Correlation of hydraulic conductivity with stratigraphy in a fractured-dolomite aquifer, northeastern Wisconsin, USA

This study integrated surface and subsurface stratigraphic data with geophysical logs and hydrogeologic data in order to characterize the hydraulic properties of the Silurian dolomite in northeastern Wisconsin. Silurian stratigraphy consists of predictable alternations of characteristic facies associations. A vertical profile of hydraulic conductivity, obtained from short-interval packer tests in a core hole that penetrates a majority of the Silurian section, indicates that hydraulic conductivity ranges over five orders of magnitude (10^–1 to 10^–6 cm/s). Matrix conductivity is generally low and varies with texture; the finer-grained restricted-marine and transitional facies being less permeable than the coarser-grained open-marine facies. High-conductivity values are generally associated with bedding-plane fractures, and fracture frequency is greater in the restricted-marine facies. High-flow features in 16 wells were identified using fluid-temperature/resistivity and heat-pulse flowmeter logs. Natural-gamma logs were used to identify the stratigraphic position of flow features in each well and to correlate flow features to specific stratigraphic horizons. By combining stratigraphic, geophysical, and hydrogeologic data, 14 high-permeability zones within the Silurian aquifer have been identified and correlated in wells more than 16 km apart. These zones parallel bedding, appear most pronounced at contacts between contrasting lithologies, and are most abundant in restricted-marine lithologies. Electronic Publication     

Three-dimensional variable-density flow simulation of a coastal aquifer in southern Oahu, Hawaii, USA

Three-dimensional modeling of groundwater flow and solute transport in the Pearl Harbor aquifer, southern Oahu, Hawaii, shows that the readjustment of the freshwater–saltwater transition zone takes a long time following changes in pumping, irrigation, or recharge in the aquifer system. It takes about 50 years for the transition zone to move 90% of the distance to its new steady position. Further, the Ghyben–Herzberg estimate of the freshwater/saltwater interface depth occurred between the 10 and 50% simulated seawater concentration contours in a complex manner during 100 years of the pumping history of the aquifer. Thus, it is not a good predictor of the depth of potable water. Pre-development recharge was used to simulate the 1880 freshwater-lens configuration. Historical pumpage and recharge distributions were used and the resulting freshwater-lens size and position were simulated through 1980. Simulations show that the transition zone moved upward and landward during the period simulated.Previous groundwater flow models for Oahu have been limited to areal models that simulate a sharp interface between freshwater and saltwater or solute-transport models that simulate a vertical aquifer section. The present model is based on the US Geological Surveys three-dimensional solute transport (3D SUTRA) computer code. Using several new tools for pre- and post-processing of model input and results have allowed easy model construction and unprecedented visualization of the freshwater lens and underlying transition zone in Hawaiis most developed aquifer.

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Electronic Supplementary Material Supplementary material is available in the online version of this article at .

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Resumen La modelación tridimensional del flujo de agua subterránea y del transporte de solutos en el acuífero de Pearl Harbor, en la parte sur de Oahu, Hawaii, muestra que el reajuste de la zona de transición agua dulce–agua salada, toma un largo tiempo a partir de cambios en el bombeo, irrigación o recarga en el sistema acuífero. Le toma alrededor de 50 años, a la zona de transición, moverse el 90% de la distancia hacia su nueva posición estacionaria. Además, el estimativo de Ghyben–Herzberg, sobre la profundidad de la interfase agua dulce–agua salada, se encuentra entre el 10 y el 50% en los contornos simulados de concentración de agua salada, de una manera compleja, durante 100 años de la historia de bombeo del acuífero. Por tanto, no es este un buen predictor de la profundidad del agua potable. Se utilizó una recarga pre – desarrollo, para simular la configuración del lente de agua dulce en 1880. Fueron utilizadas las distribuciones históricas del bombeo y de la recarga y se simularon el tamaño y posición resultantes del lente de agua dulce hasta 1980. Esas simulaciones muestran que la zona de transición se movió tierra adentro y hacia arriba, durante el periodo que se simuló.Los anteriores modelos de flujo para agua subterránea en Oahu, han sido limitados a modelos areales, que simulan una interfase abrupta entre agua dulce y agua salada, o bien han sido modelos de transporte de solutos que simulan una sección vertical del acuífero. El modelo presente está basado en el programa de computador del US Geological Survey (3D SUTRA), para transporte de solutos en tres dimensiones. Mediante el uso de varias herramientas nuevas para pre – procesamiento y post – procesamiento de las entradas y resultados del modelo, se ha permitido una construcción fácil del mismo y una visualización sin precedentes del lente de agua dulce y de la zona de transición subyacente en el acuífero más desarrollado de Hawaii.

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Résumé La modélisation tridimensionnelle de lécoulement et du transport dans la partie sud de laquifère Oahu-Hawai montre que le temps de réajustement de la zone de transition entre leau douce et leau salée est assez long et dépend de la variation des pompages et des irrigations, ainsi que de la recharge du système aquifère. Il sont nécessaires 50 ans pour que la zone de transition parcoure 90% de la distance qui la sépare de sa nouvelle position. La profondeur du biseau estimée par le schéma Ghyben–Herzberg se trouve entre les contours de 10 et 50% de la concentration de leau salée. Ce résultat a été obtenu après la simulation de lhistoire du pompage de laquifère pendant une période de 100 ans. Donc le schéma Ghyben–Herzberg conduit aux valeurs erronées de la profondeur de leau potable. La valeur de la recharge davant lexploitation de laquifère a été utilisée pour simuler la configuration des lentilles deau douce en 1880. En utilisant lhistoire du pompage et la distribution de la recharge ont on a simulé les dimensions et le positions des lentilles deau douce jusqu› en 1980. Les simulation montrent que le mouvement de la zone de transition est ascendant et vers le continent.Les modèles antérieurs de la zone dOahu ont été des modèles locaux qui ont simulé une interface nette eau douce-eau salée ou des modèles de transport bidimensionnels, dans une coupe verticale. Le modèle actuel est basé sur le code 3D-SUTRA, réalisé par le Service Géologique des États-Unis. L› utilisation des différents techniques de traitement des données a permis une construction facile du modèle, ainsi qu› une visualisation sans précédent des lentilles deau douces et de la zone de transition sous-jacente dans le plus grand aquifère du Hawai.

     

Characterization of fracture connectivity in a siliciclastic bedrock aquifer near a public supply well (Wisconsin, USA)

In order to protect public supply wells from a wide range of contaminants, it is imperative to understand physical flow and transport mechanisms in the aquifer system. Although flow through fractures has typically been associated with either crystalline or carbonate rocks, there is growing evidence that it can be an important component of flow in relatively permeable sandstone formations. The objective of this work is to determine the role that fractures serve in the transport of near-surface contaminants such as wastewater from leaking sewers, to public supply wells in a deep bedrock aquifer. A part of the Cambrian aquifer system in Madison, Wisconsin (USA), was studied using a combination of geophysical, geochemical, and hydraulic testing in a borehole adjacent to a public supply well. Data suggest that bedrock fractures are important transport pathways from the surface to the deep aquifer. These fractured intervals have transmissivity values several orders of magnitude higher than non-fractured intervals. With respect to rapid transport of contaminants, high transmissivity values of individual fractures make them the most likely preferential flow pathways. Results suggest that in a siliciclastic aquifer near a public supply well, fractures may have an important role in the transport of sewer-derived wastewater contaminants.     

Assessing aquifer susceptibility to and severity of atrazine contamination at a field site in south-central Wisconsin, USA

 A field study from October 1989 through July 1992, conducted on a 4.1-km² area in south-central Wisconsin, USA, examined the distributions of atrazine and its chlorinated metabolites in groundwater and related those distributions to the groundwater flow system. MODFLOW and PATH3D were used to assess bedrock-aquifer susceptibility to contamination. Estimated travel time from water table to bedrock surface ranges from <0.25 to >512 yr. Spatial distribution of the estimates demonstrates that increased travel time to bedrock can result from the presence of shallow surface-water bodies, greater depths to bedrock, and smaller hydraulic conductivities. Estimated travel times to local domestic wells are inversely related to atrazine and desethylated atrazine concentrations observed in water from those wells. The potential impact of long-term atrazine use on aquifer water quality was investigated using MT3D in two best-case scenarios. Uncertainties associated with predicted atrazine concentrations at various depths and times were estimated. For shallow groundwater, widespread violations of Wisconsin's current preventive action limit were predicted, but with large uncertainty stemming from uncertain estimates of input parameter values. The simulations indicate, however, that moderate inputs at the water table are very unlikely to produce violations of Wisconsin's standards deeper in the aquifer. Received, October 1997 Revised, July 1998 Accepted, July 1998     

Delineation of capture zones for municipal wells in fractured dolomite, Sturgeon Bay, Wisconsin, USA

A wellhead protection study for the city of Sturgeon Bay, Wisconsin, USA, demonstrates the necessity of combining detailed hydrostratigraphic analysis with groundwater modeling to delineate zones of contribution for municipal wells in a fractured dolomite aquifer. A numerical model (MODFLOW) was combined with a particle tracking code (MODPATH) to simulate the regional groundwater system and to delineate capture zones for municipal wells. The hydrostratigraphic model included vertical and horizontal fractures and high-permeability zones. Correlating stratigraphic interpretations with field data such as geophysical logs, packer tests, and fracture mapping resulted in the construction of a numerical model with five high-permeability zones related to bedding planes or facies changes. These zones serve as major conduits for horizontal groundwater flow. Dipping fracture zones were simulated as thin high-permeability layers. The locations of exposed bedrock and surficial karst features were used to identify areas of enhanced recharge. Model results show the vulnerability of the municipal wells to pollution. Capture zones for the wells extend several kilometers north and south from the city. Travel times from recharge areas to all wells were generally less than one year. The high seasonal variability of recharge in the study area made the use of a transient model necessary. Electronic Publication     

Integrated multi-parameter approach for delineating groundwater potential zones in a crystalline aquifer of southern India

Groundwater resources in the semi-arid regions of southern India are under immense pressure due to large-scale groundwater abstraction vis-à-vis meager rainfall recharge. Therefore, understanding and evaluating the spatial distribution of groundwater is essential for viable utilization of the resource. Here, we assess groundwater potential at the watershed scale, in a semi-arid environment with crystalline aquifer system without a perennial surface water source using remote sensing, geophysical, and GIS-based integrated multi-parameter approach. GIS-based weighed overlay analysis is performed with input parameters, viz., geology, geomorphology, lineament density, land use, soil, drainage density, slope, and aquifer thickness. The watershed is categorized into four zones, namely, “very good” (GWP4), “good” (GWP3), “moderate” (GWP2), and “low” (GWP1) in terms of groundwater potential. Overall, ~?70% of the study area falls under moderate to low groundwater potential, indicating a serious threat to the future availability of the resource. Therefore, serious measures are required for maintaining aquifer resilience in this over-exploited aquifer (e.g., restricting groundwater withdrawal from GWP1 and GWP2 zones). Further, as the aquifer is under tremendous anthropogenic pressure, rainwater harvesting and artificial recharge during monsoon are advocated for sustainable aquifer management. Due to the direct dependence of crop production vis-à-vis farmer economy on groundwater, this study is an important step towards sustainable groundwater management and can be applied in diverse hydrological terrains.     

Fluoride concentrations in a crystalline bedrock aquifer Marathon County, Wisconsin

Water samples from 2,789 private water-supply wells in Marathon County, Wisconsin reveal that fluoride concentrations in the crystalline bedrock range from <0.01 to 7.60 mg/L, with 0.6% of the values exceeding the Environmental Protection Agency’s (EPA’s) maximum contaminant level of 4 mg/L, and 8.6% exceeding the EPA’s secondary maximum contaminant level of 2.0 mg/L. Roughly a quarter of the wells contain dissolve fluoride within the range considered optimal for human health (between 0.5 and 1.5 mg/L), whereas 63.3% fall below 0.5 mg/L. Consistent with studies conducted in other regions, felsic rocks have significantly higher fluoride concentrations than mafic and metasedimentary rocks. Syenites yield the most fluoriferous groundwaters, but the highest median concentration occurs in a sodium-plagioclase granite. A relationship between plagioclase composition and fluoride concentrations suggests that dissolved fluoride levels are controlled by fluorite solubility and that higher fluoride concentrations are found in soft, sodium-rich groundwater.     

Limited denitrification in glacial deposit aquifers having thick unsaturated zones (Long Island, USA)

The goal of this study was to demonstrate how the extent of denitrification, which is indirectly related to dissolved organ carbon and directly related to oxygen concentrations, can also be linked to unsaturated-zone thickness, a mappable aquifer property. Groundwater from public supply and monitoring wells in Northport on Long Island, New York state (USA), were analyzed for denitrification reaction progress using dissolved N₂/Ar concentrations by membrane inlet mass spectrometry. This technique allows for discernment of small amounts of excess N₂, attributable to denitrification. Results show an average 15 % of total nitrogen in the system was denitrified, significantly lower than model predictions of 35 % denitrification. The minimal denitrification is due to low dissolved organic carbon (29.3–41.1 μmol L^?1) and high dissolved oxygen concentrations (58–100 % oxygen saturation) in glacial sediments with minimal solid-phase electron donors to drive denitrification. A mechanism is proposed that combines two known processes for aquifer re-aeration in unconsolidated sands with thick (>10 m) unsaturated zones. First, advective flux provides 50 % freshening of pore space oxygen in the upper 2 m due to barometric pressure changes. Then, oxygen diffusion across the water-table boundary occurs due to high volumetric air content in the unsaturated-zone catchment area.     

Groundwater flood of a river terrace in southwest Wisconsin,USA

Intense rainstorms in 2008 resulted in wide-spread flooding across the Midwestern United States. In Wisconsin, floodwater inundated a 17.7-km² area on an outwash terrace, 7.5 m above the mapped floodplain of the Wisconsin River. Surface-water runoff initiated the flooding, but results of field investigation and modeling indicate that rapid water-table rise and groundwater inundation caused the long-lasting flood far from the riparian floodplain. Local geologic and geomorphic features of the landscape lead to spatial variability in runoff and recharge to the unconfined sand and gravel aquifer, and regional hydrogeologic conditions increased groundwater discharge from the deep bedrock aquifer to the river valley. Although reports of extreme cases of groundwater flooding are uncommon, this occurrence had significant economic and social costs. Local, state and federal officials required hydrologic analysis to support emergency management and long-term flood mitigation strategies. Rapid, sustained water-table rise and the resultant flooding of this high-permeability aquifer illustrate a significant aspect of groundwater system response to an extreme precipitation event. Comprehensive land-use planning should encompass the potential for water-table rise and groundwater flooding in a variety of hydrogeologic settings, as future changes in climate may impact recharge and the water-table elevation.     

The sources and budget for dissolved sulfate in a fractured carbonate aquifer,southern Sacramento Mountains,New Mexico,USA

Climate change in the SW USA is likely to involve drier conditions and higher surface temperatures. In order to better understand the evolution of water chemistry and the sources of aqueous SO₄ in these semi-arid settings, chemical and S isotope compositions were determined of springs, groundwater, and bedrock associated with a Permian fractured carbonate aquifer located in the southern Sacramento Mountains, New Mexico, USA. The results suggest that the evolution of water chemistry in the semi-arid carbonate aquifer is mainly controlled by dedolomitization of bedrock, which was magnified by increasing temperature and increasing dissolution of gypsum/anhydrite along the groundwater flow path. The δ³⁴S of dissolved SO₄ in spring and groundwater samples varied from +9.0‰ to +12.8‰, reflecting the mixing of SO₄ from the dissolution of Permian gypsum/anhydrite (+12.3‰ to +13.4‰) and oxidation of sulfide minerals (−24.5‰ to −4.2‰). According to S isotope mass balance constraints, the contribution of sulfide-derived SO₄ was considerable in the High Mountain recharge areas, accounting for up to ∼10% of the total SO₄ load. However, sulfide weathering decreased in importance in the lower reaches of the watershed. A smaller SO₄ input of ∼2–4% was contributed by atmospheric wet deposition. This study implies that the δ³⁴S variation of SO₄ in semi-arid environments can be complex, but that S isotopes can be used to distinguish among the different sources of weathering. Here it was found that H₂SO₄ dissolution due to sulfide oxidation contributes up to 5% of the total carbonate weathering budget, while most of the SO₄ is released from bedrock sources during dedolomitization.     

Minor end moraines of the Wisconsin Valley Lobe, north-central Wisconsin, USA

Approximately 35 parallel, discontinuous glacial ridges occur in an area of about 100 km² in north‐central Wisconsin. The ridges are located between about 6 and 15 km north (formerly up‐ice) of the maximum extent of the Wisconsin Valley Lobe of the Laurentide Ice Sheet. The ridges are between 1 and 4 m high, up to 1 km long, and spaced between 30 and 80 m apart. They are typically asymmetrical with a steep proximal (ice‐contact) slope and gentle distal slope. The ridges are composed primarily of subglacial till on their proximal sides and glacial debris‐flow sediment on the distal sides. In some ridges the till and debris‐flow sediment are underlain by sorted sediment that was deformed in the former direction of ice flow. We interpret the ridges to be recessional moraines that formed as the Wisconsin Valley Lobe wasted back from its maximum extent, with each ridge having formed by a sequence of (1) pushing of sorted ice‐marginal sediment, (2) partial overriding by the glacier and deposition of subglacial till on the proximal side of the ridge, and (3) deposition of debris‐flow sediment on the distal side of the ridge after the frozen till at the crest of the ridge melted. The moraines are similar to annual recessional moraines described at several modern glaciers, especially the northern margin of Myrdalsjokull, Iceland. Thus, we believe the ridges probably formed as a result of minor winter advances of the ice margin during deglaciation. Based on this assumption, we calculate the net rate of ice‐surface lowering of the Wisconsin Valley Lobe during the period when the moraines formed. Various estimates of ice‐surface slope and rates of ice‐margin retreat yield a wide range of values for ice‐surface lowering (1.7–14.5 m/yr). Given that ablation rates must exceed those of ice‐surface lowering, this range of values suggests relatively high summer temperatures along the margin of the Wisconsin Valley Lobe when it began retreating from its maximum extent. In addition, the formation of annual moraines indicates that the glacier toe was thin, the ice surface was clean, and the ice margin experienced relatively cold winters.     

Field tracer test for denitrification in a pyrite-bearing schist aquifer

A small-scale artificial tracer test performed on a schist aquifer in Brittany has helped clarify mechanisms and kinetics of in situ autotrophic denitrification. NO₃ was injected as a pulse simultaneously with a conservative tracer -Br⁻. During the test, which lasted 210 h, 73% of the injected Br⁻ was recovered, as against only 47% of the NO₃. The 26% difference in the recovery of the two injected species is interpreted as being the result of denitrification, in part due to the direct oxidation of pyrite present in the solid aquifer according to the reaction: 5FeS₂+14NO₃⁻+4H⁺→7N₂+10SO₄²⁻+5Fe²⁺+2H₂O, and in part due to subsequent iron oxidation according to the reaction: NO₃⁻+5Fe²⁺+6H⁺→1/2N₂+5Fe³⁺+3H₂O. Despite the potential increase in SO₄ and Fe resulting from denitrification through pyrite oxidation, the concentrations of these elements in the groundwater remain moderate due to the precipitation of minerals such as jarosite and/or natroalunite. Tracer transfer takes place in a heterogeneous medium which, according to the breakthrough curves, can be simplified to a dual-porosity aquifer comprising a high-permeability (fractures or large fissures) medium of low porosity from which only minor denitrification of circulating NO₃-bearing water was observed and a low-permeability (small fissures) medium of high porosity which induces a higher denitrification rate in the circulating NO₃-bearing water. The kinetics of the denitrification reaction are high compared with results obtained for other environments and can be described by a first-order model with a half life of 7.9 days for the low-porosity medium and only 2.1 days for the high-porosity medium.     

Multiple-pumped-well aquifer test to determine the anisotropic properties of a karst limestone aquifer in Pasco County, Florida, USA

Groundwater-level data from an aquifer test utilizing four pumped wells conducted in the South Pasco wellfield in Pasco County, Florida, USA, were analyzed to determine the anisotropic transmissivity tensor, storativity, and leakance in the vicinity of the wellfield. A weighted least-squares procedure was used to analyze drawdowns measured at eight observation wells, and it was determined that the major axis of transmissivity extends approximately from north to south and the minor axis extends approximately from west to east with an angle of anisotropy equal to N4.54°W. The transmissivity along the major axis ${\left( {T_{{\xi \xi }} } \right)}$ is 14,019 m² day^–1, and the transmissivity along the minor axis ${\left( {T_{{\eta \eta }} } \right)}$ is 4,303 m² day^–1. The equivalent transmissivity $T_{e} = {\left( {T_{{\xi \xi }} T_{{\eta \eta }} } \right)}^{{1 \mathord{\left/ {\vphantom {1 2}} \right. \kern-0em} 2}} = 7,767{{\text{m}}^{2} } \mathord{\left/ {\vphantom {{{\text{m}}^{2} } {{\text{day}}^{{ - {\text{1}}}} }}} \right. \kern-0em} {{\text{day}}^{{ - {\text{1}}}} }$ , and the ratio of anisotropy is 3.26. The storativity of the aquifer is 7.52?×?10^?4, and the leakance of the overlying confining unit is 1.37?×?10^?4 day^?1. The anisotropic properties determined for the South Pasco wellfield in this investigation confirm the results of previous aquifer tests conducted in the wellfield and help to quantify the NW–SE to NE–SW trends for regional fracture patterns and inferred solution-enhanced flow zones in west-central Florida.     

Depth of the base of the Jackson aquifer, based on geophysical exploration, southern Jackson Hole, Wyoming, USA

 A geophysical survey was conducted to determine the depth of the base of the water-table aquifer in the southern part of Jackson Hole, Wyoming, USA. Audio-magnetotellurics (AMT) measurements at 77 sites in the study area yielded electrical-resistivity logs of the subsurface, and these were used to infer lithologic changes with depth. A 100–600 ohm-m geoelectric layer, designated the Jackson aquifer, was used to represent surficial saturated, unconsolidated deposits of Quaternary age. The median depth of the base of the Jackson aquifer is estimated to be 200 ft (61 m), based on 62 sites that had sufficient resistivity data. AMT-measured values were kriged to predict the depth to the base of the aquifer throughout the southern part of Jackson Hole. Contour maps of the kriging predictions indicate that the depth of the base of the Jackson aquifer is shallow in the central part of the study area near the East and West Gros Ventre Buttes, deeper in the west near the Teton fault system, and shallow at the southern edge of Jackson Hole. Predicted, contoured depths range from 100 ft (30 m) in the south, near the confluences of Spring Creek and Flat Creek with the Snake River, to 700 ft (210 m) in the west, near the town of Wilson, Wyoming. Received, May 1997 · Revised, February 1998 · Accepted, April 1998     

Relating groundwater to seasonal wetlands in southeastern Wisconsin, USA

Historically, drier types of wetlands have been difficult to characterize and are not well researched. Nonetheless, they are considered to reflect the precipitation history with little, if any, regard for possible relation to groundwater. Two seasonal coastal wetland types (wet prairie, sedge meadow) were investigated during three growing seasons at three sites in the Lake Michigan Basin, Wisconsin, USA. The six seasonal wetlands were characterized using standard soil and vegetation techniques and groundwater measurements from the shallow and deep systems. They all met wetland hydrology criteria (e.g., water within 30 cm of land surface for 5% of the growing season) during the early portion of the growing season despite the lack of appreciable regional groundwater discharge into the wetland root zones. Although root-zone duration analyses did not fit a lognormal distribution previously noted in groundwater-dominated wetlands, they were able to discriminate between the plant communities and showed that wet prairie communities had shorter durations of continuous soil saturation than sedge meadow communities. These results demonstrate that the relative rates of groundwater outflows can be important for wetland hydrology and resulting wetland type. Thus, regional stresses to the shallow groundwater system such as pumping or low Great Lake levels can be expected to affect even drier wetland types.     

Prediction of the quality of water in a proposed impoundment in Southwestern Wisconsin,USA

The probable quality of water in a large multipurpose impoundment under construction in the driftless area of southwestern Wisconsin was determined by using stream monitoring data, statistical information, and literature values for point and nonpoint nutrient loading. The impoundment drainage basin is largely rural, and much of the area slopes steeply. Point sources of N and P (sewage treatment plants and farmyards) are small relative to nonpoint sources (runoff from agriculture and forest lands). Stream flow and nutrient concentration are positively related. The major fraction of the nutrient input is from runoff from snowmelt and from early summer storms. The calculated annual loadings of total N and total P were compared to accepted static and dynamic models to predict the resultant water quality. These comparisons indicated that the impoundment would be heavily overloaded with P and so would be highly eutrophic. Owing to the nonpoint nature of the nutrient sources, they would be difficult and expensive to control. Partly as a result of this assessment, further funding for the impoundment was withdrawn.     

Identification of hydrogeochemical zones in postglacial buried valley aquifer (Wielkopolska Buried Valley aquifer,Poland)

This article presents the difficulty in identifying the hydrochemical zoning of a semi-confined aquifer, characterised by a relative small spatial differentiation of groundwater chemistry. It is shown that multivariate statistical methods can be used for the recognition and interpretation of the groundwater chemistry distribution in an aquifer. The hydrochemical zonation caused by both natural and anthropogenic processes was identified using factor analyses in combination with a classical interpretation of the hydrogeological material. The interpretation of the groundwater chemistry allows both identification of the aquifer recharge mechanism and verification of the groundwater-flow system.     

Diagnostic hydrogeologic characteristics of a karst aquifer (Kentucky, USA)

Laboratory experiments and numerical modeling have shown that dissolution in carbonate aquifers results in high-permeability channel networks. However, the lack of techniques to assess the extent and significance of these channel networks presents a major problem in characterizing carbonate aquifers. This problem was addressed by identifying the differences between two simulations (with and without channels) of the intensely studied limestone aquifer at Mammoth Cave (Kentucky, USA). Long-distance tracer-test results and spring discharges were used for assessing model accuracy as well as head measurements in wells. The channel simulation provided a much better calibration than the homogeneous porous-medium simulation and revealed five important differences: (1) convergent flow to large springs, (2) equipotentials forming troughs, (3) decreases in hydraulic gradient and (4) increases in hydraulic conductivity in a downgradient direction, and (5) substantial scaling effects. These five characteristics are also common in other carbonate aquifers and provide a means of identifying whether a carbonate aquifer is more similar to porous-medium or to karst-aquifer end members.