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21.
Manuela Lasagna Domenico Antonio De Luca Laura Debernardi Paolo Clemente 《Environmental Earth Sciences》2013,70(6):2767-2784
This paper discusses the effects of the dilution process on levels of aquifer contamination attenuation, developing analytical equations for application in theoretical and practical cases. The key finding is that, in aquifers, the dilution process causes a reduction of the contaminant concentration. Analytical equations for the assessment of the contaminant attenuation capacity, by means of the dilution process in an aquifer, are put forward. In particular, the attenuation of the contaminant concentration in an aquifer, and thus the dilution, is described by the volumetric flow rate per unit width perpendicular to the flow direction (q u). Moreover, a classification of q u was developed, considering six classes of attenuation capacity due to dilution. For the equations validation, nitrate contamination attenuation due to dilution was analysed in two sample areas in Piedmont (North-West Italy). The results confirmed the hypothesis, evidencing high nitrate concentrations in areas with low q u values, connected to low dilution rate of the contaminant in the groundwater; vice versa, low nitrate concentrations were evidenced in areas with high q u values, due to a high nitrate dilution rate. 相似文献
22.
Laura Chiaramonte Mark D. Zoback Julio Friedmann Vicki Stamp 《Environmental Geology》2008,54(8):1667-1675
This paper reports a preliminary investigation of CO2 sequestration and seal integrity at Teapot Dome oil field, Wyoming, USA, with the objective of predicting the potential risk
of CO2 leakage along reservoir-bounding faults. CO2 injection into reservoirs creates anomalously high pore pressure at the top of the reservoir that could potentially hydraulically
fracture the caprock or trigger slip on reservoir-bounding faults. The Tensleep Formation, a Pennsylvanian age eolian sandstone
is evaluated as the target horizon for a pilot CO2 EOR-carbon storage experiment, in a three-way closure trap against a bounding fault, termed the S1 fault. A preliminary geomechanical
model of the Tensleep Formation has been developed to evaluate the potential for CO2 injection inducing slip on the S1 fault and thus threatening seal integrity. Uncertainties in the stress tensor and fault
geometry have been incorporated into the analysis using Monte Carlo simulation. The authors find that even the most pessimistic
risk scenario would require ∼10 MPa of excess pressure to cause the S1 fault to reactivate and provide a potential leakage
pathway. This would correspond to a CO2 column height of ∼1,500 m, whereas the structural closure of the Tensleep Formation in the pilot injection area does not exceed
100 m. It is therefore apparent that CO2 injection is not likely to compromise the S1 fault stability. Better constraint of the least principal stress is needed to
establish a more reliable estimate of the maximum reservoir pressure required to hydrofracture the caprock. 相似文献
23.
Multiple geochemical tracers [ion chemistry, stable isotopes of water, chlorofluorocarbons (CFC), tritium] and a 25-year-long record of discharge were used to understand residence times and flow paths of groundwater seeps in the fractured rock aquifer surrounding the Mission Tunnel, Santa Barbara, California. Tritium data from individual seeps indicate that seep waters are a mixture of >45-year-old (recharged prior to the nuclear bomb tests) and young groundwater. CFC data support this interpretation, however, a two-end member mixing model cannot completely explain the age tracer data. Microbial degradation and partial re-equilibration complicate the CFC signal. Spectral analysis of precipitation and groundwater seepage records shows that seepage lags precipitation by 3 months. This delay is related to the advancement of the wetting front and increasing the number of active flow paths. Additionally, the amount of seepage produced by precipitation is less during extended periods of drought than during normal or wet periods, suggesting antecedent conditions strongly affect flow through this fractured rock aquifer. 相似文献
24.
Assessment of the role of facies heterogeneity at the fine scale by numerical transport experiments and connectivity indicators 总被引:1,自引:1,他引:1
The heterogeneity of facies at the scale of individual lithological levels controls, at a macroscopic scale, water flow and contaminant transport in porous sediments. In particular the presence of organized features such as permeable connected levels, has a significant effect on travel times and dispersion. Here, the effects of facies heterogeneity on flow and transport are studied for three blocks, whose volume is of the order of a cubic meter, dug from alluvial sediments from the Ticino valley (Italy). Using the results of numerical tracer experiments on these domains, the longitudinal dispersion coefficient is computed with an Eulerian approach based on the fit of the breakthrough curves with the analytical solution of the convective-dispersive transport equation. Moreover, the dispersion tensor is computed with a Lagrangian approach from the second order moments of particle distributions. Three types of connectivity indicators are tested: (1) connectivity function; (2) flow, transport and statistical connectivity; (3) original (intrinsic, normal and total) indicators of facies connectivity. The connectivity function provides the most complete information. Some of the transport and statistical connectivity indicators are correlated with dispersivity. The simultaneous analysis of the three indicators of facies connectivity emphasizes the fundamental geometrical features that control transport. 相似文献
25.
Groundwater inflow assessment is essential for the design of tunnel drainage systems, as well as for assessment of the environmental impact of the associated drainage. Analytical and empirical methods used in current engineering practice do not adequately account for the effect of the jointed-rock-mass anisotropy and heterogeneity. The impact of geo-structural anisotropy of fractured rocks on tunnel inflows is addressed and the limitations of analytical solutions assuming isotropic hydraulic conductivity are discussed. In particular, the study develops an empirical correction to the analytical formula frequently used to predict groundwater tunnel inflow. In order to obtain this, a discrete network flow modelling study was carried out. Numerical simulation results provided a dataset useful for the calibration of some empirical coefficient to correct the well-known Goodman’s equation. This correction accounts for geo-structural parameters of the rock masses such as joint orientation, aperture, spacing and persistence. The obtained empirical equation was then applied to a medium-depth open tunnel in Bergamo District, northern Italy. The results, compared with the monitoring data, showed that the traditional analytical equations give the highest overestimation where the hydraulic conductivity shows great anisotropy. On the other hand, the empirical relation allows a better estimation of the tunnel inflow. 相似文献
26.
Laura Carrillo Emilio Palacios-Hernández Mario Yescas Ana María Ramírez-Manguilar 《Estuaries and Coasts》2009,32(5):906-916
Salinity profiles and meteorological data were analyzed during February, May, and September 2006 in Chetumal Bay, a large,
shallow estuary of the Western Caribbean. Local meteorological conditions revealed three seasons: (1) a dry season (March–May);
(2) a wet season (June–October); and (3) the nortes season, with northerly wind events (October–February). During the nortes
and wet seasons, salinity ranged between 13 and 16 psu, and salinity was highest in the dry season, ranging between 18 and
22 psu over most of the area; a strong stratification and a significant contribution of salty water characterized this season.
Strong horizontal gradients were observed near Rio Hondo during the three seasons. Deep and narrow peculiar bathymetric features
called the pozas showed a strong stratification and a relatively high salinity. The northern part of Chetumal Bay and probably
the entire system are far from being homogeneous. 相似文献
27.
Laura Gaggero Laura Buzzi Ivan Haydoutov Luciano Cortesogno 《International Journal of Earth Sciences》2009,98(8):1853-1877
Eclogitic rocks were sampled from two zones in the basement of the Sredna Gora terrane (central western Bulgaria): (1) partially
retrogressed eclogites and amphibolites embedded in sillimanite-bearing garnet-micaschists with kyanite relics and migmatites
and (2) banded amphibolites associated with muscovite-bearing metagranites within two-mica paragneisses. Rutile relics and
oligoclase + green hornblende + epidote ± biotite pseudomorphs after garnet suggest an eclogite facies event. A tholeiitic,
transitional affinity was determined for the protoliths, suggesting a continental rift environment, consistent with several
eclogite-bearing complexes in the eastern segments of the Variscan belt that arose from the Cambro-Ordovician Gondwana break-up.
Decreasing pressure after the eclogite overprint was demonstrated by (a) diopside-albite symplectite, and (b) plagioclase
+ red–brown to green amphibole kelyphite. The early static re-equilibration, dated to 398 ± 5.2 Ma by 40Ar–39Ar technique, was followed by an amphibolite facies foliation, which was pervasive in amphibolites, gneisses and micaschists,
and poorly developed in eclogites. The lithospheric PT paths corresponding to higher and lower metamorphic gradients reflect
the juxtaposition of crustal and lithospheric mantle units, respectively. In the build-up of the basement of the Balkan orogen,
the physical properties of the lithological complexes might have influenced the collisional pattern of involved microplates. 相似文献
28.
Johan Holmberg Chris Flynn Laura Portinari 《Monthly notices of the Royal Astronomical Society》2006,367(2):449-453
We compile a sample of Sun-like stars with accurate effective temperatures, metallicities and colours (from the ultraviolet to the near-infrared). A crucial improvement is that the effective temperature scale of the stars has recently been established as both accurate and precise through direct measurement of angular diameters obtained with stellar interferometers. We fit the colours as a function of effective temperature and metallicity, and derive colour estimates for the Sun in the Johnson–Cousins, Tycho, Strömgren, 2MASS and SDSS photometric systems. For ( B − V )⊙ , we favour the 'red' colour 0.64 versus the 'blue' colour 0.62 of other recent papers, but both values are consistent within the errors; we ascribe the difference to the selection of Sun-like stars versus interpolation of wider colour– T eff –metallicity relations. 相似文献
29.
Hydrodynamics and sediment resuspension events, induced at the shoreline by a deep-draft vessel passing nearby, are described.
Measurements (pressure, currents and turbidity) were obtained at 4 Hz, on a lower beach ~50 m from a channel where large car
ferries operate in Wootton Creek, Isle of Wight. The study focuses on a representative 8-min 32-s-long record, during which
two large vessels passed the channel section. At the shore, the passage of each vessel induced a long-period water-level drawdown,
followed by a water-level oscillation (seiche) of similar period, and the short-period waves of the wake. Both drawdowns were
the main constituents of the prevailing wave pattern. The second drawdown was the largest in amplitude, in response to a higher
speed of the ferry, and the influence of the seiche which had been activated during the preceding event. Two successive peaks
of turbidity were observed shortly after this drawdown. Analyses of current velocity and direction indicate that the sediments
resuspended originated from the shallower upper beach. Anthropogenically induced erosion of the foreshore is predicted at
Wootton Creek. 相似文献
30.
Matthew J. Genge Luke Alesbrook Natasha V. Almeida Helena C. Bates Phil A. Bland Mark R. Boyd Mark J. Burchell Gareth S. Collins Luke T. Cornwell Luke Daly Hadrien A. R. Devillepoix Matthias van Ginneken Ansgar Greshake Daniel Hallatt Christopher Hamann Lutz Hecht Laura E. Jenkins Diane Johnson Rosie Jones Ashley J. King Haithem Mansour Sarah McMullan Jennifer T. Mitchell Gavyn Rollinson Sara S. Russell Christian Schröder Natasha R. Stephen Martin D. Suttle Jon D. Tandy Patrick Trimby Eleanor K. Sansom Vassilia Spathis Francesca M. Willcocks Penelope J. Wozniakiewicz 《Meteoritics & planetary science》2024,59(5):948-972
Fusion crusts form during the atmospheric entry heating of meteorites and preserve a record of the conditions that occurred during deceleration in the atmosphere. The fusion crust of the Winchcombe meteorite closely resembles that of other stony meteorites, and in particular CM2 chondrites, since it is dominated by olivine phenocrysts set in a glassy mesostasis with magnetite, and is highly vesicular. Dehydration cracks are unusually abundant in Winchcombe. Failure of this weak layer is an additional ablation mechanism to produce large numbers of particles during deceleration, consistent with the observation of pulses of plasma in videos of the Winchcombe fireball. Calving events might provide an observable phenomenon related to meteorites that are particularly susceptible to dehydration. Oscillatory zoning is observed within olivine phenocrysts in the fusion crust, in contrast to other meteorites, perhaps owing to temperature fluctuations resulting from calving events. Magnetite monolayers are found in the crust, and have also not been previously reported, and form discontinuous strata. These features grade into magnetite rims formed on the external surface of the crust and suggest the trapping of surface magnetite by collapse of melt. Magnetite monolayers may be a feature of meteorites that undergo significant degassing. Silicate warts with dendritic textures were observed and are suggested to be droplets ablated from another stone in the shower. They, therefore, represent the first evidence for intershower transfer of ablation materials and are consistent with the other evidence in the Winchcombe meteorite for unusually intense gas loss and ablation, despite its low entry velocity. 相似文献