numerical modelling of self potential signals associated with a pumping test experiment summary the study of electrical signals associated with groundwater flow is a powerful method to determine in a non invasive way the distribution of hydraulic heads in aquifers hence the distribution of the hydraulic conductivity and storativity experimental hydraulic heads and electrical self potential sp signals associated with a pumping test in an unconfined aquifer were reproduced with a numerical model based on the finite difference method for simplicity we assumed axial symmetry around the pumping well we assessed the equivalent hydraulic conductivity and specific storage of the aquifer by fitting the piezometric levels obtained in the course of the pumping against synthetic hydraulic heads produced by the model the current coupling coefficient is obtained from the best fit between the experimental and modelled sp signals at the end of the pumping phase then keeping the previously determined hydraulic parameters the relaxation of both the hydraulic heads and the sp signals were modelled and found to be consistent with the measured values the data show almost linear relationships between the hydraulic heads in the aquifer and the electrical signals recorded at the ground surface these results show that sp signals allow monitoring subsurface flow in the course of pumping experiments

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

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

granite petrogenesis in the gander zone ne newfoundland mixing of melts from multiple sources and the role of lithospheric delamination silurian to devonian granites within the gander zone of the appalachian central mobile belt in northeastern newfoundland formed adjacent to the former gondwanan continental margin following terminal closure of the iapetus ocean comparison of geochemical and isotopic characteristics of the granites with their host migmatites and metasediments amphibolite and orthogneiss constrain their potential source nd and sr isotopic compositions indicate that no single source or binary mixing product could have produced the granites instead we show that they result from multicomponent mixing involving a contribution from unexposed crystalline basement mantle or underplate and variable contamination by supracrustal host rocks the timing and composition of granite magmatism do not exhibit collisional orogenic subduction related or continental rifting characteristics hence we relate magmatism to lithospheric melting following delamination of an orogenic keel this process provides the influx of mantle derived magma into fertile crust and hence promotes lower crustal melting and primary magma mixing

3 d transient hydraulic tomography in unconfined aquifers with fast drainage response we investigate through numerical experiments the viability of three dimensional transient hydraulic tomography 3dtht for identifying the spatial distribution of groundwater flow parameters primarily hydraulic conductivity k in permeable unconfined aquifers to invert the large amount of transient data collected from 3dtht surveys we utilize an iterative geostatistical inversion strategy in which outer iterations progressively increase the number of data points fitted and inner iterations solve the quasilinear geostatistical formulas of kitanidis in order to base our numerical experiments around realistic scenarios we utilize pumping rates geometries and test lengths similar to those attainable during 3dtht field campaigns performed at the boise hydrogeophysical research site bhrs we also utilize hydrologic parameters that are similar to those observed at the bhrs and in other unconsolidated unconfined fluvial aquifers in addition to estimating k we test the ability of 3dtht to estimate both average storage values specific storage ss and specific yield sy as well as spatial variability in storage coefficients the effects of model conceptualization errors during unconfined 3dtht are investigated including 1 assuming constant storage coefficients during inversion and 2 assuming stationary geostatistical parameter variability overall our findings indicate that estimation of k is slightly degraded if storage parameters must bemore jointly estimated but that this effect is quite small compared with the degradation of estimates due to violation of structural geostatistical assumptions practically we find for our scenarios that assuming constant storage values during inversion does not appear to have a significant effect on k estimates or uncertainty bounds less

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

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

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

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

joint inversion of steady state hydrologic and self potential data for 3d hydraulic conductivity distribution at the boise hydrogeophysical research site we combine sedimentological hydraulic and geophysical information to characterize the 3d distribution of transport properties of an heterogeneous aquifer we focus on the joint inversion of hydraulic head and self potential measurements collected during an extensive experimental campaign performed at the boise hydrogeophysical research site bhrs boise idaho and involving a series of dipole tests while hydraulic head data obtained from piezometric readings in open wells represent a depth averaged value self potential signals provide an estimate of the water table location the aquifer is conceptualized as a multiple continuum where the volumetric fraction of a geo material within a cell of the numerical flow model is calculated by multiple indicator kriging the latter is implemented on the basis of available sedimentological information the functional format of the indicator variograms and associated parameters are estimated on the basis of formal model identification criteria self potential and hydraulic head data have been embedded jointly within a three dimensional inverse model of groundwater flow at the site each identified geo material category is assumed to be characterized by a constant hydraulic conductivity the latter constitute the set of model parameters the hydraulic conductivity associated with a numerical block is then calculated as a weighted average of the conductivities of the geo materials which are collocated in the block by means of multiple indicator kriging model parameters are estimated by a maximum likelihood fit between measured and modeled state variables resulting in a spatially heterogeneous distribution of hydraulic conductivity the latter is effectively constrained on the sedimentological data and conditioned on both self potential and borehole hydraulic head readings minimization of the maximum likelihood objective function allows estimating the relative weight of measurement errors associated with self potential and borehole based head data the procedure adopted allowed a reconstruction of the heterogeneity of the site with a level of details which was not obtained in previous studies and with relatively modest computational efforts further validation against dipole tests which were not used in the inversion procedure supports the robustness of the results

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

hydrodynamic parameters estimation from self potential data in a controlled full scale site abstract a multi physical approach developed for the hydrodynamic characterization of porous media using hydrogeophysical information is presented several pumping tests were performed in the hydrogeosite laboratory a controlled full scale site designed and constructed at the cnr imaa consiglio nazionale delle ricerche istituto di metodologia per l analisi ambientale in marsico nuovo basilicata region southern italy in order to obtain an intermediate stage between laboratory experiments and field survey the facility consists of a pool used to study water infiltration processes to simulate the space and time dynamics of subsurface contamination phenomena to improve and to find new relationship between geophysical and hydrogeological parameters to test and to calibrate new geophysical techniques and instruments therefore the hydrogeosite laboratory has the advantage of carrying out controlled experiments like in a flow cell or sandbox but at field comparable scale the data collected during the experiments have been used to estimate the saturated hydraulic conductivity k s ms 1 using a coupled inversion model working in transient conditions made up of the modified richards equation describing the water flow in a variably saturated porous medium and the poisson equation providing the self potential v which naturally occurs at points of the soil surface owing to the presence of an electric field produced by the motion of underground electrolytic fluids through porous systems the result obtained by this multi physical numerical approach which removes all the approximations adopted in previous works makes a useful instrument for real heterogeneous aquifer characterization and for predictive analysis of its behavior

transient pumping well flow in weakly heterogeneous formations 1 the solution of pumping well flow serves for identifying aquifer s properties most results available in the literature assume homogeneous aquifers or at most stratified structures this study investigates the unsteady well flow in heterogeneous aquifers by modeling the hydraulic conductivity as a three dimensional stationary random function of axisymmetric anisotropy and gaussian correlations the main result of the investigation is the mean drawdown in a transient flow toward a fully penetrating well pumping at a constant rate the solution is obtained in terms of one quadrature over time and is easily calculated closed form approximations of the mean head are developed for moderate and large times the mean drawdowns derived in the study generalize the theis and copper and jacob distributions for aquifers of constant transmissivity it is shown that the transmissivity which is identified by using the cooper and jacob asymptotic is precisely the effective conductivity for uniform horizontal flow khefu this is compared with the finding that the equivalent conductivity for the steady state flow approaches khefu with distance from the well indelman et al 1996

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

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

domains of spit evolution in the goro area po delta italy goro lagoon was formed during the 19th century in the southern part of the po delta its origin is related to the growth of a spit system which progressively occluded the southernmost interdistributary bay from the sea the development of the spits is due to the morphological prominence of the po delta which causes a divergent littoral drift enhanced by wave refraction over the delta front during the last century the spit was abandoned destroyed and re constructed several times because of the development of newer spits seawards using historical maps and aerial photographs three different periods are recognised featuring distinctive spit growth styles parallel fan shaped and branched the different domains of spit evolution are related to several factors mainly to the mutual influence of sediment discharge sand mining along the po river wave action over the delta front human induced subsidence and direct human interventions along the spits and for flood control

steady state hydraulic tomography in a laboratory aquifer with deterministic heterogeneity multi method and multiscale validation of hydraulic conductivity tomograms summary hydraulic tomography potentially is a viable technology that facilitates subsurface imaging of hydraulic heterogeneity to date a comprehensive validation of hydraulic tomography has not been done either at the laboratory or field scales the main objective of this paper is to examine the accuracy of hydraulic conductivity k tomograms obtained from the steady state hydraulic tomography algorithm of yeh t c j liu s 2000 hydraulic tomography development of a new aquifer test method water resources research 36 2095 2105 we first obtain a reference k tomogram through the inversion of synthetic cross hole test data generated through numerical simulations the purpose of reference k tomogram generation is to examine the ability of the algorithm to image the heterogeneity pattern under optimal conditions without experimental errors and with full control of forcing functions initial and boundary conditions as well as source sink terms parallel to the generation of synthetic data we conduct hydraulic tests at multiple scales in a laboratory aquifer with deterministic heterogeneity to generate data that are used to validate k tomograms from hydraulic tomography measurements include multiple k estimates from core slug single hole and cross hole tests as well as several unidirectional flow through experiments conducted on the sandbox under steady state conditions validation of k tomograms involved a multi method and multiscale approach proposed herein which include 1 visual comparisons of k tomograms to the true sand distributions and the reference k tomogram 2 testing the ability of the k tomogram to predict the hydraulic head distribution of an independent cross hole test not used in the computation of the k tomogram 3 comparison of the conditional mean and variance of local k from the k tomograms to the sample mean and variance of results from other measurements 4 comparison of local k values from k tomograms to those from the reference k tomogram and 5 comparison of local k values from k tomograms to those obtained from cores and single hole tests the multi method and multiscale validation approach proposed herein further illustrates the robustness of steady state hydraulic tomography in subsurface heterogeneity delineation

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

prediction of solute transport in a heterogeneous aquifer utilizing hydraulic conductivity and specific storage tomograms a sequential procedure of hydraulic tomographical inversion is applied to characterize at high resolution the spatial heterogeneity of hydraulic conductivity and specific storage at the field test site stegemuhle germany the shallow aquifer at this site is examined by five short term multilevel pumping tests with 30 pumping observation pairs between two wells utilizing travel time diagnostics of the recorded pressure response curves fast eikonal based inversion is shown to deliver insight into the sedimentary structures thus the structural information from the generated travel time tomogram is exploited to constrain full calibration of the pressure response curves based on lateral extrapolation from the measured inter well profile a three dimensional reconstruction of the aquifer is obtained it is demonstrated that calibration of spatially variable specific storage in addition to hydraulic conductivity can improve the fitting of the model while the structural features are only slightly changed at the field site two tracer tests with uranine and sodium naphthionate were also performed and their concentrations were monitored for 2 months the measured tracer breakthrough curves are employed for independent validation of the hydraulic tomographical reconstruction it is demonstrated that major features of the observed solute transport can be reproduced and structures relevant for macrodispersive tracer spreading could be resolved however for the mildly heterogeneous aquifer the tracer breakthrough curves can also be approximated by a simplified homogeneous model with higher dispersivity therefore improved validation results that capture specific characteristics of the breakthrough curves would require additional hydraulic measurements

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