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881.
882.
Stochastic delineation of wellhead protection area in fractured aquifers and parametric sensitivity study 总被引:1,自引:0,他引:1
S. Chevalier M. A. Buès J. Tournebize O. Banton 《Stochastic Environmental Research and Risk Assessment (SERRA)》2001,15(3):205-227
In many countries, the setup of protection areas around every drinking water well was instituted at a national level in order
to preserve the quality of water as well as the perennially of the resource. Wellhead protection surfaces have been defined
using capture zones showing the area influenced by a well within a certain time. A stochastic method is developed for delineating
time-related capture zones in fractured aquifers characterised by a low porosity and a high degree of fracturing. The flow
velocity within the fractures is determined statistically depending on the distribution of the fracture features and the mass
transfer solution is obtained through a particle tracking algorithm. Probabilistic capture zone curves are obtained as a function
of the travel time of particles to the well and the percentage of particles apt to be extracted up to this time. A sensitivity
study of fracture network parameters leads to the conclusion that orientations and aperture distribution of the fracture sets
are of primary importance to the wellhead protection delineation. 相似文献
883.
Three earthquakes that happened over two days in May 1951 caused extensive damage to villages in a small area of eastern El Salvador (Central America). Contemporary hypocentral solutions indicated focal depths, confirmed by re-calculations using available seismic data, of the order of 90 km, suggesting events associated with the subducted Cocos plate. Macroseismic observations strongly indicate that the earthquakes were of very shallow focus and this is supported by wave-form modeling and the appearance of seismograms recorded in Guatemala. A re-evaluation of the location and source characteristics for these events is presented, together with a fault plane solution and additional macroseismic evidence. The implications for seismic hazard and risk assessment in Central America, where shallow earthquakes of moderate magnitude, frequently occurring in clusters, pose the greatest threat to settlements which, like the area affected by these events, are concentrated along the axis of Quaternary volcanoes. 相似文献
884.
The spatial distribution and fate of petrogenic and pyrogenic hydrocarbons in coastal sediments following the Aegean Sea oil spill (Galicia, NW Spain) was investigated through a detailed study of chemical markers. Alkanes and acyclic isoprenoid hydrocarbons were degraded within six months of the accident, but triterpane and sterane distributions were still detectable and were useful in monitoring, respectively, the oil source and weathering. Aromatic steranes were also useful source indicators, and oil degradation was clear from the decrease of certain alkyl dibenzothiophene and phenanthrene isomers. The pyrogenic polycyclic aromatic hydrocarbons produced in the tanker wreck were found more persistent than the petrogenic ones. However, the presence of the oil in the sediments was recognized even one year after the accident and was found particularly preserved in the subsurface layers. 相似文献
885.
The Lherz orogenic lherzolite massif (Eastern French Pyrenees) displays one of the best exposures of subcontinental lithospheric
mantle containing veins of amphibole pyroxenites and hornblendites. A reappraisal of the petrogenesis of these rocks has been
attempted from a comprehensive study of their mutual structural relationships, their petrography and their mineral compositions.
Amphibole pyroxenites comprise clinopyroxene, orthopyroxene and spinel as early cumulus phases, with garnet and late-magmatic
K2O-poor pargasite replacing clinopyroxene, and subsolidus exsolution products (olivine, spinel II, garnet II, plagioclase).
The original magmatic mineralogy and rock compositions were partly obscured by late-intrusive hornblendites and over a few
centimetres by vein–wallrock exchange reactions which continued down to subsolidus temperatures for Mg–Fe. Thermobarometric
data and liquidus parageneses indicate that amphibole pyroxenites started to crystallize at P ≥ 13 kbar and recrystallized at P < 12 kbar. The high AlVI/AlIV ratio (>1) of clinopyroxenes, the early precipitation of orthopyroxene and the late-magmatic amphibole are arguments for
parental melts richer in silica but poorer in water than alkali basalts. Their modelled major element compositions are similar
to transitional alkali basalt with about 1–3 wt% H2O. In contrast to amphibole pyroxenites, hornblendites only show kaersutite as liquidus phase, and phlogopite as intercumulus
phase. They are interpreted as crystalline segregates from primary basanitic magmas (mg=0.6; 4–6 wt% H2O). These latter cannot be related to the parental liquids of amphibole pyroxenites by a fractional crystallization process.
Rather, basanitic liquids mostly reused pre-existing pyroxenite vein conduits at a higher structural level (P ≤ 10 kbar). A continuous process of redox melting and/or alkali melt/peridotite interaction in a veined lithospheric mantle
is proposed to account for the origin of the Lherz hydrous veins. The transitional basalt composition is interpreted in terms
of extensive dissolution of olivine and orthopyroxene from wallrock peridotite by alkaline melts produced at the mechanical
boundary layer/thermal boundary layer transition (about 45–50 km deep). Continuous fluid ingress allowed remelting of the
deeper veined mantle to produce the basanitic, strongly volatiles enriched, melts that precipitated hornblendites. A similar
model could be valid for the few orthopyroxene-rich hydrous pyroxenites described in basalt-hosted mantle xenoliths.
Received: 15 September 1999 / Accepted: 31 January 2000 相似文献
886.
Heavy metals pollution of aquatic ecosystems in the vicinity of a recently closed underground lead-zinc mine (Basque Country, Spain) 总被引:3,自引:0,他引:3
A presentation is made of the study of an underground polymetallic sulphide mine and the pollution caused by this in the adjoining aquatic ecosystems. Troya Mine is in the Basque Cantabrian region (northern Spain). The annual production of the ore deposit of over 3.7 million tons of Pb (0.9%), Zn (11.2%) and Cu (0.2%) was 300,000 t. It was open and producing from 1986-1993. The mineralization was made up of pyrite, marcasite, sphalerite, galena, chalcopyrite and arsenopyrite. Only the Zn and the Pb were mined. We studied the distribution and behaviour of the heavy metals Zn, Pb, Fe, Mn, Cu, Cr and Cd in the water column, dissolved and suspended fractions, and in the sediments of Estanda Stream and of Gezala Creek. Zn, Cd and Mn tend to be found in the water; Fe, Pb, Cu and Cr appear as an adsorbed fractionin the solid phases. Those of the second group are significantly linked to the fluvial sediments and present very high levels. The concentrations of the metals are conditioned by the waters from the mine galleries, by the leached waste, by the surface runoff, and by overflow from the spillway of the tailings pond. Our observations provide knowledge on the extent of the polluting power of the metals, the physico-chemical effects in play and the subsequent chances of recovering these highly affected environments. 相似文献
887.
M. Galindo M. Vece M. Perondi M. Monserrat Aráoz G. García M. del V. Hidalgo M. Apella M. Blesa 《Environmental Geology》2001,40(7):847-852
Major ionic composition and other chemical parameters were determined at five sampling stations on the Salí River (Province of Tucumán, Argentina). The heavy human usage of the river causes increased levels of dissolved ions, from the dissolution of halite and gypsum, and from the weathering of basic sediments. Correlations demonstrate that sodium chloride and sulphate, and calcium carbonate are the main contributors to dissolved ions in the river. In the polluted region, south of the Celestino Gelsi dam, the main source of calcium and sulphate is the dissolution of gypsum. Large amounts of halite are also dissolved. Weathering of biotite, K-feldspar and albite are suggested by the data. Conductivity, dissolved oxygen and organic matter all indicate severe contamination by organic matter (mainly from sugar-cane processing) in the lower course. The data also demonstrate a substantial improvement in water quality before the discharge of the river at the Río Hondo dam. Data from the Colorado (a tributary of the Salí River) and Medina rivers are also analyzed and compared. 相似文献
888.
Groundwater contamination: risk management and assessment for landfills in Mar del Plata, Argentina 总被引:3,自引:0,他引:3
This study presents a program for risk management in the contamination of groundwater resulting from leachate in landfills
at Mar del Plata (Argentina). The program includes prediction, prevention, monitory observation and mitigation as actions
that must be taken prior to, during, and after contamination occurs. This routine aids in the identification of weak points
and failures of the program for those who are in charge of making decisions, and will allow better use of limited financial
and technical resources based on planning, thus minimizing disconnected determinations.
Results of the prediction stage were confirmed through monitoring. The presence of a plume of contamination more than 100 m
from the landfill was shown, thus proving that implementation of a monitoring plan to follow the development of the contaminated
plume must be implemented, particularly in populated areas which depend on residential wells for their water supply.
Received: 8 May 2000 · Accepted: 14 August 2000 相似文献
889.
The Salí River hydrogeological basin is one of the most productive artesian basins in Argentina. It is located in the southeastern
part of the province of Tucumán, northwestern Argentina, and its groundwater resources are developed for water supply and
irrigation. The chemical composition of the water is strongly influenced by the interaction with the basinal sediments and
by hydrologic characteristics such as the flow pattern and time of residence.
Three hydrochemical zones are defined in the study area and the processes that control the chemical composition of the water
are manifestly different in each zone. The dissolution of halite, sodium sulphate, and gypsum explains part of the contained
Na+, K+, Cl–, SO4
2–, and Ca2+, but other processes, such as cation exchange, calcite precipitation, weathering of aluminosilicates, and gas exchange with
the atmosphere, also contribute to the water composition.
The assessment of contamination indicators, such as pH, dissolved organic matter, dissolved oxygen, phosphate, and nitrate,
indicates that the groundwater is suitable for human consumption. However, biological contamination has been detected in samples
from some wells, especially those near the Salí River.
Electronic Publication 相似文献
890.
Luis O'Dogherty Agustín Martín-Algarra Hans-Jürgen Gursky Roque Aguado 《International Journal of Earth Sciences》2001,90(4):831-846
Middle Jurassic radiolarites and associated pelagic limestones occur in the Rondaide Nieves unit of the Betic Cordillera, southern Spain. The Rondaide Mesozoic includes: (a) a thick succession of Triassic platform carbonates, comparable to the Alpine Hauptdolomit and Kössen facies; (b) Lower Jurassic pelagic limestones comparable to the Alpine Hierlatz and Adnet facies; (c) the Middle Jurassic Parauta Radiolarite Formation, described herein; and (d) a thin Upper Jurassic-Cretaceous condensed limestone succession. The Parauta Radiolarite Formation and associated limestones were studied with respect to stratigraphy, petrography, micropalaeontology (radiolarians, calcareous nanno- and microfossils) and facies. Radiolarite sedimentation occurred in the Middle Bathonian in a restricted and dysoxic deep Nieves basin, perched in the distal zone of a continental margin fringing the Tethyan ocean. This margin was adjacent to a young narrow oceanic basin between the South-Iberian margin and a continental block called Mesomediterranean Terrane. The Nieves basin was part of a marine corridor between the Proto-Atlantic and Piedmont-Ligurian basins of the Alpine Tethys. The regional tectonic position, the stratigraphical evolution since the Triassic, the age and the nature of the Mesozoic facies and the palaeogeographic relations to adjacent domains show striking analogies between the Betic Rondaide margin and coeval units of the Alps. 相似文献