Constant-head Injection Tests Research Articles

Constant-head and variable-head injection tests for determining the hydraulic parameters of an aquitard

Although specific storage (SS) is a crucial parameter for characterizing the dynamic water-release process in an aquitard, the Hvorslev analysis method is only capable of estimating the hydraulic conductivity (K), rather than SS. The Hvorslev method is based on an assumption of steady-state flow and uses the falling-head test. Considering the elastic water-release effect in an aquitard and the actual groundwater flow, two mathematical unsteady-state groundwater flow models (i.e., the constant-head and variable-head models), describing the head distribution are presented for a constant-head injection test (CHIT) and variable-head injection test (VHIT) performed in a multi-layered aquifer-aquitard system. The analytical solutions for the models are derived by Fourier transforms to estimate K and SS. The obtained K and SS values from the CHIT and VHIT were generally consistent, although the VHIT is recommended in practice. For the VHIT, estimating K using the Hvorslev analysis method under steady-state groundwater flow conditions resulted in a small relative error compared to the obtained result from the variable-head model. It was demonstrated that a certain relation existed between the constant-head and variable-head methods when the drawdown rate was lower than 1%, and so the constant-head method was applied to the VHIT data to determine K and SS. The synthetic error in the parameters was smaller than 10%, which indicated that the methods could be used interchangeably under these circumstances, thus simplifying the hydraulic parameter estimation process.

New analytical model for constant-head pumping: Considering rate-dependent factor at well screen

Non-Darcy flow due to pumping may occur at the well screen and yields some head loss. Unlike the wellbore skin yielding a constant head loss at the well, the studies in petroleum engineering indicate that the head loss due to the non-Darcy flow is proportional to the pumping rate. The head loss due to non-Darcy flow is quantified by a rate-dependent factor at the well screen. To our knowledge, such a head loss is never considered in the area of groundwater hydraulics. In light of this, this study develops a groundwater flow model for the constant-head pumping with a head loss expressed in terms of a rate-dependent factor at a fully penetrating well in a confined aquifer. A skin factor representing the head loss due to the presence of wellbore skin is also incorporated into the model. The consideration of the rate-dependent factor, however, would make the model nonlinear. The model has a steady-state flow equation with a time-dependent finite outer boundary to approximate the transient groundwater flow in the aquifer system. The solutions to the model for the drawdown and wellbore flowrate are developed and compared with the finite difference solutions. With the help of the present solutions, the sensitivity analyses of the aquifer drawdown and wellbore flowrate are made. The effects of the wellbore skin and non-Darcy flow on the drawdown are also investigated. The wellbore flowrate solution is then applied to estimate the aquifer parameters based on the field data from a constant-head injection test in a confined aquifer. The prediction of the present solution gives the best fit to the field measured data as compared with three existing solutions, indicating that the consideration of the rate-dependent factor improves the aquifer parameter estimation. The results of the parameter estimation also reflect the quality of the well installation.

Groundwater recharge, flow and stable isotope attenuation in sedimentary and crystalline fractured rocks: Spatiotemporal monitoring from multi-level wells

The use of stable isotopes from precipitation as tracers in unconsolidated porous media can be limited due to attenuation in the unsaturated zone, yet this process has been poorly constrained in fractured rock. The complexities of fractured rock systems necessitate the use of multi-level monitoring wells for the measurement of isotopic tracers with depth. These methods, however, are rarely employed in groundwater flow and recharge studies, particularly involving temporal isotope measurements in multiple rock types. To understand the attenuation of isotopic snowmelt tracers in fractured rock and explore surface connections and recharge, an investigation was undertaken at three geologically-distinct field sites in south-eastern Ontario, Canada. Results of constant head injection tests at 2-m intervals were used to identify and isolate high transmissivity zones (2–3 in each well) for the construction of eight multi-level wells (22 intervals) used for groundwater sampling. Deuterium and oxygen-18 were measured in rain (n = 64), snow (n = 67), soil water (n = 118) and groundwater (n = 594) on a bi-weekly to monthly basis over two seasonal snowmelt cycles (>1.5 years). In combination with stable isotopes, measurements of hydraulic head, groundwater temperature, specific conductance and two rounds of tritium sampling contributed to the development of a conceptual model for snowmelt recharge and flow in sandstone, limestone and crystalline rock. Seasonal variation of δ2H and δ18O was observed in all rock types indicating recent recharge and strong surface connections. The dampening and residence time of the snowmelt tracer increased with depth in crystalline rock. Tracer attenuation was highest in higher-porosity sedimentary rock and strong confining conditions were observed to inhibit recent recharge. Substantial isotopic attenuation measured in the overburden indicated that the strong snowmelt signal measured in groundwater stemmed from water infiltrating through areas with thin or no overburden. Identification of the periodic trends and distinct isotopic horizons in this study would not have been possible without the use of multi-level wells.

Hydrogeology Tests Performed in Shazaoyuan Candidate Site for China’s HLW Geodisposal

Rock mass hydraulic conductivity is one of the most important indexes for candidate site quantitative assessment of high-level radioactive waste disposal. 178 hydrogeology tests, mainly constant head injection test and pulse test, were performed in the 4 boreholes drilled in Shazaoyuan candidate site. Reliable hydraulic conductivity was obtained with transient curve matching methods. The result shows that the hydraulic conductivity was high heterogeneous; the maximum hydraulic conductivity was 9.30×10-8m/s and 93% of the sections were lower than 10-8m/s. Shazaoyuan candidate site can be inferred as one of the most potential sites for the geological disposal of China’s HLW in the view of low permeability.

Geomechanical Characterization of Zhangmu Soil-Rock Mixture Deposit

Zhangmu deposit is a typical soil-rock mixture (S-RM) deposit made up of very complicated inhomogeneous materials containing soil matrix and rock blocks of various sizes. The slope shows evidences of instability phenomena characterized by shallow landslides and several extensive cracks along slide crown, which seriously affects the life of local residents. In order to characterize the mechanical behavior of the deposit with evaluation of the actual strength parameters and permeability while taking into account the influence of the block proportion, seven test points were established for in situ S-RM and constant-head injection tests on a large scale. The results indicated a larger internal friction angle and lower cohesion for S-RM from in situ tests compared to tests results obtained from laboratory testing. Moreover, it was noted that the strength parameters were correlated with the block proportion by weight (WBP) of S-RM, while both internal friction angle and cohesion were observed to be strongly affected by a critical WBP threshold (70 %), which is in agreement with the common S-RM mechanical behavior. Furthermore, permeability increases with WBP increase to more than 70 %, denoting a similar threshold to the findings observed in strength characteristics.

Assessing Lakebed Hydraulic Conductivity and Seepage Flux by Potentiomanometer

Potentiomanometers (PMs) are commonly used to determine flux directions across interfaces between surface waters and aquifers. We describe a complementary function: estimating small-scale hydraulic conductivity (K) in a lakebed, using the constant-head injection test (CHIT) by Cardenas and Zlotnik (2003) with the PM designed by Winter et al. (1988). A piezometer with a small screen is inserted into the lakebed. Local head potential is obtained by measuring the head difference between the test point and the aquifer interface. The piezometer is then used for water injection. This technique is illustrated by measurements taken from Alkali Lake in the Sand Hills, Nebraska, United States. Lakebed K and seepage fluxes ranged from 0.037 to 0.090 m/d and Darcy velocities ranged from 0.004 to 0.027 m/d. Results were consistent with the supplementary data gathered using a modified CHIT and a cone penetrometer. The compact size of the device and the small volumes used for injection enable this method to estimate lakebed K values as low as 0.01 to 0.1 m/d, a range seldom explored in lake-aquifer interface systems.

Erratum/

GroundwaterVolume 45, Issue 2 p. 125-125 Free Access Erratum/ This article corrects the following: A Simple Constant-Head Injection Test for Streambed Hydraulic Conductivity Estimation M. Bayani Cardenas, Vitaly A. Zlotnik, Volume 41Issue 6Groundwater pages: 867-871 First Published online: December 13, 2005 First published: 29 January 2007 https://doi.org/10.1111/j.1745-6584.2006.00283.xAboutSectionsPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat In the Technical Note “A simple constant-head injection test for streambed hydraulic conductivity estimation,” M.B. Cardenas and V.A. Zlotnik (2003) presented a constant-head injection test (CHIT) method for mapping hydraulic conductivity of unconsolidated streambed sediments. There is a typographical error (namely, a misplaced parenthesis) in their equation (11) that could lead to erroneous values for the shape factor P . Equation (11) should read: (11) where A and B are coefficients originally defined by Bouwer and Rice (1976), b is the aquifer saturated thickness below the stream, l is the depth to the top of the screen from the stream-aquifer interface, L is the screen length and rw is the piezometer radius. Note that b in the natural logarithm of the second term in the right-hand side of the equation is also divided by rw. Not doing so not only results in incorrect values for P but may also result in negative arguments for the terms in the brackets leading to complex values after taking the natural logarithm. In general, this error does not change conclusions in the original note or the applicability of the CHIT method. We thank Charles F. Pitz of the Washington State Department of Ecology for bringing this error to our attention. References Bouwer, H., and R.C. Rice. 1976. A slug test for determining hydraulic conductivity of unconfined aquifers with completely of partially penetrating wells. Water Resources Research 12, no. 3: 423– 428. Wiley Online LibraryWeb of Science®Google Scholar Cardenas, M.B., and V.A. Zlotnik. 2003. A simple constant-head injection test for streambed hydraulic conductivity estimation. Ground Water 41, no. 6: 867– 871. Wiley Online LibraryCASPubMedWeb of Science®Google Scholar Volume45, Issue2March–April 2007Pages 125-125 ReferencesRelatedInformation

Hydraulic properties and scale effects investigation in regional rock aquifers, south-western Quebec, Canada

This paper reports on the characterization of hydraulic properties of regional rock aquifers carried out within a groundwater resources assessment project in the St. Lawrence Lowlands of south-western Quebec. To understand the aquifer behavior at both the fracture level and at field scale, hydraulic investigations were carried out using various aquifer tests. The groundwater flow at the local scale is controlled mostly by the fracture system. Results of the constant-head injection tests show a weak decreasing trend of hydraulic conductivity with depth indicating that a major part of the groundwater flow occurs in the first meters of the rock sequence. At the regional scale, the equivalent porous media approach is applicable. The hydraulic conductivity measurements were correlated to the scale of the aquifer tests expressed with the investigated aquifer volume. A simple interpolation procedure for the hydraulic conductivity field was developed based on the distance between field measurements and the tested aquifer volumes. The regional distribution of the hydraulic conductivity for the major fractured aquifer units indicates that dolostone is the most permeable whereas sandstone and crystalline rocks are the least permeable units.

A simple constant-head injection test for streambed hydraulic conductivity estimation.

A fast, efficient constant-head injection test (CHIT) for in situ estimation of hydraulic conductivity (K) of sandy streambeds is presented. This test uses constant-head hydraulic injection through a manually driven piezometer. Results from CHIT compare favorably to estimates from slug testing and grain-size analysis. The CHIT combines simplicity of field performance, data interpretation, and accuracy of K estimation in flowing streams.

Use of cumulative volume of constant‐head injection test to estimate aquifer parameters with skin effects: Field experiment and data analysis

In a silty sand aquifer, constant‐head injection tests (CHITs) were performed for the determination of aquifer parameters. In a CHIT the test well is overflowed by the injection of surface water. The difference between the injection flow and the overflow measured by an automated system directly yields the cumulative volume Vw(t) that enters the aquifer. Therefore the method of using Vw(t) in determining the aquifer transmissivity and the storage coefficient is developed, where well skin effects are taken into account. The semilog plot of t/Vw(t) is useful in indicating whether well skin exists around the constant‐head pumping well. If well skin is absent, the semilog plot of t/Vw(t) shows a straight line at large times, from which the transmissivity and the storage coefficient can be determined. If well skin exists, the semilog plot of t/Vw(t) exhibits two straight‐line sections occurring at small and large times, respectively. Then only the transmissivity can be determined from the slope of the large‐time straight line. In this event, aquifer drawdown/buildup observed at observation wells is needed for the determination of the storage coefficient. In fact, both the transmissivity and the storage coefficient can be determined with aquifer drawdown/buildup normalized with respect to Vw(t), regardless of well skin around the constant‐head pumping well. Once T and S are known, the skin factor of the constant‐head pumping well can be obtained from t/Vw(t).

Field Experiment and Data Analysis of a Constant-Head Injection Test with Skin Effects in a Low-Transmissivity Aquifer

In a confined, silty sand aquifer of low transmissivity, constant-rate pumping can rapidly dewater the pumping well without creating measurable drawdown at nearby observation wells. To overcome this difficulty, a constant-head test is performed by overflowing the test well by water injection. The difference between the injection rate and the overflow rate directly gives the cumulative volume Vw(t) entering the aquifer, which is characteristic of the aquifer hydrogeologic properties and can be used for parameter estimation. The field experiments include two constant-head injection tests, CHIT1 and CHIT2, performed at two different wells, respectively. Semilog plot of t/Vw(t) of CHIT2 indicates little or no skin, and the two unknown parameters of the storage coefficient and transmissivity can be uniquely determined in a similar way by the well-known Jacob semilog method. Semilog plot of t/Vw(t) of CHITl, however, shows the ex istence of well skin, and a curve matching method is developed for estimatiog the four pertinent parameters. Among them, the aquifer transmissivity can be uniquely determined while the skin transmissivity, the skin thickness, and the storage coefficient are obtained in appropriate ranges. To avoid non-unique estimates of aquifer parameters, therefore, the test well should be carefully constructed with complete and thorough well development to prevent skin region from happening. Due to the limitation of the site hydrogeology, only slug tests can be performed for the sake of validating transmissivity. The transmissivity values determined from the CHITs and from the slug tests are in good agreement, supporting the usefulness of the CHIT. The aquifer transmissivities estimated from CHITl and CHIT2 are within 14% difference, indicating that the aquifer is relatively homogeneous in the neighborhood of the two test wells.

Hydrogeological investigations at an experimental site in granite, south west England, in relation to the transport of radionuclides through fractured rock

Constant head injection tests and radioactive tracer experiments at an experimental site in the Carnmenellis granite in Cornwall have revealed a fracture permeability in which water movement is confined to discrete fractures separated by rock of low permeability. Data on flow path frequency, orientation, and effective hydraulic aperture, required for network modelling, have been obtained for a 700-m borehole, with additional hydraulic data from three other boreholes. In addition to fractures of “average” hydraulic conductivity, a small number of major hydraulic features (“main drains”) with major implications for radionuclide migration have been identified. A mean hydraulic conductivity for the granite investigated of 1.57 x 10 −7 msec −1 has been obtained, 2.08 x 10 −8 msec −1 if the major hydraulic features (with hydraulic conductivities as high as 10 −5 msec −1) are excluded.

Hydraulic testing of deep fractures in the Canadian shield

Boreholes ranging on length from 200 m to 1275 m have been tested for hydraulic parameters. A straddle packer system was used to provide transient pressure and temperature data. This equipment allowed the flexibility to undertake pulse, slug and drillstem tests, as well as ground water sampling. Constant head injection tests provided useful information for comparison purposes. Data acquisition, reduction and preliminary analysis was undertaken at the test site. Testing results show a general decrease in hydraulic conductivity with depth. Discrete fracture sets exhibit variations laterally and vertically of hydraulic conductivity of up to three orders of magnitude.