Carbonate equilibria in hydrothermal systems: First ionization of carbonic acid in NaCl media to 300°C

The ionization quotients of aqueous carbon dioxide (carbonic acid) have been precisely determined in NaCl media to 5 m and from 50° to 300°C using potentiometric apparatus previously developed at Oak Ridge National Laboratory. The pressure coefficient was also determined to 250°C in the same media. These results have been combined with selected information in the literature and modeled in two ways to arrive at the best fits and to derive the thermodynamic parameters for the ionization reaction, including the equilibrium constant, activity coefficient quotients, and pressure coefficients. The variation with temperature of the two fundamental quantities $\text{Δ}\text{V}\text{?}{}^{\mathrm{o}}$ and $\text{Δ}\text{C}\text{?}{}^{\mathrm{o}}{}_{\mathrm{p}}$ were examined along the saturation vapor pressure curve and at constant density. The results demonstrated again that for reactions with minimal electrostriction changes the magnitudes and variations of $\text{Δ}\text{C}\text{?}{}^{\mathrm{o}}{}_{\mathrm{p}}$ and $\text{Δ}\text{V}\text{?}{}^{\mathrm{o}}$ with temperature are small and, in addition, $\text{Δ}\text{C}\text{?}{}_{\mathrm{p}}$ and $\text{Δ}\text{V}\text{?}$ are approximately independent of salt concentration.The results have also been applied to an examination of the solubility of calcite as a function of pH (in a given NaCl medium) for the neutral to acidic region both for systems with fixed CO₂ pressure and systems where the calcium ion concentration equals the concentration of carbon. The pH of saturated solutions of calcite with P_CO2 of 12 bars increases from 5.1 to 5.5 between 100° and 300°C.     

The relation between typical concentrations of chemical constituents in potable water and their injurious limits

 There is an obvious similarity between the values of the typical concentrations of the inorganic and synthetic organic constituents in potable water and their injurious limits to human health. This similarity is attributed to the adaptation of man to his environment, i.e. it has resulted from natural selection. Received: 6 August 1999 · Accepted: 30 November 1999     

Discontinuity controlled probabilistic slope failure risk maps of the Altindag (settlement) region in Turkey

The evaluation of potential rock slope problems using stereographic projection techniques known as kinematic analysis is one of the most important parts of a slope stability investigation to be carried out in jointed rock media. In conventional stereoprojection techniques for the assessment of possible rock slope failures, the peak orientations of joints together with the slope geometry and the friction angle of the weakness planes are used. Other possible joint orientations which may be encountered in the rock media are ignored, although they belong to the group of joint peak orientations. In this study, nearly vertical jointed andesites cropped out at the Altindag settlement region in Ankara were studied in order to evaluate the relevance of this ignored discontinuity orientation data on slope stability. As a result, probabilistic risk maps for planar, toppling and wedge failures were produced using the kinematic rules and digital elevation model of the study area. The comparison of the distribution of the actual failures in the area and the probabilistic risk maps prepared for the study area revealed that all of the identified failures are found to be located in the higher risk zones on the probabilistic risk maps.     

COUNTERURBANIZATION IN THE FEDERAL REPUBLIC OF GERMANY*

Since Berry argued in 1976 that counterurbanization had replaced urbanization in the U.S., a debate has ensued as to whether the phenomenon also exists in Western Europe. Proponents of a developmental theory of counterurbanization contend that the phenomenon should be evident in countries which have achieved a very high level of socioeconomic development, including the Federal Republic of Germany (FRG). Most of the German and English language literature on the topic suggests the contrary for the FRG. Here urbanization and counterurbanization are restricted to specific geographic meanings, i.e., spatial agglomeration and deglomeration. Results from four interrelated tests show a trend toward counterurbanization evident as early as the 1960s in the post-war regional demographic data of the FRG.     

Urban settlement size trends in the former USSR: 1970-1989

"Based upon recently published data, this paper investigates urban settlement size trends in the former USSR and its republics during the intercensal periods of 1970-1979 and 1979-1989. Results indicate that although a trend toward largeness of the Soviet urban hierarchy continues, a slowing in this direction has occurred. Among republics, all had an increasing trend towards largeness on at least one and usually all three summary measures of urban settlement size structure. The RSFSR [Russia] and Armenia especially consistently evidenced a relatively high degree of largeness, while the former Baltic republics generally revealed a relative smallness."     

Structural elements in southeastern Quebec,northwestern Appalachians,Canada

An attempt is made to correlate and separate in terms of style and time two contrasting sets of structural elements in the northwestern part of the Appalachian Uplands in the Province of Quebec, Canada. There is sufficient evidence to indicate that a fold system with north-south trending axes is superimposed on a fold system with east-west axes. It is suggested that the two sets of structures represent pulses of one long-continued deformation accompanied by corresponding early and late phases of metamorphism.

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Zusammenfassung Es wurde versucht, in den Appalachen des südöstlichen Teiles der Provinz Quebec, Kanada, zwei ungleichzeitige tektonische Systeme verschiedenen Baustils zu trennen. Die komplexen Kleinstrukturen zeigen, da\ Ost-West streichende Faltenachsen von einer jüngeren Nord-Süd-Faltung überprägt worden sind. Der Autor ist der Meinung, da\ die zwei tektonischen Systeme, die von einer frühen und späten Phase der Metamorphose begleitet werden, den zeitlich getrennten Verformungsstadien einer Orogenese entsprechen.

     

The role of prior model calibration on predictions with ensemble Kalman filter

This paper, based on a real world case study (Limmat aquifer, Switzerland), compares inverse groundwater flow models calibrated with specified numbers of monitoring head locations. These models are updated in real time with the ensemble Kalman filter (EnKF) and the prediction improvement is assessed in relation to the amount of monitoring locations used for calibration and updating. The prediction errors of the models calibrated in transient state are smaller if the amount of monitoring locations used for the calibration is larger. For highly dynamic groundwater flow systems a transient calibration is recommended as a model calibrated in steady state can lead to worse results than a noncalibrated model with a well-chosen uniform conductivity. The model predictions can be improved further with the assimilation of new measurement data from on-line sensors with the EnKF. Within all the studied models the reduction of 1-day hydraulic head prediction error (in terms of mean absolute error [MAE]) with EnKF lies between 31% (assimilation of head data from 5 locations) and 72% (assimilation of head data from 85 locations). The largest prediction improvements are expected for models that were calibrated with only a limited amount of historical information. It is worthwhile to update the model even with few monitoring locations as it seems that the error reduction with EnKF decreases exponentially with the amount of monitoring locations used. These results prove the feasibility of data assimilation with EnKF also for a real world case and show that improved predictions of groundwater levels can be obtained.     

Bildung bromhaltiger Desinfektionsnebenprodukte nach Chlorung von Bodenseewasser in Abhängigkeit von Aufbereitungsschritten und der Bromidkonzentration

Formation of Brominated Disinfection By-products after Chlorination of Water from Lake Constance Depending on Treatment Steps and Bromide Concentration The formation of halogenated disinfection by-products (DNP) (trihalomethanes (THM), haloacetic acids (HES), haloacetonitriles (HAN), haloketones (HKE) and chloropicrin (TCNM)) was studied after chlorination (0.5 mg/L) of raw water and drinking water from Lake Constance. The objectives of this study were to investigate the effect of bromide ion on the distribution of DNP-species resulting from chlorination and to draw up a bromide mass-balance. The treatment of water from Lake Constance with ozone decreased the formation of DNP about 35% and of total organic halogens (AOX) about 45%. This decline in DNP-formation is mainly due to the formation of chloroform, dichloro- and trichloroacetic acid. Though there is only a small amount of bromide (6.2 μg/L) in water from Lake Constance, about 32% of THM, 16% of HES, and 30% of HAN contained bromine after chlorination of treated water. The addition of bromide ion (up to 1 mg/L) shifted the DNP-composition to more brominated species. The distribution of the DNP-species depends on the initial molar bromide-to-chlorine ratio. A mathematic model showed the same pattern of DNP-species depending on the initial molar bromide-to-chlorine ratio that was observed experimentally in microstrained raw water and drinking water from Lake Constance. After chlorination of microstrained raw water, 27% of the bromide were incorporated in known DNP, 34% in unknown substances, and about 39% of bromide were not converted to organic bromine. After chlorination of treated water, only 16% of the bromide were incorporated in unknown substances, whereas 34% were found in known DNP. About 50% were found as bromide again. After addition of bromide (up to 25 μg/L) to ozonated and treated water from Lake Constance, between 60 and 72% of the bromide that had reacted after chlorination were found in analyzed low-molecular DNP.