Geochemical Indicators of Intrinsic Bioremediation

A detailed field investigation has been completed at a gasoline-contaminated aquifer near Rocky Point, NC, to examine possible indicators of intrinsic bioremediation and identify factors that may significantly influence the rate and extent of bioremediation. The dissolved plume of benzene, toluene, ethylbenzene, and xylene (BTEX) in ground water is naturally degrading. Toluene and o-xylene are most rapidly degraded followed by m-, p-xylene, and benzene. Ethylbenzene appears to degrade very slowly under anaerobic conditions present in the center of the plume. The rate and extent of biodegradation appears to be strongly influenced by the type and quantity of electron acceptors present in the aquifer. At the upgradient edge of the plume, nitrate, ferric iron, and oxygen are used as terminal electron acceptors during hydrocarbon biodegradation. The equivalent of 40 to 50 mg/I of hydrocarbon is degraded based on the increase in dissolved CO₂ relative to background ground water. Immediately downgradient of the source area, sulfate and iron are the dominant electron acceptors. Toluene and o-xylene are rapidly removed in this region. Once the available oxygen, nitrate, and sulfate are consumed, biodegradation is limited and appears to be controlled by mixing and aerobic biodegradation at the plume fringes.     

A Method for Estimating Field-Scale Mass Transfer Rate Parameters and Assessing Aquifer Cleanup Times

A general method for estimating ground-water solute mass transfer rate parameters from field test data is presented. The method entails matching solute concentration and hydraulic head data collected during the recovery phase of a pumping test through application of a simulation-regression technique. Estimation of hydraulic conductivity and mass transfer rate parameter values is performed by fitting model simulations to the data. Parameter estimates are utilized to assess cleanup times for pump-and-treat aquifer remediation scenarios. Uncertainty in the cleanup time estimate is evaluated using statistical information obtained with the parameter estimation technique. Application of the method is demonstrated using a hypothetical ground-water flow and solute transport system. Simulations of field testing, parameter estimation, and remedial time frames are performed to evaluate the usefulness of the method. Sets of random noise that signify potential field and laboratory measurement errors are combined with the hypothetical data to provide rigorous testing of the method. Field tests are simulated using ranges of values for data noise, the mass transfer rate parameters, the test pumping rates, and the duration of recovery monitoring to evaluate their respective influence on parameter and cleanup time estimates. The demonstration indicates the method is capable of yielding accurate estimates of the solute mass transfer rate parameters. When the parameter values for the hypothetical system are well estimated, cleanup time predictions are shown to be more accurate than when calculated using the local equilibrium assumption.     

Comparison between fe prediction and results from dynamic centrifuge tests on tilting gravity walls

An analytical model is developed to analyze the seismic response of gravity walls retaining and founded on dry sand, with special emphasis on tilting behaviour. A well verified two-dimensional finite element code is used for this purpose. The analytical model is verified by comparing predictions to results from three dynamic centrifuge tests, with satisfactory agreement. Moreover, sensitivity analyses are carried out for one of the centrifuge test conditions to understand how the results would change if the boundary conditions and rotational stiffness of the wall were changed.     

Detecting Changes in Ground Water Quality at Regulated Facilities

The Resource Conservation and Recovery Act (PL 94–580) and related federal and state legislation have mandated routine monitoring of ground water quality at regulated facilities. The objective of the required monitoring activities is detection of adverse changes in ground water quality caused by the facilities.
Both failure to detect pollution and an incorrect determination of pollution can be very expensive. It is crucial, therefore, that monitoring programs be designed and operated to provide statistically sound information. It is equally important that users of ground water quality data understand the nature and limitations of information from monitoring.
To address the preceding issues, the authors present a general approach to analyzing ground water quality data in light of the stated monitoring objective. The suggested approach accounts for "natural" variation in background water quality through pairing of observations. The limitations of quarterly sampling for detecting small changes in quality over a short time frame are discussed.     

Mercury contribution to an adirondack lake

Elevated copper, lead, and zinc concentrations in the upper 10 to 20 cm of sediment sampled from Cranberry Lake, a large Adirondack lake, are attributed to atmospheric contributions. Pb-210 and pollen core data, however, suggest Cranberry Lake also received mercury discharges during the turn of the century when the area was the center of extensive lumbering and related activities. Elevated mercury concentrations in Cranberry Lake smallmouth bass derived from remobilization from mercury-contaminated bottom sediments which increased the bioavailability to Cranberry Lake organisms. Mercury remobilization and accumulation by fish are promoted by fluctuating pH values resulting from acid precipilation.     

Geochemistry,geochronology, and petrogenesis of a Late Precambrian (∼ 590 Ma) composite dike from the North Eastern Desert of Egypt

Late Precambrian (575–600 Ma) igneous activity in the North Eastern Desert of Egypt produced large volumes of compositionally bimodal magmas. A single composite dike was studied to further examine petrogenetic relationships between andesitic and rhyolitic melts. The dike consists of 1.5–2 m of andesite on either side of a 5–6 m wide rhyolite core. Contact relations indicate that the andesite and rhyolite simultaneously existed as porphyritic liquids. Wholerock Rb-Sr dating indicates an age of 591 Ma, but with considerable scatter. Andesite and rhyolite had similar initial⁸⁷Sr/⁸⁶Sr of 0.7032±2, indicating derivation from a low Rb/Sr source, either the upper mantle, very young upper crust, or depleted lower crust. The composition of the andesites on either margin cannot be distinguished; these are very similar to andesites of the Dokhan Volcanics of similar age. Correspondingly, the rhyolite is compositionally similar to the epizonal Pink Granites. This dike and others like it represent hypabyssal feeders for the extrusive and shallow intrusive members of the North Eastern Desert bimodal suite.Major and trace element studies of the dike rocks show no evidence of mixing. With the exception of the alkaline earths, there is no evidence of diffusional transport across the rhyolite-andesite contacts. REE patterns indicate that petrogenesis of the andesite must have left a garnetiferous residue: either 10% melting of LREE-enriched garnet lherzolite or 25% melting of eclogite, followed by a small amount of shallow fractionation. Petrogenesis of the rhyolites remains enigmatic. Partitioning of trace elements and different plagioclase compositions in andesite and rhyolite argue against an origin by liquid immiscibility. Major and trace element models indicate that the rhyolite formed by fractional crystallization of the andesite or by anatexis of young amphibolite-facies crust.

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Zusammenfassung SpÄtprÄkambrische (575–600 Ma) magmatische AktivitÄt in der »North Eastern Desert« Ägyptens förderte gro\e Mengen bimodaler Magmen. Um die petrogenetischen Beziehungen zwischen andesitischen und rhyolitischen Schmelzen zu studieren, wurde ein einzelner, »bimodaler« Gang (composite dyke) untersucht.Der Gang besteht aus einem Rand von 1,5–2 m mÄchtigem Andesit auf beiden Seiten eines 5–6 m mÄchtigen Kernbereiches von Rhyolit. Die Kontaktbeziehungen zeigen, da\ Andesite und Rhyolite gleichzeitig als porphyritische Schmelzen existierten. »Whole-Rock« Rb-Sr Datierung ergab ein Alter von 591 Ma, jedoch mit einem erheblichen Fehler. Andesit und Rhyolith hatten Ähnliche initiale⁸⁷Sr/⁸⁶Sr VerhÄltnisse von 0.7032±2, die eine Herkunft aus Bereichen mit niedrigen Rb/Sr VerhÄltnissen erkennen lassen: Oberer Mantel, sehr junge obere Kruste, oder verarmte untere Kruste. Die Zusammensetzung der Andesite von den verschiedenen Seiten des Ganges ist nicht zu unterscheiden. Sie sind den Andesiten der Dokhan Vulkanite Ähnlich und etwa gleich alt. Entsprechend sind die Rhyolite den epizonalen rosa Graniten (»pink granite«) in der Zusammensetzung Ähnlich. Dieser Gang und andere gleich ihm stellen die Zufuhrspalten für die extrusiven und seichtintrusiven Magmatite der »North Eastern Desert« bimodalen Folge dar.Haupt- und Spurenelemente der Ganggesteine zeigen keine Anzeichen einer Mischung. Mit Ausnahme der Erdalkalien gibt es keinen Hinweis auf eine Diffusion der Elemente über den Rhyolit-Andesit Kontakt. Die Verteilung der Seltenen Erden deutet auf ein granatführendes Residuum bei der Petrogenese der Andesite: entweder10% Aufschmelzen von Granat-Lherzolit, angereichert an leichten Seltenen Erden, oder 25% Aufschmelzen von Eklogit, gefolgt von geringer Fraktionierung unter niedrigem Druck.Die Petrogenese der Rhyolite bleibt unklar. Die Verteilung der Spurenelemente und die unterschiedliche Plagioklas-Zusammensetzung in Andesit und Rhyolith sprechen gegen eine Entstehung aus unvermischbaren Schmelzen. Modelle basierend auf Haupt- und Spurenelementen deuten darauf hin, da\ der Rhyolit entweder durch fraktionierte Kristallisation des Andesits entstand oder durch Anatexis junger Kruste im Bereich der Amphibolit-Fazies.

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Résumé L'activité magmatique au Précambrien supérieur (575–600 Ma) dans le »North Eastern Desert« d'Egypte a engendré de grandes quantités de magmas bimodaux. De manière à préciser les relations entre fusions andésitiques et rhyolitiques, un dyke composite a été étudié.Ce dyke est constitué d'un coeur rhyolitique de 5 à 6 m, encadré de deux bordures andésitiques de 1,5 à 2 m. Les contacts indiquent que ces deux roches ont coexisté sous la forme de liquides porphyriques. Une datation Rb-Sr sur roche totale donne un âge de 591 Ma, mais avec une approximation importante. L'andésite et la rhyolite ont un mÊme rapport initial de 0,7032±2, indiquant une source à faible rapport Rb/Sr: manteau supérieur, croûte supérieure jeune ou croûte inférieure appauvrie. Les compositions des deux bordures andésitiques sont identiques et très semblables à celle des andésites de mÊme âge du complexe volcanique du Dokhan. De mÊme, la rhyolite a une composition semblable à celle des granites roses épizonaux. Ce dyke et d'autres du mÊme type représentent les voies d'alimentation des termes extrusifs et intrusifs superficiels de la série bimodale du »North Eastern Desert«.L'étude des éléments majeurs et en traces ne montre aucun mélange entre les roches du dyke. A l'exception des alcalino-terreux, il n'existe aucune indication de diffusion des éléments à travers le contact rhyolite — andésite. La distribution des terres rares montre que la genèse de l'andésite doit avoir laissé un résidu grenatifère: soit une lherzolite à grenat enrichie en terres rares légères et représentant moins de 10% de taux de fusion, soit une éclogite (jusqu'à 25% de taux de fusion) suivie d'un léger fractionnement à basse pression.La pétrogenèse de la rhyolite reste obscure. La répartition des éléments en traces et la différence de composition du plagioclase entre l'andésite et la rhyolite plaident contre une origine par immiscibilité. Les modèles tirés des éléments majeurs et en traces indiquent comme origine pour la rhyolite soit la cristallisation fractionnée de l'andésite, soit l'anatexie de matériaux crustaux jeunes dans les conditions du facies des amphibolites.

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Field sampling in estuaries: The relationship of scale to variability

The spatial/temporal scaling problem (i.e., fitting a given research question to the dimensions of variability of the study area) is particularly pronounced in highly variable systems such as estuaries. Long-term, multidisciplinary studies in the Apalachicola Bay system were used to evaluate variation of different physical, chemical, and biological factors. Specific limitations of weekly, monthly, and quarterly sampling intervals were directly related to the efficiency of the sampling gear, the range of variation in the study parameters, and specific biological features (motility, recruitment, natural history) of infaunal macroinvertebrates and epibenthic organisms. There are families of spatial and temporal scaling phenomena that should be considered when establishing a given field sampling program. The dimensions of variation change along spatial/temporal gradients of salinity, habitat complexity, and productivity and among different levels of biological organization. The limits of variation define the needed sampling effort for a given level of estimation. Without an adequate evaluation of such variation, representative samples cannot be taken; the resulting inadequate sampling effort often precludes reliable comparisons and robust generalization. There is a continuum of scaling dimensions (and sampling problems) that ranges from small-scale experimental approaches to system-wide analyses. Misapplication of such scaling estimates has led to overgeneralization of experimental results. Currently, there is widespread misapplication of combinations of unrelated, limited sampling efforts to broad-scale resource problems. The loss of valuable estuarine resources is favored by the lack of adequate scientific databases that are consistent with the dimensions of the individual study areas. Unless experimental studies and field sampling programs are scaled to the dimensions of the research problem and the study area in question there will be a continued proliferation of trivial studies at one end of the continuum and the progressive deterioration of estuarine resources at the other.