Artículos de revistas: "Aquitard"

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Wang, Quanrong, Junxia Wang, Hongbin Zhan y Wenguang Shi. "New model of reactive transport in a single-well push–pull test with aquitard effect and wellbore storage". Hydrology and Earth System Sciences 24, n.º 8 (18 de agosto de 2020): 3983–4000. http://dx.doi.org/10.5194/hess-24-3983-2020.

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Abstract. The model of single-well push–pull (SWPP) test has been widely used to investigate reactive radial dispersion in remediation or parameter estimation of in situ aquifers. Previous analytical solutions only focused on a completely isolated aquifer for the SWPP test, excluding any influence of aquitards bounding the tested aquifer, and ignored the wellbore storage of the chaser and rest phases in the SWPP test. Such simplification might be questionable in field applications when test durations are relatively long because solute transport in or out of the bounding aquitards is inevitable due to molecular diffusion and cross-formational advective transport. Here, a new SWPP model is developed in an aquifer–aquitard system with wellbore storage, and the analytical solution in the Laplace domain is derived. Four phases of the test are included: the injection phase, the chaser phase, the rest phase and the extraction phase. As the permeability of the aquitard is much smaller than the permeability of the aquifer, the flow is assumed to be perpendicular to the aquitard; thus only vertical dispersive and advective transports are considered for the aquitard. The validity of this treatment is tested against results grounded in numerical simulations. The global sensitivity analysis indicates that the results of the SWPP test are largely sensitive (i.e., influenced by) to the parameters of porosity and radial dispersion of the aquifer, whereas the influence of the aquitard on results could not be ignored. In the injection phase, the larger radial dispersivity of the aquifer could result in the smaller values of breakthrough curves (BTCs), while there are greater BTC values in the chaser and rest phases. In the extraction phase, it could lead to the smaller peak values of BTCs. The new model of this study is a generalization of several previous studies, and it performs better than previous studies ignoring the aquitard effect and wellbore storage for interpreting data of the field SWPP test reported by Yang et al. (2014).

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2

Shaw, R. Joel y M. Jim Hendry. "Hydrogeology of a thick clay till and Cretaceous clay sequence, Saskatchewan, Canada". Canadian Geotechnical Journal 35, n.º 6 (1 de diciembre de 1998): 1041–52. http://dx.doi.org/10.1139/t98-060.

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Clay-rich glacial till and Cretaceous clay are common throughout the Interior Plains of North America. Quantifying groundwater flow through these aquitards has implications for solute transport in aquitards and protection of underlying aquifers. Groundwater flow through a two-tiered aquitard system was investigated using laboratory and field methods at a test site in Saskatchewan, Canada. The aquitard system consists of 80 m of uniform, plastic clay-rich Battleford till (deposited 12-18 ka BP) disconformably overlying 77 m of late Cretaceous plastic marine clay (Snakebite Member, deposited 70-72 Ma BP). The upper 3-4 m of till is oxidized and fractured whereas the remainder is unoxidized. For the scales investigated, results suggested that hydraulic conductivity, K, is independent of scale for relatively thick till and clay bedrock deposits. Analysis of slug tests in the unoxidized till and laboratory tests on cores of unoxidized till yielded geometric mean K values of 5.4 × 10-11 and 2.7 × 10-11 m/s, respectively. Laboratory K tests of clay samples yielded a geometric mean K of 4.3 × 10-12 m/s. Bulk K of the clay was estimated to be 2.3 × 10-12 m/s assuming steady-state flow through the till and clay. The present-day groundwater velocity through the aquitard system was estimated to be between 0.5 and 0.8 m/10 ka downward based on the measured K values, measured hydraulic gradients, and measured porosities. Results suggested that pore water in much of the till was introduced during or shortly after glaciation.Key words: hydrogeology, aquitards, Cretaceous clay, Battleford till, hydrogeologic properties, geotechnical properties.

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3

Trieu, Duc Huy, Ngoc Thanh Tong, Van Lam Nguyen, Ba Quyen Pham, Dai Phuc Hoang y Hoai Thu Trinh. "Classification of hydrogeological structure along the Red River in the Hanoi area". Tạp chí Khoa học và Công nghệ Biển 21, n.º 3 (30 de septiembre de 2021): 299–310. http://dx.doi.org/10.15625/1859-3097/16431.

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Hanoi city has abundant groundwater, supplemented by the surface water (mainly Red River) all year round, and the extensive shallow aquifers, which are easily exploited by large-diameter wells. There always exists some open hydrogeological windows in the Red River area with an open structure; therefore, the groundwater has a strained hydraulic relationship with the Red River water system Along the Red River from Ba Vi to the end of Phu Xuyen district, there are nine regions with three types and four sub-types of different hydrogeological structures. In particular, the sub-type I-A of the groundwater has a tight hydraulic correlation with the Red River since the hydrogeological structure of the Red River bottom includes three aquifers: Holocene (qh), upper Pleistocene (qp2), and lower Pleistocene (qp1) that constructs a hydraulic system. The sub-type I-B is characterized by the hydrogeological structure at the Red River bottom, including the aquitard in Vinh Phuc and two aquifers qp2 and qp1, which form a hydraulic system. The sub-type II-A is distinguished by the fact that the Red River crosses the aquifer qh; there are no aquitards between the aquifer qh and qp2 to form a hydraulic system; the aquitard separates the aquifer qp1. The sub-type II-B is identified by the fact that the Red River crossing the aquifer qh; there is an aquitard between the aquifer qh and qp2; there are no aquitards between the aquifer qp2 and qp1 so that can create a hydraulic system. Type III has a solid existence of both aquifers and aquitards; thus, the hydraulic relationship between the Red River and the aquifers qp2 versus qp1 is inferior.

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4

Murray, Titus A. y William L. Power. "A framework for inclusion of faults in coal seam gas risk assessments". APPEA Journal 61, n.º 2 (2021): 695. http://dx.doi.org/10.1071/aj20066.

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Assessments for coal seam gas (CSG) projects may be required to consider the potential hydrological impacts of faults on surface and near-surface groundwater assets. This study presents three distinct end-member geological scenarios and outlines methods for characterising fault-related groundwater flow within a risk assessment context. Scenario 1: a regional aquitard isolates the water assets from the coal seams. There is little risk of leakage across the aquitard because there are no faults, or because the faults have maximum displacements less than the thickness of the aquitard. Scenario 2: a region-wide aquitard is not present, and the seams and the groundwater assets are located within the same groundwater system. In this scenario, CSG development may cause pressure changes to propagate parallel to the strike and dip of the fault in the fault damage zones. Scenario 3: regional aquitard(s) are present, but larger displacement faults breach the aquitards, allowing for possible combinations of across-fault connections between the different aquifers, and between aquifers and the coal seams. In this scenario, potential flow pathways between the groundwater and the CSG field need to be characterised using Allan Maps (fault plane profiles). It is essential to compare calculated flow rates of any new or potentially new flow pathways with the predevelopment flow regime. It is also important to recognise that flow estimates are best made using a Darcy’s law treatment for flow across fault zones and within the aquifers, and a Snow’s law treatment (discrete fracture network) for flow through fractures in fault damage zones.

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5

Burbey, Thomas J. "Parameter estimation of a multiple aquifer-aquitard system from a single extensometer record: Las Vegas, Nevada, USA". Proceedings of the International Association of Hydrological Sciences 382 (22 de abril de 2020): 51–56. http://dx.doi.org/10.5194/piahs-382-51-2020.

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Abstract. The purpose of this investigation is to develop a semi-analytical procedure for quantifying aquifer and aquitard properties from a single extensometer record in lieu of the time-consuming development of more complex numerical models to quantify and constrain these parameter values. Despite a limited 12-year record and the fact that water levels both decline and increase on an annual basis, estimates of both aquifer and aquitard parameters have been reasonably estimated at the Lorenzi extensometer site in Las Vegas Valley, Nevada when compared to the estimates developed numerically. The key factors that allow for accurate estimates of elastic and inelastic skeletal specific storage and hydraulic conductivity of the aquitards and elastic specific storage and hydraulic conductivity of the intervening aquifers is the presence of pumping cycles at multiple frequencies, and measured heads at all the aquifer units covered in the extensometer record and the inherent assumption that the aquitards have identical hydrologic characteristics and are homogeneous and isotropic. This latter assumption is also a usual limitation in numerical modelling of these settings because of the complex temporal head relationships occurring within the aquitards that are rarely, if ever, measured.

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6

Chuang, M. H., C. S. Huang, G. H. Li y H. D. Yeh. "Groundwater fluctuations in heterogeneous coastal leaky aquifer systems". Hydrology and Earth System Sciences Discussions 7, n.º 4 (9 de julio de 2010): 4473–99. http://dx.doi.org/10.5194/hessd-7-4473-2010.

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Abstract. In the past, the coastal leaky aquifer system, including an unconfined aquifer on the top, a confined aquifer at the bottom, and an aquitard in between, was commonly assumed to be homogeneous and of an infinite extent in the horizontal direction. The leaky aquifer system may however be nonhomogeneous and of a finite extent due to variations in depositional and post depositional processes. Thus, in the paper, the leaky aquifer system is divided into several horizontal regions for simulating the heterogeneity involved in both the confined aquifer and aquitard. A one-dimensional analytical model is developed for describing the head fluctuation in such a heterogeneous leaky aquifer system. The head of the upper unconfined aquifer is assumed to remain constant. It is found that both the length and location of the discontinuous aquitards presented in the coastal area have significant effects on the amplitude and phase shift of the head fluctuation in the confined aquifer. In addition, the influences of both the heterogeneous aquifer and aquitard on the spatial head distribution are investigated.

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7

Burt, Abigail. "Three-dimensional hydrostratigraphy of the Orangeville Moraine area, southwestern Ontario, Canada". Canadian Journal of Earth Sciences 55, n.º 7 (julio de 2018): 802–28. http://dx.doi.org/10.1139/cjes-2017-0077.

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Regional-scale three-dimensional modelling of Quaternary sediments in the Orangeville Moraine area of southwestern Ontario has been completed as part of the Ontario Geological Survey groundwater initiative and provides an improved understanding of the glacial history and conceptual hydrostratigraphic framework for that region. Older (Marine Isotope Stage (MIS) 3–5) diamicton, glaciolacustrine, glaciofluvial, and rare nonglacial deposits forming regional aquitards and local aquifers are found in the northwestern part of the area. Catfish Creek Till, deposited during the Last Glacial Maximum (LGM) (MIS 2), forms a key aquitard and stratigraphic marker at depth. Diamicton, fine-textured glaciolacustrine sediments, and the gravel, sand, and silt conduit and subaqueous fan sediments that constitute the overlying Orangeville Moraine were deposited in an ice-walled lake formed between ice lobes during retreat from the LGM. Diamicton deposited during late-glacial ice margin fluctuations forms the upper aquitard unit and buries the edges of the moraine. The Orangeville Moraine is the largest aquifer in the area, and is partially confined by the upper tills. Thick fine-textured glaciolacustrine deposits, Catfish Creek Till, and older aquitards separate the moraine from bedrock aquifers across most of the area. Depending on hydraulic gradients, buried bedrock valleys with gravel and sand fills have the potential to recharge the bedrock aquifer.

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8

Chuang, M. H., C. S. Huang, G. H. Li y H. D. Yeh. "Groundwater fluctuations in heterogeneous coastal leaky aquifer systems". Hydrology and Earth System Sciences 14, n.º 10 (11 de octubre de 2010): 1819–26. http://dx.doi.org/10.5194/hess-14-1819-2010.

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Abstract. In the past, the coastal leaky aquifer system, including two aquifers and an aquitard between them, was commonly assumed to be homogeneous and of infinite extent in the horizontal direction. The leaky aquifer system may however be heterogeneous and of finite extent due to variations in depositional and post depositional processes. In this paper, the leaky aquifer system is divided into several horizontal regions for the heterogeneous aquitard and underlying aquifer. A one-dimensional analytical model is developed for describing the head fluctuation in such a heterogeneous leaky aquifer system. The hydraulic head of the upper unconfined aquifer is assumed constant. It is found that both the length and location of the discontinuous aquitards presented in the coastal area have significant effects on the amplitude and phase shift of the head fluctuation in the lower aquifer. In addition, the influence of the formation heterogeneity on the spatial head distribution is also investigated.

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9

Burbey, Thomas J. "Extensometer forensics: what can the data really tell us?" Hydrogeology Journal 28, n.º 2 (7 de diciembre de 2019): 637–55. http://dx.doi.org/10.1007/s10040-019-02060-6.

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AbstractExtensometer data have an advantage over satellite-based data for monitoring land subsidence in that extensometer data provide continuous measurements (hourly or better temporal resolution) at very high precision (several tens of microns) over a known depth interval; the latter is important for isolating groundwater pumping from other causes of land subsidence attributed to tectonics or eustatic adjustments in the Earth’s crust. This investigation aims to identify a semi-analytical procedure for quantifying aquifer and aquitard properties from a single extensometer record in lieu of the time-consuming development of more complex numerical models to quantify and constrain these parameter values. In spite of a limited 12-year record and the fact that water levels both decline and increase on an annual basis, this study successfully and reasonably estimated both aquifer and aquitard parameters at the Lorenzi extensometer site in Las Vegas Valley, Nevada (USA), when compared to the estimates developed numerically. The key factors that allow for estimates of elastic and inelastic skeletal-specific storage and hydraulic conductivity of the aquitards and elastic specific storage and hydraulic conductivity of the intervening aquifers is the presence of pumping cycles at multiple frequencies, and measured heads at all the aquifer units covered in the extensometer record. There is an inherent assumption that the aquitards possess the same hydrologic characteristics and are homogeneous and isotropic. This assumption is also a usual limitation in numerical modeling of these settings because of the complex temporal head relationships occurring within the aquitards that are rarely, if ever, measured.

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10

Husain, Muin M., John A. Cherry, Scott Fidler y Shaun K. Frape. "On the long-term hydraulic gradient in the thick clayey aquitard in the Sarnia region, Ontario". Canadian Geotechnical Journal 35, n.º 6 (1 de diciembre de 1998): 986–1003. http://dx.doi.org/10.1139/t98-057.

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Much of the southwestern part of Ontario between Lake Huron and Lake Erie has a thin freshwater aquifer overlain by an aquitard of Late Pleistocene clayey glaciolacustrine deposits and underlain by a thick Devonian shale aquitard. In a large area east of the St. Clair River, where the Quaternary aquitard is 30-50 m thick, groundwater of Pleistocene origin (identified by 18O and 2H signature) occurs in the aquifer and in the bottom part of the Quaternary aquitard. Numerous piezometer nests in the aquitard show a downward hydraulic gradient with depth. In some areas, the aquitard has downward gradients only in the upper part and upward gradient in the lower part, indicating a transient condition. The piezometer nests in the clayey aquitard also show an increase in Cl- concentration with depth. Long-term piezometer monitoring at two sites show a major shift in the aquitard hydraulic gradient since 1983 and a large rise in head in the underlying aquifer. Analyses of initial aquifer water levels, reported in well drilling records, indicate a large decline in the potentiometric surface of the aquifer between the 1940's and the 1970's followed by a recent rise in the surface in part of the region. This pattern is consistent with well drilling and water use records indicating that 7000 wells were installed in the aquifer in the three decades since 1940 and that groundwater use has greatly diminished in the past 10-15 years due to rural pipeline distribution of lake and river water. The hydraulic gradient in the aquitard is slowly adjusting to the rise in the aquifer potentiometric surface. One-dimensional solute transport modelling provides close matches to the vertical profiles of Cl- migrating upward from the aquifer since deglaciation, 15 000 - 18 000 years before present, by diffusion with little or no advection. The lack of advection indicates a near-neutral long-term hydraulic gradient. As the withdrawal rate of water from the aquifer continues to decline, it is expected that the hydraulic head in the aquitard in much of the area westward of the recharge area will continue to adjust for many decades.Key words: clay, aquitard, aquifer, water use, hydraulic gradient.

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11

Li, Zhaofeng, Zhifang Zhou, Mingyuan Li, Boran Zhang y Beibing Dai. "Delayed Drainage of a Largely Deformed Aquitard due to Abrupt Water Head Decline in Adjacent Aquifer". Geofluids 2018 (21 de noviembre de 2018): 1–12. http://dx.doi.org/10.1155/2018/2326491.

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A governing equation of drawdown was put forward to describe the one-dimensional large-strain consolidation behavior of an aquitard without consideration of the creeping effect. An analytical solution was derived to characterize the drawdown variation in the aquitard subjected to sudden hydraulic head decline in adjacent confined aquifer. The characteristics of the groundwater dynamics and water balance in the aquitard have been analyzed based on the analytical solution. A comparison analysis of results has been made between the large-strain theory and the classical small-strain theory. The type-curve fitting method was used to determine the hydrogeological parameters, on the basis of the observed variations of aquitard deformation with time. The analytical solution was thus validated by a comparison with the observed experimental results. It is found that the water drainage of aquitard is obviously delayed in response to the water head decline in the adjacent aquifer. All delayed water release from the aquitard terminates when the consolidation time reaches the value of l2/cv0. The aquitard deformation predicted by the large-strain theory is less than that given by the small-strain theory, and the prediction discrepancy of these two theories increases with the increasing soil compressibility.

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12

Anochikwa, Collins Ifeanyichukwu, Garth van der Kamp y S. Lee Barbour. "Interpreting pore-water pressure changes induced by water table fluctuations and mechanical loading due to soil moisture changes". Canadian Geotechnical Journal 49, n.º 3 (marzo de 2012): 357–66. http://dx.doi.org/10.1139/t11-106.

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Pore pressures within saturated subsurface formations respond to stress changes due to loading as well as to changes in pore pressure at the boundaries of the formation. The pore-pressure dynamics within a thick aquitard in response to water table fluctuations and mechanical loading due to soil moisture changes have been simulated using a coupled stress–strain and groundwater flow finite element formulation. This modelling approach isolates the component of pore-pressure response of soil moisture loading from that caused by water table fluctuations, by using a method of superposition. In this manner, the contributions to pore-pressure fluctuations that occur as a result of surface moisture loading (e.g., precipitation, evapotranspiration) can be isolated from the pore-pressure record. The required elastic stress–strain properties of the aquitard were obtained from the measured pore-pressure response to barometric pressure changes. Subsequently, the numerical simulations could be calibrated to the measured response by adjusting only the hydraulic conductivity. This paper highlights the significance of moisture loading effects in pore-pressure observations and describes an efficient technique for obtaining in situ stress–strain and hydraulic properties of near-surface aquitards.

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13

Husain, Muin M., John A. Cherry y Shaun K. Frape. "The persistence of a large stagnation zone in a developed regional aquifer, southwestern Ontario". Canadian Geotechnical Journal 41, n.º 5 (1 de septiembre de 2004): 943–58. http://dx.doi.org/10.1139/t04-040.

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An extensive groundwater zone of exceptionally negative δ18O (17.5 to 16.0) exists in a thin, regional, freshwater aquifer between Lake St. Clair and the southern shore of Lake Huron in southwestern Ontario. The zone occurs at the interface between the overlying thick Quaternary clay aquitard of glaciolacustrine origin and the underlying bedrock shale. This isotope signature, which is 7 more negative (lighter) than modern water, indicates a Late Pleistocene origin of the aquifer water. This zone occurs only where the Quaternary aquitard is greater than 35 m thick. In the Quaternary aquitard, the Pleistocene isotope signature extends upward from the aquifer and then has a gradational transition to signature resembling modern water (10) near the ground surface. This regional-scale study of the aquiferaquitard system indicates that the pattern of flow of the aquifer has allowed the persistence of the Pleistocene groundwater since the aquitard was deposited approximately 10 000 years before present. As part of the regional study, a two-dimensional groundwater flow model was used to assess the origin and persistence of the Pleistocene zone under natural conditions. The persistence of the Pleistocene zone was also assessed based on water budgets prepared from aquifer use history and aquiferaquitard parameters. Our study finds that the low yield and poor quality of groundwater in this zone have caused minimal use, resulting in the persistence of the Pleistocene groundwater since the beginning of major aquifer use in the 1940s.Key words: regional aquifer, aquitard, Pleistocene water, stagnation, aquifer use.

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14

Macumber, Phillip G. "Hydraulically Disconnected Rivers in the Highlands and Southern Riverine Plain of S.E Australia". Sustainability 15, n.º 1 (3 de enero de 2023): 865. http://dx.doi.org/10.3390/su15010865.

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The rivers of south-eastern Australia flow within a complex meander tract (Coonambidgal Formation) formed by phases of Quaternary stream activity. Pumping tests, hydrochemistry and groundwater monitoring of the Campaspe, Loddon and Murray River Valleys show that for significant parts of their courses, the rivers and their associated strip aquifers form a single integrated hydraulic unit perched above and disconnected from the regional water table by an underlying aquitard developed at the top of a varyingly thick and temporally dynamic vadose zone. Loss to the regional aquifer is not restricted to the riverbed but covers the entire width of the Coonambidgal Formation aquifer, which is one or two orders of magnitude greater. River-bed flux is not a measure of net river loss. Through diffusion and dispersion from the overlying saturated zone, aquitard enhancement or development is augmented by chemical processes active towards the top of the vadose zone. Unlike river-bed clogging, chemical clogging of aquifers is progressive and permanent. Post-European instability in the studied groundwater systems has seen catchment wide groundwater rises of up to 0.25 m/y. or 25 metre over the last century. Under the pre-existing norm of deeper water tables, disconnected streams would have been more numerous with the present aquitards being a legacy of that regime.

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15

Rowe, R. Kerry y Prebaharan Nadarajah. "Evaluation of the hydraulic conductivity of aquitards". Canadian Geotechnical Journal 30, n.º 5 (1 de octubre de 1993): 781–800. http://dx.doi.org/10.1139/t93-070.

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The evaluation of the bulk vertical hydraulic conductivity of an aquitard based on its response to the pumping of an adjacent aquifer is examined using Biot's theory. Consideration is given to the errors in interpretation of the results of pumping tests which arise as a result of the time lag associated with different types of piezometers as well as the length of the piezometer. Factors to allow for correction of these errors are presented. Although these factors are originally developed for isotropic aquitards, they can be used for anisotropic aquitards with appropriate modifications described in the paper. A comparison is made between the results obtained from diffusion theory (as assumed in the development of techniques currently used in practice) and the more rigorous Biot's theory. The application of the technique is illustrated by two examples. Key words : hydraulic conductivity, field test, analysis, pumping test, piezometers, anisotropy.

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16

Priestley, Stacey C., Tavis Kleinig, Andrew J. Love, Vincent E. A. Post, Paul Shand, Martin Stute, Ilka Wallis y Daniel L. Wohling. "Palaeohydrogeology and Transport Parameters Derived from 4He and Cl Profiles in Aquitard Pore Waters in a Large Multilayer Aquifer System, Central Australia". Geofluids 2017 (2017): 1–17. http://dx.doi.org/10.1155/2017/9839861.

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A study of chloride and 4He profiles through an aquitard that separates the Great Artesian Basin from the underlying Arckaringa Basin in central Australia is presented. The aquitard separates two aquifers with long water residence times, due to low recharge rates in the arid climate. One-dimensional solute transport models were used to determine the advective flux of groundwater across the aquitard as well as establish any major changes in past hydrological conditions recorded by variations of the pore water composition. This in situ study showed that both diffusion and slow downward advection (vz=0.7 mm/yr) control solute transport. Numerical simulations show that an increase in chloride concentration in the upper part of the profile is due to a reduction in recharge in the upper aquifer for at least 3000 years. Groundwater extraction since 2008 has likely increased chloride and 4He concentrations in the lower aquifer by pulling up water from deeper layers; however, there has been insufficient time for upward solute transport into the pore water profile by diffusion against downward advection. The transport model of 4He and chloride provides insight into how the two aquifers interact through the aquitard and how climate change is being recorded in the aquitard profile.

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17

Clark, Ian D., M. Jim Hendry, Jean-Michel Matray, Douglas Kip Solomon y H. Niklaus Waber. "Aquitard Fluids and Gases". Geofluids 2018 (3 de julio de 2018): 1–2. http://dx.doi.org/10.1155/2018/6283687.

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18

Rezaei, Abolfazl, Mohammad Zare y Hongbin Zhan. "Aquitard Horizontal Dispersion on Reactive Solute Transport in an Aquifer–Aquitard System". Transport in Porous Media 113, n.º 3 (31 de mayo de 2016): 695–716. http://dx.doi.org/10.1007/s11242-016-0719-6.

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19

Lourens, A., M. F. P. Bierkens y F. C. van Geer. "Updating hydraulic properties and layer thicknesses in hydrogeological models using groundwater model calibration results". Hydrology and Earth System Sciences Discussions 12, n.º 4 (24 de abril de 2015): 4191–231. http://dx.doi.org/10.5194/hessd-12-4191-2015.

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Abstract. Usually, subsoil data for groundwater models are generated from borehole data, using upscaling techniques. Since the assumed hydraulic properties for litho-classes in boreholes are uncertain, and upscaling may add inaccuracies, the groundwater model has to be calibrated. In this paper, a method is presented that uses a calibrated groundwater model to improve the quality of a hydrogeological model (layer thickness and hydraulic properties) as obtained from borehole data. To achieve this, all borehole data are defined by random variables and related to aquifer and aquitard properties at the same support as the groundwater model, using complete probability density functions. Subsequently, the calibrated parameter values of the groundwater model are assumed to be the truth and are used to find the most likely combination of layer thicknesses and hydraulic conductivities for the lithological layers making up the aquifer or aquitard. The presented example is an application of the proposed method to aquitards. Nevertheless, the method can be applied to aquifers as well. The analysis of the results gives rise to the discussion about the correctness of the hydrogeological interpretation of the borehole data as well as the correctness of the calibration results of the groundwater flow model. In order to make the problem tractable, computationally feasible, and avoid assumptions about the distribution form, piecewise linear probability density functions are used, instead of parametrized functions.

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20

Filippini, Maria, Beth L. Parker, Enrico Dinelli, Philipp Wanner, Steven W. Chapman y Alessandro Gargini. "Assessing aquitard integrity in a complex aquifer – aquitard system contaminated by chlorinated hydrocarbons". Water Research 171 (marzo de 2020): 115388. http://dx.doi.org/10.1016/j.watres.2019.115388.

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21

Woobaidullah, A. S. M., Md Ariful Islam, Md Zakir Hossain y Md Shahidul Islam. "Geo-electrical resistivity survey for fresh groundwater investigation in Mirsharai Economic Zone, Chittagong in the south-eastern coastal areas of Bangladesh". Journal of Nepal Geological Society 60 (16 de septiembre de 2020): 181–94. http://dx.doi.org/10.3126/jngs.v60i0.31262.

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Salinity in the groundwater is one of the major concerning issues in the coastal region of Bangladesh. Mirsharai Economic Zone, Mirsharai Upazila in the south-eastern coastal region of Chittagong District of Bangladesh, requires substantial amount of fresh groundwater supply for industrial and household use. The purpose of this study is to delineate the aquifer system of the study area and to determine the extension of potential fresh water aquifer for groundwater development through geophysical electrical resistivity sounding survey. Vertical Electrical Sounding in conjunction with borehole data provides information about the saline-fresh water interface, depth distribution, thickness of the fresh-water aquifers and local lithology. Lithological cross section shows that the sedimentary deposition and aquifer-aquitard distribution of this region are irregular even within a short spatial distance. The surface layer of top soil of clay or silty clay composition identified as aquitard shows resistivity in the ranges from 1.24 Ωm to 11 Ωm. This aquitard is underlain by a sand layer acting as shallow aquifer of varying thickness shows resistivity ranging mostly from 1.9 Ωm to 11Ωm reflecting the pore space water as saline to brackish. A second aquitard is underlain by the shallow aquifer of varying thickness. A deep fresh water aquifer, overlain by the second aquitard, shows resistivity in the range of 16 Ωm to73 Ωm indicating the pore space water as fresh. But the aquifer is interrupted by clay/silty clay layersat the deeper part in the middle portion. This study provides depth to the fresh water aquifer as wellas probable suitable regions for groundwater development.

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22

Broster, B. E. y D. A. Pupek. "The significance of buried landscape in subsurface migration of dense non-aqueous phase liquids; the case of perchloroethylene in the Sussex Aquifer, New Brunswick". Environmental and Engineering Geoscience 7, n.º 1 (1 de febrero de 2001): 17–29. http://dx.doi.org/10.2113/gseegeosci.7.1.17.

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Abstract At Sussex, New Brunswick, dissolved perchloroethylene (PCE) as high as 28.0 mu g/liter, was detected within the upper aquifer and in concentrations to 1.6 mu g/liter within the lower aquifer that serves as the main source of municipal water supply. Predominantly formed as an esker ridge, the lower aquifer consists of well-sorted, glaciofluvial/ice-contact, sand and gravel layers mostly confined by underlying till and/or bedrock and an overlying unit of laminated silt-clay glaciolacustrine sediments (middle aquitard). The middle aquitard is in turn overlain by an upper aquifer of variable thickness, extending from a depth of about 18 m to near surface, consisting of coarsening-upward sand and gravel, with occasional lenses of clay, silt and diamicton. A dispersal plume was identified by contouring PCE concentrations from 72 samples from the upper aquifer; PCE was not detected in 16 surface soil samples. The highest concentrations imply that the PCE originated from a surface spill near the urban business center and that subsurface migration was influenced significantly by a buried relict river channel cut into the middle aquitard. Scouring along the channel bottom cut through the middle aquitard and intersected the esker ridge of the underlying water supply aquifer, forming windows through the aquitard. Contamination of the lower aquifer has likely originated from the PCE being drawn through these windows during pumping of a water-supply well that is now out of service. Results indicate that withdrawal rates and placement of original municipal water wells, as well as the stratigraphy, conductivity and topography of subsurface units are controlling factors in Dense Non-Aqueous Phase Liquid migration at this site.

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23

Zhang, Yu, Zuodong Jin, Yunlong Hou, Bingbing Han y Charles Ntakiyimana. "Fluid-Solid Coupling Effect on Numerical Simulation of Deep Foundation Pit Deformation in Soft Soil Area". Applied Sciences 12, n.º 21 (6 de noviembre de 2022): 11242. http://dx.doi.org/10.3390/app122111242.

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Groundwater is abundant in soft soil areas, which has a significant impact on the excavation deformation of foundation pits. In this paper, based on the monitoring of deep foundation pits with waterproof curtains in Shanghai deep foundation pits, COMSOL Multiphysics is used to model the layers of the foundation pits and establish a two-dimensional seepage-consolidation coupled model for hierarchical dewatering excavation. The feasibility of numerical simulation of regional foundation pits, the modeling method of the foundation pit seepage model is explored, and the presence or absence of waterproof curtains, and the influence of aquitards on the horizontal displacement of foundation pits and surface settlement outside the pits is analyzed. The research shows that the simulated foundation pit deformation values are in good agreement with the actual monitoring values and that the effect of dewatering and seepage has a great influence on the foundation pit deformation. The waterproof curtain has a significant effect on reducing the drop in the water level outside the pit and controlling the surface settlement. After installing a waterproof curtain, the amount of ground settlement is reduced, but the disadvantage is that the deformation of the enclosure structure increases. Finally, the influence of aquitard on the deformation of foundation pit excavation is simulated, and the distribution characteristics of the flow network diagram under different permeability coefficients are analyzed. According to the analysis of the foundation pit deformation law and flow network diagram, it is considered that the waterproof curtain can effectively reduce the influence of aquitard on foundation pit deformation.

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24

Huang, Ming-hua y Dun Li. "A One-Dimensional Fractional-Derivative Viscoelastic Model for the Aquitard Consolidation of an Aquifer System". Geofluids 2019 (2 de mayo de 2019): 1–11. http://dx.doi.org/10.1155/2019/5685134.

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Land subsidence resulting from the withdrawal of groundwater is one of the problems of major importance to geosciences and geomechanics. In order to analyze the phenomena of land subsidence, this study attempts to constitute a more reliable prediction model to simulate the consolidation process of the aquifer system under the drawdown of groundwater. A fractional-derivative viscoelastic model is introduced to characterize the rheological properties of the aquitard, and the equation governing the consolidation process is established on the basis of the one-dimensional consolidation theory. The semianalytical solutions for the pore-water pressure, the settlement of aquitard, and the degree of consolidation are deduced using both finite sine transform and Laplace transform. Then, the comparisons of two special cases are performed to validate the correctness of the proposed model. The variations in the degree of consolidation and settlement of the aquitard are simulated to analyze the consolidation behavior of the aquifer system, and the influences of model parameters and the drawdown speed of groundwater are investigated.

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25

Wang, Ye, Mao-sheng Zhang, Fu-sheng Hu, Ying Dong y Kun Yu. "A Coupled One-Dimensional Numerical Simulation of the Land Subsidence Process in a Multilayer Aquifer System due to Hydraulic Head Variation in the Pumped Layer". Geofluids 2018 (2018): 1–12. http://dx.doi.org/10.1155/2018/4083439.

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After exploitation of groundwater had been reduced and the groundwater level of the confined aquifer had risen, land subsidence was observed to continue rather than cease for several years according to the layer-wise mark monitoring data in Xi’an. To analyze the phenomena, a numerical model of a coupled one-dimensional multilayer aquifer system is developed to represent land subsidence due to hydraulic head variation in the pumped layer. The numerical simulation results show that the pressure head in other layers does not rise immediately when the hydraulic head in the pumped layer starts to recover after pumping ceases. In addition, after the pumping is stopped, a dividing point can be found in aquitards next to the pumped layer, with the aquitards being divided into two parts: a compressed part and a rebounding part. The dividing points move toward the side and away from the pumped layer with the transferring of pore pressure in the aquitard. The results of the simulation also show that there is a transition period between land subsidence and rebound. In this transition period, land could continue to subside even though the hydraulic head in the pumped layer begins to recover.

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26

Stoyanov, Nikolay, Stefan Dimovski y Aleksey Benderev. "Hydrogeological models for the conditions causing the occurrence of manganese in wells for groundwater extraction from the terrace of the Vacha River, Southern Bulgaria". Review of the Bulgarian Geological Society 83, n.º 3 (diciembre de 2022): 259–62. http://dx.doi.org/10.52215/rev.bgs.2022.83.3.259.

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The presented study examines the problem caused by the groundwater pollution in the alluvial aquifer complex formed in the terrace of the Vacha River. Two working hypotheses are considered. In the first one is accepted that the aquitard is regionally well sustained and limits the penetration of Mn-contaminated waters into the lower aquifer. In the second one is assumed that there are hydrogeological windows in the aquitard, through which active mass exchange between the two aquifers can take place and manganese can occur in the pumping wells after their exploitation is started.

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27

Malama, Bwalya, Devin Pritchard-Peterson, John J. Jasbinsek y Christopher Surfleet. "Assessing Stream-Aquifer Connectivity in a Coastal California Watershed". Water 13, n.º 4 (5 de febrero de 2021): 416. http://dx.doi.org/10.3390/w13040416.

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We report the results of field and laboratory investigations of stream-aquifer interactions in a watershed along the California coast to assess the impact of groundwater pumping for irrigation on stream flows. The methods used include subsurface sediment sampling using direct-push drilling, laboratory permeability and particle size analyses of sediment, piezometer installation and instrumentation, stream discharge and stage monitoring, pumping tests for aquifer characterization, resistivity surveys, and long-term passive monitoring of stream stage and groundwater levels. Spectral analysis of long-term water level data was used to assess correlation between stream and groundwater level time series data. The investigations revealed the presence of a thin low permeability silt-clay aquitard unit between the main aquifer and the stream. This suggested a three layer conceptual model of the subsurface comprising unconfined and confined aquifers separated by an aquitard layer. This was broadly confirmed by resistivity surveys and pumping tests, the latter of which indicated the occurrence of leakage across the aquitard. The aquitard was determined to be 2–3 orders of magnitude less permeable than the aquifer, which is indicative of weak stream-aquifer connectivity and was confirmed by spectral analysis of stream-aquifer water level time series. The results illustrate the importance of site-specific investigations and suggest that even in systems where the stream is not in direct hydraulic contact with the producing aquifer, long-term stream depletion can occur due to leakage across low permeability units. This has implications for management of stream flows, groundwater abstraction, and water resources management during prolonged periods of drought.

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28

Wahyono, Sri Cahyo, Sudarningsih, Fahriadi, Totok Wianto y Amar Vijai Nasrulloh. "FRESHWATER POTENTIAL BASED ON IDENTIFICATION OF AQUIFER LAYER IN BALANGAN COUNTY, INDONESIA". Journal of Southwest Jiaotong University 57, n.º 5 (30 de octubre de 2022): 457–66. http://dx.doi.org/10.35741/issn.0258-2724.57.5.36.

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Groundwater is a reservoir of fresh water located beneath the ground surface in soil pore spaces and the fractures of lithology formations. Groundwater contained in the aquifer layer has a certain depth. Aquifer layer measurement was conducted with five tracks using the AGI Super Sting R1 IP tool with a spacing of 25 m and a track length of 675 m in Balangan County. This study aims to determine the 2D cross-sectional model, analyze lithology types, and determine the depth, thickness, and aquifer type in the study area based on the resistivity value. The results showed that the study area includes two rock formations – the Dahor and Warukin formations. The Dahor formation is clay with a resistivity value of 1–28.284 m, sandy clay 28.284–99.055 m, and sand 99.055–800 m. The Warukin formation is clay with a resistivity value of 1–10 m, sandy clay 10–31.623 m, and sand 31.623–100 m. Aquifer layer estimation shows that track 1 has a free aquifer and contains aquitard rock. Next, track 2 has a confined aquifer and contains rocks that are both aquifer and aquitard. Then, track 3 has a free aquifer type and contains rocks that are aquifer and aquitard. Track 4 has two measurements with a depressed aquifer and contains rocks that are aquifer. Finally, Track 5 has a depressed aquifer and contains aquitard rock. This study shows the existence of groundwater deposits in the thickness of the aquifer layer in Balangan County, Indonesia.

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29

Runkel, Anthony C., Robert G. Tipping, Jessica R. Meyer, Julia R. Steenberg, Andrew J. Retzler, Beth L. Parker, Jeff A. Green, John D. Barry y Perry M. Jones. "A multidisciplinary-based conceptual model of a fractured sedimentary bedrock aquitard: improved prediction of aquitard integrity". Hydrogeology Journal 26, n.º 7 (1 de junio de 2018): 2133–59. http://dx.doi.org/10.1007/s10040-018-1794-2.

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30

Du, Yao, Teng Ma, Yamin Deng, Shuai Shen y Zongjie Lu. "Sources and fate of high levels of ammonium in surface water and shallow groundwater of the Jianghan Plain, Central China". Environmental Science: Processes & Impacts 19, n.º 2 (2017): 161–72. http://dx.doi.org/10.1039/c6em00531d.

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31

TAKEUCHI, Mio. "Role of Aquitard in Subsurface Microbial Activity". Journal of Geography (Chigaku Zasshi) 116, n.º 6 (2007): 915–21. http://dx.doi.org/10.5026/jgeography.116.6_915.

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32

Ortega-Guerrero, Adrian, John A. Cherry y David L. Rudolph. "Large-Scale Aquitard Consolidation Near Mexico City". Ground Water 31, n.º 5 (septiembre de 1993): 708–18. http://dx.doi.org/10.1111/j.1745-6584.1993.tb00841.x.

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33

Sridharan, K., M. Sekhar y M. S. Mohan Kumar. "Analysis of an Aquifer-water table aquitard system". Journal of Hydrology 114, n.º 1-2 (marzo de 1990): 175–89. http://dx.doi.org/10.1016/0022-1694(90)90080-h.

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34

Krainer, Karl, Gerfried Winkler, Sabine Pernreiter y Thomas Wagner. "Unusual catchment runoff in a high alpine karst environment influenced by a complex geological setting (Northern Calcareous Alps, Tyrol, Austria)". Hydrogeology Journal 29, n.º 8 (29 de septiembre de 2021): 2837–52. http://dx.doi.org/10.1007/s10040-021-02405-0.

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AbstractGarber Schlag (Q-GS) is one of the major springs of the Karwendel Mountains, Tyrol, Austria. This spring has a unique runoff pattern that is mainly controlled by the tectonic setting. The main aquifer is a moderately karstified and jointed limestone of the Wetterstein Formation that is underlain by nonkarstified limestone of the Reifling Formation, which acts as an aquitard. The aquifer and aquitard of the catchment of spring Q-GS form a large anticline that is bound by a major fault (aquitard) to the north. Discharge of this spring shows strong seasonal variations with three recharge origins, based on δ18O and electrical conductivity values. A clear seasonal trend is observed, caused by the continuously changing portions of water derived from snowmelt, rainfall and groundwater. At the onset of the snowmelt period in May, the discharge is composed mainly of groundwater. During the maximum snowmelt period, the water is dominantly composed of water derived from snowmelt and subordinately from rainfall. During July and August, water derived from snowmelt continuously decreases and water derived from rainfall increases. During September and October, the water released at the spring is mainly derived from groundwater and subordinately from rainfall. The distinct discharge plateau from August to December and the following recession until March is likely related to the large regional groundwater body in the fissured and moderately karstified aquifer of the Wetterstein Formation and the tectonic structures (anticline, major fault). Only a small portion of the water released at spring Q-GS is derived from permafrost.

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35

Campos‐Enríquez, J. O., O. Delgado‐Rodríguez, R. Chávez‐Segura, P. Gómez‐Contreras, E. L. Flores‐Márquez y F. S. Birch. "The subsurface structure of the Chalco sub‐basin (Mexico City) inferred from geophysical data". GEOPHYSICS 62, n.º 1 (enero de 1997): 23–35. http://dx.doi.org/10.1190/1.1444123.

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The Chalco sub‐basin, the hydrogeological reserve of Mexico City, is located in the southern portion of Mexico City's basin, an intramontane valley located at 2200 m a.s.l. in the Trans‐Mexican Volcanic Belt (Central Mexico). Several geophysical studies (dc resistivity, seismic refraction, gravity, well‐logging) have been conducted in this area. The objectives of these independent surveys were different and of regional and local scopes. This study represents the first comprehensive effort to assimilate and interpret the data available to date from the area of the Chalco sub‐basin and to infer its main basinal characteristics. According to the topography we obtained of the basement, a northeast‐southwest structural high separates the sub‐basin into two portions. The western portion is asymmetric and deeper than the eastern one. An east‐west half graben‐like structure is located in the western portion. This structure could make possible an east‐west fluid flow at depth, and it also implies a differential subsidence. It was also possible to establish the stratigraphy of the volcano‐sedimentary infill. The gravity models give the interface: (1) between lacustrine sediments (aquitard) and the granular aquifer and (2) between the granular aquifer and the basaltic container. The resistivity boundaries correspond to the contact zone between saline and fresh water in the aquitard and semiconfined aquifer respectively, and they correlate with the existence of a vertical flow of saline fluids from the aquitard to the aquifer. The estimate of the volume of fluids contained in the granular aquifer range between 2 and [Formula: see text].

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36

Mei, Jinling, Hong Cao, Guanyong Luo y Hong Pan. "Analytical Method for Groundwater Seepage through and Beneath a Fully Penetrating Cut-off Wall Considering Effects of Wall Permeability and Thickness". Water 14, n.º 23 (6 de diciembre de 2022): 3982. http://dx.doi.org/10.3390/w14233982.

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A fully penetrating cut-off wall is a vertical seepage barrier that fully penetrates an aquifer and is embedded in an underlying aquitard to a certain depth. Groundwater seepage with this type of wall occurs through three paths: leakage through the body of the wall in the aquifer, leakage through the body of the wall embedded in the aquitard, and seepage under the wall. Seepage through the first path can be simply treated as one-dimensional flow. However, due to the mutual influence of seepage through the latter two paths, the seepage problem is complicated and still needs to be studied. An analytical method is proposed to solve this problem in this study. Mathematic expressions for flow rate and head value are obtained by superposition of drawdowns of two exact models, namely, the model with only leakage through the wall body and the model with only seepage under the wall, respectively. Exact solutions are quoted or derived for the exact models, but they involve Legendre’s elliptic integrals of the first and third kinds. To facilitate an engineering application, approximate models of the exact models are introduced and their solutions are applied to the analytical formulas. The accuracy and applicability of the proposed method are verified compared with the numerical method. The proposed method provides a simple but effective method for quickly estimating the quantity of seepage in the aquitard (including leakage through the wall body and seepage under the wall) when simultaneously considering the effects of wall permeability and thickness.

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37

Cardimona, Steven J., William P. Clement y Katharine Kadinsky‐Cade. "Seismic reflection and ground‐penetrating radar imaging of a shallow aquifer". GEOPHYSICS 63, n.º 4 (julio de 1998): 1310–17. http://dx.doi.org/10.1190/1.1444432.

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In 1995 and 1996, researchers associated with the US Air Force’s Phillips and Armstrong Laboratories took part in an extensive geophysical site characterization of the Groundwater Remediation Field Laboratory located at Dover Air Force Base, Dover, Delaware. This field experiment offered an opportunity to compare shallow‐reflection profiling using seismic compressional sources and low‐frequency ground‐penetrating radar to image a shallow, unconfined aquifer. The main target within the aquifer was the sand‐clay interface defining the top of the underlying aquitard at 10 to 14 m depth. Although the water table in a well near the site was 8 m deep, cone penetration geotechnical data taken across the field do not reveal a distinct water table. Instead, cone penetration tests show a gradual change in electrical properties that we interpret as a thick zone of partial saturation. Comparing the seismic and radar data and using the geotechnical data as ground truth, we have associated the deepest coherent event in both reflection data sets with the sand‐clay aquitard boundary. Cone penetrometer data show the presence of a thin lens of clays and silts at about 4 m depth in the north part of the field. This shallow clay is not imaged clearly in the low‐frequency radar profiles. However, the seismic data do image the clay lens. Cone penetrometer data detail a clear change in the soil classification related to the underlying clay aquitard at the same position where the nonintrusive geophysical measurements show a change in image character. Corresponding features in the seismic and radar images are similar along profiles from common survey lines, and results of joint interpretation are consistent with information from geotechnical data across the site.

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38

Zhuang, Chao, Zhifang Zhou y Walter A. Illman. "A Joint Analytic Method for Estimating Aquitard Hydraulic Parameters". Groundwater 55, n.º 4 (10 de enero de 2017): 565–76. http://dx.doi.org/10.1111/gwat.12494.

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39

Adar, Eilon y Ronit Nativ. "Isotopes as tracers in a contaminated fractured chalk aquitard". Journal of Contaminant Hydrology 65, n.º 1-2 (agosto de 2003): 19–39. http://dx.doi.org/10.1016/s0169-7722(02)00237-1.

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40

McMahon, P. "Aquifer/aquitard interfaces: mixing zones that enhance biogeochemical reactions". Hydrogeology Journal 9, n.º 1 (16 de febrero de 2001): 34–43. http://dx.doi.org/10.1007/s100400000109.

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41

Ezra, Shai, Shimon Feinstein, Alex Yakirevich, Eilon Adar y Itzhak Bilkis. "Retardation of organo-bromides in a fractured chalk aquitard". Journal of Contaminant Hydrology 86, n.º 3-4 (agosto de 2006): 195–214. http://dx.doi.org/10.1016/j.jconhyd.2006.02.016.

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42

Peffer, Jeffrey R. "Complex Aquifer-Aquitard Relationships at an Appalachian Plateau Site". Ground Water 29, n.º 2 (marzo de 1991): 209–17. http://dx.doi.org/10.1111/j.1745-6584.1991.tb00512.x.

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43

Nativ, Ronit y Ilan Nissim. "Characterization of a Desert Aquitard- Hydrologic and Hydrochemical Considerations". Ground Water 30, n.º 4 (julio de 1992): 598–606. http://dx.doi.org/10.1111/j.1745-6584.1992.tb01536.x.

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44

Gardner, W. Payton, Glenn A. Harrington y Brian D. Smerdon. "Using excess 4He to quantify variability in aquitard leakage". Journal of Hydrology 468-469 (octubre de 2012): 63–75. http://dx.doi.org/10.1016/j.jhydrol.2012.08.014.

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45

Sekhar, M., M. S. Mohan Kumar y K. Sridharan. "Parameter estimation in an aquifer-water table aquitard system". Journal of Hydrology 136, n.º 1-4 (agosto de 1992): 177–92. http://dx.doi.org/10.1016/0022-1694(92)90010-s.

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46

Robertson, W. D., B. M. Russell y J. A. Cherry. "Attenuation of nitrate in aquitard sediments of southern Ontario". Journal of Hydrology 180, n.º 1-4 (mayo de 1996): 267–81. http://dx.doi.org/10.1016/0022-1694(95)02885-4.

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47

Waldron, B. A., J. B. Harris, D. Larsen y A. Pell. "Mapping an aquitard breach using shear-wave seismic reflection". Hydrogeology Journal 17, n.º 3 (2 de diciembre de 2008): 505–17. http://dx.doi.org/10.1007/s10040-008-0400-4.

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48

Wang, Quanrong y Hongbin Zhan. "Radial reactive solute transport in an aquifer–aquitard system". Advances in Water Resources 61 (noviembre de 2013): 51–61. http://dx.doi.org/10.1016/j.advwatres.2013.08.013.

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49

Liu, Xiaotian, Jianxiu Wang, Tianliang Yang, Lujun Wang, Na Xu, Yanxia Long y Xinlei Huang. "Dewatering-Induced Stratified Settlement around Deep Excavation: Physical Model Study". Applied Sciences 12, n.º 18 (6 de septiembre de 2022): 8929. http://dx.doi.org/10.3390/app12188929.

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The multi-aquifer and multi-aquitard system (MAMA) is a typical geological structure in deltas. Thus, the risks and challenges to settlement control and environmental protection are increased when demand for underground space extends to deeper strata. In this study, dewatering-induced stratified settlement in MAMA is divided into three stages according to whether the overlying aquitard is coupled with groundwater seepage. Subsequently, large physical model tests were carried out. Seepage and compression in the overlying strata come after the compression in the confined aquifer and the coordinated deformation in the overlying strata. The soil is compressed under the seepage drive within the hydraulic gradient range, while the soil above it is still affected by coordinated deformation and shows expansion. Dewatering-induced uneven settlement will cause damage to existing foundations and underground structures. Large-scale and uninterrupted excavation and dewatering are the main reasons for the continuous development of land subsidence. Although artificial groundwater recharging can reduce the settlement of the existing building, underground structure, and surrounding strata, a reasonable space arrangement is needed.

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50

Ge, Qin, Xing Liang, Menggui Jin, Jing Li y Yan Liu. "Cl− as a Chemical Fingerprint of Solute Transport in the Aquitard-Aquifer System of the North Jiangsu Coastal Plain, China". Geofluids 2017 (2017): 1–16. http://dx.doi.org/10.1155/2017/6131547.

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Detailed vertical profiles of Cl− in porewaters through the aquitard-aquifer system were used to yield solute transport mechanism and build a conceptual model regarding evolution processes and transport time of natural tracer migration in North Jiangsu coastal plain, China. One-dimensional vertical simulated models of Cl− profiles illustrate that diffusion appeared to be the dominant solute transport mechanism in the aquitard-aquifer system. A downward groundwater flow did not improve the fitness between simulated and measured values. Several simulated models were constructed and suggested that the evolution of the Cl− profiles is mainly ascribed to the introduction of seawater and freshwater of transgression-regression to the first confined aquifer and the upper boundary. Groundwater in the first confined aquifer recharged by the Late Pleistocene glacial meltwater (25–15 ka BP) was supported in response to the low Cl− concentrations. The shallow groundwater in the first confined aquifer and porewater with high salt were attributable to the Holocene seawater intrusion. These timeframes were also consistent favorably with the results of previous studies into the palaeohydrology of the study area.

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