifer or the aquitard influences the estimates in distinct manners finally we show that by combining the parameter estimates obtained from the different analysis procedures information about the heterogeneity of the leaky aquifer system may be inferred

characterizing co2 plumes in deep saline formations comparison and joint evaluation of time lapse pressure and seismic tomography abstractmonitoring the migration of sequestered co2 in deep heterogeneous reservoirs is inherently difficult geophysical methods have been successfully used but flow conditions are only indirectly linked to the measured properties besides geophysical methods pressure tomography pt is proposed as an alternative method to depict the structure of deep saline formations for co2 sequestration and to continuously delineate co2 plumes in contrast to more established geophysical measurements pressure transients are directly related to flow properties which allows for the estimation of permeability we investigate the influence of aquifer heterogeneity on pt performance and we compare the pt results to crosshole seismic tomography st multilevel fluid injections and high frequency p wave pulses are induced in a simulated deep borehole and the recorded signals at another well are processed by a traveltime inversion scheme the reservoir structure is inferred by clustering the inverted hydraulic diffusi

a field assessment of high resolution aquifer characterization based on hydraulic travel time and hydraulic attenuation tomography 1 in this study the potential of an inversion approach based on hydraulic travel time and hydraulic attenuation tomography was assessed both hydraulic travel time and hydraulic attenuation tomography are based on the transformation of the transient groundwater flow equation into the eikonal equation using an asymptotic approach the eikonal equation allows the calculation of pressure propagation and attenuation along trajectories which is computationally efficient the attenuation and travel time based inversion approaches are naturally complementary hydraulic travel times are determined by the hydraulic diffusivity a combination of hydraulic conductivity and specific storage whereas the attenuation is determined solely by specific storage the potential of our hydraulic tomographical approach was investigated at a well characterized sand and gravel aquifer located in the leine river valley near gottingen germany the database for the hydraulic inversion consists of 392 cross well slug interference tests performed between five wells in which the positions of the sources injection ports and the receivers observation ports isolated with double packer systems were varied between tests the results have shown that the combination of hydraulic travel time and hydraulic attenuation tomography allows the reconstruction of the diffusivity and storage distribution in two and three dimensions with a resolution and accuracy superior to that possible with type curve analysis

a geostatistical inverse method for variably saturated flow in the vadose zone a geostatistical inverse technique utilizing both primary and secondary information is developed to estimate conditional means of unsaturated hydraulic conductivity parameters saturated hydraulic conductivity and pore size distribution parameters in the vadose zone measurements of saturated hydraulic conductivity and pore size distribution parameters are considered as the primary information while measurements of steady state flow processes soil water pressure head and degree of saturation are regarded as the secondary information this inverse approach relies on the classical linear predictor cokriging theory and takes the advantage of the spatial cross correlation between the soil water pressure head and each of the following degree of saturation saturated hydraulic conductivity and a pore size distribution parameter using an approximate perturbation solution for steady variably saturated flow under general boundary conditions the cross covariances between the primary and secondary information are derived the approximate solution is formulated on the basis of a first order taylor series expansion of a discretized finite element equation the sensitivity matrix in the solution is evaluated by an adjoint state sensitivity approach for flow in heterogeneous media under variably saturated conditions through several numerical examples the inverse model demonstrates its ability to improve the estimates of the spatial distribution of saturated hydraulic conductivity and pore size distribution parameters using the secondary information

should hydraulic tomography data be interpreted using geostatistical inverse modeling a laboratory sandbox investigation the robust performance of hydraulic tomography ht based on geostatistics has been demonstrated through numerous synthetic laboratory and field studies while geostatistical inverse methods offer many advantages one key disadvantage is its highly parameterized nature which renders it computationally intensive for large scale problems another issue is that geostatistics based ht may produce overly smooth images of subsurface heterogeneity when there are few monitoring interval data therefore some may question the utility of the geostatistical inversion approach in certain situations and seek alternative approaches to investigate these issues we simultaneously calibrated different groundwater models with varying subsurface conceptualizations and parameter resolutions using a laboratory sandbox aquifer the compared models included 1 isotropic and anisotropic effective parameter models 2 a heterogeneous model that faithfully represents the geological features and 3 a heterogeneous model based on geostatistical inverse modeling the performance of these models was assessed by quantitatively examining the results from model calibration and validation calibration data consisted of steady state drawdown data from eight pumping tests and validation data consisted of data from 16 separate pumping tests not used in the calibration effort results revealed that the geostatistical inversion approach performed the best among the approaches compared although the geological model that faithfully represented stratigraphy came a close second in addition when the number of pumping tests available for inverse modeling was small the geological modeling approach yielded more robust validation results this suggests that better knowledge of stratigraphy obtained via geophysics or other means may contribute to improved results for ht

inferring field scale properties of a fractured aquifer from ground surface deformation during a well test fractured aquifers which bear valuable water resources are often difficult to characterize with classical hydrogeological tools due to their intrinsic heterogeneities here we implement ground surface deformation tools tiltmetry and optical leveling to monitor groundwater pressure changes induced by a classical hydraulic test at the ploemeur observatory by jointly analyzing complementary time constraining data tilt and spatially constraining data vertical displacement our results strongly suggest that the use of these surface deformation observations allows for estimating storativity and structural properties dip root depth lateral extension of a large hydraulically active fracture in good agreement with previous studies hence we demonstrate that ground surface deformation is a useful addition to traditional hydrogeological techniques and opens possibilities for characterizing important large scale properties of fractured aquifers with short term well tests as a controlled forcing

characterization of aquifer heterogeneity using transient hydraulic tomography 1 hydraulic tomography is a cost effective technique for characterizing the heterogeneity of hydraulic parameters in the subsurface during hydraulic tomography surveys a large number of hydraulic heads i e aquifer responses are collected from a series of pumping or injection tests in an aquifer these responses are then used to interpret the spatial distribution of hydraulic parameters of the aquifer using inverse modeling in this study we developed an efficient sequential successive linear estimator ssle for interpreting data from transient hydraulic tomography to estimate three dimensional hydraulic conductivity and specific storage fields of aquifers we first explored this estimator for transient hydraulic tomography in a hypothetical one dimensional aquifer results show that during a pumping test transient heads are highly correlated with specific storage at early time but with hydraulic conductivity at late time therefore reliable estimates of both hydraulic conductivity and specific storage must exploit the head data at both early and late times our study also shows that the transient heads are highly correlated over time implying only infrequent head measurements are needed during the estimation applying this sampling strategy to a well posed problem we show that our ssle can produce accurate estimates of both hydraulic conductivity and specific storage fields the benefit of hydraulic tomography for ill posed problems is then demonstrated finally to affirm the robustness of our ssle approach we apply the ssle approach to a hypothetical three dimensional heterogeneous aquifer

a salt tracer test monitored with surface ert to detect preferential flow and transport paths in fractured karstified limestones in hard rock aquifers fractured zones constitute adequate drinking water exploitation areas but also potential contamination paths one critical issue in hydrogeological research is to identify characterize and monitor such fractured zones at a representative scale a tracer test monitored with surface electrical resistivity tomography ert could help by delineating such preferential flow paths and estimating dynamic properties of the aquifer however multiple challenges exist including the lower resolution of surface ert compared with crosshole ert the finite time that is needed to complete an entire data acquisition and the strong dilution effects we conducted a natural gradient salt tracer test in fractured limestones to account for the high transport velocity we injected the salt tracer continuously for four hours at a depth of 18 m we monitored its propagation with two parallel ert profiles perpendicular to the groundwater flow direction concerning the data acquisition we always focused

hydraulic conductivity imaging from 3 d transient hydraulic tomography at several pumping observation densities 1 3 d hydraulic tomography 3 d ht is a method for aquifer characterization whereby the 3 d spatial distribution of aquifer flow parameters primarily hydraulic conductivity k is estimated by joint inversion of head change data from multiple partially penetrating pumping tests while performance of 3 d ht has been studied extensively in numerical experiments few field studies have demonstrated the real world performance of 3 d ht here we report on a 3 d transient hydraulic tomography 3 d tht field experiment at the boise hydrogeophysical research site which is different from prior approaches in that it represents a baseline analysis of 3 d tht performance using only a single arrangement of a central pumping well and five observation wells with nearly complete pumping and observation coverage at 1 m intervals we jointly analyze all pumping tests using a geostatistical approach based on the quasi linear estimator of kitanidis 1995 we reanalyze the system after progressively removing pumping and or observation intervals significant progressive loss of information about heterogeneity is quantified as reduced variance of the k field overall reduced correlation with slug test k estimates at wells and reduced ability to accurately predict independent pumping tests we verify that imaging accuracy is strongly improved by pumping and observational densities comparable to the aquifer heterogeneity geostatistical correlation lengths discrepancies between k profiles at wells as obtained from ht and slug tests are greatest at the tops and bottoms of wells where ht observation coverage was lacking

detection of karst conduit patterns via hydraulic tomography a synthetic inverse modeling study abstract karst aquifers are geologic media that consist of enlarged solution conduits the geometry of such conduits is very difficult to delineate and its hydraulic parameters such as hydraulic conductivity k and specific storage ss are difficult to estimate hydraulic tomography ht shown to successfully map the hydraulic heterogeneity of porous and fractured rock aquifers may also be effective in karst aquifers in this study we utilize two synthetic karst aquifers with the branchwork and network conduit patterns bcp and ncp to explore the ability of ht to map conduit patterns and their hydraulic parameters prior to the ht analysis forward models are built to study groundwater flow through synthetic karst aquifers to generate data and to gain insights into flow patterns forward modeling results reveal that 1 flow rates at the outlet of the bcp model is higher than the ncp model even when the same water injection rates are applied at the wells 2 the location of the injection well has a significant impact on the flow rate at the outlet and 3 flow lines mainly follow the conduit pattern these results suggest that the accurate mapping of karst networks is critical next the ht analysis of these data is conducted using a set of six models bcp and ncp to map the heterogeneity of different conduit systems under steady state and transient flow conditions inverse modeling results reveal that the estimated k maps become more reliable as the number of injection tests and the corresponding monitoring data are increased in the ht analysis moreover the results of the bcp model is closer to the original conduit pattern in comparison to the ncp model a comparative study of three inverse models with different number of observation wells and assuming the availability of geological data has shown that a more reliable pattern of the conduits can be mapped by adding geological information even when a small number of observation wells are available overall our results confirm the feasibility of ht in detecting major conduits as well as being able to differentiate between the bcp and ncp network types

the origin of fluids in the salt beds of the delaware basin new mexico and texas abstract oxygen and hydrogen isotope analyses have been made of 1 brines from several wells in the salt deposits of the delaware basin 2 inclusion fluids in halite crystals from the erda no 9 site and 3 local ground waters of meteoric origin the isotopic compositions indicate that the brines are genetically related and that they probably originated from the evaporation of paleo ocean waters although highly variable in solute contents the brines have rather uniform isotopic compositions the stable isotope compositions of brine from the erda no 6 site 826 3 m depth and fluid inclusions from the erda no 9 site are variable but remarkably regular and show that 1 mixing with old or modern meteoric waters has occurred the extent of mixing apparently decreasing with depth and 2 water in the erda no 6 brine may have originated from the dehydration of gypsum alternatively the data may reflect simple evaporation of meteoric water on a previously dry marine flat stable isotope compositions of all the waters analyzed indicate that there has been fairly extensive mixing with ground water throughout the area but that no significant circulation has occurred the conclusions bear importantly on the suitability of these salt beds and others as repositories for nuclear waste

on the importance of geological data for three dimensional steady state hydraulic tomography analysis at a highly heterogeneous aquifer aquitard system abstract hydraulic tomography ht has been shown to map subsurface heterogeneity accurately through the joint interpretation of multiple pumping tests previous research has shown that smooth hydraulic conductivity k estimates are obtained beyond where pumping observation data are available using the geostatistical inversion approach when the inversion begins with a homogeneous k and when data densities are not high however geological data are typically available through outcrops and borehole logs to provide geological variability therefore we investigate the usefulness of geological data for ht analysis at a highly heterogeneous field site by 1 comparing calibrated geological models of two different resolutions to two homogeneous and four highly parameterized geostatistical inverse models in terms of both model calibration and validation performances as well as correspondence of estimated k values with permeameter estimated k profiles along boreholes and 2 using geological models as prior information for the geostatistical inversion approach results reveal that the simultaneous calibration of geological models to seven pumping test data yields k values that correctly reflect the general patterns of vertical distributions of permeameter estimated k we also find that the geostatistical inversion approach using a geological model as prior information performs better for both model calibration and validation than using a homogenous k as a prior and more importantly improves the correspondence of k estimates to permeameter test results along wells as well as in preserving geological features where drawdown measurements are lacking overall our results suggest the joint use of both geological and pumping test data for ht analysis when accurate geological data are available

mapping soil layers using electrical resistivity tomography and validation sandbox experiments abstract knowledge of the geologic structure at a field site is a useful piece of information for hydrologic modeling since it can serve as more site specific prior information about the hydraulic parameter patterns at the site than generic spatial statistics widely accepted electrical resistivity tomography ert survey for mapping subsurface anomalies could be a viable tool for acquiring this information however their ability to delineate geologic structures has not been thoroughly investigated in this study two dimensional ert numerical experiments were first conducted to study the effects of boundary conditions on the dipole dipole and pole pole array configurations an ert setup subsequently was implemented in a sandbox consisting of complex layers of different sands a continuous copper wire was installed along the sides of the sandbox to impose potential boundaries using data collected with the pole pole array in the sandbox under different degrees of drainage and the successive linear estimator sle algorithm we show that ert yields electrical conductivity estimates of complex layer structures with small uncertainties in addition using sle with physically meaningful correlation scales as prior information can lead to an electrical conductivity field that is consistent with visually observed layer structures the correlation scale concept also was demonstrated to provide guidance to the design of the electrode spacing in the surveys moreover the estimated field was validated by predicting electrical potential fields from two independent ert surveys using electrodes at different locations results of this study suggest that the combination of ert and sle is a viable geophysical survey tool for mapping geologic layer structures research significance this study develops a method to implement prescribed potential boundaries for enhancing the pole pole ert survey illustrates the importance of correlation scales and develops an approach for validating ert results

joint inversion in coupled quasi static poroelasticity geodetic surveys now provide detailed time series maps of anthropogenic land subsidence and uplift due to injection and withdrawal of pore fluids from the subsurface a coupled poroelastic model allows the integration of geodetic and hydraulic data in a joint inversion and has therefore the potential to improve the characterization of the subsurface and our ability to monitor pore pressure evolution we formulate a bayesian inverse problem to infer the lateral permeability variation in an aquifer from geodetic and hydraulic data and from prior information we compute the maximum a posteriori map estimate of the posterior permeability distribution and a gaussian approximation of the posterior computing the map estimate requires the solution of a large scale minimization problem subject to the poroelastic equations for which we propose an efficient newton conjugate gradient optimization algorithm the covariance matrix of the gaussian approximation of the posterior is given by the inverse hessian of the log posterior which we construct by exploiting low rank properties of the data misfit hessian first and second derivatives are computed using adjoints of the time dependent poroelastic equations allowing us to fully exploit transient data using three increasingly complex model problems we find the following general properties of poroelastic inversions augmenting standard hydraulic well data by surface deformation data improves the aquifer characterization surface deformation contributes the most in shallow aquifers but provides useful information even for the characterization of aquifers down to 1 km in general it is more difficult to infer high permeability regions and their characterization requires frequent measurement to resolve the associated short response timescales in horizontal aquifers the vertical component of the surface deformation provides a smoothed image of the pressure distribution in the aquifer provided that the mechanical properties are known coupled poroelastic inversion is therefore a promising approach to detect flow barriers and to monitor pore pressure evolution

an application of hydraulic tomography to a deep coal mine combining traditional pumping tests with water inrush incidents abstract water inrush incidents threaten the safety of coal mining understanding of hydrogeologic parameter distributions is critical for preventing water related hazards in coal mines during the deep mining 1000 m under the north china plain water from water bearing strata discharges into coal seams through geologic conduits i e water inrush due to the fractured zone under the floor of working faces in this study a water inrush incident was exploited as an active stimulus a 3d groundwater flow model was built for the eighth member of the middle ordovician system in xingdong coal mine using this model and an inverse approach we first checked if the data from the incident and an independent pumping test carry non redundant information about the heterogeneity of the mine afterward we combined these datasets to conduct a large scale approximately 10 km hydraulic tomography ht analysis the estimated hydraulic conductivity distribution from the ht analysis is found consistent with the distribution of known geologic faults that is a cluster of faults is characterized as a high conductivity zone a high conductivity zone is identified at locations close to the water inrush location which is the high cement consumption zone during the grouting project finally results of this study promote exploiting the water inrush events as a ht survey for mapping geologic structures over a large area

geostatistical inverse modeling of the transmissivity field of a heterogeneous alluvial aquifer under tidal influence summary the record of the head fluctuations of an alluvial aquifer connected to the estuary of a river submitted to tidal influence can be used to reconstruct the transmissivity field of the aquifer a markov chain monte carlo mcmc sampler is used to invert the transmissivity field at a set of pilot points our approach is first successfully benchmarked on a synthetic case study then we present a real case study in which both a semi confined aquifer and a shallow unconfined aquifer are connected to the estuary of the seine river in the western north of france these aquifers experience strong tidal variations up to 8 4 m this test site is equipped with a series of seventeen wells in which the temporal fluctuations of water heads associated with megatidal forcing were recorded during several years in addition to the use of the pilot points method a zoning parameterization with 45 zones is used to determine the vertical leakage coefficient from the semi confined aquifer into the shallow unconfined aquifer the distribution of the vertical leakage coefficient is determined by inverting the hydraulic head at a set of wells localized in the semi confined aquifer we determine jointly the distribution of the hydraulic transmissivity and the vertical leakage from the semi confined into the unconfined aquifer using 72 pilot points the storage coefficient is assumed to be constant over the whole domain its value is determined from three pumping tests that show a consistent value for this parameter log10s 5 and 0 11 as a variance in our approach there are 119 model parameters 72 transmissivity values at the pilot points 45 values of the vertical leakage coefficient and two parameters sill and range for the isotropic variogram the spatial distribution of the hydraulic transmissivity agrees qualitatively with the soil texture variations observed in the semi confined aquifer and core samples analysis

a view toward the future of subsurface characterization cat scanning groundwater basins 1 in this opinion paper we contend that high resolution characterization monitoring and prediction are the key elements to advancing and reducing uncertainty in our understanding and prediction of subsurface processes at basin scales first we advocate that recently developed tomographic surveying is an effective and high resolution approach for characterizing the field scale subsurface fusion of different types of tomographic surveys further enhances the characterization a basin is an appropriate scale for many water resources management purposes we thereby propose the expansion of the tomographic surveying and data fusion concept to basin scale characterization in order to facilitate basin scale tomographic surveys different types of passive basin scale cat scan technologies are suggested that exploit recurrent natural stimuli e g lightning earthquakes storm events barometric variations river stage variations etc as sources of excitations along with implementation of sensor networks that provide long term and spatially distributed monitoring of excitation as well as response signals on the land surface and in the subsurface this vision for basin scale subsurface characterization faces many significant technological challenges and requires interdisciplinary collaborations e g surface and subsurface hydrology geophysics geology geochemistry information and sensor technology applied mathematics atmospheric science etc we nevertheless contend that this should be a future direction for subsurface science research

sequential aquifer tests at a well field montalto uffugo scalo italy 1 this paper investigates our ability to characterize an aquifer using a sequential aquifer test in a well field that consists of six wells during the test we pumped water out from the aquifer at one well and monitored the water level changes at the rest of the wells to obtain a set of five well hydrographs by pumping at another of the six wells we obtained another set of five hydrographs this procedure was repeated until each of the six wells was pumped we then analyzed the six sets of hydrographs using the classical drawdown time the drawdown distance and the drawdown distance time methods results of the analysis confirm recent findings that the transmissivity estimates vary significantly at early time and stabilize at late time at late time the estimated values from all hydrographs are similar overall but vary slightly according to the locations of the pumping and observation wells in contrast storage coefficient estimates stabilized rapidly to distinct values associated with the well locations we subsequently used a hydraulic tomography approach to include all hydrographs from the sequential aquifer test to estimate the spatially varying transmissivity and storage coefficient fields the estimated fields appear to be realistic they reflect the geologic setting and the behaviors of the well hydrographs although more definitive confirmation is needed

a revisit of drawdown behavior during pumping in unconfined aquifers received 16 march 2010 revised 7 february 2011 accepted 7 march 2011 published 6 may 2011 1 in this study the s shaped log log drawdown time curve typical of pumping tests in unconfined aquifers is reinvestigated via numerical experiments like previous investigations this study attributes the departure of the s shape from the drawdown time behavior of the confined aquifer to the presence of an additional source of water unlike previous studies this sourceof water isreinvestigated byexaminingthetemporal and spatial evolution of the rate of change in storage in an unconfined aquifer during pumping this evolution is then related to the transition of water release mechanisms from the expansion of water and compaction of the porous medium to the drainage of water from the unsaturated zone above the initial water table and initially saturated pores as the water table falls during the pumping of the aquifer afterward the 1 d vertical drainage process in a soil column is simulated results of the simulation show that the transition of the water release mechanisms in the 1 d vertical flow without an initial unsaturated zone can also yield the s shaped drawdown time curve as in an unconfined aquifer we therefore conclude that thetransitionofthewaterreleasemechanismsandverticalflowintheaquiferarethecauseof the s shaped drawdown time curve observed during pumping in an unconfined aquifer we also find that the moisture retention characteristics of the aquifer material have greater impact than its relative permeability characteristics on the drawdown time curve furthermore influences of the spatial variability of saturated hydraulic conductivity specific storage and saturated moisture content on the drawdown curve in the saturated zone are found to be more significant than those of other unsaturated properties finally a cross correlation analysis reveals that the drawdown at a location in a heterogeneous unconfined aquifer is mainly affected by local heterogeneity near the pumping and observation wells applications of a model assuming homogeneity to the estimation of aquifer parameters as such may require a large number of observation wells to obtain representative parameter values in conclusion we advocate that the governing equation for variably saturated flow through heterogeneous media is a more appropriate and realistic model that explains the s shaped drawdown time curves observed in the field

a travel time based hydraulic tomographic approach 1 hydraulic tomography is a method to identify the three dimensional spatial distribution of hydraulic properties in the subsurface we propose a tomographic approach providing the inversion of travel times of hydraulic or pneumatic tests conducted in a tomographic array the inversion is based on the relation between the peak time of a recorded transient pressure curve and the diffusivity of the investigated system the development of a transformation factor enables the inversion of further travel times besides the peak time of a transient curve as the early travel times of the curve are mainly related to preferential flow features while the inversion based on late travel times are reflecting an integral behavior it can be assumed that the different inversion results reflect the properties of the overall system by comparing the different reconstructions the system interpretation therefore becomes more comprehensive and reliable furthermore the similarity of the proposed hydraulic tomographic approach to seismic travel time tomography allows us to apply the inversion algorithms which are used for seismic tomography we therefore apply the method of staggered grids which enables to refine the grid resulting in a higher nominal resolution to data from a set of interference tests arranged in a tomographic array the tests were conducted in an unsaturated fractured sandstone cylinder in the laboratory the three dimensional reconstructions of the diffusivity distribution are found to be highly reliable and robust in particular the mapped fracture of the sandstone cylinder coincides with our reconstructed diffusivity distribution

inferring spatial distribution of the radially integrated transmissivity from pumping tests in heterogeneous confined aquifers 1 hydrologists routinely analyze pumping test data using conventional interpretation methods that are based on the assumption of homogeneity and that consequently yield single estimates of representative flow parameters however natural subsurface formations are intrinsically heterogeneous and hence the flow parameters influencing the drawdown vary as the cone of depression expands in time in this paper a novel procedure for the analysis of pumping tests in heterogeneous confined aquifers is developed we assume that a given heterogeneous aquifer can be represented by a homogeneous system whose flow parameters evolve in time as the pumping test progresses at any point in time the interpreted flow parameters are estimated using the ratio of the drawdown and its derivative observed at that particular time the procedure is repeated for all times yielding time dependent estimates of transmissivity ti t and storativity si t based on the analysis of the sensitivity of drawdown to inhomogeneities in the t field the time dependent interpreted transmissivity values are found to be a good estimate of tg r the geometric mean of the transmissivity values encompassed within a progressively increasing radius r from the well the procedure is illustrated for gaussian heterogeneous fields with ln t variances up to a value of 2 the impact of the separation distance between the pumping well and observation point on data interpretation is discussed the results show that information about the spatial variability of the transmissivity field can be inferred from time drawdown data collected at a single observation point

identifying flow networks in a karstified aquifer by application of the cellular automata based deterministic inversion method lez aquifer france the distributed modeling of flow paths within karstic and fractured fields remains a complex task because of the high dependence of the hydraulic responses to the relative locations between observational boreholes and interconnected fractures and karstic conduits that control the main flow of the hydrosystem the inverse problem in a distributed model is one alternative approach to interpret the hydraulic test data by mapping the karstic networks and fractured areas in this work we developed a bayesian inversion approach the cellular automata based deterministic inversion cadi algorithm to infer the spatial distribution of hydraulic properties in a structurally constrained model this method distributes hydraulic properties along linear structures i e flow conduits and iteratively modifies the structural geometry of this conduit network to progressively match the observed hydraulic data to the modeled ones as a result this method produces a conductivity model that is composed of a discrete conduit network embedded in the background matrix capable of producing the same flow behavior as the investigated hydrologic system the method is applied to invert a set of multiborehole hydraulic tests collected from a hydraulic tomography experiment conducted at the terrieu field site in the lez aquifer southern france the emergent model shows a high consistency to field observation of hydraulic connections between boreholes furthermore it provides a geologically realistic pattern of flow conduits this method is therefore of considerable value toward an enhanced distributed modeling of the fractured and karstified aquifers

meridional overturning circulation stability and ocean feedbacks in a box model a box model of the inter hemispheric atlantic meridional overturning circulation is developed including a variable pycnocline depth for the tropical and subtropical regions the circulation is forced by winds over a periodic channel in the south and by freshwater forcing at the surface the model is aimed at investigating the ocean feedbacks related to perturbations in freshwater forcing from the atmosphere and to changes in freshwater transport in the ocean these feedbacks are closely connected with the stability properties of the meridional overturning circulation in particular in response to freshwater perturbations a separate box is used for representing the region north of the antarctic circumpolar current in the atlantic sector the density difference between this region and the north of the basin is then used for scaling the downwelling in the north these choices are essential for reproducing the sensitivity of the meridional overturning circulation observed in general circulation models and therefore suggest that the southernmost part of the atlantic ocean north of the drake passage is of fundamental importance for the stability of the meridional overturning circulation with this configuration the magnitude of the freshwater transport by the southern subtropical gyre strongly affects the response of the meridional overturning circulation to external forcing the role of the freshwater transport by the overturning circulation m ov as a stability indicator is discussed it is investigated under which conditions its sign at the latitude of the southern tip of africa can provide information on the existence of a second permanently shut down state of the overturning circulation in the box model m ov will be an adequate indicator of the existence of multiple equilibria only if salt advection feedback dominates over other processes in determining the response of the circulation to freshwater anomalies m ov is a perfect indicator if feedbacks other than salt advection are negligible

capturing aquifer heterogeneity comparison of approaches through controlled sandbox experiments 1 groundwater modeling has become a vital component to water supply and contaminant transport investigations these models require representative hydraulic conductivity k and specific storage ss estimates or a set of estimates representing subsurface heterogeneity currently there are a number of approaches for characterizing and modeling k and ss heterogeneity in varying degrees of detail but there is a lack of consensus for an approach that results in the most robust groundwater models with the best predictive ability the main goal of this study is to compare different heterogeneity modeling approaches e g effective parameters geostatistics geological models and hydraulic tomography when input into a forward groundwater model and used to predict 16 independent cross hole pumping tests we first characterize a sandbox aquifer through single and cross hole pumping tests and then use these data to construct forward groundwater models of various complexities both homogeneous and heterogeneous distributions two effective parameter models are constructed 1 by taking the geometric mean of single hole test k and ss estimates and 2 calibrating effective k and ss estimates by simultaneously matching the response at all ports during a cross hole test heterogeneous models consist of spatially variable k and ss fields obtained via 1 kriging single hole data 2 calibrating a geological model and 3 conducting transient hydraulic tomography zhu and yeh 2005 the performance of these parameter fields are then tested through the simulation of 16 independent cross hole pumping tests our results convincingly show that transient hydraulic tomography produces the smallest discrepancy between observed and simulated drawdowns

comparative study of transient hydraulic tomography with varying parameterizations and zonations laboratory sandbox investigation the final publication is available at elsevier via http dx doi org 10 1016 j jhydrol 2017 09 045 2017 this manuscript version is made available under the cc by nc nd 4 0 license http creativecommons org licenses by nc nd 4 0

cross correlation analysis and information content of observed heads during pumping in unconfined aquifers 1 using a first order cross correlation analysis this paper investigates the relationship between observed heads and hydraulic properties in the saturated and vadose zones at different times and locations of three dimensional unconfined aquifers during pumping tests cross correlation analysis is a weighted sensitivity analysis casted into a stochastic framework it determines the relative impact of each parameter with respect to others in time and space on the observed heads according to uncertainty or spatial variability of each parameter it reveals the information content in measured drawdowns about heterogeneity during a pumping test in an unconfined aquifer which is critical for aquifer parameter estimation based on a synthetic numerical example our cross correlation analysis reveals that heads in the saturated zone at late times carry the greatest nonsymmetrically weighted information content about the hydraulic conductivity ks distribution within the cone of depression on the other hand heads in the saturated zone at early times contain the most information about the specific storage ss heterogeneity in a narrow region between the observation and pumping locations during intermediate and late times heads in the saturated zone largely reflect the effects of saturated water content s and pore size parameter in the thin unsaturated region near the water table above the pumping and observation locations at last heads in the vadose zone at late times carry the greatest information about s and around the observation point

a field proof of concept of tomographic slug tests in an anisotropic littoral aquifer hydraulic tomography is increasingly recognized as a characterization approach that can image pathways or barriers to flow as well as their connectivity in this study we assess the performance of a transient analysis of tomographic slug test head data in estimating heterogeneity in horizontal hydraulic conductivity kh hydraulic conductivity anisotropy the ratio between vertical and horizontal hydraulic conductivity kv kh and specific storage ss under actual field conditions the tomographic experiment was carried out between two wells in a moderately heterogeneous and highly anisotropic silt and sand littoral aquifer in this field proof of concept the inversion of the two dimensional 2d head dataset was computed with a 2d radial flow algorithm that considers kh kv kh ss and wellbore storage effects this study demonstrated that a transient analysis of tomographic slug tests is able to capture the key features of the littoral environment of the test the vertical profiles of kh and kv are indeed in agreement with those from other field and laboratory tests and ss values exhibit physically plausible profiles furthermore the simulation of independent inter well hydraulic tests slug and pumping tests screened over the entire aquifer using resolved kh kv kh and ss tomograms produce responses very close to field observations this study demonstrates that the effects of fine scale heterogeneity that induces k anisotropy at larger scales can be captured through a transient analysis of tomographic slug tests which are very difficult to quantify otherwise with conventional hydraulic tests thus allowing a better representation of properties controlling flow and transport in aquifer systems