Assessment of groundwater vulnerability to pollution: a combination of GIS, fuzzy logic and decision making techniques

The assessment of groundwater vulnerability to pollution aims at highlighting areas at a high risk of being polluted. This study presents a methodology, to estimate the risk of an aquifer to be polluted from concentrated and/or dispersed sources, which applies an overlay and index method involving several parameters. The parameters are categorized into three factor groups: factor group 1 includes parameters relevant to the internal aquifer system’s properties, thus determining the intrinsic aquifer vulnerability to pollution; factor group 2 comprises parameters relevant to the external stresses to the system, such as human activities and rainfall effects; factor group 3 incorporates specific geological settings, such as the presence of geothermal fields or salt intrusion zones, into the computation process. Geographical information systems have been used for data acquisition and processing, coupled with a multicriteria evaluation technique enhanced with fuzzy factor standardization. Moreover, besides assigning weights to factors, a second set of weights, i.e., order weights, has been applied to factors on a pixel by pixel basis, thus allowing control of the level of risk in the vulnerability determination and the enhancement of local site characteristics. Individual analysis of each factor group resulted in three intermediate groundwater vulnerability to pollution maps, which were combined in order to produce the final composite groundwater vulnerability map for the study area. The method has been applied in the region of Eastern Macedonia and Thrace (Northern Greece), an area of approximately 14,000 km². The methodology has been tested and calibrated against the measured nitrate concentration in wells, in the northwest part of the study area, providing results related to the aggregation and weighting procedure.     

Migration in a transitional economy: Beyond the planned and spontaneous dichotomy in Vietnam

Migration is frequently portrayed as a negative force in its relationship with economic and social development. This negative perception is exhibited through describing population movements as either ‘forced’ (e.g. political and environmental refugees) or ‘voluntary’ movements (e.g. economic and uninhibited relocation). This paper examines the limitations of this conceptual dualism. It points out that the dualistic approach, widely used in the context of developing countries, simplifies a highly complex phenomenon by ignoring its essential heterogeneity and spatial and temporal dynamics. As such, it is limited in explaining and understanding the globally diversified, historically and politically contextualised situations. Focusing on the migratory experiences of contemporary Vietnam, the study identifies major patterns and trends of population mobility in the country in the past fifty years. It shows that despite the state’s continued attempts to reshape the spatial distribution of population over recent historical periods, the policy outcomes with respect to population mobility have been swayed as much by individuals and their families in pursuit of their own aspirations and livelihoods as by state plans. The Vietnam case has provided evidence of a much more complicated relationship between migration and livelihoods than the conceptual dichotomy assumes, and the opportunity for a richer set of policy options. We argue that the evidence from Vietnam, and elsewhere, warrants an integrated approach to studying migration, combining analysis at the macro- and micro-levels with the nexus lying at the critical decision-making point of the individual or household.     

Calorimetric study of the stability of spinelloids in the system NiAl2O4-Ni2SiO4

Enthalpies of solution in molten 2 PbO · B₂O₃ at 974 K were measured for four spinelloids, phases I (0.75 NiAl₂O₄ · 0.25 Ni₂SiO₄), II (0.60 NiAl₂O₄ · 0.40 Ni₂SiO₄), III and IV (0.50 NiAl₂O₄ · 0.50 Ni₂SiO₄) in the system NiAl₂O₄ · Ni₂SiO₄. The enthalpies (in cal per 4-oxygen mol) of formation from NiAl₂O₄ and Ni₂SiO₄ spinels are: phase I, 945±366; phase II, 1072±360; phase III, 2253±390; phase IV, 3565±544. Using these enthalpy data in combination with phase relations at high pressure at 1373 K, positive entropies of formation of the spinelloids from NiAl₂O₄ and Ni₂SiO₄ spinels were estimated (in cal mol^?1 K^?1): phase I, 1.2; phase II, 1.5; phase III, 2.0–2.3; phase IV, 3.0–3.1. The thermochemical data obtained above suggest that the spinelloids are “entropy-stabilized” phases with partially disordered cation distributions. The configurational entropies of the spinelloids were calculated based on the observed cation distribution in each spinelloid phase. The positive entropies of formation of the spinelloids from the spinel endmembers are due primarily to the configurational entropies although small positive vibrational entropy changes may also exist.     

Thermochemical study of glasses in the system NaAlSi3O8-KAlSi3O8-Si4O8 and the join Na1.6Al1.6Si2.4O8-K1.6Al1.6Si2.4O8

Enthalpies of solution in 2PbO · B₂O₃ at 981 K have been measured for glasses in the system albite-orthoclase-silica and along the join Na_1.6Al_1.6Si_2.4O₈-K_1.6Al_1.6Si_2.4O₈. The join KAlSi₃O₈-Si₄O₈ shows zero heat of mixing similar to that found previously for NaAlSi₃O₈-Si₄O₈ glasses. Albite-orthoclase glasses show negative heats of mixing symmetric about Ab₅₀Or₅₀ (W_n = ? 2.4 ± 0.8 kcal). Negative heats of (Na, K) mixing are also found at $\text{Si}\text{(Si + Al)}\text{= 0.6.}$ Ternary excess enthalpies of mixing in the glassy system Ab-Or-4Q are positive but rarely exceed 1 kcal mol^?1.Using earlier studies of the thermodynamic properties of the crystals, the present calorimetric data and the “two-lattice” entropy model, the albite-orthoclase phase diagram is calculated in good agreement with experimental data. Attempts to calculate albite-silica and orthoclase-silica phase diagrams reveal complexities probably related to significant (but unknown) mutual solid solubility between cristobalite and alkali feldspar and to the very small heat and entropy of fusion of SiO₂.     

Thermochemical study of glasses in the system CaMgSi2O6-CaAl2SiO6

High temperature solution calorimetry of glasses in the system CaMgSi₂O₆ (Di)-CaAl₂SiO₆ (CaTs) show them to have negative enthalpies of mixing with a regular enthalpy parameter, W_H, of -11.4 ± 0.7 kcal. Negative heats of mixing between alumina-rich and alumina-poor glasses seem to be a general phenomenon in aluminosilicates and are not confined only to glassy systems containing anorthite as a component. The thermodynamic behavior of glasses in the system SiO₂-Ca_0.5;AlO₂-CaMgO₂ appears to vary in a smooth fashion, with small positive heats of mixing near SiO₂ and substantial negative heats of mixing for other compositions. The exothermic behavior with increasing $\text{A1}\text{(Al + Si)}$ may be related to local charge balance of M²⁺ and Al³⁺. The negative heats of mixing in MgCaSi₂O₆-CaAl₂SiO₆, MgCaSi₂O₆-CaAl₂Si₂O₈ and NaAlSi₃O₈-CaAl₂Si₂O₈ glasses are in contrast to the positive heats of mixing found in MgCaSi₂O₆-CaAl₂SiO₆ (pyroxene) and NaAlSi₃O₈-CaAl₂Si₂O₈ (high plagioclase) crystalline solid solutions.     

On stilpnomelane in some Romanian Carpathian crystalline formations

Summary The stilpnomelane minerals in the epimetamorphic series of the Romanian Carpathians are divided into four genetic groups. Some ferrostilpnomelanes from metamorphic iron-, manganese- and sulfide-ores have been studied optically, chemically, by differential thermal analysis, thermogravimetric analysis, X-ray diffraction, and IR absorption spectroscopy. Several conclusions on the chemical constitution and the widespread occurence of ferrostilpnomelane in the metamorphic ores of the Carpathians are given.

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Über Stilpnomelan in einigen kristallinen Formationen in den rumänischen Karpaten

Zusammenfassung Die Stilpnomelanvorkommen aus dem epimetamorphen Kristallin der rumänischen Karpaten werden in vier genetische Gruppen eingeteilt. Einige aus metamorphosierten Eisen-, Mangan- und Sulfiderzen stammende Ferrostilpnomelane wurden optisch, chemisch, mit Differentialthermoanalyse, Thermogravimetrie, Röntgenbeugung und Ultrarot-Absorptionsspektroskopie untersucht. Als Schlußfolgerungen ergeben sich einige allgemeine Hinweise über die Zusammensetzung des Ferrostilpnomelans in den Kristallinerzen der Karpaten.

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Mit 5 Figures     

The quartz-coesite-stishovite transformations: new calorimetric measurements and calculation of phase diagrams

High temperature solution calorimetry of synthetic quartz, coesite and stishovite provides enthalpies of transition. ΔH₉₇₅⁰ for quartz-coesite and ΔH₂₉₈⁰ for coesite-stishovite transition are 320 ± 70 and 11700 ± 410 cal mol^?1, respectively. The present transformation enthalpy data represent a small but significant revision of those of Holm et al. Using the published phase equilibrium data, thermal expansivity, compressibility and heat capacity data, ΔS₉₇₅⁰ for the quartz-coesite and ΔS₂₉₈⁰ for the coesite-stishovite transition are ?1.2 ± 0.1 and ?1.0 ± 0.4 cal K^?1 mol^?1, respectively. These thermochemical data are used to calculate phase boundaries of the transitions. The calculated quartz-coesite transition boundary agrees well with the one determined experimentally by Bohlen and Boettcher. The calculated coesite-stishovite boundary is generally consistent with data by Yagi and Akimoto and by Suito.     

A Raman spectroscopic study of glasses along the joins silica-calcium aluminate,silica-sodium aluminate,and silica-potassium aluminate

Aluminosilicate glasses with compositions along the joins silica-calcium aluminate, silica sodium aluminate and silica-potassium aluminate have been prepared by conventional and solar melting techniques and studied by Raman spectroscopy. The Raman spectra of crystalline calcium aluminate, anorthite and silica polymorphs are discussed in relation to their crystal structures, and compared with the spectra of the corresponding glasses. The glass and crystal spectra are generally comparable, suggesting similar vibrational structures. These crystals have structures based on tetrahedral aluminosilicate frameworks, and a similar molecular structure is suggested for the glasses, although it is noted that the Raman spectra do not directly characterize the aluminate polyhedra. Within the three glass series, our interpretation of the unresolved high-frequency bands shows the appearance of discrete bands near 1120, 1000, 930 and 890 cm^?1 as the silica content is decreased. This is compared with the behaviour of high-frequency bands in simple silicate systems, and used to suggest that the four bands in the aluminosilicate systems are due to stretching vibrations of silicate tetrahedra bound to one, two, three and four aluminium atoms. The spectra of calcium, sodium, potassium and lithium aluminosilicate glasses with similar silica contents are compared, and interpreted by the above model. This is used to construct a simple model for the effect of metal cation on aluminosilicate molecular groups in the glass structure, consistent with the results of calorimetric studies on similar systems.