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Characterization of large-scale aquifer heterogeneity in glacial outwash by analysis of slug tests with oscillatory response, Cape Cod, Massachusetts
... Aquifer-testing data were analyzed using the software AQTESOLV version 4.5 (Duffield, 2007). Analysis of slug-test data used the methods of Bouwer and Rice (1976), Springer and Gelhar (1991), and model of Hyder and others (1994). The Bouwer and Rice (1976) method is best suited for application to unconfined aquifers and has various assumptions relating to aquifer penetration, well screen position, and well flow behavior (Butler, 1997). ...
... The Bouwer and Rice (1976) method is best suited for application to unconfined aquifers and has various assumptions relating to aquifer penetration, well screen position, and well flow behavior (Butler, 1997). The Springer and Gelhar (1991) method was used to account for inertial effects in the wells and the oscillatory responses seen in the study area. The Springer and Gelhar (1991) solution also incorporates frictional well loss in small-diameter wells (Butler, 1997). ...
... The Springer and Gelhar (1991) method was used to account for inertial effects in the wells and the oscillatory responses seen in the study area. The Springer and Gelhar (1991) solution also incorporates frictional well loss in small-diameter wells (Butler, 1997). The Hyder and others (1994) model was useful when the presence of a variable behavior between rising-head and falling-head tests was observed, potentially because of interferences between the aquifer material and the well bore (Butler, 1997), commonly known as "well-skin effects," which were evident during one test. ...
From 2018 through 2020, the U.S. Geological Survey, in cooperation with the Air Force Civil Engineering Center, conducted an integrated study of the Fountain Creek alluvial aquifer located near Colorado Springs, Colorado. The objective of the study was to characterize hydrologic conditions for the alluvial aquifer pertinent to the potential for transport of solutes. Specific goals of this report were to characterize the groundwater hydrology of the area, to quantify groundwater and surface-water interactions, to estimate hydraulic properties of the aquifer using aquifer testing, and to complete numerical simulations of groundwater flow.
Synoptic groundwater-level elevation measurements completed throughout this study, and as part of other U.S. Geological Survey programs between 1994 and 2020, indicate groundwater-level elevations fluctuate on annual and interannual timeframes. Groundwater-level fluctuations likely were caused by temporally variable groundwater recharge and discharge components in the area, with many wells showing maximum groundwater-level elevations during the winter months (November through March). From an interannual perspective, groundwater-level fluctuations appear to have reached maximum values during 2000 to 2003, decreased during 2003 to 2006, and remained relatively constant since that time, with the exception of several wells which have displayed rising groundwater-level elevations since 2018. Spatial evaluation of groundwater-level elevations indicates groundwater flow is generally from northeast to southwest within the vicinity of several alluvial paleochannels occurring along the northeastern margin of the aquifer. Within the center of the aquifer along Fountain Creek, groundwater flow is generally from north to south, approximately paralleling surface-water flow. To quantitatively understand the potential effect of groundwater recharge and groundwater pumping on fluctuations in groundwater-level elevation, a statistical transfer-function-noise model was applied. Results of the statistical model indicate throughout most of the aquifer, fluctuations were primarily the result of recharge seasonality. In the main stem of the aquifer where groundwater pumping wells were more concentrated, however, groundwater-level elevation fluctuations were also attributable to groundwater pumping through time.
Three-dimensional evaluation of the aquifer geometry near Fountain Creek was combined with synoptic streamflow measurement and accounting of stream gains and losses to evaluate groundwater and surface-water interactions in the study area. Streamflow gain or loss calculations indicate Fountain Creek both gains from and loses flow to the alluvial aquifer, and gaining or losing reaches of the stream may be partially controlled by the depth to bedrock near the stream. Reaches with streamflow gains tend to coincide with areas where the estimated depth to bedrock is decreasing, meaning the alluvial aquifer is likely thinning in these areas and groundwater-flow paths may be converging and discharging groundwater to the stream. Losing reaches tended to coincide with locally greater depth to bedrock where the alluvial aquifer is likely thicker and has greater storage potential for surface water lost from Fountain Creek.
Results of aquifer testing indicate hydraulic conductivity, estimated from slug tests and single-well pumping tests, ranged from 0.32 to 1,410 feet per day (ft/d) and 4.13 to 664 ft/d, respectively. These results are similar to the range of values from previous aquifer tests in the study area. Hydraulic conductivities from aquifer testing for this study were generally greater than the estimates of previous slug tests and had a mean value less than the estimates from previous pumping tests. Spatial evaluation of aquifer testing results indicates hydraulic conductivity tends to be greater in the main stem of the alluvial aquifer and lower in paleochannels upgradient from the main stem of the aquifer. The spatial variation in hydraulic conductivity may be attributed to the geomorphologic processes that formed the alluvial aquifer. Compacted sediment in the paleochannels has not been potentially transported sufficient distance to cause grain-size sorting, resulting in a poorly sorted deposit and lower hydraulic conductivities. In the central portion of the alluvial aquifer, near Fountain Creek, the sediments have been transported farther from their source areas and are likely better sorted, removing finer grained sediments that would cause lower hydraulic conductivity.
A numerical groundwater-flow model was calibrated for the Fountain Creek alluvial aquifer for 2000–19 to simulate water-budget components, groundwater-flow directions, and groundwater-flow paths. The model simulated precipitation recharge, groundwater and surface-water interactions, evapotranspiration, high-volume groundwater pumping by pumping wells, and external inflows and outflows occurring along the boundaries of the alluvial aquifer. Model calibration was completed using manual and automated approaches, the latter of which assisted in quantifying model results sensitivity to input parameters. The calibrated model corresponds well with groundwater-level elevation observations, with a mean residual (observed minus simulated groundwater-level elevation) equal to −0.60 feet. Simulated groundwater base flow to streams was typically within 10 percent of base flow estimated by independent methods. Groundwater and surface-water interactions represented the largest water-budget components of the aquifer, with the second largest groundwater discharge component coming from pumping wells. Groundwater and surface-water interactions represent both the largest gain and loss terms in the water budget, because these interactions differ spatially, meaning in some areas of the model domain groundwater is being recharged by streams, whereas in other areas, groundwater is discharged to streams. Estimates of advective groundwater-flow paths indicate pumping wells may capture groundwater recharged from losing streams and groundwater that flows into the main stem of the alluvial aquifer from paleochannels.
... Several mathematical models are available in the hydrogeology literature for analyzing this transient response in confined [1,5,[8][9][10][11][12] and unconfined [3,[13][14][15][16][17][18] aquifers to infer aquifer hydraulic properties. Here, hydraulic properties refer to hydraulic conductivity (or permeability), anisotropy, specific storage, and, in the case of unconfined aquifers, specific yield. ...
... Field studies have shown that the pressure perturbation in a well can respond in two ways: monotonic decay of the perturbation to the initial static level or an oscillatory response where the amplitude of the oscillation decays with time as the well head returns to the initial static state. The former are referred to as overdamped responses and are associated with low-permeability formations, and the latter, are termed underdamped, and are typical of high-permeability formations [2,6,14]. ...
... Butler [12] extended the KGS model of Hyder et al. [15] to oscillatory behavior by incorporating momentum balance in the wellbore for all possible degrees of well penetration of a confined aquifer. The momentum balance equation of Springer and Gelhar [14] given in equation (20) was extended to allow for head continuity at the interface between well and the aquifer using [12] ...
Slug tests are a widely used method for characterizing aquifers because they can be performed quickly, with minimal equipment and labor, and without the need to dispose of produced water. They involve rapid displacement of the water level in a well, followed by continuous measurement of the water level as it reequilibrates. Several mathematical models available in the hydrogeology literature are summarized here. The tests are classified according to: (i) the type of perturbation (solid versus pneumatic slug); (ii) the type of response (overdamped versus oscillatory); and (iii) the type of aquifer (confined versus unconfined). Examples are included of the graphical approach using slug‐test data to estimate aquifer properties. Computational tools and software available for more complex models are mentioned briefly. Emerging works on slug tests focus on the use of slug tests to characterize heterogeneity through their integration into hydraulic tomography. They are used in multilevel single‐well tests and in cross‐hole tests with packers and with direct‐push technology to generate vertical logs of hydraulic parameters including hydraulic conductivity and storage.
... The same response was recorded at Yair 4 and 6 boreholes which are also located at the damage zone. The damage zone in the dolomite rock is in a phreatic aquifer, with the model which was used to solve the slug tests under these conditions, being the model by Springer and Gelhar (1991). The model assumptions are: (1) the aquifer has infinite areal extent; (2) the aquifer is homogeneous and of uniform thickness; (3) the aquifer is unconfined; (4) the test well is fully or partially penetrated; (5) the flow is quasi-steady state; (6) the water volume injected into or discharged from the well instantaneously. ...
... The damage zone in the chert rock is in a confined aquifer; therefore, the model used to solve these slug tests was that of Butler (1998). The model assumptions are the same as in Springer and Gelhar (1991), apart from the aquifer being confined. The permeability values of the damage zone on both sides of the fault core were found to be 2×10 −10 -3.5×10 −10 m 2 ( Table 1). ...
... These slug tests were solved with the Bouwer and Rice (1976) model. The model assumptions are the same as in the Springer and Gelhar (1991) model, and the analyzed data showed a double straight-line effect (two slopes), which is not uncommon when plotting the log of the normalized head vs. time (Fig. 9). This effect refers to the rapid draining of the filter pack followed by a slower response controlled by the aquifer (Butler 1998). ...
Fault zone architecture plays an important role in flow regimes of hydrological systems. Fault zones can act as conduits, barriers, or conduits/barrier systems depending on their spatial architecture. The goal of this study is to determine the fault-zone permeability structure and its effect on the local hydrogeological system in the Dead Sea fault system. Permeability was measured on small-scale outcrop plug samples at four faults along the Dead Sea fault system, and large-scale slug tests in four boreholes, in different parts of the fault, at Yair fault in Israel. The research results show that values in the damage zone are two to five orders of magnitude higher than those of the fault core (~3.5 × 10−10, 1 × 10−15 m2 respectively), resulting in an anisotropic permeability structure for the overall fault zone and preferable flow parallel to the fault. A set of injection tests in the Yair fault damage zone revealed a water-pressure-dependent behavior. The permeability of this zone increases when employing a higher water pressure in the fault fracture-dominated damage zone, due to the reopening of fractures.
... They described the impact of inertia-induced oscillations on both pumping and slug tests and demonstrated that the magnitude of these oscillations is determined primarily by the transmissivity of the test interval and the length of the water column in the well. A number of models for slug tests in highly permeable systems have been developed on the basis of that work [e.g., Van der Kamp, 1976;Krauss, 1977;Kipp, 1985;Kabala et al., 1985;Springer and Gelhar, 1991;McElwee and Zenner, 1998;Zurbuchen et al., 2002]. These models differ in their representations of slug-induced flow in the well and adjacent portions of the aquifer. ...
... Most slug tests, however, are carried out in wells that are screened across a limited portion of the aquifer (partially penetrating wells). Although approximate models are used for the analysis of slug tests performed in this configuration [e.g., Springer and Gelhar, 1991], the viability of these approximate representations has not been assessed. ...
... Previously, in the absence of a rigorous solution, approximate methods were developed for the analysis of slug tests performed in partially penetrating wells. For example, Springer and Gelhar [1991] extended the method of Bouwer and Rice [1976] to highly permeable unconfined aquifers, while analogous approaches have been used to extend the Hvorslev [1951] method to high-K confined aquifers [Butler, 1998]. All of these approximate approaches, however, are based on the assumption that the contribution Table 1; a = 2.84 Â 10 4 , F l % 0.00; fully penetrating well plots use same screen length as partially penetrating plots to facilitate comparisons between the two). of specific storage can be ignored (quasi steady state assumption). ...
A semianalytical solution is presented for a mathematical model describing the flow of groundwater in response to a slug or pumping test in a highly permeable, confined aquifer. This solution, which is appropriate for wells of any degree of penetration and incorporates inertial mechanisms at both the test and observation wells, can be used to gain new insights into hydraulic tests in highly permeable settings. The oscillatory character of slug- and pumping-induced responses will vary considerably across a site, even in an essentially homogeneous formation, when wells of different radii, depths, and screen lengths are used. Thus variations in the oscillatory character of responses do not necessarily indicate variations in hydraulic conductivity (K). Existing models for slug tests in partially penetrating wells in high-K aquifers neglect the storage properties of the media. That assumption, however, appears reasonable for a wide range of common conditions. Unlike in less permeable formations, drawdown at an observation well in a high-K aquifer will be affected by head losses in the pumping well. Those losses, which affect the form of the pumping-induced oscillations, can be difficult to characterize. Thus analyses of observation-well drawdown should utilize data from the period after the oscillations have dissipated whenever possible. Although inertial mechanisms can have a large impact on early-time drawdown, that impact decreases rapidly with duration of pumping and distance to the observation well. Conventional methods that do not consider inertial mechanisms should therefore be viable options for the analysis of drawdown data at moderate to large times.
... In the past 70 years, researchers have proposed more than 50 types of mathematical models to calculate hydraulic conductivity, which basically include all kinds of situations from pressure bearing to nonpressure, complete well to incomplete well. Among them, the relatively mature models mainly include the Hvorslev model (Hvorslev 1951), the Bouwer-Rice model (Bouwer and Rice 1976), and the Springer-Gelhar model (Springer and Gelhar 1991), which realize the mathematical treatment of overdamping and underdamping attenuation. The hydraulic conductivity estimation formula is shown in Table 5. ...
... In the sounding method, the measuring electrode spacing is fixed, the power supply electrode spacing changes from small to large, and the distribution of underground electrical resistivity along the depth direction is observed. As an array measurement method, high-density electrical method integrates profile method and sounding method and develops resistivity measure- Table 5 Formulae for estimating hydraulic conductivity by slug test (Bouwer and Rice 1976;Hvorslev 1951;Springer and Gelhar 1991) r c -the casing radius (m), r we -the effective radius of the filter tube (m), K r -the horizontal hydraulic conductivity of the aquifer within the influence radius (m/d), L-the length of the filter tube in the saturated aquifer under static conditions (m), T L -the basic time interval (d), R-the influence radius (m), h 0 -the maximum water level drawdown (m), h t -the dynamic water level that changes with time during the water level recovery process (m), C D -a dimensionless damping parameter, g-the gravitational acceleration (m/ s 2 ), l e -the effective length of the water column in the well (m) ...
Earth/rock-fill dams and embankments are the main water retaining structures in hydraulic projects, and they can effectively resist floods and are of great significance for protecting people's lives and property. Leakage is a common problem in these structures. Investigation activities, including geotechnical, geoelectric, and tracing methods, are required to locate the leakage path and provide a basis for risk mitigation and reinforcement. These three methods provide information on different leakage characteristics, uncertainties, and spatiotemporal distributions. This work first introduces the micro-mechanism of internal erosion and then, provides a site case base for leakage investigation of earth/rock-fill dams and embankments from all over the world. For each investigation method, the basic principle, investigation process, data interpretation, and future potential are summarized. It should be emphasized that geotechnical, geoelectric, and tracing methods are placed on an equal level to assist dam managers and researchers in selecting the most appropriate method to assess dam leakage against specific geological backgrounds and structural types. Finally, the advantages, disadvantages, and applicable conditions of each investigation method are compared. The role of surface investigation methods and internal investigation methods in different stages of leakage is explained. The application of combined methods is discussed at four levels, and a new combined method is proposed.
... Prickly Pear Creek, bounding the eastern portion of the smelter site and supplying water to Upper Lake at the southern site boundary, is the largest of the four principal streams flowing into the valley. During a hydrologic study performed by the U.S. Geological Survey in 1990/1991(Briar and Madison, 1992, streamflow in Prickly Pear Creek was highest during the months of May and June and lowest during the months of December and January. The principal sources of recharge to the Helena Valley aquifer system as inferred by the 1990/1991 study are infiltration from streams, infiltration from irrigation-related sources, and inflow from fractures in surrounding bedrock. ...
... This type of test provides the instantaneous change in hydraulic head needed for the performance of meaningful slug tests in media with high hydraulic conductivity. The response data were analyzed using the methods of Bouwer and Rice (1976), Springer and Gelhar (1991), and Butler and Garnett (2000). Measurements were made during constant-rate ground water extraction to define the distribution of ground water flow to the well. ...
Contamination of ground-water resources by arsenic is a widespread environmental problem; consequently, there is an escalating need for developments and improvements of remedial technologies to effectively manage arsenic contamination in ground water and soils. In June 2005, a 9.1 m long, 14 m deep, and 1.8 to 2.4 m wide (in the direction of ground-water flow) pilot-scale permeable reactive barrier (PRB) was installed at a former metal smelting facility. The reactive barrier was designed to treat ground water contaminated with moderately high concentrations of both arsenite and arsenate. The reactive barrier was installed over a 3-day period using bio-polymer slurry methods and modified excavating equipment for deep trenching. The reactive medium was composed entirely of granular iron. A monitoring network of approximately 40 ground-water sampling points was installed in July 2005. Monitoring results indicate arsenic concentrations >25 mg L-1 in wells located hydraulically upgradient of the PRB. Within the PRB, arsenic concentrations are reduced to 2 to <0.01 mg L-1. After 2 years of operation, monitoring points located within 1 m of the downgradient edge of the PRB showed significant decreases in arsenic concentrations at depths intervals impacted by the emplaced zerovalent iron. Arsenic removal in the PRB results from several pathways involving adsorption to iron oxide and iron sulfide surfaces. These different uptake processes lead to multiple oxidation states and bonding environments for arsenic in the reactive medium as indicated using spectroscopic methods. This report covers aspects of site characterization, remedial design and implementation, and monitoring results for this pilot-scale PRB, including a flux-based analysis for arsenic.
... A Campbell Scientific CR3000 Micrologger recorded the signals at 50 Hz with a packer interval of 20 cm. Springer and Gelhar's [1991] analytical solution was used to analyze the recorded signals, because this solution takes into account oscillatory water levels, which are commonly observed in highly conductive aquifers. ...
... On the other hand, chamber 2 (Figure 8d) was obtained, indicating a relatively high conductivity (3 3 10 23 m/s) as derived from the oscillatory behavior. [Springer and Gelhar, 1991]. Likewise, at approximately the same elevation as chamber 2 of well MC4, another slug signal was recorded corresponding to a lower value of K (5 3 10 24 m/s) (Figure 8e). ...
Pilot points are typical means for calibration of highly parameterized numerical models. We propose a novel procedure based on estimating not only the pilot point values, but also their number and suitable locations. This is accomplished by a trans-dimensional Bayesian inversion procedure that also allows for uncertainty quantification. The utilized algorithm, reversible-jump Markov-Chain Monte Carlo (RJ-MCMC), is computationally demanding and this challenges the application for model calibration. We present a solution for fast, approximate simulation through the application of a Bayesian inversion. A fast pathfinding algorithm is used to estimate tracer travel times instead of doing a full transport simulation. This approach extracts the information from measured breakthrough curves, which is crucial for the reconstruction of aquifer heterogeneity. As a result, the “smart pilot points” can be tuned during thousands of rapid model evaluations. This is demonstrated for both a synthetic and a field application. For the selected synthetic layered aquifer, two different hydrofacies are reconstructed. For the field investigation, multiple fluorescent tracers were injected in different well screens in a shallow alluvial aquifer and monitored in a tomographic source-receiver configuration. With the new inversion procedure, a sand layer was identified and reconstructed with a high spatial resolution in 3-D. The sand layer was successfully validated through additional slug tests at the site. The promising results encourage further applications in hydrogeological model calibration, especially for cases with simulation of transport. This article is protected by copyright. All rights reserved.
... The well development, involving the extraction of at least 36 l of water using a manually operated peristaltic pump, was repeated for several series of slug tests in each well in order to assess the quality of the well conditions and spot faulty test conditions or possible measurement errors. We analyzed the slug tests using AQTESOLV fitting the analytical solutions of Bouwer and Rice (1976) for overdamped conditions and Springer and Gelhar (1991) for underdamped conditions to the data. ...
... The slug tests showed overdamped responses for nine wells with an exponential head recovery to static water levels within 30 s. Seven wells showed critically damped behavior and a recovery to static levels within 2 s, and three wells showed an underdamped response with strong inertia effects and a recovery within 3-8 s. The analysis of the slug test measurements using the solutions of Springer and Gelhar (1991) and Bouwer and Rice (1976) gave values of hydraulic conductivity between 1.9 9 10 -4 and 7.4 9 10 -3 m/s with an average value of 2.4 9 10 -3 m/s and a standard deviation of 2 9 10 -3 m/s. ...
Stratigraphic heterogeneity is a key controlling factor for flow and transport in groundwater systems. In this case study, we have combined two- and three-dimensional images of electric resistivity with hydrogeological data to delineate such stratigraphic heterogeneity at a loop of River Steinlach close to Tübingen, Germany, where we estimated spatially varying aquifer parameters using established evaluation techniques. We developed a three-layer stratigraphic model consisting of heterogeneous sandy gravel overlain by a fine alluvium including top soil, and underlain by sandstone weathered at its top. The sandy gravel makes up the aquifer unit while we interpret the sandstone as aquitard. We classified the area into two stratigraphic segments based on resistivity data. The Southern segment consists of a thicker alluvium where the aquifer material contains more clay than in the Northern segment. Two different stratigraphic structures were also delineated at the Southern and Northern segments, respectively. These structures are visible in inversion results as low-resistivity features trending in the SE–NW in the Southern segment and NE–NW in the Northern segment. Both structures may be previous flow paths of River Steinlach, and the low permeability material overlying them may impair flow exchange in the area. We performed slug and pumping tests to estimate the hydraulic conductivity (K) of the aquifer. The K distributions show slight variation with higher values obtained at wells within the Northern segment and close to the river bank. A qualitative comparison of measured hydraulic conductivities with the resistivity distribution shows good agreement of the spatial patterns. The stratigraphic and hydraulic heterogeneities delineated in this work are important for experimental and modeling studies of flow, transport, and hyporheic exchange at the site.
... This commonly occurs in wells with extremely long well fluid columns (i.e., large water mass within the well column) and/or within wells that penetrate highly permeable aquifers. As noted in Butler (1998), unconfined aquifer tests exhibiting under-damped behavior should be analyzed using the model presented in Springer and Gelhar (1991), which has been modified by Butler and Garnett (2000) to include partially penetrating well conditions. Tests exhibiting under-damped behavior should be conducted using very small stress level applications. ...
... Standard analytical methods include type-curve and Bouwer and Rice methods described in Spane et al. 2002. high permeability characteristics include, methods described in Springer and Gelhar (1991), Butler (1998), McElwee and Zenner (1998), Butler and Garnett (2000), Zurbuchen et al. (2002), and Butler et al. (2003). Because of the ease provided by a spreadsheet-based approach, the test analysis method presented in Butler and Garnett (2000) was used for the analysis of all IDF site tests, which exhibited high permeability response characteristics. ...
This data package is a compilation of existing geologic data from the Integrated Disposal Facility Site for use in the 2005 Performance Assessment. The data were compiled from both surface and subsurface geologic sources. The surface mapping has been published previously. The quality and uncertainty of the data are discussed. The 2004 report was modified to include results of studies of the shearwave velocity of sediments at and near the IDF site, which were performed for the Waste Treatment Plant and groundwater monitoring wells 299-E17-26 and 299-E24-24. The conclusions of the original report have not changed with the new data.
... For standard Hanford Site RCRA wells exhibiting under-damped test conditions, the maximum stress level utilized for such test sites should not generally exceed ~1/10 of the saturated well-screen length. Methods for analyzing unconfined aquifer tests exhibiting high permeability under-, over-or critically damped characteristics include techniques described in Springer and Gelhar (1991), Butler (1997), McElwee and Zenner (1998), Butler and Garnett (2000), Zurbuchen et al. (2002), and Butler et al. (2003). Because of the ease provided by a spreadsheet-based approach, the analysis method presented in Butler and Garnett (2000) was used for the analysis of all tests exhibiting under-damped response behavior (i.e., high permeability/oscillatory pattern). ...
... or type-curve (Section 3.1.1.2) methods. As noted previously, methods that can be employed for analyzing unconfined aquifer tests exhibiting high permeability characteristics include methods described in Springer and Gelhar (1991), Butler (1997), McElwee andZenner (1998), McElwee (2001), Butler and Garnett (2000), and Zurbuchen et al. (2002). Because of the ease provided by a spreadsheet-based approach, the test analysis method presented in Butler and Garnett (2000) was used for tests exhibiting high permeability response characteristics, i.e., under-or criticallydamped. ...
This report presents results obtained from detailed hydrologic characterization of the unconfined aquifer system conducted at the Hanford Site.
... The slug tests eventually induce rigid motion controlled by the aquifer permeability, and a long-established literature [Hvorslev, 1951;Bouwer and Rice, 1976] estimates the property for damped slug tests in moderately permeable soil. Underdamped slug tests exhibit a periodic, aquifer controlled response at $0.1 Hz frequency for deeper wells in more permeable formations, and the theory of van der Kamp [1976] and Springer and Gelhar [1991] describes the rigid motion. Proesser [1981] and Zemansky and McElwee [2005] qualitatively document the higher-frequency disturbances that obscure the transient response of the aquifer immediately after the opening of the valve. ...
... The resulting vertical pressure gradient exceeds the weight of the water column by the amount p O /L, and this excess accelerates the rigid water column as an underdamped slug test. The rigid theory is well established [Springer and Gelhar, 1991], and takes equation (19) as an initial condition. Ostendorf et al. [2005] derive an expression for the underdamped pressure P in the rigid water column ...
We model and measure the dissipation of water hammer induced by well casing and water elasticity with rapid valve opening at the start of a pneumatic slug test. The higher-frequency water hammer can obscure slower, aquifer-controlled, underdamped oscillations of the rigid water column, so a quantitative description of the elastic motion improves the ability of a slug test to calibrate the aquifer permeability k. Internal friction attenuates the water hammer, subject to a known headspace pressure at the air/water interface and equilibrium pressure at the top of the well screen. An analytical elastic solution is presented and matched to an existing rigid motion analysis, with matching predicated on k exceeding 7 × 10−14 m2 and appreciable water hammer dissipation during the first cycle of the slug test. The model is accurately calibrated with data from underdamped slug tests in a PVC monitoring well in the Plymouth-Carver Aquifer. The calibrated casing elasticity value suggests that effective lateral soil stress appreciably stiffened the casing.
... This is typically achieved by either dropping a slug mass into a well (Cooper et al., 1967) or pneumatically pressurizing the water column in a well (Butler Jr., 1998;Malama et al., 2011), a configuration referred to as a single well test. Several mathematical models are available in the hydrogeology literature for analyzing confined (Cooper et al., 1967;Bredehoeft and Papadopulos, 1980;Zurbuchen et al., 2002;Butler Jr. and Zhan, 2004) and unconfined (Bouwer and Rice, 1976;Springer and Gelhar, 1991;Hyder et al., 1994;Spane, 1996;Zlotnik and McGuire, 1998;Malama et al., 2011) aquifer slug test data under the Darcian flow regime. Consideration of slug tests under non-Darcian flow regimes may be found in Quinn et al. (2013) and Wang et al. (2015). ...
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 linearised 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.
... This method was needed for meaningful slug tests in the high-hydraulic conductivity media at these sites. The response data were analyzed using the methods of Bouwer and Rice (1976) and Springer and Gelhar (1991). ...
The use of green infrastructure in many areas could potentially mitigate local problems such as flooding, water shortages, etc. Three diverse locations were selected to study the effects of green infrastructure on groundwater quality based on climate, geology, type of infrastructure used, and geographic location. Results of these case studies are reported.
... All overdamped responses observed in the field occurred in the deeper mini-piezometer and recovered in 2-8 min. The overdamped responses were analyzed using the Bouwer and Rice (1976) method and the underdamped responses were analyzed with different models (e.g., Butler & Healey, 1998;Hyder et al., 1994;Springer & Gelhar, 1991) using to incorporate frictional losses into the solutions assuming steady flow. ...
Engineered multilevel systems (MLS) are one of the few viable options for collecting spatial and temporal datasets in 3-D complex groundwater flow systems. However, these monitoring systems present challenges for hydraulic testing due to small port tubing diameters. In this study, equipment was developed to enable pneumatic slug testing of a G360 MLS, fitted with 1/2-inch ID open tubes that extend from the monitoring ports to the surface. Of the eight ports tested, four exhibited overdamped slug test responses, while underdamped responses were observed in the remaining four ports. It is expected that friction in the small diameter tubing is not negligible, and additional flow constrictions are introduced when installing a transducer in the tubing, effectively changing the open tube geometry to an annulus around the transducer body and around the transducer cable. Steady flow models for annular flow, widely available in the literature, were used to assess tube friction for the overdamped tests. However, for underdamped tests that oscillate quickly, a mathematical solution for unsteady oscillatory flow through an annulus was derived. The results of this study show that it is important to account for frictional and inertial losses to obtain good transmissivity (T) estimates from slug tests conducted in small diameter tubing. Assuming steady flow through small annuli will not introduce appreciable error when calculating the water level; however, if steady flow through the open tube below the transducer is assumed when calculating the formation head, T values can be underestimated by as much as 80%.
... All overdamped responses observed in the field occurred in the deeper mini-piezometer and recovered in 2-8 min. The overdamped responses were analyzed using the Bouwer and Rice (1976) method and the underdamped responses were analyzed with different models (e.g., Butler & Healey, 1998;Hyder et al., 1994;Springer & Gelhar, 1991) using to incorporate frictional losses into the solutions assuming steady flow. ...
... The method consists of raising the water table by using a vacuum pump and monitoring the decrease in water table over time with a 1 s time interval. The groundwater table falling curve was analyzed in AQTESOLV using Bouwer and Rice's method for partially penetrating wells in unconfined aquifers (Bouwer & Rice, 1976), Hvorslev (1951) for partially penetrating wells in confined aquifer, and Springer and Gelhar (1991) when oscillatory responses were observed in the slug test. Two slug tests were performed at each screen and the value of permeability used for comparison was calculated by averaging the result of the two tests. ...
... The early publications reporting on underdamped slug test analyses used transient flow equations containing both storativity (S) and T, on data collected from open holes in fractured rock, with assumed S values assigned (e.g., Kabala et al., 1985;Kipp, 1985;Ross, 1985;van der Kamp, 1976). The first use of zero storage models for underdamped slug test analysis was presented by Springer and Gelhar (1991) using data collected from an unconfined sand and gravel aquifer at the U.S. Geological Survey field site in Cape Cod, Massachusetts. Their model incorporated a momentum balance into the Bouwer and Rice (1976) model. ...
Slug tests generating oscillating (underdamped) responses are common in high-transmissivity (T) zones, and the nature of the response depends on the plumbing of the test equipment and the formation properties. The standard approach for obtaining T is to measure pressure shallow in the riser pipe to obtain an accurate estimate of flow and then predict the formation response from this shallow measurement by accounting for friction and acceleration assuming steady flow conditions (parabolic radial velocity profile). In this study a mathematical solution is developed for unsteady oscillatory laminar flow that shows non-parabolic radial velocity profiles resulting in larger frictional losses, which are out of phase with the average flow velocity, indicating that errors are introduced when using the standard approach for underdamped slug test analysis. The unsteady flow model produces correction factors that can be used to improve the standard approach for predicting the formation pressure; however, not all errors are eliminated. Consequently, a new procedure is presented and applied to underdamped slug tests observed in fractured rock that avoids errors associated with quantifying inertial and frictional effects along the test equipment. This is achieved through the use of two transducers, where one is placed shallow in the water column to infer flow, and one is placed inside the test interval to represent the formation pressure. Comparison of T estimated by the new procedure to T derived from constant head step tests show better agreement than T obtained when predicting the formation pressure from a shallow pressure measurement.
... Le fluide s'écoule dans le milieu, et la pression diminue dans le temps en fonction de la conductivité hydraulique de la fracture. Traditionnellement, les résultats des "Pulses-tests" sont interprétés en considérant un comportement hydraulique linéaire [Hvorslev, 1951], [Cooper et al., 1967], [Bouwer and Rice, 1976], [Krauss, 1974[Krauss, , 1977, [Van der Kamp, 1976], [Wang, 1977], [Barker, 1983[Barker, , 1988, [Kipp, 1985], [Springer and Gelhar, 1991]. Cependant, ces modèles restent souvent imprécis (± 30%), et ne rendent pas compte des effets non-linéaires largement observés dans le cas des formations à forte conductivité hydraulique. ...
Le présent document a pour vocation de dresser une synthèse des travaux relatifs au programme de recherche financé sur le BCRD, intitulé « Analyse du comportement hydromécanique des massifs rocheux fracturés à partir d’essais in situ et de modélisation».
Après analyse du contexte et de l’état de l’art, nous avons choisi de porter nos efforts essentiellement sur l’amélioration de la caractérisation hydromécanique du milieu rocheux fracturé à partir d’expérimentations in situ, en s’attachant à quantifier les écarts avec le résultat d’une caractérisation de laboratoire sur échantillons. Cette amélioration a été rendue possible par le développement de nouveaux outils de caractérisation et de méthodes d’interprétation basées sur la modélisation numérique.
Nous avons tout d’abord bénéficié de la mise au point, en collaboration avec le laboratoire Géoscience-Azur de l’université de Nice et la société TELEMAC, d’une sonde amovible d’auscultation du comportement hydromécanique in situ des fractures réalisant des mesures simultanées de pression-déplacement. Les mesures sont basées sur la technologie des capteurs à fibre optique qui présentent un grand nombre d’avantages par rapport aux mesures classiques (mesures plus précises et plus stables, capteurs plus petits, grande rapidité de réponse, mesures non affectées par le champ magnétique). Le dispositif a été validé en laboratoire et in situ.
Le site de Coaraze s’est révélé particulièrement adapté à l’étude du comportement hydromécanique des milieux fracturés pour des raisons liées à sa géologie et sa géométrie d’abord, mais aussi parce qu’il a fait l’objet, depuis 1997, de nombreux travaux de thèse qui nous ont été très utiles. Dans le cadre de ce programme, l’instrumentation déjà existante sur le site a été complétée par des mesures faites en forage à l’aide de la sonde amovible. Deux types d'expérimentations ont été effectués dont les objectifs sont respectivement d’étudier le comportement hydromécanique global du massif fracturé sous l’effet des variations de pressions « naturelles » du massif (mesures passives) et de caractériser les fractures individuellement en les sollicitant par injection ou par pompage (mesures actives).
Les mesures réalisées in situ ont du être filtrées afin d’éliminer les fréquences correspondant au bruit instrumental de chaque capteur et du système d’acquisition. Un logiciel a été développé par Géosciences Azur, avec la participation du doctorant de l’INERIS, permettant de lire les différents signaux mesurés et d’appliquer différents types de filtrage selon la forme et la fréquence du signal échantillonné.
Parallèlement, nous avons développé et utilisé la modélisation numérique pour tenter de reproduire et d’analyser, plus en profondeur, les résultats des expérimentations et des essais de laboratoire. Nous avons utilisé le logiciel RESOBLOK pour représenter la géométrie du massif rocheux fracturé et les logiciels UDEC et 3DEC pour simuler la réponse du milieu à une sollicitation hydromécanique.
Un modèle géométrique déterministe du site de Coaraze a été construit à partir des relevés de fracturation. Signalons à ce propos qu’une nouvelle technique de mesure de la fracturation, basée sur l’utilisation d’un tachéomètre haute précision, a été mise au point et évaluée. Un traitement de ces mesures a permis de déterminer l’orientation et la position des différentes fractures. Les données de fracturation ont permis de construire un modèle à grande échelle du site de Coaraze dont la taille correspond à celle de la zone investiguée qui s’inscrit dans un cube d’environ 40 m de côté. Un modèle plus petit et plus précis (cube de 6 à 8 m de côté) a également été mis au point autour de la zone d’injection pour la simulation des essais d’injection et de pompage.
Les simulations hydromécaniques ont consisté à reproduire de la façon la plus fidèle possible les expérimentations in situ. Elles ont conduit à une remise en cause partielle des modèles classiques (relation deTerzaghi, loi cubique) in situ. On a notamment :
• mis en évidence in situ, la nécessité de reformuler la relation de Terzaghi comme suit : s’n = sn - P [1-Sc], où Sc est la surface de contact (normalisée) de la fracture qui est une fonction de la rugosité de la fracture et de la contrainte normale effective ;
• remis en cause in situ la loi d’écoulement de Poiseuille sur la base des décalages temporels constatés entre les évolutions mesurées et calculées. Nous avons montré qu’une modification de cette loi, en introduisant un coefficient prenant en compte la rugosité de la fracture, et donc la tortuosité des écoulements, permettait d’obtenir une légère amélioration des simulations. Une amélioration de la prise en compte de la sollicitation dans le modèle (ou on n’imposerait plus la chronique des pressions mesurées au point d’injection, mais la chronique du débit injecté) pourrait permettre d’améliorer cette analyse et de consolider ces conclusions.
Une caractérisation hydromécanique en laboratoire au L3S de Grenoble a également été réalisée à partir d’échantillons de fractures de taille décimétrique prélevés sur le site de Coaraze. L’objectif de ces essais est à la fois de déterminer les caractéristiques hydromécaniques des fractures à l’échelle du laboratoire et d’évaluer l’effet des paramètres morphologiques dans les lois d’écoulement, dans le comportement mécanique ou dans les relations de couplage hydromécanique. Cet objectif a été incomplètement atteint à échéance du programme, le travail sur les aspects morphologiques étant toujours en cours dans le cadre d’une collaboration avec le LAEGO. L’analyse des essais sur les joints de stratification doit également être réalisée.
Un certain nombre de résultats a pu toutefois être mis en évidence. Ainsi, une relation quasi linéaire entre la raideur normale de la fracture instrumentée R4 (échantillon F1) et la contrainte normale a été établie (pour 0 < sn < 100 MPa). Elle s’explique classiquement par l’augmentation de la surface de contact de la fracture. L’interprétation des essais hydromécaniques par modèle analytique conduit à une valeur d’ouverture hydraulique comprise entre 0,03 mm (pour une contrainte normale de 65 MPa) et 0,06 mm (pour une contrainte normale nulle).
La comparaison des débits mesurés et calculés (par modélisation numérique de l’essai) a montré qu’il était nécessaire de modifier également la relation entre ouverture hydraulique et ouverture mécanique en introduisant un terme f pour traduire la diminution du couplage entre ces deux ouvertures lorsque la contrainte normale augmente (a = a0 + f.un , avec 0 < f < 1), et vraisemblablement l’existence d’une ouverture résiduelle sous forte contrainte normale. La diminution de f avec la contrainte normale est à relier à l’augmentation progressive de la surface de contact. Ces résultats viennent confirmer des hypothèses ou des observations déjà faites par de nombreux auteurs.
Les modélisations des essais de laboratoire et des expérimentations in situ permettent également de préciser la valeur des ouvertures hydrauliques et des raideurs normales des fractures et de mettre en évidence un effet d’échelle. Sous une contrainte effective d’environ 0,1 MPa (représentative des conditions in situ), on observe en effet un rapport de 1 à 10 entre pour les valeurs d’ouverture hydraulique, et de 5 à 1 (environ) pour la raideur normale entre les résultats de laboratoire et les résultats in situ. Cette effet d’échelle est assez difficile à établir précisément, car on a pu observer in situ de fortes hétérogéneités au sein d’une même fracture.
Parallèlement aux travaux réalisés sur le site de Coaraze, et dans un souci d’adapter le modèle prédictif à l’objectif qu’on lui assigne et au contexte dans lequel il devra opérer, nous avons exploré une autre approche pour décrire le comportement hydromécanique d’un réseau de fractures. En effet, pour certaines problématiques, l’échelle de la modélisation est nécessairement plus importante et ne permet plus de prendre en compte l’ensemble de la fracturation de façon explicite. On privilégie, dans ce cas, l’approche continue, qui suppose qu’à une certaine échelle et dans certaines conditions, le milieu fracturé peut être décrit par un milieu continu équivalent.
Pour clore cette conclusion, soulignons à nouveau les acquis de ce programme. Ils sont de trois ordres : technologique, scientifique et méthodologique. D’un point de vue technologique, l’apport principal a été la mise au point d’une sonde amovible permettant de faire des mesures par fibres optiques très précises des variations de pression et de déplacement dans une fracture. Du point de vue scientifique, notre contribution concerne l’évaluation in situ des lois d’écoulement et de couplage hydromécanique des fractures et la quantification d’un effet d’échelle entre les résultats de laboratoire et les résultats in situ. D’un point de vue méthodologique enfin, nous avons amélioré les méthodes de reconnaissance de la géométrie des réseaux de fractures par tachéométrie et la caractérisation des propriétés hydromécaniques des fractures in situ par une simulation numérique précise des expérimentations.
De nombreux compléments sont bien sûr à prévoir pour consolider les résultats présentés ici. Les résultats des essais de laboratoire n’ont pas encore été totalement analysés. Nous souhaitons en particulier établir une relation entre la variation de l’espace des vides de la fracture et les sollicitations hydromécaniques imposées en s’inspirant des nombreux travaux existant sur le sujet (citons notamment [Gentier, 2003]). Ceci devrait permettre de préciser le sens physique des paramètres que l’on a introduit dans les lois d’écoulement et de couplage pour améliorer la qualité des simulations. L’idéal serait ensuite de pouvoir déterminer une relation directe (macroscopique) entre ces paramètres, la rugosité des fractures et la sollicitation hydromécanique (sn, P).
Nous avons pas étudié dans ce programme le comportement des fractures en cisaillement. Les sollicitations directes sur les fractures instrumentées étaient normales, même si elles pouvait induire indirectement des sollicitions tangentielles sur d’autre fractures avoisinantes (nous avons vu, par modélisation, le cisaillement des joints de stratification dans le cas des pulses-test). La sonde amovible pourrait être améliorée pour mesurer les déplacements relatifs des épontes dans toutes les directions de l’espace (c’est envisagé) ce qui permettra d’étudier plus finement ce phénomène en instrumentant ensuite simultanément fracture et joint de stratification. L’interprétation de ces nouvelles mesures permettrait d’évaluer la raideur tangentielle in situ des discontinuités et son évolution éventuelle au cours de l’expérimentation.
Le comportement des fractures en condition non saturée pourrait également être étudié sur le site de Coaraze puisqu’il est possible de faire varier la hauteur du niveau piezométrique par ouverture et fermeture d’une vanne. Toutefois, ce travail nécessiterait un complément d’instrumentation et l’amélioration préalable des outils de modélisation.
Une suite est prévue dans le cadre le programme BCRD-DRS01-03 sur le comportement hydromécanique des milieux poreux et fracturés (à double porosité) qui a démarré début 2005. Afin de bénéficier pleinement des acquis, nous avons souhaité notamment réaliser les premières expérimentations de ce nouveau programme sur ce même site. Nous prévoyons, dans ce cadre, de réaliser des expérimentations de durée suffisamment longue pour que les termes d’échanges matrice/fracture soient mesurables. Dans un second temps, nous envisageons de travailler sur un site localisé dans le grès vosgien où le contraste de perméabilité entre matrice et les fractures (plus faible) devrait permettre de mettre plus facilement en évidence les effets matriciels.
La présentation exhaustive de ce travail de recherche n’était pas possible dans le cadre de cette synthèse. Des compléments pourront être trouvés dans de nombreuses publications relatives aux différents travaux réalisés (3 publications dans des revues scientifiques internationales, 4 dans des colloques) et également dans le mémoire de doctorat de Frédéric Cappa qui sera soutenu très prochainement.
[The purpose of this document is to provide a summary of the work relating to the research program funded by the BCRD, entitled "Analysis of the hydromechanical behavior of fractured rock masses based on in situ tests and modeling".
After analyzing the context and the state of the art, we have chosen to focus our efforts mainly on improving the hydromechanical characterization of the fractured rock environment based on in situ experiments, by focusing on quantifying the differences with the result of a laboratory characterization on samples. This improvement was made possible by the development of new characterization tools and interpretation methods based on numerical modeling.
We first benefited from the development, in collaboration with the Géoscience-Azur laboratory of the University of Nice and the TELEMAC company, of a removable probe for auscultating the in situ hydromechanical behavior of fractures, performing simultaneous pressure-displacement measurements. The measurements are based on fiber optic sensor technology, which offers many advantages over conventional measurements (more accurate and stable measurements, smaller sensors, high response speed, measurements not affected by the magnetic field). The device has been validated in the laboratory and in situ. The Coaraze site has proven to be particularly suitable for studying the hydromechanical behavior of fractured media, firstly for reasons related to its geology and geometry, but also because it has been the subject of numerous thesis studies since 1997, which have been very useful to us. As part of this program, the instrumentation already existing on the site was supplemented by measurements made in drilling using the removable probe. Two types of experiments were carried out, the objectives of which were respectively to study the overall hydromechanical behavior of the fractured massif under the effect of the "natural" pressure variations of the massif (passive measurements) and to characterize the fractures individually by stressing them by injection or pumping (active measurements).
The measurements carried out in situ had to be filtered in order to eliminate the frequencies corresponding to the instrumental noise of each sensor and the acquisition system. A software was developed by Géosciences Azur, with the participation of the INERIS doctoral student, to read the different measured signals and apply different types of filtering according to the shape and frequency of the sampled signal.
At the same time, we developed and used numerical modeling to try to reproduce and analyze, in more depth, the results of the experiments and laboratory tests. We used the RESOBLOK software to represent the geometry of the fractured rock massif and the UDEC and 3DEC software to simulate the response of the environment to a hydromechanical stress.
A deterministic geometric model of the Coaraze site was constructed from the fracturing measurements. It should be noted in this regard that a new technique for measuring fracturing, based on the use of a high-precision tacheometer, was developed and evaluated. Processing of these measurements made it possible to determine the orientation and position of the various fractures. The fracturing data made it possible to construct a large-scale model of the Coaraze site, the size of which corresponds to that of the investigated area, which fits into a cube with sides of approximately 40 m. A smaller and more precise model (cube with sides of 6 to 8 m) was also developed around the injection zone for the simulation of injection and pumping tests. The hydromechanical simulations consisted of reproducing the in situ experiments as faithfully as possible. They led to a partial questioning of the classic models (Terzaghi relation, cubic law) in situ. In particular, we have:
• highlighted in situ the need to reformulate the Terzaghi relationship as follows: ’n = n - P [1-Sc], where Sc is the (normalized) contact surface of the fracture which is a function of the fracture roughness and the effective normal stress;
• called into question in situ the Poiseuille flow law on the basis of the time lags observed between the measured and calculated evolutions. We have shown that a modification of this law, by introducing a coefficient taking into account the roughness of the fracture, and therefore the tortuosity of the flows, made it possible to obtain a slight improvement in the simulations. An improvement in the consideration of the stress in the model (or we would no longer impose the chronicle of the pressures measured at the injection point, but the chronicle of the injected flow) could make it possible to improve this analysis and consolidate these conclusions.
A laboratory hydromechanical characterization at the L3S in Grenoble was also carried out using decimetric fracture samples taken from the Coaraze site. The objective of these tests is both to determine the hydromechanical characteristics of the fractures on a laboratory scale and to evaluate the effect of morphological parameters in the flow laws, in the mechanical behavior or in the hydromechanical coupling relationships. This objective was incompletely achieved at the end of the program, as work on the morphological aspects was still in progress as part of a collaboration with LAEGO. Analysis of the tests on the stratification joints must also be carried out. However, a certain number of results could be highlighted. Thus, a quasi-linear relationship between the normal stiffness of the instrumented fracture R4 (sample F1) and the normal stress was established (for 0 < sn < 100 MPa). It is classically explained by the increase in the contact surface of the fracture. The interpretation of the hydromechanical tests by analytical model leads to a hydraulic opening value between 0.03 mm (for a normal stress of 65 MPa) and 0.06 mm (for a zero normal stress).
The comparison of the measured and calculated flow rates (by numerical modeling of the test) showed that it was necessary to also modify the relationship between hydraulic opening and mechanical opening by introducing a term f to translate the decrease in the coupling between these two openings when the normal stress increases (a = a0 + f.un , with 0 < f < 1), and probably the existence of a residual opening under high normal stress. The decrease in f with the normal stress is to be linked to the progressive increase in the contact surface. These results confirm hypotheses or observations already made by many authors.
Modeling of laboratory tests and in situ experiments also makes it possible to specify the value of hydraulic openings and normal stiffnesses of fractures and to highlight a scale effect. Under an effective stress of approximately 0.1 MPa (representative of in situ conditions), we observe a ratio of 1 to 10 between the values of hydraulic opening, and 5 to 1 (approximately) for the normal stiffness between the laboratory results and the in situ results. This scale effect is quite difficult to establish precisely, because we were able to observe strong heterogeneities in situ within the same fracture.
In parallel with the work carried out on the Coaraze site, and in order to adapt the predictive model to the objective assigned to it and the context in which it will have to operate, we explored another approach to describe the hydromechanical behavior of a fracture network. Indeed, for some issues, the modeling scale is necessarily larger and no longer allows the entire fracturing to be taken into account explicitly. In this case, we favor the continuous approach, which assumes that at a certain scale and under certain conditions, the fractured medium can be described by an equivalent continuous medium. To conclude this conclusion, let us once again emphasize the achievements of this program. They are of three types: technological, scientific and methodological. From a technological point of view, the main contribution was the development of a removable probe allowing very precise measurements by optical fibers of pressure and displacement variations in a fracture. From a scientific point of view, our contribution concerns the in situ evaluation of the flow laws and hydromechanical coupling of fractures and the quantification of a scale effect between laboratory results and in situ results. Finally, from a methodological point of view, we have improved the methods for recognizing the geometry of fracture networks by tacheometry and the characterization of the hydromechanical properties of fractures in situ by precise numerical simulation of the experiments.
Many additions are of course to be expected to consolidate the results presented here. The results of the laboratory tests have not yet been fully analyzed. In particular, we wish to establish a relationship between the variation of the fracture void space and the imposed hydromechanical stresses by drawing inspiration from the many existing works on the subject (notably [Gentier, 2003]). This should make it possible to specify the physical meaning of the parameters that have been introduced into the flow and coupling laws to improve the quality of the simulations. The ideal would then be to be able to determine a direct (macroscopic) relationship between these parameters, the roughness of the fractures and the hydromechanical stress (sn, P).
We did not study the behavior of fractures in shear in this program. The direct stresses on the instrumented fractures were normal, even if they could indirectly induce tangential stresses on other neighboring fractures (we saw, by modeling, the shearing of the stratification joints in the case of the pulse tests). The removable probe could be improved to measure the relative displacements of the walls in all directions of space (this is envisaged) which will allow to study this phenomenon more finely by then simultaneously instrumenting fracture and stratification joint. The interpretation of these new measurements would allow to evaluate the in situ tangential stiffness of the discontinuities and its possible evolution during the experiment. The behavior of fractures in unsaturated conditions could also be studied on the Coaraze site since it is possible to vary the height of the piezometric level by opening and closing a valve. However, this work would require additional instrumentation and the prior improvement of modeling tools.
A follow-up is planned within the framework of the BCRD-DRS01-03 program on the hydromechanical behavior of porous and fractured media (with dual porosity) which began in early 2005. In order to fully benefit from the acquired knowledge, we wanted in particular to carry out the first experiments of this new program on this same site. In this framework, we plan to carry out experiments of a sufficiently long duration so that the matrix/fracture exchange terms are measurable. In a second phase, we plan to work on a site located in the Vosges sandstone where the permeability contrast between matrix and fractures (lower) should make it easier to highlight the matrix effects.
The exhaustive presentation of this research work was not possible within the framework of this synthesis. Additional information can be found in numerous publications relating to the various works carried out (3 publications in international scientific journals, 4 in conferences) and also in the doctoral dissertation of Frédéric Cappa which will be defended very soon.]
... In order to obtain a falling head curve, vacuum was applied, raising the water level ca. 1 m, and then released to let the water level drop (Hinsby et al. 1992). The groundwater falling head curves were analysed using Bower and Rice's method (Bouwer & Rice 1976) for screens located in the confined aquifer, Hvorlev's method (Hvorslev 1951) for screens located in the unconfined aquifer, and Springer and Gelhar's method (Springer & Gelhar 1991) for slug tests showing oscillatory responses. ...
At contaminated sites, knowledge about geology and hydraulic properties of the subsurface and extent of the contamination is needed for assessing the risk and for designing potential site remediation. In this study, we have developed a new approach for characterizing contaminated sites through time-domain spectral induced polarization. The new approach is based on: (1) spectral inversion of the induced polarization data through a reparametrization of the Cole-Cole model, which disentangles the electrolytic bulk conductivity from the surface conductivity for delineating the contamination plume; (2) estimation of hydraulic permeability directly from the inverted parameters using a laboratory-derived empirical equation without any calibration; (3) the use of the geophysical imaging results for supporting the geological modelling and planning of drilling campaigns. The new approach was tested on a data set from the Grindsted stream (Denmark), where contaminated groundwater from a factory site discharges to the stream. Two overlapping areas were covered with seven parallel 2-D profiles each, one large area of 410 m ×90m(5melectrode spacing) and one detailed area of 126m×42m(2melectrode spacing). The geophysical results were complemented and validated by an extensive set of hydrologic and geologic information, including 94 estimates of hydraulic permeability obtained from slug tests and grain size analyses, 89 measurements of water electrical conductivity in groundwater, and four geological logs. On average the IP-derived and measured permeability values agreed within one order of magnitude, except for those close to boundaries between lithological layers (e.g. between sand and clay), where mismatches occurred due to the lack of vertical resolution in the geophysical imaging. An average formation factor was estimated from the correlation between the imaged bulk conductivity values and the water conductivity values measured in groundwater, in order to convert the imaging results from bulk conductivity to water conductivity. The geophysical models were actively used for supporting the geological modelling and the imaging of hydraulic permeability andwater conductivity allowed for a better discrimination of the clay/lignite lithology from the porewater conductivity. Furthermore, high water electrical conductivity values were found in a deep confined aquifer, which is separated by a low-permeability clay layer from a shallow aquifer. No contamination was expected in this part of the confined aquifer, and confirmation wells were drilled in the zone of increased water electrical conductivity derived from the geophysical results.Water samples from the new wells showed elevated concentrations of inorganic compounds responsible for the increased water electrical conductivity in the confined aquifer and high concentrations of xenobiotic organic contaminants such as chlorinated ethenes, sulfonamides and barbiturates. © The Author(s) 2018. Published by Oxford University Press on behalf of The Royal Astronomical Society.
... The method consists of raising the water table by using a vacuum pump and monitoring the decrease in water table over time with a 1 s time interval. The groundwater table falling curve was analyzed in AQTESOLV using Bouwer and Rice's method for partially penetrating wells in unconfined aquifers (Bouwer & Rice, 1976), Hvorslev (1951) for partially penetrating wells in confined aquifer, and Springer and Gelhar (1991) when oscillatory responses were observed in the slug test. Two slug tests were performed at each screen and the value of permeability used for comparison was calculated by averaging the result of the two tests. ...
In this study, we present the prediction of permeability from time domain spectral induced polarization (IP) data, measured in boreholes on undisturbed formations using the El-log logging-while-drilling technique. We collected El-log data and hydraulic properties on unconsolidated Quaternary and Miocene deposits in boreholes at three locations at a field site in Denmark, characterized by different electrical water conductivity and chemistry. The high vertical resolution of the El-log technique matches the lithological variability at the site, minimizing ambiguity in the interpretation originating from resolution issues. The permeability values were computed from IP data using a laboratory-derived empirical relationship presented in a recent study for saturated unconsolidated sediments, without any further calibration. A very good correlation, within 1 order of magnitude, was found between the IP-derived permeability estimates and those derived using grain size analyses and slug tests, with similar depth trends and permeability contrasts. Furthermore, the effect of water conductivity on the IP-derived permeability estimations was found negligible in comparison to the permeability uncertainties estimated from the inversion and the laboratory-derived empirical relationship.
... We followed best-practice recommendations (Butler et al., 2003;Zurbuchen et al., 2002) and processed our data according to Butler (1998), Butler et al. (2003), and McElwee and Zenner (1998) with the software AQTESOLV-Professional (www.aqtesolv.com). We applied the model of Bouwer and Rice (1976) for over-damped response data in uncon-10 fined aquifers, whereas for under-damped response data (with oscillatory behaviour), the model of Springer and Gelhar (1991) was used. In confined aquifers, we analyzed the response data with over-damped behaviour with the model of Bouwer and Rice (1976), whereas for the under-damped response data, the model of Butler (1998) was the most appropriate. ...
River restoration projects have been launched over the last two decades to improve the ecological status and water quality of regulated rivers. As most restored rivers are not monitored at all, it is difficult to predict consequences of restoration projects or analyze why restorations fail or are successful. It is thus necessary to implement efficient field assessment strategies, for example by employing sensor networks that continuously measure physical parameters at high spatial and temporal resolution. This paper focuses on the design and implementation of an instrumentation strategy for monitoring changes in bank filtration, hydrological connectivity, groundwater travel time and quality due to river restoration. We specifically designed and instrumented a network of monitoring wells at the Thur River (NE Switzerland), which is partly restored and mainly channelized since more than 100 years. Our results show that bank filtration – especially in a restored section with alternating riverbed morphology – is variable in time and space. Consequently, our monitoring network sensing physical and sampling chemical water quality parameters was adapted in response to that variability. Although not available at our test site, we consider long-term measurements – ideally initialized before and continued after restoration – as a fundamental step, towards predicting consequences of river restoration for groundwater quality. As a result, process-based models could be adapted and evaluated using these types of high-resolution data sets.
... This is typically achieved by either dropping a slug mass into a well (Cooper et al., 1967) or pneumatically pressurizing the water column in a well (Butler, 1998;Malama et al., 2011), a configuration referred to as a single well test. Several mathematical models are available in the hydrogeology literature for analyzing confined (Cooper et al., 1967;Bredehoeft and Papadopulos, 1980;Zurbuchen et al., 2002;Butler and Zhan, 2004) and unconfined (Bouwer and Rice, 1976;Springer and Gelhar, 1991;Hyder et al., 1994;Spane, 1996;Zlotnik and McGuire, 1998;Malama et al., 2011) aquifer slug test data under the Darcian flow regime. Consideration of slug tests under non-Darcian flow regimes may be found in Quinn et al. (2013) and Wang et al. (2015). ...
... A minimum of four rising and four falling head tests were conducted in each well with the transient response being captured by a pressure transducer. The K was estimated by fitting the head response in each test to the solution of Springer and Gelhar (1991), developed for unconfined aquifers. ...
Small-scale point velocity probe (PVP)-derived velocities were compared to conventional large-scale velocity estimates from Darcy calculations and tracer tests, and the possibility of upscaling PVP data to match the other velocity estimates was evaluated. Hydraulic conductivity was estimated from grain-size data derived from cores, and single-well response testing or slug tests of onsite wells. Horizontal hydraulic gradients were calculated using 3-point estimators from all of the wells within an extensive monitoring network, as well as by representing the water table as a single best fit plane through the entire network. Velocities determined from PVP testing were generally consistent in magnitude with those from depth specific data collected from multilevel monitoring locations in the tracer test, and similar in horizontal flow direction to the average hydraulic gradient. However, scaling up velocity estimates based on PVP measurements for comparison with site-wide Darcy-based velocities revealed issues that challenge the use of Darcy calculations as a generally applicable standard for comparison. The Darcy calculations were shown to underestimate the groundwater velocities determined both by the PVPs and large-scale tracer testing, in a depth-specific sense and as a site-wide average. Some of this discrepancy is attributable to the selective placement of the PVPs in the aquifer. Nevertheless, this result has important implications for the design of in situ treatment systems. It is concluded that Darcy estimations of velocity should be supplemented with independent assessments for these kinds of applications.
© 2015, National Ground Water Association.
... Wylie and Magnuson (1995) developed a spreadsheet modeling technique by simplifying the solution of van der Kamp (1976). Springer and Gelhar (1991) employed a simplified equation of pipe hydraulics to describe the inertial effect of moving water in the wellbore and presented a solution to determine the hydraulic conductivity of an unconfined aquifer, where the aquifer groundwater flow was modeled by the solution of Bouwer and Rice (1976). McElwee and Zenner (1998) derived a new solution of slug test by using the Navier-Stokes equation for flow in the wellbore and the Hvorslev model for flow in the aquifer, of which the robustness of solution was subsequently tested by field data (McElwee, 2001). ...
Slug test has been commonly applied to determine the near-well aquifer properties because of its logistical and economic advantages over other aquifer tests. Instantaneously increasing or decreasing the water level inside a slug test well will generate a significant hydraulic gradient near the well screen-aquifer interface (particularly at early stage of slug test), which may result in near-well aquifer flow deviated from Darcian behavior. However, previous studies on slug test rarely considered non-Darcian flow process associated with the slug test. In this study, a transient model of slug test in a leaky confined aquifer was established considering non-Darcian horizontal flow in the aquifer, and Darcian and vertical flow in the aquitard. The non-Darcian flow in the aquifer was described by the Izbash (power-law) equation. A finite-difference solution was presented for solving the non-linear model of slug test, the accuracy of which was tested through comparison with a previous analytical solution. By analyzing the sensitivities of dimensionless aquitard leakance (αD), non-Darcian index (n), and ratio of well screen radius versus well casing radius (χ) on the water level recovery (WLR) of slug test, one could conclude that the rate of WLR increased with the decrease of n for a given time. The WLR curve of Darcian flow (n = 1) was above the curves of non-Darcian flow, including fully developed turbulent flow. There was a deflection point for each WLR curve without the aquitard leakance in log–log scales, and the slope of the curve approached a constant after such a point. The effects of aquitard leakance on WLR for non-Darcian case appeared later than Darcian case. The normalized sensitivity coefficients of WLR with respect to n, αD and χ were negative, and they were most sensitive to n and least to αD.
... The wells were all thoroughly developed via extended pumping prior to the slug testing. The water level displacement datasets were analyzed using a mathematical solution developed by Springer and Gelhar (1991) designed for unconfined aquifers and accommodating oscillatory water level responses. ...
Hydrogeological setting has profound effects on microbial effectiveness in in situ treatment.•We design and implement an in situ denitrification method to reduce groundwater nitrate concentrations near impacted wells.•Field challenges included natural aquifer heterogeneity and aerobic groundwater conditions.•Results indicate significant nitrate mass can be removed by targeting high nitrate mass flux zones in the aquifer.•The approach will have general applicability for public supply wells in a wide range of geologic settings.
... This method employs a quasi-steady-state model that ignores elastic storage in the aquifer. Springer and Gelhar (1991) extended the method to include inertial effects. Dagan's (1978) method is used in wells screened across the water table in a homogeneous, anisotropic, unconfined aquifer. ...
The slug test offers a fast and inexpensive field method of obtaining localized hydraulic conductivity values. In this paper, we applied this procedure in a 'fontanili' zone lo-cated in the middle Venetian Plain (Villaverla, VI). In this site, 34 piezometers are present in a small area of 1.5 ha, which intercepts a shallow unconfined aquifer. The experimental data, obtained by 59 slug tests, were processed with three different methods of analysis: Hvorslev, Bouwer-Rice and KGS, to obtain a permeability characterization of the area and iden-tify the real differences between the considered solutions. Two slug tests were also analyzed using a three-dimensional finite difference groundwater flow model. By comparing the different methods used in the same piezometer, we obtained highly similar values of permeability, while the numeri-cal simulation of slug tests suggests that KGS is the best method for estimating hydraulic conductivity. At the same time, we can identify a considerable heterogeneity in the area of investigation; indeed, the slug test estimates of hydraulic conductivity (K) range over three orders of magnitude (from 2.6E-06 to 3.8E-03 m/s). This wide range of values confirms the high stratigraphic hetero-geneity also observed during the coring. Riassunto: Lo slug test è un metodo veloce ed economico che per-mette di stimare la conducibilità idraulica nell'intorno del pozzo o piezometro in cui viene realizzato. In questo articolo tale metodologia viene applicata per caratteriz-zare la conducibilità idraulica di un campo sperimentale ubicato in corrispondenza della fascia delle risorgive nella media pianura veneta (Villaverla, VI). Questo campo sperimentale, che si estende su un area di circa 1.5 ha, è costituito da 34 piezometri filtranti l'ac-quifero superficiale freatico. I risultati di 59 slug tests sono stati analizzati secondo tre diversi modelli interpretativi: Hvorslev, Bouwer-Rice e KGS, al fine di ca-ratterizzare la permeabilità dell'area oggetto di studio e di identifi-care le effettive differenze tra i metodi considerati. I risultati di due slug tests sono stati analizzati anche attraverso la modellazione nu-merica tridimensionale alle differenze finite del flusso sotterraneo. La comparazione dei risultati derivati dall'applicazione dei diver-si modelli interpretativi su uno stesso piezometro mostra valori di conducibilità idraulica molto simili, mentre i risultati della model-lazione numerica suggeriscono che il metodo KGS è il più affidabile e preciso per la stima di tale parametro. I risultati delle prove evidenziano un'estrema eterogeneità dell'area oggetto di studio con valori di conducibilità idraulica (K) che varia-no entro 3 ordini di grandezza (da 2.6E-06 a 3.8E-03 m/s). Questo ampio range di valori trova conferma nell'elevata eterogeneità stra-tigrafica osservata durante la realizzazione dei piezometri.
... Because of this, slug tests exhibiting these response characteristics cannot be analyzed quantitatively with the Bouwer and Rice or standard type-curve methods. High-K analysis methods that can be employed for analyzing unconfined aquifer tests exhibiting response behavior that is either critically damped or under damped include those described in Springer and Gelhar (1991), Butler (1998), McElwee andZenner (1998), McElwee (2001), Butler and Garnett (2000), and Zurbuchen et al. (2002). Because of the ease provided by a spreadsheet-based approach, the test-analysis method presented in Butler and Garnett (2000) is preferred for analyzing tests exhibiting critically damped behavior. ...
... The DPSTs were performed as rising-head tests in temporary DP monitoring wells with a screened interval of 1.06 m length. The DPST-based K values were derived using the method of Springer and Gelhar (1991) with the correction of Butler (2002) for small-diameter wells (Tinter 2012). Examples of the data obtained at five locations up to depths of approximately 15 m are displayed in Figure 3. Data beyond the lower limit of the tool ranges were discarded. ...
Direct push (DP) technologies are typically used for cost-effective geotechnical characterization of unconsolidated soils and sediments. In more recent developments, DP technologies have been used for efficient hydraulic conductivity (K) characterization along vertical profiles with sampling resolutions of up to a few centimetres. Until date, however, only a limited number of studies document high-resolution in situ DP data for three-dimensional conceptual hydrogeological model development and groundwater flow model
parameterization. This study demonstrates how DP technologies improve building of a conceptual hydrogeological model. We further evaluate the degree to which the DP-derived hydrogeological parameter K, measured across different spatial scales, improves performance of a regional groundwater flow model. The study area covers an area of ~60 km² with two overlying, mainly unconsolidated sand, aquifers separated by a 5-7 m
thick highly heterogeneous clay layer (in north-eastern Belgium). The hydrostratigraphy was obtained from an analysis of cored boreholes and about 265 cone penetration tests (CPTs). The hydrogeological parameter K was derived from a combined analysis of core and CPT data and also from hydraulic direct push tests. A total of 50 three-dimensional realizations of K were generated using a non-stationary multivariate geostatistical approach.
To preserve the measured K values in the stochastic realizations, the groundwater model Krealizations were conditioned on the borehole and direct push data. Optimization was performed to select the best performing model parameterization out of the 50 realizations. This model outperformed a previously developed reference model with homogeneous K fields for all hydrogeological layers. Comparison of particle tracking simulations,
based either on the optimal heterogeneous or reference homogeneous groundwater model flow fields, demonstrate the impact DP-derived subsurface heterogeneity in K can have on groundwater flow and solute transport. We demonstrated that DP technologies, especially when calibrated with site-specific data, provide high-resolution 3D subsurface data for building more reliable conceptual models and increasing groundwater
flow model performance.
... By Yen-Chen Huang & Hund-Der Yeh test, e.g., Hvorslev (1951), Cooper et al. (1967), Bouwer and Rice (1976), Springer and Gelhar (1991), Hyder et al. (1994), and Butler (1998). ...
Yeh and Chen (J Hydro 342(3–4):283-294, 2007) integrated a slug test solution for a well having a finite-thickness skin with the simulated annealing (SA) to determine the hydraulic parameters of the skin zone and formation zone. Some results obtained in positive-skin scenarios are however not accurate if compared with the target values of the parameters. This study first employs the sensitivity and correlation analyses to quantify the relationship between two normalized sensitivities and analyze the resulting errors in parameter estimates. It is found that the inaccuracy in parameter estimates can be attributed to following two problems: (1) the normalized sensitivities of the skin thickness and hydraulic conductivity are highly correlated and (2) the SA algorithm is very sensitive to round-off error in well-water-level (WWL) data. A parameter identification approach is thus developed based on the extended Kalman filter (EKF) coupled with the solution used by Yeh and Chen (J Hydro 342(3–4):283-294, 2007) to determine the parameters in six positive-skin scenarios where the parameters were not accurately determined before. We show that previous two problems can be overcome by the proposed approach because it is designed to account for uncertainties of measurements. Moreover, the EKF can save 99.8% and 99.9% computing time when compared with the results using the SA in analyzing 20 WWL data and 47 WWL data, respectively.
... Pneumatic slug tests within the more conductive portions of the aquifer and within the PRB were performed using a method based on Butler (1997) that utilizes air pressure and vacuum to initiate instantaneous changes in head within the well combined with high frequency monitoring of the aquifer response using data loggers and pressure transducers. The aquifer response data obtained during the slug tests were analyzed using the methods of Bouwer and Rice (1976) or Springer and Gelhar (1991), depending on the character of the observed response. Pneumatic slug tests were also performed in vertical profiles of temporary well points installed at one location upgradient of the PRB and at two locations within the PRB. ...
The fifteen-year performance of a granular iron, permeable reactive barrier (PRB; Elizabeth City, North Carolina) is reviewed with respect to contaminant treatment (hexavalent chromium and trichloroethylene) and hydraulic performance. Due to in-situ treatment of the chromium source zone, reactive and hydraulic longevity of the PRB has outlived the mobile chromate plume. Chromium concentrations exceeding 3μg/L have not been detected in regions located hydraulically down-gradient of the PRB. Trichloroethylene treatment has also been effective, although non-constant influent concentrations of trichloroethylene have at times resulted in incomplete dechlorination. Daughter products: cis-1,2-dichloroethylene, vinyl chloride, ethene, and ethane have been observed within and down-gradient of the PRB at levels <10% of the influent trichloroethylene. Analysis of potentiometric surfaces up-gradient and across the PRB suggests that the PRB may currently represent a zone of reduced hydraulic conductivity; however, measurements of the in-situ hydraulic conductivity provide values in excess of 200m/d in some intervals and indicate no discernible loss of bulk hydraulic conductivity within the PRB. The results presented here are particularly significant because they provide the longest available record of performance of a PRB. The longevity of the Elizabeth City PRB is principally the result of favorable groundwater geochemistry and hydrologic properties of the site.
... methods. Methods that can be employed for analyzing unconfined aquifer tests exhibiting high permeability characteristics include, methods described in Springer and Gelhar (1991), Butler (1998), McElwee and Zenner (1998), Butler and Garnett (2000), and Zurbuchen et al. (2002). Because of the ease provided by a spreadsheet-based approach, the test analysis method presented in Butler and Garnett (2000) was used for tests exhibiting high permeability response characteristics. ...
This report provides the results of detailed hydrologic characterization tests conducted within newly constructed Hanford Site wells during FY 2002. Results from the tests provide hydrologic information that supports the needs of RCRA waste management characterization and sitewide groundwater monitoring and modeling programs and reduces the uncertainty of groundwater flow conditions at selected Hanford locations.
... We followed best-practice recommendations (Butler et al., 2003;Zurbuchen et al., 2002) and processed our data according to Butler (1998), Butler et al. (2003), and McElwee and Zenner (1998) with the software AQTESOLV-Professional (www.aqtesolv.com). We applied the model of Bouwer and Rice (1976) for over-damped response data in unconfined aquifers, whereas for under-damped response data (with oscillatory behaviour), the model of Springer and Gelhar (1991) was used. In confined aquifers, we analyzed the response data with over-damped behaviour with the model of Bouwer and Rice (1976), whereas for the underdamped response data, the model of Butler (1998) was the most appropriate. ...
River restoration projects have been launched over the last two decades to improve the ecological status and water quality of declined rivers. As most restoration projects are not monitored at all, we can hardly predict consequences of restoration projects, nor can we analyze why they fail or why they are successful. To overcome this lack of data, efficient field assessment strategies have to be implemented, for example, by employing sensor networks that continuously measure physical parameters at high spatial and temporal resolution. Without detailed environmental process understanding, predictions on revitalisation remain speculations. We focus on the design and implementation of an instrumentation strategy for monitoring changes in bank filtration, groundwater quality, hydrological connectivity and travel time due to river restoration. We specifically designed and instrumented a network of monitoring wells at the Swiss River Thur (NE Switzerland), which is partly restored and mainly channelized since more than 100 years. Our results show that bank filtration - especially in restored sections with changing river bed morphology - is variable in time and space. Consequently, monitoring networks sensing physical and sampling chemical water quality parameters have to be adapted in response to that variability. To predict consequences of river restoration for groundwater quality, long-term measurements - ideally initialized before and continued for a long time after restoration - are fundamental. As a result, process-based models can be adapted and evaluated using these types of high resolution data sets.
... Subsequently, the aquifer parameters are identified by fitting an appropriate mathematical solution or graphical type curves with the slug test data. Several slug test mathematical models can be found in the groundwater literature (e.g., Hvorslev, 1951;Cooper et al., 1967;Bouwer and Rice, 1976;Springer and Gelhar, 1991;Hyder et al., 1994;Butler, 1998). In addition, some software, e.g., AQTESOLV (Duffield, 2002), which includes the above-mentioned models has been developed to analyze the slug test data. ...
Slug test is considered to reflect the hydraulic parameters in the vicinity of the test well. The aquifer parameters are usually identified by fitting an appropriate mathematical solution or graphical type curves with slug test data. In this paper, we developed an approach by combining [Moench, A.F., Hsieh, P.A., 1985. Analysis of slug test data in a well with finite-thickness skin. In: Memoirs of the 17th International Congress on the Hydrogeology of Rocks of Low Permeability, U.S.A. Members of the International Association of Hydrologists, Tucson, AZ, vol. 17, pp. 17–29] and simulated annealing (SA) approach to estimate five parameters, i.e., three skin parameters and two aquifer parameters. The three skin parameters are hydraulic conductivity, specific storage, and thickness of the wellbore-skin zone, while the two aquifer parameters are hydraulic conductivity and specific storage of the formation zone. It is worthy to note although the thickness of the wellbore-skin zone is usually taken as an input data for the data-analyzed software, it is actually an unknown parameter that cannot be measured directly. This paper proposes a methodology for estimating the thickness of the wellbore-skin zone with other hydraulic parameters at the same time.
... Fig. 6 shows representative examples of measured head responses in clusters C5 and C7. Estimates of K r from slug tests obtained using the Springer and Gelhar (1991) method reveal that the hydraulic conductivity is 1.5-2 times larger at intermediate aquifer depth than in shallow and deep aquifer parts at the cluster C5. The responses at the cluster C7 do not show the high conductivity, which corresponds well to the measured time-drawdown data from the pumping test. ...
Analytical solutions of drawdown in unconfined aquifers are widely applied for determining the specific yield, Sy, and the horizontal and the vertical hydraulic conductivity Kr and Kz, respectively. In many previous studies, estimates of Sy and Kz were observed to be highly variable and physically unrealistic. This has been attributed to the conceptualization of flow above the declining water table and aquifer heterogeneity in the applied models. We present the analysis of time-drawdown data from a pumping test instrumented with depth-differentiated observation piezometers arranged in clusters. Applying homogeneous anisotropic aquifer models in combination with nonlinear least squares parameter identification techniques, the data were analyzed in different groups: analysis of data from individual piezometer clusters and simultaneous analysis of the entire data set from all piezometer clusters (global analysis). From the cluster analyses, estimates of Sy and Kz exhibit large variances and depart from a priori estimates inferred from the hydrostratigraphy. Parameter estimates from the global analysis do not fall within the parameter bounds (minimum and maximum values) defined by the cluster analyses. While heterogeneity appears to be the important reason for large parameter variances, we discuss the influence of rarely considered aquifer return flow on drawdown and the inconsistent results from the cluster and global analyses. We corroborate our findings with data on hydraulic gradients, slug test data, and results from the application of a more realistic numerical flow model.
... In all cases, slug tests in the lab sink exhibited an initially oscillatory response (critically-damped), recovering to near static conditions within 3 to 4 seconds ( Figure 5). This is typical of high-K conditions where the inertial forces of water exceed those offered by the surrounding porous medium (Springer and Gelhar 1991;Butler 1998). Since there is no formational resistance within the water-filled sink, the responses are attributed to the combined inertial forces of the water and the resistive effects of the tubing and screen. ...
This report summarizes FY08 activities conducted under the Remediation and Closure Sciences Project.
Salinity, or total dissolved solids (TDS), of the Colorado River is a major concern in the southwestern United States where the river provides water to about 40 million people for municipal and industrial use and is used to irrigate about 5.5 million acres of land. Much of the salinity in the Colorado River Basin is derived from natural interactions of surface water and groundwater with various geologic materials (rocks, soils, and alluvial deposits). The Dolores River in southwest Colorado is a major tributary of the Colorado River that historically accounts for about 6 percent of the salinity load to the Upper Colorado River Basin with the Paradox Valley being the primary source of salinity to the Dolores River. The Paradox Valley, one of several salt-anticline valleys in the region, is a fault-bounded topographic basin aligned with and exposing an underlying salt-anticline core. Salt deposits in the Pennsylvanian Paradox Formation of the Hermosa Group form an elongated salt diapir oriented northwest to southeast that is up to 12,000 feet (ft) thick beneath the present valley floor. Surface erosion, groundwater circulation, and weathering during Tertiary and Quaternary valley formation contributed to development of a cap rock, collapse features, breccia, and brine at the top of the exposed salt diapir. Today (2023), brine occurring in the brecciated cap rock and underlying salt deposits is in hydraulic connection with an overlying freshwater alluvial aquifer, and depending on seasonal river stage and hydrologic conditions, the brine discharges to the Dolores River causing the observed increase in salinity as the river crosses the Paradox Valley.
To reduce salinity concentrations in the Dolores River, the Bureau of Reclamation (Reclamation) operates the Paradox Valley Unit (PVU). The PVU project consists of nine shallow brine pumping wells near the Dolores River and one deep disposal well where the brine is injected for disposal. When operational, the PVU pumping wells extract brine from the base of the alluvial aquifer that is piped and injected into a deep disposal well about 3 miles southwest of the PVU. The PVU became fully operational July 1, 1996, and by 2015, operation of the PVU had reduced salinity concentrations in the Dolores River by as much as 70 percent compared to pre-PVU conditions. In response to a 4.5 magnitude earthquake, injection operations, and thus PVU pumping, were ceased from March 2019 to June 2022. A trial period of PVU operation began in June 2022 with a reduced injection rate, and thus PVU pumping rate, of about two-thirds capacity to gather additional information and guide future operational decisions.
In cooperation with Reclamation, the U.S. Geological Survey (USGS) developed this report to present the current (2023) understanding of groundwater and brine occurrence and discharge to the Dolores River in the Paradox Valley. Results from the compilation of spatial datasets, groundwater sampling and age dating, and aquifer tests are presented to provide improved understanding of the Paradox Valley hydrogeology, to supply datasets for a numerical groundwater-flow and brine-transport model, and to support future operations of the PVU. The hydrogeologic data provided herein, along with the most recent loading analysis for the Dolores River in the Paradox Valley, and a previous conceptual model for brine discharge to the river are used to present a conceptual understanding of groundwater occurrence in the Paradox Valley.
Slug tests are one of the most common field methods for estimating local hydraulic conductivity, for fast and low-cost characterization of aquifer heterogeneity. In highly permeable zones, underdamped responses, identified by oscillations of the water level, are generally observed. Several analytical solutions have been developed for modeling underdamped slug test responses. Interpreting these tests in fractured rocks can be challenging due to system complexity, which ultimately raises questions about the appropriate model for interpreting a given dataset. In order to obtain insights on this fundamental problem for slug test analyses in fractured rocks, a complete evaluation on three transient solutions for linear, radial and spherical flow configuration extended to include inertial and wellbore skin effects in a fully penetrating well is proposed. A first comparison between these transient solutions and the classical steady-state model shows that, in some cases, the latter may underestimate hydraulic conductivity. Next, parameter sensitivity and uncertainty analyses were conducted on each solution to evaluate the classical problem of non-uniqueness between models and parameters. As expected, the results from sensitivity analysis show that the hydraulic conductivity parameter is the most sensitive regardless of model configuration. For specific storage, sensitivity is important for the linear model, moderate for the radial model and negligible for the spherical model. For the skin factor, however, sensitivity is negligible for the linear model, moderate for the radial model and most important for the spherical model. These results were next confirmed by performing Bayesian inferences using Markov Chain Monte Carlo technique to evaluate uncertainty on each parameter. Uncertainties appear significant for negligibly sensitive parameters but nearly insignificant for the most sensitive parameters. For all flow configurations, hydraulic conductivity appears however to be accurately estimated. Examples of interpretations for data collected in fractured rocks illustrate the application of these models and provide some recommendations.
The slug test is a common field technique for obtaining local hydraulic parameters near wells, applied, for example, for the hydrogeological investigation at contaminated sites. Although many slug test models have been developed for interpretation of measurements, only a few of them have considered heterogeneous conditions, and water column inertial effects are usually neglected. In this paper, we propose a novel three‐dimensional slug test model (3DHIM) for application in heterogeneous aquifers, considering inertial effects associated with skin effects and linear friction forces. After comparison with existing analytical and numerical solutions of slug tests, the model is applied to an aquifer analog to simulate a series of slug tests. The results from single‐well slug tests show that the well geometry (i.e., the well radius, well depth, and screen length) has an impact on the water level response. For cross‐well slug tests, the results indicate that the water level fluctuations not only include information on the hydraulic signal propagation process in the aquifer but also on well characteristics, such as wellbore storage and inertial effects. These effects cause a phase shift and amplitude change of the water level fluctuation. As the observation and test wells have a good hydraulic connection and similar well geometry, the water level amplitude could be amplified relative to aquifer pressure at the measured position. Therefore, we suggest considering wellbore storage and in‐well inertial effects in slug test‐based subsurface investigations, otherwise the parameter estimates based on well water levels may include errors, particularly in highly permeable layers.
A simple parameter estimation procedure, designated as integration-based estimation (IBE), was introduced to determine the hydraulic properties of an aquifer using slug test models subjected to certain flow geometries such as radial and spherical flows. The basic idea behind the proposed IBE approach is to link an integration value at pre-defined normalized head levels for field data with that of a theoretical type curve. The IBE method removes the need for the implementation of the classical graphical matching process which would be ineffective to acquire aquifer parameters for non-ideal aquifer conditions. As the second aspect of this study, a new decision tool was suggested to determine the suitable slug test model to be utilized for the site data since diagnosing the flow character properly is of crucial importance for following a convenient analysis procedure. The estimation performance and limitation of the proposed IBE method were tested for several slug test scenarios including radial and spherical flow models with a number of synthetically generated data sets as well as a field application. Results reveal that the IBE together with the identification methodology not only is able to retrieve aquifer parameters as reliable as the existing techniques in the literature but also diagnoses the flow character precisely as demonstrated in this study.
Slug tests are a commonly used method to determine the hydraulic conductivity of strata near a borehole. The tests involve recording the water level (pressure) response in a well to an instantaneous increase or lowering of water level. Slug tests have the advantage of being quick, inexpensive to perform, and do not generate water that requires disposal, which is an important consideration at contaminated sites. The quality of data obtained from slug tests is strongly dependent on well and borehole conditions, particularly skin effects. Multiple-level slug tests performed on a single well or borehole are used to obtain hydraulic conductivity-versus-depth profiles. Straddle-packer and single-packer tests allow for the evaluation of hydraulic properties and collection of water samples from discrete intervals. Pressure transient testing is an important tool in oil and gas industry that has applications in groundwater investigations for evaluation of aquifer properties and wellbore conditions.
The auto hydrogeological parameters monitoring and data processing system is developed to improve efficiency of hydrogeological tests, and the slug test is introduced instead of conventional hydrogeological test. It dramatically shortens the test period and decreases the working intensity under in-situ conditions with relatively low costs because pumping and observation wells are not required. The post processing system is developed, which deals with the data of steady flow pumping test, unsteady flow pumping test and slug test at the same time, and the test reports are offered timely. Through comparative application under in-situ conditions, it is proved that the system can satisfy engineering demand, which is a good substitute for conventional hydrogeological test.
Slug tests performed using mini-piezometers with internal diameters as small as 0.43 cm can provide a cost effective tool for hydraulic characterization. We evaluated the hydraulic properties of the apparatus in a laboratory environment and compared those results with field tests of mini-piezometers installed into locations with varying hydraulic properties. Based on our evaluation, slug tests conducted in mini-piezometers using the fabrication and installation approach described here are effective within formations where the hydraulic conductivity is less than 1 × 10(-3) cm/s. While these constraints limit the potential application of this method, the benefits to this approach are that the installation, measurement, and analysis is cost effective, and the installation can be completed in areas where other (larger diameter) methods might not be possible. Additionally, this methodology could be applied to existing mini-piezometers previously installed for other purposes. Such analysis of existing installations could be beneficial in interpreting previously collected data (e.g., water-quality data or hydraulic head data).
© 2015, National Ground Water Association.
Determination of the hydraulic conductivity using the Direct-Push Injection Logger U. Schneidewind1, S. Lessoff2, P. Blum3,C. Leven-Pfister1, P. Dietrich1, 1 Helmoltz - Centre for Environmental Research (UFZ), Leipzig, Germany 2 Tel Aviv University, Faculty of Engineering, Tel Aviv, Israel 3 University of Tübingen, Centre for Applied Geoscience (ZAG), Tübingen, Germany Abstract The hydraulic conductivity K is one of the parameters of main interest and the basis for describing flow and transport in aquifers. In many cases a level of detail is required regarding K that can hardly be achieved with conventional hydrogeological tests. Over the last 15 years, the Direct-Push (DP) technology has been developed for shallow unconsolidated aquifers as a means of rapidly obtaining information on aquifer parameters in the absence of classical monitoring wells. Some of those techniques such as the Direct-Push slug test (DPST) provide absolute hydraulic conductivity values, however are time-consuming. Other techniques such as the Direct- Push injection logger (DPIL) are much faster and allow for a higher subsurface resolution, but only provide relative hydraulic conductivity values (Kr) that have to be transformed into absolute ones. In this work DPIL data was gathered for the unconfined heterogeneous aquifer at Lauswiesen test site in Southern Germany near the city of Tübingen. It was found that the aquifer consists of two zones of different heterogeneity and hydraulic conductivity. In order to gain more information on the hydraulic conductivity, relative K-values from DPIL measurements were correlated with K-values from DPST assuming a linear relationship giving a coefficient of determination of R2 = 0.67. Variogram analysis provide a vertical integral scale of 0.25-0.35 m and a horizontal integral scale of 1.5-3.0 m for ln(Kr) values. Nevertheless, additional work still remains to be done to address the problem of different support scales of the DPST (30-60 cm) and DPIL (2.5 cm) methods.
Slug test is a common characterization method that estimates aquifer hydraulic conductivity rapidly and economically. To characterize the hydraulic property near the borehole YS-4 in the Korea Atomic Energy Research Institute (KAERI) site, slug tests were performed, and oscillatory hydraulic responses were observed. We analyzed the observations with the modified Hvorslev and Bouwer&Rice methods considering the casing inertia, and then the results were compared with those from the general Hvorslev and Bouwer&Rice methods. The estimated hydraulic conductivities from the modified methods are ranged from to m/sec, but those from the general ones are ranged from to m/s, which shows that the oscillatory responses should be analyzed with consideration of the flowing water inertia effect.
Keywords: Hyporheic flow Geomorphology Floodplain age MODFLOW Willamette River LiDAR s u m m a r y Field-calibrated models of hyporheic flow have emphasized low-order headwater systems. In many cases, however, hyporheic flow in large lowland river floodplains may be an important contributor to ecosystem services such as maintenance of water quality and habitat. In this study, we used a network of shallow monitoring wells, Light Detection and Ranging (LiDAR), and continuous monitoring to param-eterize and calibrate stochastic three-dimensional ground water models for a 9.7 km 2 (2400 acres) area along a naturally-meandering section of the Willamette River floodplain in Oregon. This large river flood-plain is representative of other similar systems. Steady-state simulations were done representing the wet winter and dry summer seasons. During the dry season, hyporheic flow was oriented along the floodplain elevation gradient and median steady-state residence times in small islands and bars were on the order of months. In the larger islands steady-state residence times were on the order of years. In the wet season, flow was oriented laterally away from the river and quickly intercepted and returned to the surface water system in alcoves and cutoffs connected to the river, and recharge due to infiltration of precipitation pre-vented hyporheic flow through older island areas. In the younger islands, median steady-state residence times ranged from about 6.1 Â 10 1 to 1.6 Â 10 2 days. In the model domain overall, the steady-state dry season median pathline length was about 8.2 Â 10 2 with a maximum length of about 5.7 Â 10 3 m. For the wet season, the median was about 2.0 Â 10 2 m with a maximum length of about 3.5 Â 10 3 m. Wet season hyporheic water penetrated deeper into the lower permeability geologic units by an order of mag-nitude, as compared to the dry season. This was likely due to the absence of precipitation infiltration dur-ing the dry season. We used particle tracking in order to characterize residence time distributions for hyporheic water. We found two behaviors: lognormal decay with shorter distributions of residence times, and heavy tailing, following power-law behavior. Interestingly, we found the heavy tailing behav-ior more during the wet season when mean residence times were short. This result implies that even though some rates of hyporheic flow were relatively fast, there were also zones of relatively stagnant water causing this large variation in residence time. Observed slopes for log–log plots of the histograms fell in the range of 2.3–5.6. This behavior appeared to be restricted to regions affected by natural river meandering, where avulsions create isolated islands. In some areas, land managers may consider revet-ment removal as a means to convert channelized systems to more natural systems with shallower depths in the main channel, meander scrolls, and alcoves that can enhance hyporheic flow. The results of this study provide information on how such decisions may affect the extent of hyporheic flow that may occur as a large river returns to its natural geomorphological dynamics. Published by Elsevier B.V.
Crosshole radar tomography is often used in geological, hydrological and engineering investigations to map shallow subsurface electrical properties, viz. dielectric permittivity and electrical conductivity. These properties are closely linked to important hydrogeological parameters like salinity, water content, porosity and pore structure, clay content, and lithological variations. Common practice is to invert crosshole radar data with ray-based tomographic algorithms using first arrival traveltimes and first cycle amplitudes. However, the resolution of conventional standard ray-based inversion schemes for crosshole ground penetrating radar (GPR) is limited, because only a fraction of the information contained in the radar data is used. The resolution can be improved significantly by using a full-waveform inversion that considers the entire waveform, or significant parts thereof. Recently, a 2D time-domain vectorial full-waveform crosshole radar inversion code was developed that includes the vector properties of the electric field and simultaneously updates the permittivity and conductivity parameters. Here, this inversion code has been modified by allowing optimized acquisition setups that reduce the acquisition time and computational costs significantly. This is achieved by minimizing the number of transmitter points and maximizing the number of receiver positions instead of a conventional setup that uses an equal number of transmitter and receiver positions. To improve the low ray-coverage close to the transmitter borehole, a semi-reciprocal setup was employed which entailed populating the original receiver borehole with new transmitter positions (and conversely populating the original transmitter borehole with a dense array of receiver positions). This improved algorithm was employed to invert crosshole GPR data acquired within a gravel aquifer (depth range 4-10 m) in the Thur valley, Switzerland. The simulated traces of the final model obtained by the full-waveform inversion fit the observed traces very well in the lower part of the section and reasonably well in the upper part of the section. Compared to the ray-based inversion, the results from the full-waveform inversion show significantly higher resolution images. Comparison of the inversion results with borehole logs shows that porosity logs obtained from Neutron-Neutron data correspond very well with the GPR porosities derived from the permittivity distribution in the depth range 6 m - 8 m and that there is a strong qualitative agreement at greater depths. Furthermore, there is a good correspondence between the conductivity tomograms and the natural Gamma logs at the boundary of the gravel layer and the underlying lacustrine clay sediments at a depth of approximately 9.5 m. This layer was not clearly identified in the ray-based tomogram. Due to the presence of the water table, and associated refracted/reflected waves, the upper traces are not well fitted and the upper 2 m in the permittivity and conductivity tomograms are not reconstructed reliably because the unsaturated zone is not yet incorporated into the inversion domain.
Radius changes along the flow path inside a well can have a substantial nonlinear impact on head responses to a slug test. The present paper investigates the applicability of head loss formulas rooted in steady-state pipe hydraulics to account for minor and major head losses in transient slug test analysis. Such nonlinear head losses, which frequently occur when using a packer for test initiation, have not systematically been investigated before. Packer-internal turbulence is accounted for based on Colebrook's formula, while minor head losses originating at the inlet and outlet of the packer are treated by Borda Carnot-type head loss formulas. The analysis of a specifically designed set of 12 slug tests provides extended experimental evidence of the applicability of these nonlinear head loss formulas when accounting for well bore-internal turbulence and minor head losses in transient slug test analysis.
In Berlin many wells are constructed with an additional small diameter bypass tube flanged on to the large diameter casing and running parallel to the later upward to the surface. The response to a slug test conducted in such a well is usually characterised by significant water level oscillations developing inside the branched pipe system. In the present paper, a general non-linear model is developed for the analysis of slug tests performed in bypassed wells. The model includes skin effects, non-linear head losses due to internal well bore fluid friction, minor losses originating at radius changes along the flow path inside the well, and inertial effects of the water columns contained within the primary casing and the bypass. Pipe flow inside the branched tubing system is described by the one-dimensional conservation law of the mechanical energy of the well bore fluid. Aquifer flow is quantified by a convolution-type approach. The coupled well-aquifer system is governed by an integro-differential equation representing the mean mechanical energy of the total well bore fluid and, coupled to it, by a non-linear ordinary differential equation which accounts for mechanical energy fluctuations between the water columns inside the main casing and the bypass. Both equations are solved by finite difference approximations coupled to point iterative numerical techniques. An application of the model to field data suggests that non-linear hydraulic head losses originating inside the well bore may cause the measured head responses to depend on the initial displacement. A packer used to initiate a slug test can induce these non-linear distortions through the combined effect of minor losses originating at the inlet and the outlet of a small diameter packer flow-through tube and internal fluid friction potentially developing inside that packer passage. As classical linear theories do not allow for the analysis of such phenomena, a model accounting for these non-linear processes should be used if field data show significant dependencies on the initial slug height.
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