Long-term Pumping Test Research Articles

Scale Effect on Hydraulic Properties of Pore-Fissure Deep Rock Formations and Its Importance for the Mining Shaft-Sinking Process

The problem of hydraulic parameters estimation lies in the depth: the deeper the rock formation, the more expensive and difficult the field tests and samples acquisition, and the more challenging the technical issues. The article assesses the Triassic sandstone’s drainage potential at the stage of shaft sinking. It focuses on parameter analysis in varied scales, from drill-core sample laboratory testing, through a single well drawing test, to long-term pumping and recovery tests in the well with observation piezometers. The obtained results are compared to the values estimated in the past using different methods. Finally, the paper states whether it is reliable to forecast pore-fissure sandstone drainage potential based only on core samples’ laboratory tests. This research proved that lab tests underestimate pore-fissure rocks’ hydraulic parameters (mean hydraulic conductivity k = 9.79 × 10−8 m/s) tenfold more than long-term pumping tests (mean k = 4.45 × 10−7 m/s). However, it can be concluded that the group of so-called “witness samples”, 10% of all core samples with a top value of the hydraulic conductivity tested in the laboratory, can be representative of the aquifer and comparable to the values obtained in pumping tests. With this in mind, we recommend using the highest values of hydrogeological parameters from laboratory tests based on the worst-case scenario. Therefore, it is possible to forecast inflows to the shafts reliably. This methodology is recommended only for rocks of porous and pore-fissure character.

Estimating the specific yield of the Pampeano aquifer, Argentina, using superconducting gravimeter data

Specific yield is a key parameter for the sustainable management of unconfined aquifers, since it relates water-table fluctuations to aquifer storage-changes and thus impacts water supply. However, estimating specific yield is still a challenge due to theoretical and methodological limitations. Water-storage changes in the aquifer and in the overlying unsaturated soil profile cause local changes in gravity that can be recorded by high-precision superconducting gravimeters. In this work, a novel methodology to estimate specific yield from superconducting gravimeter data is presented. The proposed methodology is based on a hydrogravimetric model that estimates the gravity response due to the loss and gain of water mass in the soil profile using rainfall, water-table and air-temperature data. The model is applied to a study site of the Pampeano aquifer in Argentina where a continuous 1-year record of superconducting gravimeter measurements is available. The specific yield value obtained using this methodology is 0.11 ± 0.039, which is validated by means of a long-term pumping test performed at the study site. The proposed method constitutes a promising alternative to the available tools for estimating specific yield, by taking advantage of superconducting gravity data.

Inter-aquifer connectivity between Australia’s Great Artesian Basin and the overlying Condamine Alluvium: an assessment and its implications for the basin’s groundwater management

Coal seam gas (CSG), or coal bed methane, developments in sedimentary basins such as the Great Artesian Basin (GAB) in Australia, have the potential to impact on aquifers overlying and underlying the target coal formations. The extent to which this may occur depends upon the degree of hydrogeological connectivity between the coal formations and the surrounding aquifers or aquifer systems, with general implications for groundwater management. In southeast Australia, one such aquifer system, the Condamine Alluvium (CA), overlies the Walloon Coal Measures (WCM), which is a formation of the GAB and also a target for CSG production. To investigate the connectivity between the two systems, multiple lines of investigation were employed involving field investigations, data gathering and analysis (including reinterpretation of geology, multivariate hydrochemistry analysis, regional water-level mapping, drilling and coring across the contact zone, multiple piezometer installations, long-term pumping tests, groundwater-level monitoring and local-scale modelling). The study found a low level of connectivity between the GAB and the overlying CA. A layer of undifferentiated basement clay (referred to as the ‘transition zone’)—a mixture of alluvial clay and weathered basement—provides an effective impediment to flow across the CA and the underlying GAB formations. Results from the study potentially have wider application across the GAB and sedimentary basins where younger alluvial sediments associated with river systems frequently overlie the erosional surface.

Hydrogeological characterization to determine the deterioration of water quality in the a yarada media aquifer

The aim is to hydrogeologically characterize the La Yarada Media aquifer using the parameters by means of long-term pumping tests (Jacob and Theis recovery methods), as well as to characterize the water quality referred to the physicochemical parameters according to the current regulations and verify the possible deterioration of water quality in the aquifer. Between 2010 and 2015, 42 pumping tests were used, determining that the transmissivity to the southeast fluctuates between 602 and 4 235 m2/d (high to very high), indicating that the aquifer is free and has good hydraulic conditions, to the northwest it fluctuates between 53 and 494 m2/d, representing low and medium values, related to the tuffs of the Huaylillas Formation —being the area most affected by the continuous decrease in the piezometer level—. To the southeast, the permeability fluctuates between 13 and 86 m/d, high values unlike the sector located to the northwest where the permeability has a fluctuation between 1 and 9.8 m/d, representing low values. The overexploitation of the aquifer has caused that high and average values of transmissivity and permeability, now change to means and lows respectively in Settlement 4, since this static level was in the Quaternary deposits and has now descended, being in contact with the Huaylillas formation. Even more, it has caused the water quality to go from acceptable to bad, evidencing its deterioration that is related to the increase of the exploitation volumes and the decrease of the secondary recharge of water of good quality.

Hydrogeologic and Paleo-Geographic Characteristics of Riverside Alluvium at an Artificial Recharge Site in Korea

This study showed the hydrogeological characteristics of an alluvial aquifer that is composed of sand, silt, and clay layers in a small domain. It can be classified into a lower high-salinity layer and an upper freshwater layer and contains shells and remnant paleo-seawater (average 5000 μS/cm) due to sea level fluctuation. Geological and electrical conductivity logging, a long-term pumping test, and multi-depth water quality measurements were conducted at pumping, injection, and observational wells to evaluate the hydrogeologic properties, identify the optimal recharge rate, and assess artificial recharge. Using a hydraulic test, a large difference in drawdown and salinity appeared at the radially located observational wells because of the difference in hydraulic connectivity between the wells in the small study area. It was concluded that the hydraulic anisotropy and heterogeneity of the alluvial aquifer should be carefully examined when locating an injection well and considering the efficient design of artificial recharge.

Analysis of Saline Intrusion into a Coastal Aquifer: A Case History of Legacy Issues and Challenges to Water Security

Coastal aquifers are subject to seawater intrusion. Therefore, managing freshwater aquifers in coastal areas remain challenging. At present, determining safe yields from the coastal aquifers to prevent seawater intrusion is primarily based on the use of numerical simulation-optimization models or by the use of analytical models based on the Ghyben-Herzberg principle. This study examines the cause and effects of seawater intrusion into a coastal aquifer, Lincoln Basin in southern Eyre Peninsula, South Australia and shows that application of simple techniques would have prevented seawater intrusion. Three freshwater lenses, Lincoln A, B, and C of the Lincoln Basin, located about 13 km southwest of Port Lincoln township, have been developed as a town water supply source in 1960. The capacity of the basin has been assessed by three long-term pumping tests. Based on pump tests results, three areas were developed to supply 2×106 m3 per year distributed across three lenses as lens A : four wells to supply 0.84×106 m3, lens B: four wells to supply 0.5×106 m3 and lens C: four wells to supply 0.66 ×106 m3. Neither recharge to the freshwater lenses nor a water balance had been assessed, and a precautionary approach to groundwater extraction was not followed. The apparent driver for managing the basin was demand for the township. In this study, we assessed the recharge using two methods; water-table fluctuation (WTF) and the conventional chloride mass balance (CMB) method. Total recharge to the freshwater lenses is estimated at 1.6×106 m3 per year which is less than the average annual groundwater extraction from the basin during the 1961-1977 periods (average 2.14×106 m3). As a result mining of the groundwater storage has occurred in the basin leading to saline intrusion, upconing and lateral flow of brackish water into wellfield areas. The total volume extracted from the basin was 35×106 m3, which exceeded the average recharge over the 15 year period, 24×106 m3. Using analytical methods, the seawater/freshwater interface movement from its original position was estimated to be 35 m in lens A, 337 m in lens B and 188 m in lens C. For each pumping well at maximum discharge rate, the transient interface location directly underneath the well was calculated. This results in interface rises under pumping wells in lens A of 3.8 m, lens B of 0.5 m, and in lens C about 0.7 m. According to the risk-based groundwater allocation method, maximum extraction would have been as a proportion of 25% of the annual recharge. Thus, maximum annual abstraction limits for lens A, B and C would have been 210×103 m3, 72×103 m3 and 130×103 m3, totaling 412×103 m3.

Conceptualization of flow and transport in a limestone aquifer by multiple dedicated hydraulic and tracer tests

Limestone aquifers are of great interest as a drinking water resource in many countries. They often have a complex crushed and fractured geology, which makes the analysis and description of flow and transport processes in such aquifers a challenging task. In this study, the solute transport behavior including fracture-matrix interaction in hydrogeological units of a limestone aquifer in eastern Denmark was characterized by designing, conducting and interpreting six depth-specific tracer tests involving natural- and forced-gradient conditions with multiple tracers representing different diffusion properties. To determine flow parameters, the tracer tests were complemented by a comprehensive set of depth-specific borehole and hydraulic tests.Based on the tests, a new and stronger conceptual understanding was developed for the different aquifer units. The investigated limestone aquifer is composed of a glacially crushed unit and two fractured units, with calcarenitic and bryozoan limestone of similar hydraulic properties. Hydraulic tests revealed that the crushed unit has a lower hydraulic conductivity than the fractured limestone units, likely due to the crushed conditions with small limestone clusters and small-aperture fractures potentially filled with fine material.In the fractured limestone units, a distinct preferential flow and primary transport along major horizontal fractures was inferred from the tracer tests under forced-gradient conditions. The dominant horizontal fractures were identified on impeller flow logs and appear connected between wells, having an extent of up to several hundred meters. Connectivity between the aquifer units was investigated with a long-term pumping test and tracer tests, revealing restricted vertical flow and transport. A very pronounced hydraulic conductivity contrast between major fractures and matrix could also be inferred from the borehole and hydraulic tests, which is consistent with the findings from the tracer tests. The difference in the matrix diffusion behavior of the simultaneously injected tracers and a long tailing in the breakthrough curves revealed that matrix diffusion has a strong influence on the solute transport in the fractured limestone.

Groundwater Storage Change Estimation Using Combination of Hydrogeophysical and Groundwater Table Fluctuation Methods in Hard Rock Aquifers

This study aims to estimate the groundwater storage change of hard rock aquifers in the face of change. For this, the approach developed consisted initially in the implementation of 5 Magnetic Resonance Soundings (MRS) around the observation wells realized and monitored from 2014 to 2015 in the Sanon experimental site. In a second step, we determined the storage change using the MRS data and the water table fluctuation method. The MRS data show that the water content varies spatially from 4.5 to 1.3%. The maximum value is recorded at the central valley where a piezometric dome is observed. The specific yield varies from 2.4% in the central valley to 1.3% at the outlet. The renewed water resource is estimated at 116 mm in the central valley and 32 mm at the outlet, which corresponds respectively to 13 and 3% of the annual rainfall. The renewed water resource is consistent with the annual recharge. Thus, the combination of the MRS geophysical approach and water table fluctuation method is an efficient, fast and cheaper (compared with long-term pumping test) tool for the estimation of groundwater storage changes.

Taking into Account the Role of the Weathering Profile in Determining Hydrodynamic Properties of Hard Rock Aquifers

The present study aims at understanding the role of the structure and the geometry of the weathering profile on the hydrodynamic behavior of hard rock aquifers. We first described 2D geophysical cross sections of weathering profiles realized and validated on an experimental site. Next, we implemented five long-term pumping tests in wells drilled at various locations of these cross sections. Finally, we chose the appropriate analytical solutions to determine the hydrodynamic parameters in consistence with the structure and the geometry of the weathering profile. Results reveal that land covers, weathering type and thickness, presence of no flow boundaries, etc. are all factors that explain the flow regime, which appears therefore much less unpredictable. In other words, the 2D geophysical data are enough to locate the best permeable areas, or the areas where the structure of the aquifer without impervious boundaries and with leakage favor a good long-term behavior of the well. The values of aquifer’s transmissivity vary between 5.10−3 and 4.10−5 m2/s. The storage varies between 0.06 and 7.10−7. The variability of these parameters from site to site reflects the high heterogeneity of hard rock aquifers.

Analysis of multiwell pumping tests in a confined aquifer under variations in the production rate and atmospheric pressure

Problems of the interpretation of long-term multiwell pumping tests that account for variations in the production rate and atmospheric pressure are considered. The barometric efficiency and corrections of actual drawdowns are calculated for the Udomlya groundwater basin; spatiotemporal development of the depression cone is analyzed. The hydrogeodynamic parameters are used for calibration of a numerical model of the groundwater basin and prediction of the periodic compensation water system for recharging the cooling lakes of the Kalinin Nuclear Power Plant.

Long-term Pumping Test and Ert to Visualize Hydrogeologic Barriers in Heterogeneous and Karstic Coastal Aquifers

In coastal areas, groundwater may represent the main resource for human needs. The over-exploitation of coastal aquifers could cause seawater intrusion that induces depletion both in quality and quantity of the water resource, with no negligible environmental impacts. Moreover, locally geological heterogeneities of the aquifer can affect the flow and transport processes. In such cases, an integrated hydro-geophysical approach could provide useful information to evaluate the response of the aquifer and to estimate changes in the main hydraulic parameters such as transmissivity and permeability. In this study Electrical Resistivity Tomography (ERT) survey combined with traditional techniques of measuring the main groundwater parameters have been performed to assess the hydrogeological properties of a coastal heterogeneous aquifer. The conventional interpretation of pumping test drawdown allowed to detect a hydraulic barrier located to a specific distance with respect to the pumping well; furthermore, the transmissivity of the portion of aquifer involved in the pumping and the corresponding changes of its hydraulic conductivity due to the presence of the barrier has been estimated. Confirming the conventional interpretation of the pumping test drawdowns, the ERT image was able to locate the hydraulic barrier over space, visualizing a high resistive body, located below the water table.

Impact of a very low enthalpy plant on a costal aquifer: a case study in Southern Italy

The interest in the low-enthalpy geothermal resources is growing, owing to its wide availability, and the possibility of overcoming the problems related to energy storage. Among the low-enthalpy plants, the installation in coastal areas of the open-loop groundwater heat pump (GWHP) systems, that use groundwater as the geothermal fluid, is particularly attractive because of the presence of shallow aquifers. Nevertheless, these aquifers are often affected by seawater intrusion, so strict monitoring before GWHP installation is needed to check the feasibility of the plant. This work reports a detailed quali-quantitative characterization of a costal aquifer, in Southern Italy, for its exploitation as a very low enthalpy geothermal resource. The main groundwater parameters were monitored to assess the groundwater suitability to be used as geothermal fluid. A long-term pumping test, simulating the designed open-loop GWHP system, was performed to evaluate its potential impact on seawater intrusion. The results revealed that the open-loop GWHP plant do not affect the quali-quantitative equilibrium of the studied coastal aquifer. Furthermore, the study demonstrated that the used methodological approach is proper for the early assessment of the feasibility of the GWHP plant without affecting the seawater intrusion processes, and with minimum impact.

Estimating the in situ porosity of sandy soils sampled in boreholes

This paper deals with sandy aquifers. It explains how to use parameters of borehole samples, and data of mechanical tests performed in boreholes, to assess the in situ values of porosity. The concepts of maximum and minimum void ratios, emax and emin, are presented with the results of studies trying to predict their values. Predictive equations are proposed to link the values of emax and emin to that of the coefficient of uniformity CU of the grain size distribution curve, and the roundness factor RF of solid particles. Once the values of emax and emin have been estimated, those of the in situ void ratio e and porosity n can be assessed from the data of in situ mechanical tests, for example split spoon tests. An example evaluation is presented for an unconfined sand aquifer, which was investigated using boreholes, field tests, laboratory tests, slug tests in monitoring wells, and a long-term pumping test.

Numerical modeling of the hydraulic signatures of horizontal and inclined faults

Pumping tests in discontinuous media are commonly interpreted using radial/non-radial flow analytical models, which do not account for a large range of multistage real signatures that combine both flow types. The term radial is employed in Barker’s sense, referring to the cross-flow area growth with a flow dimension (n) equal to 2, while multistage refers to a flow response of several time periods with successive n values. Synthetic domains are used to numerically investigate the flow behaviour of faulted media, specifically the effect of fault inclination on multistage signatures. Simulations are performed using single faults surrounded by a permeable matrix to characterize drawdown series and to identify hydrodynamic scenarios associated with some diagnostic multistage n sequences. The n sequence 2 – < 2 – 2 results from interactions between the matrix and a horizontal to weakly inclined fault, while 2 – 1.5 – 2 corresponds to a higher fault inclination and is a combination of the generalized horizontally and vertically faulted models. These results improve the interpretation of ambiguous drawdown series from long-term pumping tests. This provides a better hydraulic characterization of faulted environments, allowing assessment of fault and matrix properties such as fault inclination. The approach is successfully tested on real datasets.

Groundwater abstraction through river-bed collector well: a case study based on geophysical and hydrological investigation

Owing to lack of rational basis, design of radial collector (RC) well often becomes a confusing task for the designers arising out of a wide difference between the anticipated yield and the observed yield from RC wells. In this study, a long-term pumping test was carried out at three different sites (near Kharagpur City, India) on Kasai river bed and in its close proximity in order to design sub-surface RC well for water supply to Kharagpur City. The appropriate hydrological approaches were employed to estimate values of aquifer parameters, viz. storage coefficient (S) and coefficient of transmissibility (T) for the aforesaid sites under study, which were found to be in the ranges of 0.00129–0.068 and 810–2573 m3/day-m, respectively. This article reports the rationality of design methods of sub-surface RC well, based on image theory and model study, which was adequately supported with geophysical investigations. An RC well-system was designed following the aforesaid two methods and was constructed at the proposed Site-II, which was found to be the most favourable one based on remote sensing survey, geophysical studies, and hydrological investigations. In the trial operating stage of the RC well, commissioned at Site II, the observed yield was compared with the designed (predicted) values. Trial field (yield) test data at Site II showed that the designed yield of 24 million litres per day (MLD) based on model study was closer to field data (21 MLD) than that (8 MLD) obtained based on image theory.

ICONE19-43560 Interpretation of Hydrogeological Characteristics based on Data from Long-Term Cross-Hole Pumping Test

ICONE19-43560 Interpretation of Hydrogeological Characteristics based on Data from Long-Term Cross-Hole Pumping Test

Low-temperature geothermal potential of the flooded Gaspé Mines, Québec, Canada

The low-temperature geothermal potential of the flooded Gaspé Mines, near Murdochville, Québec, Canada, has been estimated from a long-term pumping test and numerical groundwater flow modelling. A former mining shaft was used to pump water for 3 weeks at a rate averaging 0.062 m 3/s (3720 L/min). A mean recovery temperature equal to 6.7 °C and a maximum drawdown of 3.63 m were observed during this test. The observed drawdown was reproduced with a three-dimensional finite element model that simulates groundwater flow through the mine workings and surrounding rock mass. The model was then used to simulate longer-term pumping performed for heat recovery. Modelling results combined with a simplified energy balance calculation suggest that a sustainable energy extraction rate is attained at a pumping rate of 0.049 m 3/s (2940 L/min), with a corresponding geothermal energy production potential of 765 kW, assuming a return water temperature of 3 °C. This energy could be extracted with heat pumps and used for space heating at the town's industrial park.

Flow to a Well in a Five‐Layer System with Application to the Oxnard Basin

Nearly 40 years ago, Neuman (1968) developed an analytical solution for drawdown in a system of three aquifers separated by two aquitards when one of the aquifers is pumped at a constant rate. Whereas the simpler case of two aquifers separated by one aquitard has been presented by Neuman and Witherspoon (1969a), the full five-layer solution has not been previously evaluated. We do so here using numerical inversion of its Laplace-transformed version and present selected results graphically in dimensionless form. The solution demonstrates that the effect of pumping propagates across all five layers, adding emphasis to a question previously raised by Neuman and Witherspoon about the validity of leaky aquifer theories that disregard drawdowns in unpumped aquifers. A large-scale, long-term pumping test spanning three aquifers separated by two aquitards near Oxnard, California, has been conducted and analyzed by Neuman and Witherspoon (1972). They evaluated the vertical hydraulic diffusivities of the aquitards using the Neuman-Witherspoon ratio method and their specific storage values on the basis of laboratory consolidation tests. We reinterpret the Oxnard pumping test by coupling the five-layer analytical solution of Neuman (1968) with the parameter estimation code PEST (Doherty 2002) and validate our results against drawdowns from a subsequent pumping test at the site. Our parameter estimates compare favorably with those of Neuman and Witherspoon (1972).

The Channel Network Model and Field Applications

AbstractThe Channel Network model describes the fluid flow and solute transport in fractured media. The model is based on field observations, which indicate that flow and transport take place in a threedimensional network of connected channels. The channels are generated in the model from observed stochastic distributions and solute transport is modelled taking into account advection and rock interactions, such as matrix diffusion and sorption within the rock. The most important site-specific data for the Channel Network model are the conductance distribution of the channels and the flow-wetted surface. The latter is the surface area of the rock in contact with the flowing water. These parameters may be estimated from hydraulic measurements. For the Äspö site, several borehole data sets are available, where a packer distance of 3 metres was used. Numerical experiments were performed in order to study the uncertainties in the determination of the flowwetted surface and conductance distribution. Synthetic data were generated along a borehole and hydraulic tests with different packer distances were simulated.The model has previously been used to study the Long-term Pumping and Tracer Test (LPT2) carried out in the Äspö Hard Rock Laboratory (HRL) in Sweden, where the distance travelled by the tracers was of the order hundreds of metres. Recently, the model has been used to simulate the tracer tests performed in the TRUE experiment at HRL, with travel distance of the order of tens of metres. Several tracer tests with non-sorbing and sorbing species have been performed.

Analysis of a long-term pumping and tracer test using the channel network model

Water flow and solute transport in a fractured medium are described by the Channel Network model, CHAN3D. In the field and in the model, most of the flow and transport take place in fracture zones. CHAN3D was used to simulate a long-term pumping and tracer test called LPT2. In the first simulations, no calibrations, conditioning or parameter adjustments were made to better fit the experimental results. Instead, as much as possible of the available field data were used. In six different paths the simulations predicted breakthrough that should be observable. However, only two of the performed tracer tests resulted in breakthrough of solutes. Some possible reasons for the scant recovery is discussed. In the analysis of LPT2, the impact of the flow rates at the injection positions, flow porosity and interaction with the rock matrix were studied.