Regional Groundwater Flow Patterns Research Articles

Effects of shield brine on the safe disposal of waste in deep geologic environments

The salinity of groundwater increases with depth in the Canadian Shield (up to 1.3 kg/L of density). The existence of brine can be critically important for the safe geologic disposal of radioactive wastes, as dense brine can significantly retard the upward migration of radionuclides released from repositories. Static and flushing conditions of the deep brine are analyzed using a U-tube analogy model. Velocity reduction due to the presence of dense brine is derived under flushing conditions. A set of illustrative numerical simulations in a two-dimensional cross section is presented to demonstrate that dense brine can significantly influence regional groundwater flow patterns in a shield environment. It is implied from the results that (1) the existence of Shield brine can be an indicator of a hydrogeologically stable environment, (2) activities near ground surface may not perturb the stable groundwater environment in the deep brine region, and thus, (3) the deep brine region can be considered as a candidate geologic site for the safe disposal of waste. In addition to brine, other issues associated with long-term waste disposal, such as geological, glacial and seismic events, may need to be considered for the safe storage of spent nuclear fuel in a shield environment.

Remediation of TCE-contaminated groundwater by a permeable reactive barrier filled with plant mulch (Biowall)

A pilot-scale permeable reactive barrier filled with plant mulch was installed at Altus Air Force Base in Oklahoma, USA to treat trichloroethylene (TCE) contamination in groundwater emanating from a landfill. The barrier was constructed in June 2002. It was 139 meters long, 7 meters deep, and 0.5 meters wide. The barrier is also called a Biowall because one of the mechanisms for removal of TCE is anaerobic biodegradation. This study aimed at evaluating the performance of the pilot-scale Biowall after its installation. Data from over four years' monitoring indicated that the Biowall greatly changed geochemistry in the study area and stimulated TCE removal. The concentration of TCE in the Biowall and downgradient of the Biowall was greatly reduced as compared to that in ground water upgradient of the Biowall, while the concentration of cis-DCE in the Biowall and downgradient of the Biowall was much higher than that observed upgradient of the Biowall. Over time, the concentration of vinyl chloride in the Biowall and downgradient of the Biowall increased. Dehalococcoides DNA was detected within and downgradient of the Biowall, corresponding to the observation that vinyl chloride was produced at these locations. Results from a tracer study indicated that the regional groundwater flow pattern ultimately determined the flow direction in the area around the Biowall. The natural groundwater velocity was estimated at an average of 0.060 ± 0.015 m/d.

The Basin of Mexico aquifer system: regional groundwater level dynamics and database development

The aquifer system of the Basin of Mexico is the main source of water supply to the Mexico City Metropolitan Zone. Management of the Basin’s water resources requires improved understanding of regional groundwater flow patterns, for which large amounts of data are required. The current study analyses the regional dynamics of the potentiometric groundwater level using a new database called the Basin of Mexico Hydrogeological Database (BMHDB). To foster the development of a regional view of the aquifer system, data on climatological, borehole and runoff variables are part of the BMHDB. The structure and development of the BMHDB are briefly explained and then the database is used to analyze the consequences of groundwater extraction on the aquifer’s confinement conditions using lithology data. The regional analysis shows that the largest drawdown rates are located north of Mexico City, in Ecatepec (a region that has not yet received attention in hydrogeological studies), due to wells that were drilled as a temporary solution to Mexico City’s water-supply problem. It is evident that the aquifer has changed from a confined to an unconfined condition in some areas, a factor that is responsible for the large subsidence rates (40 cm/year) in some regions.

Implications for karst hydrology from 3D geological modeling using the aquifer base gradient approach

We use the gradient of the aquifer base to investigate the hydrology of mature, shallow karst systems. We first present a 3D geological model of the Gempen plateau (NW Switzerland) that reveals the geometry of aquifers and aquitards and their displacement at faults, then transfer the 3D geological model to a hydrological model. The transformation is based on a conceptual karst model approximating subsurface flow in mature, shallow karst systems to open surface flow on the top of the uppermost aquitard or aquifer base. The gradient of this surface is expected to mainly influence regional groundwater flow patterns. We use the hydrological model to delineate spring catchment areas. The discharge areas and corresponding catchment areas of the model are compared with the occurrence of springs in the study area and with hydraulic links confirmed by tracer tests. We also describe the way in which the hydrological model contributes to identifying flow processes. The proposed aquifer base gradient approach enhances vulnerability assessment in mature, shallow karst regions by (1) localizing catchment areas as a precondition of source protection strategies and (2) indicating dominant flow processes associated with individual springs.

Spatial variation in groundwater-related resource supply influences freshwater benthic algal assemblage composition

The landscape position of a lake relative to local and regional groundwater flow patterns has important ecosystem consequences. The local hydraulic gradient sets up seepage regimes, influences hydrologic and nutrient budgets, and alters site stoichiometry (molar N:P). However, little is known about the biotic (ecological) consequences of groundwater–lake coupling. We investigated the relationship between groundwater flux (resource supply rates), resource supply ratios, and species patterns of benthic algae in Sparkling Lake, Wisconsin, USA, a north-temperate flow-through seepage lake. Nutrient fluxes of seepage waters influenced both local benthic algal biomass and species composition. Sites of high groundwater discharge (HGD) were characterized by low N:P flux, high algal biovolume, and low species richness and diversity. In contrast, low groundwater discharge (LGD) and low groundwater recharge (LGR) sites had high N:P, low algal biovolume, and high richness and diversity. HGD sites were dominated by diatoms and cyanobacteria characteristic of high P, whereas LGD and LGR sites were characterized by taxa associated with low P. Many species were unique to the local flow regimes, increasing overall benthic algal species richness in Sparkling Lake.

Hydrogeological aspects of fault zones on various scales in theRoer Valley Rift System

The impact of faults on the groundwater flow system in the Roer Valley Rift System (RVRS) is demonstrated with examples from outcrop scale to regional scale. Faults in the RVRS can form strong barriers to horizontal groundwater flow as well as enhanced vertical groundwater flow paths at the same location. The strongly anisotropic hydraulic conductivity distribution within fault zones has important implications for the modeling of groundwater flow in sedimentary aquifer systems that are cut by faults. In this study, the hydraulic behavior of fault zones is studied at different scales. An outcrop study over the Geleen Fault zone shows deformation mechanisms as particulate flow and clay smearing in great detail. Qualitative and quantitative image analysis allows for an estimate of the micro-scale variation of the hydraulic properties within a fault zone. Additional core-plug measurements indicate that the damage zone around fault zones may form preferential flow paths. On a larger scale, observations over the Peel Boundary fault near the village of Uden also indicate that vertical groundwater flow close to the fault is enhanced, which results in a discharge of the underlying aquifers at the location of the fault zone. Finally, on a regional scale, hydraulic head patterns around the lignite mining areas in Germany show the importance of faults and the variation of their hydraulic properties to regional groundwater flow patterns.

Controls on the discharge of Chalk streams of the Berkshire Downs, UK.

The water quality and biological functioning of major UK rivers draining permeable basins cannot be fully understood without knowledge of the spatial and temporal controls on the aquifer-river system. In this paper, hydrogeological features of Chalk streams feeding the Thames, the focus of this special issue, are described. Large-scale features, such as line sinks along the Thames and major tributaries such as the Kennet, tend to determine the regional groundwater flow patterns in the Chalk aquifer, whereas the complex characteristics of the Chalk dominate the local spatial and temporal patterns of groundwater discharge to the tributaries draining the dip slopes. These different controls are described and illustrated by particular reference to the Lambourn (a sub-catchment of the Kennet) and Pang catchments. Various issues requiring further investigation are also highlighted.

Geostatistical mapping of leakance in a regional aquitard, Oak Ridges Moraine area, Ontario, Canada

The Newmarket Till forms a regionally extensive aquitard separating two major aquifer systems in the Greater Toronto area, Canada. The till is incised, and sometimes eroded entirely, by a network of sand- and gravel-filled channels forming productive aquifers and, locally, high-conductivity windows between aquifer systems. Leakage through the till may also be substantial in places. This study investigates the spatial variability of aquitard leakance in order to assess the relative importance of recharge processes to the lower aquifers. With a large database derived from water-well records and containing both hard and soft information, the Sequential Indicator Simulation method is used to generate maps of aquitard thickness and window probability. These can be used for targeting channel aquifers and for identifying potential areas of recharge to the lower aquifers. Conductivities are modeled from sparse data assuming that their correlation range is much smaller than the grid spacing. Block-scale leakances are obtained by upscaling nodal values based on simulated conductivity and thickness fields. Under the "aquifer-flow'' assumption, upscaling is performed by arithmetic spatial averaging. Histograms and maps of upscaled leakances show that heterogeneities associated with aquitard windows have the largest effect on regional groundwater flow patterns.

Hydrogeothermal Studies in New Mexico and Implications for Ground-Water Resources

Subsurface temperatures and heat-flow data provide valuable information on both regional and local ground-water flow patterns. In the San Juan Basin of northwestern New Mexico and southwestern Colorado, heat-flow data are used to estimate basin-scale horizontal flow and predict hydraulic conductivities much higher than values measured in pumping tests or laboratory studies. Along the central Rio Grande rift in the Albuquerque Basin, hot water at depth may be present at a number of locations; however, the hydrogeology is such that warm springs are absent. In south-central New Mexico, along the southern Rio Grande rift, a number of warm springs result from tectonic activity and erosion exposing aquifers which allow deeply-circulating ground water to come near surface. In the Roswell Basin of southeastern New Mexico, recharge to the Pecos River deep aquifer is predicted from depths of ~1,000–1,500 m; in addition a ground-water divide appears present near the Mescalero ridge. On the Llano Estacado downward ground-water movement from the surface is suggested to depths of ~1,000–1,500 m. Along the Rio Grande at Bosque del Apache and Canutillo, and along the Pecos River at Artesia, there appear to be dual-flow systems with river water moving downward to depths of ~50–100 m, while upward flow of ground water occurs from much greater depths. This implies separation of the ground-water systems at these locales, an important ramification regarding the recharge of different zones. The deep pumping at Canutillo appears to have exceeded the natural recharge, and this may well be the case at other locales where pumping depths are below river recharge. Shallow pumping at Canutillo appears to have caused a much greater recharge from the river than was the prepumping case.

INTERACTIONS BETWEEN GROUND WATER AND SURFACE WATER IN THE SUWANNEE RIVER BASIN, FLORIDA1

ABSTRACT: Ground water and surface water constitute a single dynamic system in most parts of the Suwannee River basin due to the presence of karst features that facilitate the interaction between the surface and subsurface. Low radon‐222 concentrations (below background levels) and enriched amounts of oxygen‐18 and deuterium in ground water indicate mixing with surface water in parts of the basin. Comparison of surface water and regional ground water flow patterns indicate that boundaries for ground water basins typically do not coincide with surface water drainage subbasins. There are several areas in the basin where ground water flow that originates outside of the Suwannee River basin crosses surface water basin boundaries during both low‐flow and high‐flow conditions. In a study area adjacent to the Suwannee River that consists predominantly of agricultural land use, 18 wells tapping the Upper Floridan aquifer and 7 springs were sampled three times during 1990 through 1994 for major dissolved inorganic constituents, trace elements, and nutrients. During a period of above normal rainfall that resulted in high river stage and high ground water levels in 1991, the combination of increased amounts of dissolved organic carbon and decreased levels of dissolved oxygen in ground water created conditions favorable for the natural reduction of nitrate by denitrification reactions in the aquifer. As a result, less nitrate was discharged by ground water to the Suwannee River.

An application of factor analysis for the study of the hydrogeological conditions in Plio-Pleistocene aquifers of NW Achaia (NW peloponnesus, Greece)

R- andQ-mode factor analysis is applied to 51 groundwater samples collected from wells drilled in the Plio-Pleistocene aquifers of NW Achaia, Greece. The purpose ofR- andQ-mode factor analysis application is to identify (i) the regional groundwater flow pattern, and (ii) the deterioration of groundwater quality. Sixteen hydrogeological parameters are used in order to examine their importance and to provide significant insight into their correlations. In theR-mode factor analysis, a six-factor model is suggested which can explain more than 77.5% of the total variance. The contribution of each factor at every site (factor scores) also is computed. Maps are constructed showing the geographical distribution of the factor scores. From these maps, the high salinity areas are delineated (seawater intrusion, possible appearance of halite layers) and the areas with elevated contribution of karastic-water are defined. Using theQ-mode correspondence analysis the meaning of the electrical conductivity as the most important variable in groundwater quality characterization is demonstrated.

Hydrogeothermal studies across the Pecos River Valley, southeastern New Mexico

Heat-flow values calculated along a profile in southeast New Mexico are used to study the regional ground-water flow pattern. The west-east profile extends from the Sacramento Mountains, across the southern part of the Roswell artesian basin, to the New Mexico–Texas border. The heat-flow data are generally calculated from bottom-hole temperatures estimated at various depths, and are therefore thought to reflect depth-dependent anomalies (principally ground-water flow). Two major positive heat-flow anomalies, interpreted to indicate upward ground-water flow, are present along the profile. A narrow anomaly in the western part of the profile is consistent with upward ground-water movement along the western boundary of a buried Precambrian horst. A rather broad anomaly in the middle of the profile appears to be associated with cross-formational flow and discharge to the Pecos River. Both anomalies may be associated with upward flow from depths of 915 or 1220 m and possibly 1524 m in the western region, but probably not deeper than 1829 m. Vertical ground-water flow appears to be absent just east of the Mescalero Ridge; farther east on the High Plains, the data are generally consistent with downward ground-water flow at depths of 610–1220 or 1524 m.

The subsurface geology of Central and Northern Negev with possible implications on the regional ground water flow pattern

The hydrogeological properties of the Kurnub Group sequence in the central and northern Negev were reassessed following a broadly expanding data base. Over most of the study area, the Kurnub Group is composed of permeable horizons. The most pronounced aquiferous zone extends in the belt of the three breached anticlines (Makhteshim) toward the Dead Sea area whereas the least impervious zone was discerned north- and northwestward from this belt. The present-day relief at the base of the Kurnub Group is outlined by prominent structural highs. Major structural depressions are located close to the Dead Sea as well as in northwestern Negev and in the Coastal Plain of the Negev and its offshore. Three major subsurface structures i.e. the Dabbeshet, Gerar and the Judea blocks were formed along parallel, NE-striking Upper Cretaceous reverse faults (preceding normal faults). The amount of vertical displacements along these faults generally exceeds the thickness of impervious layers over- and underlying the Kurnub Group thus facilitating groundwater flow from the Arad Group into the Kurnub sequence and from the latter into the Judea Group aquifer. It appears that the Kurnub Group aquifer plunges from the structural highs of Ramon and Kurnub, toward the Dead Sea 3utlet, to the Sharsheret-Sedot Akiva basin and beneath the Coastal Plain. It also plunges westward to Shezaf and to the Sukkot-Julie low and further beneath the shelf. The new geological evidence and its hydrogeological implications provide solutions for various previously unexplained salinization processes and hydrochemical phenomena such as the ever increasing salinity in the Beer Sheva well-field, the high salinities and the particularly low U-concentrations in groundwater extracted from the Judea Group aquifer south of Beer Sheva, their thermal anomalies and high Fe +2 concentrations.

Regional changes in groundwater flow patterns and effects on groundwater composition

Wetlands on the Vecht river plain in the Netherlands are threatened by pollution of ground water on the adjacent ridge ‘Het Gooi’. To assess the impact of this pollution, information is needed on the present groundwater flow pattern and hydrochemical processes occurring during flow. In the determination of hydrochemical processes past changes in flow patterns must be taken into consideration. Over the past 600 years impoldering and groundwater extraction have induced important hydrological changes in the study area. Exercises with a two-dimensional finite difference groundwater model were used to study the effects of these changes on regional groundwater flow patterns. Steady-state simulations along a vertical section were carried out for four different points in time, namely, the 14th century, 1885, 1941 and 1985. Changes in flow patterns are inferred from a comparison of the steady-state simulations. The results indicate that groundwater flow changed from a simple pattern under natural conditions to a complex flow pattern dominated by artificially man-controlled hydraulic heads at present. The computer simulations are used to estimate the effect of changes in flow patterns on regional groundwater composition. Data on the distribution of chloride and oxygen-18 in ground water provide a verification of the estimated effects and information on the present position of the fresh-brackish groundwater interface in the study area. Isochrones calculated by the model are used to estimate the position of this front where data on water composition are absent. The future displacement of the fresh-brackish groundwater front is inferred from the position of successive isochrones, assuming that the present flow pattern will remain in steady state. The computer simulations provide a general framework for the determination of hydrochemical processes in future studies addressing the impact of groundwater pollution on wetlands in the river plain.

Aquifers in the benin formation (miocene—recent), eastern Niger delta, Nigeria: Lithostratigraphy, hydraulics, and water quality

A regional lithostratigraphic and hydraulic interpretation is presented for the upper 0–300 m of the Benin Formation where groundwater is abstracted in the Rivers State, Nigeria. The aquifers are predominantly sand beds with minor clays, lignite, and conglomerate intercalations. The sands are very fine to coarse grained, subangular to subrounded, poor to fairly well sorted and mostly lithic arenites. A maximum thickness greater than 50 m is developed in places and vertical stacking is common. Most of the conglomerate beds have a matrix support fabric and appear restricted to the east as the lignite beds. An east-west trending belt, about central to the state, seems to contain more clay interbeds. The transmissivity values for the aquifers range from 1.05 × 10−2 to 11.3 × 10−2 m2/sec, while the coefficient of storage varies between 1.07 × 10−4 and 3.53 × 10−4 and specific capacity values lie between 19.01 and 139.8 m3/h/m drawdown. These values suggest that the aquifers have very good capacity to transmit groundwater. The static water level map shows a north-to-south regional groundwater flow pattern except in the northeast (Imo River catchment area) where the flow is northeast to southwest. The groundwater quality is very good and compares favorably with WHO standards for drinking water. However, relatively high iron and chloride values are localized in time and space. Deposition of the aquifer materials is thought to have occurred in alluvial fan, fluvial channel, tidal channel, intertidal flat, beach, and related microenvironments.

Regional distribution of 3He anomalies in the Icelandic crust

The distribution of 3He in geothermal fluids of Iceland has been investigated in detail. Samples were selected to: (1) examine relationships between 3 He 4 He in basalts and geothermal waters; (2) assess the influence of in situ produced radiogenic He on the pattern of 3 He 4 He variation; and (3) the influence of regional groundwater flow patterns on the distribution of 3He anomalies. The present results for 64 samples when combined with previously published data demonstrate a close correspondence between He isotope ratios in basalts and geothermal fluids. He isotope ratios ( R = 3 He 4 He exceeding the normal MORB range of 8 ± 1 R a ( R a = air 3 He 4 He ) are widespread in Iceland, and occur both in the volcanic zones and areas of older crust. Mass-balance considerations indicate that radiogenic He produced in the Icelandic crust makes a minor contribution only to the overall He budget but its presence may be reflected by the small number of R R a-values of < 8. Primarily, the range in R R a ratios reflects variability in the He signature of mantle-supplied melts. The presence of high R R a-values in older parts of the Icelandic crust does not appear to arise from dispersal of 3He from the neovolcanic zones by the regional groundwater flow pattern. Rather, contemporary degassing of melts, usually without a surface volcanic expression, appears to be widespread in Iceland even in areas where the crust is up to ⩾ 10 Ma. In these locations the melt fractions must be small and mostly freeze into the Icelandic crust.

Stream functions and equivalent freshwater heads for modeling regional flow of variable‐density groundwater: 2. Application and implications for modeling strategy

Stream functions and equivalent freshwater heads are used to simulate steady state flow of variable‐density groundwater in a regional, cross‐sectional flow model through the Palo Duro Basin, Texas, where fluid densities vary between 1.0 and 1.15 g/cm3. Centroid‐consistent velocities computed from the stream function solution allow a more precise interpretation of local flow patterns in cross‐sectional models than those from the head solution. Effects of significant fluid density variation on the regional groundwater flow pattern are studied by comparing simulation results that incorporate spatially varying, time‐invariant densities with those that assume uniform density. Modeling shows that the regional groundwater flow pattern in the Palo Duro Basin is not significantly affected by variations in fluid densities, indicating that the topographically driven flow component dominates buoyancy forces associated with dense brines. An exception is near the eastern boundary where high fluid densities cause stronger downward flow. However, simulated equivalent freshwater heads in the variable‐density model differ significantly from simulated heads in the freshwater density model, which is important for model calibration. In addition to the well‐known problems of hydraulic parameter and boundary condition uncertainties, modeling strategies for regional flow systems require consideration of uncertainties associated with fluid density and evaluation of equivalent freshwater head data.

Hydrogeological provinces and groundwater flow systems in Scotland

Synopsis There are two principal hydrogeological provinces in Scotland: the Caithness and Moray Firth province, and the Midland Valley province (Central Lowlands). Regional groundwater flow patterns are developed in these provinces with deep-seated, but slow, transport of groundwater. Shallower local systems are also present. Annual recharge of up to 500 mm occurs to the more permeable aquifers at outcrop but is much reduced to less permeable aquifers and areas covered by till. Baseflow is related to the hydraulic conductivity of the aquifer and is highest in parts of Morayshire and Fife.

洪積台地における地下水の三次元的流動

The groundwater flow system in an upland area which faces a lake is analyzed to investigate thefollowing aspects: (1) the role of dissected valley on a groundwater drainage system; (2) interaction betweenupland groundwater and lake water; and (3) the regional groundwater flow patterns. Threedimensionalanalyses are used to represent the actual phenomenon of the groundwater flow system bymeans of tracer method. Environmental tritium and water quality are used as groundwater tracer, andwater samples arc obtained in a regional scale. For the interpretation of tritium data, groundwater agesare estimated using the convolution integral method with consideration of infiltration rates as theweighting function.The results, which are of a preliminary stage, indicate that: (1) two main rivers and dissected valleysare playing important role as the groundwater drainage system of the upland; (2) groundwater isrecharged in the upland area and is primarily discharged to the river or valley as a whole; (3) thegroundwater flow interactions between upland and lake are not occurred actively; and (4) groundwater,deeper than about 20 meter below sea level, flows very slowly as a different flow systm from thosein the upper layers.

Groundwater flow systems in the arid crystalline province of Southern Sinai

ABSTRACT A hydrogeological research project was conducted in the arid crystalline province of the Southern Sinai. To gain a better understanding of regional groundwater flow patterns, Landsat images as well as air photos were used. Three main flow systems were investigated: (1) The flow system occurring along longitudinal regional crustal fractures with the direction parallel to the Gulf of Elat Rift; this system captures the flow in the main wadi beds draining eastwards. (2) The flow system found in shallow fractured rocks, capturing the flow in small tributaries in the upper part of the drainage basin. (3) The system of dikes governing the flow regime in wadi beds draining westwards. The preliminary estimate of the recharge into the fractured crystalline aquifers and the interconnected gravel bed aquifers is in the order of magnitude of 10–15% of the total precipitation.