Natural Geological Formations Research Articles

Dynamic interaction of heavy metals and mineralogical shifts in stream sediments exposed to MSW landfill leachate in a semi-arid basaltic terrain

Investigating concentrations and spatial patterns of physicochemical parameters in landfill leachate and their profound impacts on stream sediments is an important issue for environmental sustainability. Therefore, the present study showed that the specifics landfill leachate and its interactions with stream sediments within the unique geological context of semi-arid basaltic terrain of the Deccan Volcanic Province in Pune, India. Employing advanced geo-accumulation indices and crystal phase differentiation methods, the study unveils the intricate metamorphosis of heavy metals and mineralogical composition, tracing the transformative journey from leachate to sediments. Noteworthy revelations emerge, particularly in the striking associations between heavy metals and the mineralogical composition, which encompasses primary and secondary minerals (calcite, quartz, and Fe–Mg oxides). These findings underscore the acceleration of weathering processes within this distinctive geological milieu. The 'geo-accumulation index' exhibits pronounced elevations in proximity to the landfill site, with persistence downstream, reliant upon the evolving weathering and accumulation dynamics. The lower reaches of the study area have higher concentrations of various heavy metals (Fe, Mn, Zn, Cr, Cu, Ni, Co, Hg, As, and Cd). These heavy metals are primarily sequestered within silt-dominated sediments conquered by augite, olivine and plagioclase minerals. Present research reveals the complex interplay between heavy metals in leachate and their physical and chemical interactions with sedimentary materials. These gradational shifts in mineralogy and geochemistry serve as compelling evidence of the transformative impact of leachate discharge within the distinctive basaltic geological framework. This study offers valuable insights into the complex environmental processes occurring at the intersection of landfill leachate and natural geological formations, enhancing the understanding of the dynamic geochemical interactions that shape this semi-arid basaltic terrain.

Contamination risk assessment and distribution of rare trace metal(loid)s in surface soil of Cerrito Blanco, Mexico using various contamination indices

In many regions of the world, soil contamination of trace metal(loid)s has become a serious problem. Several studies have used contamination risk indices to identify potential risks arising from excessive pollution, but the majority of these analyses have only focused on anthropogenic sources, making data from these studies less meaningful than those from the added past mining sites, which are considered in the present study. The main objective of this study was to examine the contamination of rare trace metal(loid)s in surface soil near the vicinity of historical mining activities. The concentrations and contamination risks of five rare trace metal(loid)s (B, Ba, Sb, Sn, and V) in surface soils were analysed for 39 soil samples collected from the surrounding areas of the past mining areas of Cerrito Blanco, Matehuala in San Luis Potosi, Mexico. The region has a long history of mining activities that has resulted in the release of trace metal(loid)s into the environment. The evaluation of the contamination risk was performed using single standard indices (i.e., geo-accumulation index and contamination factor) and multi-element standard indices (i.e., degree of contamination, modified degree of contamination, pollution load index, metal pollution index, and Nemerow pollution index). The mean trace metal(loid)s concentration in surface soils followed in the decreasing order barium (Ba) > boron (B) > vanadium (V) > antimony (Sb) > tin (Sn), with corresponding values of 48.15, 12.37, 5.36, 1.62, and 1.58 mg/kg, respectively. Evaluated contamination indices revealed that most of the soil samples were not polluted and were below the reference value. The measured values obtained from these indices revealed that the contamination is only caused by past mining activities and natural geological formations. The GIS interpolation technique was used to assess the spatial distribution patterns and mapping process of trace metal(loid)s. However, the contaminated area was less than 10 % of the studied area calculated using a traditional technique, which relies on the proportion of contaminated samples. The significance of this study lies on the processes contributing to soil contamination in Mexico's historical mining regions. The findings offer essential insights for developing appropriate remediation strategies and safeguards to improve soil quality. By considering not only anthropogenic sources but also historical mining activities, this work contributes to a more comprehensive understanding of soil contamination risks and broadens the scope of research in this field.

Arsenic toxicity: sources, pathophysiology and mechanism.

Arsenic is a naturally occurring element that poses a significant threat to human health due to its widespread presence in the environment, affecting millions worldwide. Sources of arsenic exposure are diverse, stemming from mining activities, manufacturing processes, and natural geological formations. Arsenic manifests in both organic and inorganic forms, with trivalent meta-arsenite (As3+) and pentavalent arsenate (As5+) being the most common inorganic forms. The trivalent state, in particular, holds toxicological significance due to its potent interactions with sulfur-containing proteins. The primary objective of this review is to consolidate current knowledge on arsenic toxicity, addressing its sources, chemical forms, and the diverse pathways through which it affects human health. It also focuses on the impact of arsenic toxicity on various organs and systems, as well as potential molecular and cellular mechanisms involved in arsenic-induced pathogenesis. A systematic literature review was conducted, encompassing studies from diverse fields such as environmental science, toxicology, and epidemiology. Key databases like PubMed, Scopus, Google Scholar, and Science Direct were searched using predetermined criteria to select relevant articles, with a focus on recent research and comprehensive reviews to unravel the toxicological manifestations of arsenic, employing various animal models to discern the underlying mechanisms of arsenic toxicity. The review outlines the multifaceted aspects of arsenic toxicity, including its association with chronic diseases such as cancer, cardiovascular disorders, and neurotoxicity. The emphasis is placed on elucidating the role of oxidative stress, genotoxicity, and epigenetic modifications in arsenic-induced cellular damage. Additionally, the impact of arsenic on vulnerable populations and potential interventions are discussed. Arsenic toxicity represents a complex and pervasive public health issue with far-reaching implications. Understanding the diverse pathways through which arsenic exerts its toxic effects is crucial to developing effective mitigation strategies and interventions. Further research is needed to fill gaps in our understanding of arsenic toxicity and to inform public health policies aimed at minimising exposure.Arsenic toxicity is a crucial public health problem influencing millions of people around the world. The possible sources of arsenic toxicity includes mining, manufacturing processes and natural geological sources. Arsenic exists in organic as well as in inorganic forms. Trivalent meta-arsenite (As3+) and pentavalent arsenate (As5+) are two most common inorganic forms of arsenic. Trivalent oxidation state is toxicologically more potent due to its potential to interact with sulfur containing proteins. Humans are exposed to arsenic in many ways such as environment and consumption of arsenic containing foods. Drinking of arsenic-contaminated groundwater is an unavoidable source of poisoning, especially in India, Bangladesh, China, and some Central and South American countries. Plenty of research has been carried out on toxicological manifestation of arsenic in different animal models to identify the actual mechanism of aresenic toxicity. Therefore, we have made an effort to summarize the toxicology of arsenic, its pathophysiological impacts on various organs and its molecular mechanism of action.

Study on CO2 transport in fractal porous media for a Hausdorff fractal derivative advection-dispersion model

PurposeThe classical advection-dispersion equation (ADE) model cannot accurately depict the gas transport process in natural geological formations. This paper aims to study the behavior of CO2 transport in fractal porous media by using an effective Hausdorff fractal derivative advection-dispersion equation (HFDADE) model.Design/methodology/approachAnomalous dispersion behaviors of CO2 transport are effectively characterized by the investigation of time and space Hausdorff derivatives on non-Euclidean fractal metrics. The numerical simulation has been performed with different Hausdorff fractal dimensions to reveal characteristics of the developed fractal ADE in fractal porous media. Numerical experiments focus on the influence of the time and space fractal dimensions on flow velocity and dispersion coefficient.FindingsThe physical mechanisms of parameters in the Hausdorff fractal derivative model are analyzed clearly. Numerical results demonstrate that the proposed model can well fit the history of gas production data and it can be a powerful technique for depicting the early arrival and long-tailed phenomenon by incorporating a fractal dimension.Originality/valueTo the best of the authors’ knowledge, first time these results are presented.

In-situ physical properties of reclaimed lands in Singapore

Reclaimed land construction is crucial for sustainable development of the land-scarce city-state of Singapore. To characterize the physical properties of two different types of reclaimed lands — one with well-sorted sands and the other with municipal solid waste — we conduct both active and passive seismic surveys at the sites and compare them with natural geologic formations. From the multichannel surface wave analysis, we observe more complex features related to mode kissing, mode jump, and mode loss on the dispersion spectra of the reclaimed lands, indicating complex subsurface structures. To utilize multiple orders of Rayleigh waves for inversion, we design a quantitative procedure to optimize the mode-order assignment. Seismic data and inverted results show that an older municipal solid waste landfill is more heterogeneous and stronger in its shear strength compared to the younger landfill. The reclaimed land filled with sand is more homogeneous and weaker in shear strength than the natural sedimentary rock formation. The contrast of physical properties at the four sites suggest a significant acceleration in soil hardening when landfill materials are chemically reactive with each other and with the environment. These in-situ measurements are crucial for civil engineering constructions and redevelopment of reclaimed lands in the future.

Taksonomska i ekološka analiza flore lokaliteta „Đavolja Varoš“ (Južna Srbija)

Djavolja Varoš, one of the most atractive natural geological formations of errosive origin in Serbia, is situated in the south of the country, and protected by national legislation as a Natural Monument. The taxonomic and ecological analysis of flora in this area has not been processed yet, so we performed a survey of flora in this locality. Plant species were collected, herbarized, and taxonomic and biological spectrum analyses were conducted. This field study revealed that the vascular flora of the study area was made up of 130 constituent species, which belonged to 81 genera and 41 families. The biological spectrum of the flora is characterised by high presence of hemicryphytes (38%) and geophytes (20%).

Between Natural and Anthropogenic Coastal Landforms: Insights from Ground Penetrating Radar and Sediment Analysis

Both natural and anthropogenic coastal landforms characterize Penang Island. As years have passed it is a challenge to differentiate the genuineness of landmasses created by natural geological formations or by coastal reclamation projects. An account is given of the environmental impact of solid wastes used for reclaiming land in coastal areas of Penang and of the impact of a major sewage outfall in the western channel. Leaching of heavy metals was shown to be one of the main sources of contamination from solid wastes. This paper presents eight lines of ground penetrating radar (GPR) surveys and sediment analysis to identify the anthropogenic interventions that shaped the urban landscape of Penang Island by excavations, filling, and embankment construction along the coastline and differentiate it from the natural one. The surveys were implemented in two locations, the Batu Ferringhi area, representing the natural coastline, and Persiaran Bayan Indah (the Queensbay Mall area), representing the anthropogenic coastal landform. The apparent depth of penetration that was achieved using a 250-MHz antenna is limited (less than 5 m). The results show between natural and anthropogenic sediment recorded different radar facies. In complement mode, mean grain size distribution, sorting, skewness, and kurtosis graphics of sediment samples from both sites correspond with the GPR data. This technique can likely be applied to the developing coast, where natural and anthropogenic coastal landform data is incomplete, considering future coastline development.

Inspirative geology -the influence of natural geological formations and patterns on contemporary landscape design

Throughout the history of landscape design, we have witnessed many examples where natural features were used as symbolic elements of manmade landscapes and gardens. This influence of landscape geology had its impact on contemporary landscape architecture, resulting in diverse and innovative applications, which are the main topic of our discussion. The article is intended to demonstrate the trend of drawing inspiration from natural landscape features in contemporary landscape architecture in a new and complex way, focusing particularly on the influence of geology, geomorphology and tectonics. A study was conducted on twelve available, published contemporary landscape projects from the last two decades analysing the imitation of nature in the designs, with photo documentation and description. The aim is to identify how ‘native geology’ can influence today’s landscape architecture, which formations are inspirative, where and how they are integrated to the contemporary artistic design. Furthermore, in order to develop a complex understanding on how these references applied to the sites enhance the experience of the space. The selected projects are compared according to pairs of contrasting qualities that are related to measurable characteristics of a space. This will finally lead to identifying some common trends of today’s landscape architecture in applying this geology-inspired design approach.

Understanding and creating biocementing beachrocks via biostimulation of indigenous microbial communities.

Bacterially induced precipitation of minerals leading to cementation of natural geological formations has been well recorded in a variety of environments. A range of microbial pathways and geochemical processes have been found to influence the cementation processes; but detailed formation mechanisms and biogeochemical relationships are still not very clear. There has been a growing demand for the application of bacterially driven biocementation in a number of geotechnical engineering applications recently. Here, we aimed to unpin the mechanisms behind the formation of actively mineralising beachrock sediments at Lucky Bay in Western Australia to understand the natural accretionary processes and potential of indigenous bacterial communities in biocementation. We observed ferruginous, aluminosilicate and carbonate cements along with extensive extra polymeric substances, borings with possible microbial activities in certain sections of native beachrock sediments. Cement precipitation under calcium- and iron-rich microenvironments sourced from seawater and iron creek seems to be driven by both biogenic and abiogenic processes in nature. Native microbial communities with a dominance of the genera Halococcus and Marinobacter were recorded. Enrichment of native bacterial communities under seawater media conditions was conducted which lead to successful biomineralisation of calcitic and ferruginous cements under in vitro conditions although the community composition changed significantly. Nanomechanical properties of natural and laboratory synthesised cement crystals showed that engineered biocement is highly promising. The results of this study clearly demonstrate biological influence in the formation of natural cements and hint significant potential of biostimulation which can be harnessed for different engineering applications including coastal erosion.

Aplicación de la fotogrametría automatizada y de técnicas de iluminación con herramientas SIG para la visualización y el análisis de una piedra con relieves antropomorfos

<p><strong>Extended Abstract:</strong></p><p>We present a methodological approach for the representation, visualisation and analysis of three-dimensional (3D) models of meaningful details in stone reliefs provided by digital documentation tools and subsequent processing. For this aim, anthropomorphous shapes engraved on a flat stone slab found in Sierra de Fontcalent (Alicante) are studied. The object under consideration was located near two archaeological sites, Cova del Fum–a cave with presence of the Chalcolithic material (López, 2010)–and the archaeological site of Fontcalent, with remains from different phases of occupation spanning from 7th-6thBC to the 20thcentury (Ximénez, 2012).</p><p>In the last few years, the use of digital tools provided by new technologies and software development has left traditional work methodology behind (De Reu et al., 2014)while enabling the development of new approaches to both minimise heritage alteration and provide objective and accurate information (Lopez-Menchero, Marchante, Vincent, Cárdenas, & Onrubia, 2017). 3D documentation allows recording of cultural heritage at a reasonable cost with precision and quality through digital photography and SfM (Structure from Motion) photogrammetry with specialised software (De Reu et al., 2013).</p><p>In this project, recording and documentation with digital photography and automated photogrammetric techniques are applied to the Fontcalent stone slab for its digitisation and subsequent 3D representation. From the resulting model, a two-folded line of study is obtained. On the one hand, a Digital Elevation Model (DEM) is generated to study the microtopographies of the stone with geographic analysis techniques provided by Geographic Information Systems (GIS) from different lighting conditions and surface reflections, which are calculated by hillshading or LRM (Local Relief Model) for the interpretation of the object (Carrero-Pazos, Vilas, Romaní, & Rodríguez, 2014;Gawior, Rutkiewicz, Malik & Wistuba, 2017).On the other hand, from both the 3D model and the point cloud, the study is completed with the application of the methods of analysis and visualisation based on the Morphological Residue Model (MRM) which stands out every single detail of the surface morphology of the object (Caninas, Pires, Henriques, & Chambino, 2016;Correia, Pires, & Sousa, 2014). Further visualisations are based on Reflectance Transformation Imaging (RTI) which provides different shadows and reflections over the object from the application of a multidirectional illumination (Happa et al., 2010; Malzbender, Gelb, Wolters, & Zuckerman, 2000; Mudge et al., 2010).</p><p>The results thus obtained of the Fontcalent stone slab allow us to visualise several characteristic elements. The anthropomorphous figure awaking interest is also combined with the figure resulting from different visualisations applied with GIS techniques which may resemble a zoomorph. The use of visualisation techniques shown in this study has been fundamental in order to recognise the latter element. The composition reveals a zigzag line already appreciated before the study so that it is interesting to check if visualisations based on GIS techniques are able to highlight it though being shallow incisions. In our experience regarding this study, visualisation by using the hillshading technique shows a greater level of 3D detail than that provided by the application of the sky-view factor technique which offers a flattering view. However, the former technique may occasionally show shadows which hide other details, unlike the latter technique which plots the entire slab surface illuminated while differentiating the associated microtopography on the basis of its marks. The use of shaders in combination with hillshading and particularly combined with high pass filtering, contributes to improving the visualisation and accuracy of shadowed areas. As a result, we conclude that the results obtained in this work by lighting techniques with GIS add a greater level of detail in comparison to those provided by the mesh or the point cloud.</p><p>The study of the Fontcalent stone slab paves the way for two working hypotheses to be developed: on the one hand, its anthropological origin possibly related to the Chalcolithic, and on the other hand, its study as natural geological formations with ichnofossils.</p><p>The digitisation of cultural heritage with available 3D technologies should be a mandatory requirement when facing any study, analysis or intervention. With the current development of such techniques, we have verified their contribution to fundamental characteristics in the corresponding stages of visualisation and study. Thus, the proposed methodology is presented as an accurate and complete alternative for the study and analysis of the existing cultural heritage, and opens new ways for the revision, reinterpretation and revaluation of the previously evaluated heritage through traditional techniques.</p>

Porosity and tortuosity influence on geophysical properties of an artificially cemented sand

Electrical resistivity, saturated hydraulic permeability and P wave velocity are investigated for an artificially cemented sand. The calibration of some known equations used in geophysical characterization tests relating these properties is done considering the presence of artificial bonds. In this case bonds are the hydrated cemented minerals coating the grains. An extensive set of experimental tests was performed, which data is presented in the paper. Artificially cemented sands were prepared with different cement dosages and different water/cement ratios in weight for each dosage. Bonds distribution in the tests performed was controlled by the water used in grout preparation.Known relationships between the geophysical properties studied and porosity, and between electrical resistivity and P wave velocity or hydraulic conductivity, were adopted and calibrated to identify constants to be used for the sand-cement mixtures. Although the different scales, the values found for these constants were compared with those usually found in natural geological formations tested in similar conditions. The existence of such relationships show that it is possible to detect such materials through in situ data interpretation, however scale effects and log resolution must be considered to define the constants for field data.The results are commented considering the presence of the electrically conductive hydrated cement minerals, and how they affect porosity and tortuosity considered in the calibration of the relationships adopted. It is proposed different tortuosities for electrical current and water flow for the cases when electrical conduction through the electrically charged surfaces is more important than through the free liquid phase in the interconnected pores of the saturated material.

Discrete fracture model for coupled flow and geomechanics

We present a fully implicit formulation of coupled flow and geomechanics for fractured three-dimensional subsurface formations. The Reservoir Characterization Model (RCM) consists of a computational grid, in which the fractures are represented explicitly. The Discrete Fracture Model (DFM) has been widely used to model the flow and transport in natural geological porous formations. Here, we extend the DFM approach to model deformation. The flow equations are discretized using a finite-volume method, and the poroelasticity equations are discretized using a Galerkin finite-element approximation. The two discretizations—flow and mechanics—share the same three-dimensional unstructured grid. The mechanical behavior of the fractures is modeled as a contact problem between two computational planes. The set of fully coupled nonlinear equations is solved implicitly. The implementation is validated for two problems with analytical solutions. The methodology is then applied to a shale-gas production scenario where a synthetic reservoir with 100 natural fractures is produced using a hydraulically fractured horizontal well.

Underwater Archaeological Exploration of the Mayan Cenotes

Cenotes are natural geological formations, commonly known as sinkholes, which are often linked to subterranean galleries with groundwater. These natural wells constitute complex and dynamic hydraulic systems that have a long history of interaction with the surrounding civilizations. These ‘time capsules’ contain information pertaining to the symbolic and religious aspects linked to the Mayan culture, as well as to geological processes in the Peninsula of Yucatán. Archaeologists, geologists and biologists are working together to study these unique sites using specialized speleological diving techniques. However, the cenotes have also become a tourist attraction and a spot favoured by sports divers. Consequently, treasure hunting has become a constant threat. A sustainable management programme should permit both public enjoyment of these unique cultural heritage sites and ensure their preservation.

Lagrangian simulation of multidimensional anomalous transport at the MADE site

Contaminant transport through regional‐scale natural geological formations typically exhibits several “anomalous” features, including direction‐dependent spreading rates, channeling along preferential flow paths, trapping of solute in relatively immobile domains, and/or the local variation of transport speed. Simulating these plume characteristics can be computationally intensive using a traditional advection‐dispersion equation (ADE) because anomalous features of transport generally depend on local‐scale subsurface properties. Here we develop an alternative simulation approach that solves the full nonlocal, multidimensional, spatiotemporal fractional‐order ADE with variable coefficients in a Lagrangian framework using a novel non‐Markovian random walk method. This model allows us to simulate anomalous plumes without the need to explicitly define local‐scale heterogeneity. The simple model accurately simulates the tritium plume measured at the extensively characterized MADE test site.

Multiscale Description and Upscaling of Fluid Flow in Subsurface Reservoirs

Natural geological formations are complex objects, involving geological, mechanical, physico-chemical processes occurring over very wide length scales and time scales. Phenomena ranging from the molecular scale to several hundred of kilometers may influence the overall behaviour of fluid transport in a geological formation. For example, wettability properties, themselves due to molecular effects, have a very strong impact on the water/oil displacements in oil reservoirs. Analogously, reservoir heterogeneities that cover a large range of spatial scales play an essential role to channel fluid-flows, especially when they are coupled with non linearities inherent to fluid dynamics. In order to face this complexity, and to be able to hierarchize the influence of the various relevant geological and physico-chemical phenomena, it is thus essential to handle a multiscale description of fluid transport in these reservoirs. This is an essential tool to help reservoir engineers to focus on the crucial phenomena that control the flow. This helps them to integrate data, and this results in a lowering of the uncertainties of the reservoir description that enhances economical decisions. In this paper, we present classical upscaling approaches, as well as more recent multiscale concepts.

Fractional advection‐dispersion equation: A classical mass balance with convolution‐Fickian Flux

The classical form of the partial differential equation governing advective‐dispersive transport of a solute in idealized porous media is the advection‐dispersion equation (ADE). This equation is built on a Fickian constitutive theory that gives the local dispersive flux as the inner product of a constant dispersion tensor and the spatial gradient of the solute concentration. Over the past decade, investigators in subsurface transport have been increasingly focused on anomalous (i.e., non‐Fickian) dispersion in natural geologic formations. It has been recognized that this phenomenon involves spatial and possibly temporal nonlocality in the constitutive theory describing the dispersive flux. Most recently, several researchers have modeled anomalous dispersion using a constitutive theory that relies on fractional, as opposed to integer, derivatives of the concentration field. The resulting ADE itself is expressed in terms of fractional derivatives, and they are described as “fractional ADEs.” Here we show that the fractional ADE is obtained as a special case of the authors’ convolution‐Fickian nonlocal ADE [Cushman and Ginn, 1993]. To obtain the fractional ADE from the convolution‐Fickian model requires only a judicial choice of the wave vector and frequency‐dependent dispersion tensor.

Scaling of fracture connectivity in geological formations

A new method to quantify fracture network connectivity is developed and applied to analyze two classical examples of fault and joint networks in natural geological formations. The connectivity measure accounts for the scaling properties of fracture networks, which are controlled by the power law length distribution exponent a, the fractal dimension D and the fracture density. The connectivity behavior of fracture patterns depends on the scale of measurement, for a < D + 1, but is independent of scale for a > D + 1. Analysis of the San Andreas fault system shows that a < D+1 and that the connectivity threshold is reached only at a critical length scale. In contrast, for a typical sandstone joint pattern, a ≈ D + 1, which is on the cusp where the connectivity threshold is highly sensitive to the minimum fracture length in the system.

The epidemiology of chemical contaminants of drinking water

A number of chemical contaminants have been identified in drinking water. These contaminants reach drinking water supplies from various sources, including municipal and industrial discharges, urban and rural run-off, natural geological formations, drinking water distribution materials and the drinking water treatment process. Chemical contaminants for which epidemiologic studies have reported associations include the following: aluminium, arsenic, disinfection by-products, fluoride, lead, pesticides and radon. Health effects reported have included various cancers, adverse reproductive outcomes, cardiovascular disease and neurological disease. In evaluating epidemiologic studies for risk assessment, considering whether the study design was qualitative (hypothesis generating) or quantitative (hypothesis testing) is important and whether sufficient epidemiologic data of a quantitative nature exists to determine the dose–response curve. Each of the chemical contaminants mentioned are summarized by study designs (qualitative and quantitative) and whether a dose–response curve based on epidemiologic data has been proposed. Environmental epidemiology studies are driven by environmental exposures of interest. For drinking water contaminants, the design of epidemiologic studies and their interpretation should consider the following exposure issues: the source of the contaminant; other sources of the contaminant; the route of exposure; the frequency, duration and magnitude of exposure; the ability to document an actual internal dose; and the ability to document the dose to the target organ. Health effects of concern have other risk factors that must be measured in the conduct of these studies. In evaluating epidemiologic studies, potential errors and biases that may occur must be considered given the very low magnitude of associations (less than 2.0 for either odds ratio or risk ratio). Given the issues, the next generation of drinking water epidemiologic studies should include a multidisciplinary team beyond traditional epidemiologists and statisticians. Study teams will require toxicologists, chemists, engineers and exposure assessors. Arsenic is briefly discussed as an example of the importance of susceptible populations. Disinfection by-products are discussed as an example of epidemiologic studies of mixtures.

A Stochastic Approach to the Characterization of Lithofacies From Surface Seismic and Well Data

Heterogeneity of natural geologic formations strongly influences groundwater flow and contaminant migration. This study presents a formal stochastic approach for the integration of surface seismic data and well data into the identification of the spatial arrangement (location, geometry, and interconnectedness) of lithofacies and incorporating this information in the estimation of the log permeability probability density function (pdf). To achieve this goal, normal move‐out (NMO) corrections are applied to the seismic reflection data to estimate interval seismic velocities. Calibration curves constructed from the well logs transform these velocity estimates into a lithology indicator prior probability field. From the well data and the indicator prior probability field, the indicator covariance function and its associated confidence limits are computed. Neighboring lithology logs and the indicator covariance function are then combined to update the indicator probability field. The conditional log permeability pdf is finally computed by weighting the log permeability distribution of each lithology with respect to its indicator probability field. The effectiveness of the proposed procedure is shown to depend on the quality of the seismic data and the degree of correlation between seismic and hydrogeologic soil properties. A synthetic case study is performed which shows that the surface seismic and well data complement each other with optimal results achieved when both types of data are incorporated into a joint identification procedure.

Heterogeneous porous media in hydrology

In natural geologic formations, flow and transport‐related processes are perturbed by multidimensional and anisotropic material heterogeneities of diverse sizes, shapes, and origins (bedding, layering, inclusions, fractures, grains, for example). Heterogeneity tends to disperse and mix transported quantities and may initiate new transfer mechanisms not seen in ideally homogeneous porous media. Effective properties such as conductivity and dispersivity may not be simple averages of locally measured quantities.The special session, “Effective Constitutive Laws for Heterogeneous Porous Media,” convened at AGU's 1992 Fall Meeting in San Francisco, addressed these issue. Over forty‐five contributions, both oral and poster, covering a broad range of physical phenomena were presented. The common theme was the macroscale characterization and modeling of flow and flow‐related processes in geologic media that are heterogeneous at various scales (from grain size or fracture aperture, up to regional scales). The processes analyzed in the session included coupled hydro‐mechanical processes; Darcy‐type flow in the saturated, unsaturated, or two‐phase regimes; tracer transport, dilution, and dispersion. These processes were studied for either continuous (porous) or discontinuous (fractured) media.