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To improve the accuracy of estimated hydraulic parameters such as hydraulic conductivity and specific storage in confined aquifers with high permeability, and provide a scientific explanation for the nonlinear oscillation phenomenon of test well water levels, this study established a slug test model that takes into account the skin and non-Darcy flow effects, as well as inertial force action. The skin effect was described by Robbin boundary conditions and the non-Darcy flow effect was explained by the Forchheimer equation; momentum balance equation expressed the inertial force action . The Laplace transform method was used to derive the analytical solution of this model. Then the impacts of three factors on estimating of hydraulic parameters were analyzed using field data. The results show that the influences of skin effect, non-Darcy flow effect, and inertia force action on the parameter estimation cannot be ignored. More specifically, the higher values of the dimensionless skin factor (Sw), the Forchheimer coefficient (γ), and the vertical distance (l) between the water level in the well and the top of the confined aquifer after instantaneous water injection, the slower rate of water level recovery. As the value of Sw increases, the amplitude of water level oscillation decreases, whereas the amplitudes of water level oscillation increase with larger values of γ and l. Ignoring the skin effect, non-Darcy flow effect or inertia force will lead to underestimating hydraulic conductivity and specific storage. The results can provide theoretical guidance and technical support for the inversion of hydraulic parameters in fractured confined aquifers.

Copyright of Hydrogeology & Engineering Geology / Shuiwendizhi Gongchengdizhi is the property of Hydrogeology & Engineering Geology Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Hydrogeology Journal is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Journal of Groundwater Hydrology is the property of Japanese Association of Groundwater Hydrology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Hydrogeology Journal is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

• Laboratory experiments tend to result in lower aquitard K and higher aquitard S s. • Elastic S s is about one order of magnitude lower than inelastic S s. • For ϕ below 0.25, aquitard K tends to increase with ϕ and decrease vice versa. • Inelastic S s generally corresponds to ϕ > 0.37 and elastic S s to ϕ < 0.37. • ϕ outperforms other factors in predicting S s and is significant for predicting K. Aquitard hydraulic conductivity (K), specific storage (S s) and porosity (ϕ) are critical to the modeling of flow and mass and heat transport in groundwater systems, yet comprehensive insights into their statistical characteristics remain limited. This study compiles 456 K values from 47 studies, 202 S s values from 49 studies and 239 ϕ values from 18 studies, followed by rigorous statistical analysis of aquitard K , S s and ϕ with dependence on the features of test method, lithology and burial depth. Additionally, the interrelationships among K , S s and ϕ are analyzed. A predictive model for aquitard K and S s is developed utilizing the random forest (RF) approach. The statistical findings unearth that laboratory experiments tend to yield lower K while higher S s , particularly when burial depths are less than 50 m. Clay, silt clay, and glacial till exhibit comparable K values, in contrast to significantly lower K values observed in shale formations. Aquitard K , S s , and ϕ exhibit depth-decaying characteristics. Between two adjacent depth intervals, 0 – 50 m, 50 – 150 m and >150 m, there is nearly an order of magnitude difference in either K or S s. Aquitard K tends to increase with ϕ when ϕ is below 0.25 and decreases vice versa. This phenomenon is probably attributed to the significant amount of immobile-bound water adhering to clayey particles within the aquitard with a high ϕ value, which reduces the pore space available for water flow. Elastic S s , which indicates recoverable aquitard groundwater depletion, is about one order of magnitude lower than inelastic S s , which indicates permanent aquitard groundwater depletion, implying that the majority of groundwater depletion from aquitards under long-term groundwater exploitation is non-recoverable. The RF-based predictive model indicates that ϕ is a highly important feature for predicting K and outperforms lithology, test method and burial depth in predicting S s. The statistical findings of this study present a valuable basis for aquitard hydraulic parameters. [ABSTRACT FROM AUTHOR]

Copyright of Hydrogeology Journal is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Cassia fistula L. (Sanskrit: Aragvadha, family: Caesalpinaceae) is used as a mild laxative in traditional medicine. Ancient texts advocate specific storage of its matured and ripe fruits under a pit filled with sand or soil. The present study was designed to compare the physicochemical, organoleptic and other biochemical parameters of the fruit pulp, stored under usual and specific conditions as mentioned in ancient texts. The sample kept under a pit showed higher total phenolics, flavonoids and anthraquinone levels along with reduced total and reducing sugars. The increased antioxidant activity of the pit-stored sample due to higher total phenolics and flavonoids levels as revealed from the DPPH radical scavenging assay may enhance its medicinal attributes, justifying ancient claim of specific storage of the fruits. [ABSTRACT FROM AUTHOR]

Copyright of Hydrogeology Journal is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This paper describes a comprehensive investigation to accurately determine the hydraulic permeability k and the specific storage S s of a shale sample. One-dimensional pressure transient tests were conducted on a cylindrical sample under various levels of pore and confining pressures. For the boundary conditions, the upstream pressure was kept constant using a syringe pump, and the downstream storage was minimized for reducing the test duration. Both the downstream pressure and the upstream fluid flow into the sample were continuously recorded throughout the transient period. To estimate the hydraulic properties, the curve fitting technique was applied to the pressure and flow data using theoretical curves. We found that the pressure curve was sensitive to the ratio of hydraulic permeability to the specific storage (k / S s), but not sufficient to determine the individual components (k and S s). The upstream flow curve was sensitive to the specific storage but less sensitive to the permeability. Based on our sensitivity analysis, we present a combination of two objective functions of flow and pressure data to optimize both hydraulic properties with reasonable uncertainty. An alternative is to first use the flow data to determine S s and then use pressure data with the predetermined S s to obtain the remaining k. [ABSTRACT FROM AUTHOR]

Accurate knowledge of permeability is crucial for successful management of groundwater, petroleum resources, and subsurface contaminant remediation. The oscillating pore pressure method is a popular laboratory technique for permeability measurements of porous rock samples. We develop a novel data processing approach that utilizes a broad, multifrequency range of data and inverts it for permeability. We reprocess published data and demonstrate that our methodology outperforms traditional data reduction techniques, as our inversion results show a better fit to pressure trends. To better understand the effect of frequency on phase and amplitude data and to verify our inversion approach, we numerically simulate oscillating pore pressure experiments for four rock samples. We document a strong deviation of experimentally obtained phase data starting at 0.3 Hz oscillation frequency. A possible explanation for this deviation is poroelastic coupling during pressure diffusion. Our method can be used for robust determination of permeability and rapid prediction of experimental results using numerical simulation, ultimately improving the analysis of experimental permeability measurements. Key Points: We present a novel inversion method for processing of oscillating pore pressure dataWe show that the inverted permeability values are accurate and fit pressure trendsNumerical simulations of oscillating pore pressure experiments are in close agreement with the experimental data and analytical solutions [ABSTRACT FROM AUTHOR]

This paper presents a new modelling approach to quantify the hydraulic diffusivity of low‐permeability unconsolidated porous media under confined saturated‐flow conditions in the laboratory. The derived analytical solution for the transient variation of the hydraulic head after flow interruption was applied to experimental data obtained from continuous measurements of the water pressure at two locations in the soil column. Three soil samples made of a mixture of natural bentonite (at different mass fractions) and medium sand were studied during a series of stepwise constant flow rates of water. The numerical results well fit the experimentally measured decrease of the dimensionless hydraulic head. The study shows that the increase of the mass fraction of bentonite in the soil sample from 10 to 30% is accompanied by a strong decrease of the hydraulic diffusivity from 2.4 × 10−2 to 1.1 × 10−3 m2 s−1, which is clearly due to the decrease of the hydraulic conductivity of the soil sample. The specific storages obtained for each of the three samples are in the same order of magnitude and seem to decrease with the increase of mass fraction of bentonite. However, they clearly reflect the predominant portion of the compressibility of the porous medium compared with that of water. Compared with reported literature values for clayey soils, the specific storage values in this study are slightly higher, varying within the range of 2 × 10−3 to 8.1 × 10−3 m−1.. The experimental results also give insight into the limitations of the modelling approach. In the case of low‐permeability soils (K < 2 × 10−6 ms−1) and steady‐flow conditions with low Reynolds numbers, for example, Re < 0.003, it is recommended to choose a time duration for flow interruption between subsequent flow rate steps of longer than 5 s. For high‐permeability porous media, to increase the precision of the quantified hydraulic diffusivity, it might be useful to select a measuring frequency significantly higher than 1 Hz. [ABSTRACT FROM AUTHOR]

Groundwater specific storage varies by orders of magnitude, is difficult to quantify, and prone to significant uncertainty. Estimating specific storage using aquifer testing is hampered by the nonuniqueness in the inversion of head data and the assumptions of the underlying conceptual model. We revisit confined poroelastic theory and reveal that the uniaxial specific storage can be calculated mainly from undrained poroelastic properties, namely, uniaxial bulk modulus, loading efficiency, and the Biot‐Willis coefficient. In addition, literature estimates of the solid grain compressibility enables quantification of subsurface poroelastic parameters using field techniques such as cross‐hole seismic surveys and loading efficiency from the groundwater responses to atmospheric tides. We quantify and compare specific storage depth profiles for two field sites, one with deep aeolian sands and another with smectitic clays. Our new results require bulk density and agree well when compared to previous approaches that rely on porosity estimates. While water in clays responds to stress, detailed sediment characterization from a core illustrates that the majority of water is adsorbed onto minerals leaving only a small fraction free to drain. This, in conjunction with a thorough analysis using our new method, demonstrates that specific storage has a physical upper limit of ≾ 1 . 3 · 1 0 − 5 m−1. Consequently, if larger values are derived using aquifer hydraulic testing, then the conceptual model that has been used needs reappraisal. Our method can be used to improve confined groundwater storage estimates and refine the conceptual models used to interpret hydraulic aquifer tests. [ABSTRACT FROM AUTHOR]

An analytical solution is developed for predicting two-dimensional transient seepage into ditch drainage network receiving water from a non-uniform steady ponding field from the surface of the soil under the influence of source/sink in the flow domain. The flow domain is assumed to be saturated, homogeneous and anisotropic in nature and have finite extends in horizontal and vertical directions. The drains are assumed to be standing vertical and penetrating up to impervious layer. The water levels in the drains are unequal and invariant with time. The flow field is also assumed to be under the continuous influence of time–space dependent arbitrary source/sink term. The correctness of the proposed model is checked by developing a numerical code and also with the existing analytical solution for the simplified case. The study highlights the significance of source/sink influence in the subsurface flow. With the imposition of the source and sink term in the flow domain, the pathline and travel time of water particles started deviating from their original position and above that the side and top discharge to the drains were also observed to have a strong influence of the source/sink terms. The travel time and pathline of water particles are also observed to have a dependency on the height of water in the ditches and on the location of source/sink activation area. [ABSTRACT FROM AUTHOR]

Abstract: The governing equations for subsurface flow codes in a deformable porous media are derived from the balance of fluid mass and Darcy's equation. One class of these codes, which we call general subsurface flow codes (GSFs), allow for more general constitutive relations for material properties such as porosity, permeability and density. Examples of GSFs include PFLOTRAN, FEHM, TOUGH2, STOMP, and some reservoir simulators such as BOAST. Depending on the constitutive relations used in GSFs, an inconsistency arises between the standard groundwater flow equation and the governing equation of GSFs, and we clarify that the reason for this inconsistency is because the Darcy's equation used in the GSFs should account for the velocity of fluid with respect to solid. Due to lack of awareness of this inconsistency, users of the GSFs tend to use a porosity‐pressure relationship that comes from the standard groundwater flow equation and assumes that the relative velocity is already accounted for. For the Theis problem, we show that using this traditional relationship in the GSFs leads to significantly large errors. We propose an alternate porosity‐pressure relationship that is consistent with the derivation of the governing equations in the GSFs where the solid velocity is not tracked, and show that, with this relationship, the results are more accurate for the Theis problem. The purpose of this note is to make the users and developers of these GSFs aware of this inconsistency and to advocate that the alternate porosity model derived here should be incorporated in GSFs. [ABSTRACT FROM AUTHOR]

Most of the analytical and numerical models of tunnel groundwater inflow ignore the excavation process, leading to inaccurate prediction of discharge rate. A dynamic modeling approach was introduced by redevelopment of MODFLOW to simulate the change of groundwater flow step by step in accord with tunnel excavation. The drilling tunnel was conceptualized as a changing boundary condition, which was modeled by dividing the drilling process into a series of successive steps. The impact of permeability heterogeneity on groundwater flow was studied through a comparison between a homogeneous hydraulic conductivity case and a synthetic heterogeneous one. It was found that the discharge rate at drilling front kept stable in the homogeneous case, resulting in a linear increase in the total discharge rate, similar to the analytical solution by Perrochet (2005). In contrast, the front and total discharge rate were influenced significantly by the variability of permeability in the heterogeneous case. The time-dependent discharge rate at a given place was subject to an exponential decay for both cases with the maximum inflow occuring at the beginning of excavation. The relationship between discharge rate and hydraulic properties was further investigated in a high- K zone. It revealed that maximum discharge rate was proportional to hydraulic conductivity ( K) and specific storage ( Ss). The decaying rate of discharge was time-dependent and also proportional to the value of K and Ss. The water budget analysis demonstrated that water released from storage of the high- K zone was the major source of tunnel discharge at early times. [ABSTRACT FROM AUTHOR]

The hydraulic properties of geologic formations, such as specific storage and hydraulic conductivity, are known to vary spatially due to formation heterogeneity; however, they may also change temporally if the formation undergoes mechanical disturbance such as occurs during mining. Characterising changes in hydraulic properties is important for groundwater systems that are disturbed by mining. Conventional hydrogeological investigations rely on literature derived values or limited programs of field testing (e.g. pumping test) to define specific storage; but these approaches do not consider the change in compressibility that may occur due to mechanical disturbance. This paper presents, for the first time, direct in situ measurements of the changes in compressibility, and consequently specific storage, as a result of mechanical disturbance within geologic formations overlying underground mining operations. The in situ measurements of compressibility are derived in this study from the pore-pressure response to barometric loading or strains induced by earth tides. Even prior to disturbance, the compressibility obtained from in situ measurements was found to be an order of magnitude lower than that measured on core samples by unconfined strength test in the laboratory. The differences in compressibility for the intact formation are likely due to sample disturbance and the differences in strain level imposed by the field and laboratory methods. The increase in compressibility of the overburden rock varied with the location of the monitoring site relative to longwall extraction and the level of strain the formation sustained. The study found that quantifying the changes in compressibility, and consequently specific storage, as a result of mine-induced disturbance is critical to our understanding of subsidence, the extent of depressurization, and the impact that mining may have on regional groundwater flow systems. [ABSTRACT FROM AUTHOR]

An analytical solution in the form of infinite series is developed for predicting time-dependent three-dimensional seepage into ditch drains from a flat, homogeneous and anisotropic ponded field of finite size, the field being assumed to be surrounded on all its vertical faces by ditch drains with unequal water level heights in them. It is also assumed that the field is being underlain by a horizontal impervious barrier at a finite distance from the surface of the soil and that all the ditches are being dug all the way up to this barrier. The solution can account for a variable ponding distribution at the surface of the field. The correctness of the proposed solution for a few simplified situations is tested by comparing predictions obtained from it with the corresponding values attained from the analytical and experimental works of others. Further, a numerical check on it is also performed using the Processing MODFLOW environment. It is noticed that considerable improvement on the uniformity of the distribution of the flow lines in a three-dimensional ponded drainage space can be achieved by suitably altering the ponding distribution at the surface of the soil. As the developed three-dimensional ditch drainage model is pretty general in nature and includes most of the common variables of a ditch drainage system, it is hoped that the drainage designs based on it for reclaiming salt-affected and water-logged soils would prove to be more efficient and cost-effective as compared with designs based on solutions developed by making use of more restrictive assumptions. Also, as the developed model can handle three-dimensional flow situations, it is expected to provide reliable and realistic drainage solutions to real field situations than models being developed utilizing the two-dimensional flow assumption. This is because the existing two-dimensional solutions to the problem are actually valid not for a field of finite size but for an infinite one only. [ABSTRACT FROM AUTHOR]

The deep borehole (DB) experiment gave the opportunity to acquire hydraulic parameters in a hydraulically undisturbed zone of the Opalinus Clay at the Mont Terri rock laboratory (Switzerland). Three methods were used to estimate hydraulic conductivity and specific storage values of the Opalinus Clay formation and its bounding formations through the 248 m deep borehole BDB-1: application of a Poiseuille-type law involving petrophysical measurements, spectral analysis of pressure time series and in situ hydraulic tests. The hydraulic conductivity range in the Opalinus Clay given by the first method is 2 × 10-6 × 10 m s for a cementation factor ranging between 2 and 3. These results show low vertical variability whereas in situ hydraulic tests suggest higher values up to 7 × 10 m s. Core analysis provides economical estimates of the homogeneous matrix hydraulic properties but do not account for heterogeneities at larger scale such as potential tectonic conductive features. Specific storage values obtained by spectral analysis are consistent and in the order of 10 m, while formulations using phase shift and gain between pore pressure signals were found to be inappropriate to evaluate hydraulic conductivity in the Opalinus Clay. The values obtained are globally in good agreement with the ones obtained previously at the rock laboratory. [ABSTRACT FROM AUTHOR]

Accurate determination of groundwater state of confinement and compressible storage properties at vertical resolution over depth is notoriously difficult. We use the hydraulic head response to atmospheric tides at 2 cpd frequency as a tracer to quantify barometric efficiency ( BE) and specific storage ( Ss) over depth. Records of synthesized Earth tides, atmospheric pressure, and hydraulic heads measured in nine piezometers completed at depths between 5 and 55 m into unconsolidated smectitic clay and silt, sand and gravel were examined in the frequency domain. The barometric efficiency increased over depth from ∼0.05 in silty clay to ∼0.15 in sands and gravels. BE for silty clay was confirmed by calculating the loading efficiency as 0.95 using rainfall at the surface. Specific storage was calculated using effective rather than total moisture. The differences in phase between atmospheric pressure and hydraulic heads at 2 cpd were ∼180° below 10 m indicating confined conditions despite the low BE. Heads in the sediment above a fine sand and silt layer at 12 m exhibited a time variable phase difference between 0° and 180° indicating varying confinement. Our results illustrate that the atmospheric tide at 2 cpd is a powerful natural tracer for quantifying groundwater state of confinement and compressible storage properties in layered formations from hydraulic heads and atmospheric pressure records without the need for externally induced hydraulic stress. This approach could significantly improve the development of conceptual hydrogeological model used for groundwater resource development and management. [ABSTRACT FROM AUTHOR]

• HT surveys in 2019 and 2020 to test the reproducibility of estimated K and S s. • 3D K and S s fields are reproducible even when boundary conditions are varied. • Improved reproducibility observed when inverting with higher data density. • Accurate geological information included as initial guess improved reproducibility. • HT has the potential for mapping changes in K and S s heterogeneity over time. Over the past two decades, geostatistics-based hydraulic tomography (HT) has been proven to be a robust method for subsurface heterogeneity characterization. However, the reproducibility of estimated parameter fields, namely the hydraulic conductivity (K) and specific storage (S s), obtained over different data collection periods and under different flow scenarios have been rarely studied. In this study, we investigate the reproducibility and predictivity of HT estimates using data collected in 2019 and 2020 at a field site of varying boundary conditions underlain by sedimentary units in Japan, with different data density and prior geological information. Model performance of each case is evaluated qualitatively and quantitatively by examining results from model calibration, self-validation and cross-validation, in terms of parameter fields comparison, drawdown matches and cross-correlation distributions. Results of this study reveal that: 1) overall, the parameter fields for 2019 and 2020 HT estimates are generally reproducible, while fine-scale discrepancy exists; 2) they are also found to be reproducible in terms of consistency of estimated geostatistical parameters; 3) higher levels of reproducibility and predictivity associated with estimated K and S s fields are obtained when higher data density is included for geostatistical inverse modeling with more accurate prior geological information; and 4) the different spatial distributions of cross-correlation between head and parameter fields induced through the significant variation of the groundwater flow field from 2019 to 2020 strengthen the notion of reproducibility of HT results. These results collectively suggest that HT has the potential for mapping changes to K and S s heterogeneity over time broadening its future applications to various practical problems. [ABSTRACT FROM AUTHOR]

A method is presented for obtaining depth-discrete values of specific storage ( Ss ) from single-hole hydraulic tests in fractured rock boreholes using straddle packers (1.5–17 m test intervals). Low flow constant head (CH) step tests analyzed using the Thiem method provide transmissivity ( T ) values free from non-Darcian error. Short-term, constant-rate pumping tests (0.5–2 h) analyzed using the Cooper-Jacob approximation of the Theis method provide S from the hydraulic diffusivity using the Darcian T value from the CH step test. This synergistic use of two types of hydraulic tests avoids the common source of error when pumping tests (injection or withdrawal) are conducted at higher flow rates and thereby induce non-Darcian flow resulting in the underestimation of T. Other errors, such as well bore storage and leakage, can also substantially influence S by causing a shift in the time axis of the Cooper-Jacob semi-log plot. In this approach, the Darcian T values from the CH step tests are used in the analysis of the transient pumping test data for calculating S throughout the pumping test using the Cooper-Jacob approximation to minimize all of the aforementioned errors, resulting in more representative S values. The effect of these non-idealities on the measured drawdown is illustrated using the Theis equation with the Darcian T and S values to calculate drawdown for comparison to measured data. The Ss values for tests in sandstone obtained from this approach are more consistent with confined aquifer conditions than values derived from the traditional Cooper-Jacob method, and are within the range of field and lab values presented from a compilation of literature values for fractured sandstone. (10 −7 –10 −5 m −1 ) This method for obtaining Ss values from short-interval, straddle packer tests improves the estimation of both K and Ss and provides opportunity to study their spatial distribution in fractured rock. [ABSTRACT FROM AUTHOR]

A modified version of a published slug test model for unconfined aquifers is applied to cross-hole slug test data collected in field tests conducted at the Widen site in Switzerland. The model accounts for water-table effects using the linearized kinematic condition. The model also accounts for inertial effects in source and observation wells. The primary objective of this work is to demonstrate applicability of this semi-analytical model to multi-well and multi-level pneumatic slug tests. The pneumatic perturbation was applied at discrete intervals in a source well and monitored at discrete vertical intervals in observation wells. The source and observation well pairs were separated by distances of up to 4 m. The analysis yielded vertical profiles of hydraulic conductivity, specific storage, and specific yield at observation well locations. The hydraulic parameter estimates are compared to results from prior pumping and single-well slug tests conducted at the site, as well as to estimates from particle size analyses of sediment collected from boreholes during well installation. The results are in general agreement with results from prior tests and are indicative of a sand and gravel aquifer. Sensitivity analysis show that model identification of specific yield is strongest at late-time. However, the usefulness of late-time data is limited due to the low signal-to-noise ratios. [ABSTRACT FROM AUTHOR]

The one-dimensional diffusion equation was solved to understand the pressure and flow behaviors along a cylindrical rock specimen for experimental boundary conditions of constant upstream pressure and constant downstream storage. The solution consists of a time-constant asymptotic part and a transient part that is a negative exponential function of time. This means that the transient flow exponentially decays with time and is eventually followed by a steady-state condition. For a given rock sample, the transient stage is shortest when the downstream storage is minimized. For this boundary condition, a simple equation was derived from the analytic solution to determine the hydraulic permeability from the initial flow rate during the transient stage. The specific storage of a rock sample can be obtained simply from the total flow into the sample during the entire transient stage if there is no downstream storage. In theory, both of these hydraulic properties could be obtained simultaneously from transient-flow stage measurements without a complicated curve fitting or inversion process. Sensitivity analysis showed that the derived permeability is more reliable for lower-permeability rock samples. In conclusion, the constant head method with no downstream storage might be more applicable to extremely low-permeability rocks if the upstream flow rate is measured precisely upstream. [ABSTRACT FROM AUTHOR]

Good constraints on hydrogeological properties are an important first step in any quantitative model of groundwater flow. Field estimation of permeability is difficult as it varies over orders of magnitude in natural systems and is scale-dependent. Here we directly compare permeabilities inferred from tidal responses with conventional large-scale, long-term pumping tests at the same site. Tidally induced water pressure changes recorded in wells are used to infer permeability at ten locations in a densely fractured sandstone unit. Each location is either an open-hole well or a port in a multilevel monitoring well. Tidal response is compared at each location to the results of two conventional, long-term and large scale pumping tests performed at the same site. We obtained consistent values between the methods for a range of site-specific permeabilities varying from ∼10−15 m2 to 10−13 m2 for both open wells with large open intervals and multilevel monitoring well. We conclude that the tidal analysis is able to capture passive and accurate estimates of permeability. [ABSTRACT FROM AUTHOR]