共查询到20条相似文献，搜索用时 406 毫秒
1.
Partitioning tracer method for quantifying the residual saturation of refined petroleum products in saturated soil 总被引：1，自引：1，他引：0
The effective site assessment is crucial to the successful remediation of the subsurface contaminated with light nonaqueous
phase liquids (LNAPLs). Recent studies showed that large spatial volumes of the subsurface contaminated with LNAPLs could
be investigated with the partitioning tracer method. This study investigated the applicability of the partitioning tracer
method for detecting and quantifying refined petroleum products in a saturated aquifer containing alluvial soil or weathered
granite soil. In the batch-partitioning experiments, the partition coefficients of alcohol tracers between the petroleum mixture
and water were measured, and they were found to be increased in proportion to the boiling points of the alcohol tracers when
the molecular weights of the alcohol tracers were similar. The sorption isotherm experiments indicated that a considerable
amount of 4-methyl-2-pentanol was sorbed into Jumunjin sand (JS) or weathered granite soil (WGS). In the column experiments,
it was confirmed that the partitioning tracer method could be used as a method for detecting the presence of the petroleum
mixture in saturated soil, and the residual saturation of the petroleum mixture in the soil column prepared by firstly contaminating
with the petroleum mixture and secondly saturating with water was measured higher than that in the soil column prepared by
firstly saturating and secondly contaminating. The highest accuracy of estimation using the partitioning tracer method was
found for 2-ethyl-1-butanol and the lowest accuracy was found for 4-methyl-2-pentanol. 相似文献
2.
A poroelastic numerical model is presented to evaluate three-dimensional consolidation due to groundwater withdrawal from desaturating anisotropic porous media. This numerical model is developed based on the fully coupled governing equations for groundwater flow in deforming variably saturated porous media and the Galerkin finite element method. Two different cases of unsaturated aquifers are simulated for the purpose of comparison: a cross-anisotropic soil aquifer, and a corresponding isotropic soil aquifer composed of a geometrically averaged equivalent material. The numerical simulation results show that the anisotropy has a significant effect on the shapes of three-dimensional hydraulic head distribution and displacement vector fields. Such an effect of anisotropy is caused by the uneven partitioning of the hydraulic pumping stress between the vertical and horizontal directions in both groundwater flow field and solid skeleton deformation field. Copyright © 1999 John Wiley & Sons, Ltd. 相似文献
3.
This study evaluated remedial alternatives for a petroleum-contaminated site where an unconfined aquifer composed of a sandy layer of about 3–3.5 m thickness is covered by alluvial deposits and reclaimed soil of about 1.5 m thickness. Precambrian gneiss, of low permeability, lies below the sandy layer. The shallow water table is about 3 m below the surface, but shows high fluctuations of up to 1.5 m in response to precipitation events. The unsaturated soil near the water table and the groundwater are highly contaminated with petroleum hydrocarbons, especially toluene, which have apparently leaked from storage tanks. Selection of the remedial alternatives required consideration of the relevant laws on soil and groundwater conservation in Korea, the results of risk analysis and the hydrogeological conditions. The contaminated area has been divided into zones in which different remediation goals are set based on risk analysis and the degree of natural attenuation. It is estimated that the clean-up goal can be achieved in two years by the combined use of a trench drain and well point pumping to collect the contaminated groundwater for treatment, and a dual air injection system for the contaminated soil. 相似文献
4.
Quantification of the saturation degree of nonaqueous phase liquid in the vadose zone using hydrocarbon partitioning tracers 总被引：1，自引：1，他引：0
Partitioning tracer tests, as an alternative to the core sampling method, were conducted to quantify the degree of saturation
of water and nonaqueous phase liquids (NAPL) in the vadose zone. Hydrocarbon gases, which have less effect on global warming
than conventional tracers, were used as partitioning tracers. Column tests using CH4, C3H5, and C4H10 as non-partitioning and partitioning tracers were performed to determine the retardation factor and partition coefficient
of the tracer into water and NAPL. The retardation factors of these tracers were estimated to be in the range of 1.0–7.0 based
on breakthrough curves of the tracers. The partition coefficient of C3H5 to water and diesel phase was calculated to be 0.57 and 8.45, respectively. For a heavier tracer, C4H10, the partition coefficient to the water and diesel phases was 1.2 and 40.5, respectively. The average value of water and
diesel saturation estimated from column tests agreed well with known values in unsaturated soil. A residence time longer than
7.5 h within soil pores was found to provide local equilibrium partitioning of the tracer to the diesel phase. The concentration
of tracer had no effect on the partitioning process. 相似文献
5.
Acidification of groundwater lags behind acid deposition due to the relatively long water residence time in conjunction with
various buffering processes in the soil zone and deeper aquifer (chemical weathering, cation exchange, sulfate sorption, and
N uptake by the biomass). Extensive field data from eight forested catchments in the Bunter Sandstone of the Black Forest,
including results from water budget studies and hydrochemical analysis of stream and spring waters, were used to simulate
the future evolution of ground-water acidification with the MAGIC model. The present acid deposition exceeds the “critical
load” (here meaning buffering due to chemical weathering and protonation of organic acids) in six of eight catchments. Two
catchments are well buffered because they contain carbonate-bearing layers in the Upper Bunter sandstone. Transient buffering
(i.e., cation exchange, N uptake, the sulfate sorption) thus far prevents worse acidification, but this effect will decline
in the future. For one of the poorly buffered catchments (Seebach), a two-layer simulation was carried out, based on extensive
data from 10 years of measurements. Validation of the long-term simulations by hydrochemical and soil data was hampered by
strong annual variations but generally supported by paleolimnological studies. In the future, reductions in the S deposition
by 20% and the N deposition by 10% up to the year 2030 are assumed as the most probable scenario. N uptake through soil and
vegetation will come to an end as suggested by decreasing C/N ratios of the organic matter. This process is arbitrarily included
in the simulations. In the periglacial soil layer, acidification will decrease until the year 2030 and then approach a steady-state
condition. In the fractured aquifer, acidification will also proceed at a decreasing rate; however, sulfate desorption up
to the year 2130, the end of simulated period, will prevent earlier remediation. Despite a significant reduction in S deposition
since the mid-1980s, further efforts are necessary to reduce the emission of acidifying substances. Liming in the recharge
area is partially effective to ameliorate “shallow” groundwater but largely fails to ameliorate “deeper” groundwater in the
sandstone aquifer.
Received: 30 July 1996/Accepted: 23 January 1997 相似文献
6.
Groundwater is a very important natural resource in Khanyounis Governorate (the study area) for water supply and development.
Historically, the exploitation of aquifers in Khanyounis Governorate has been undertaken without proper concern for environmental
impact. In view of the importance of quality groundwater, it might be expected that aquifer protection to prevent groundwater
quality deterioration would have received due attention. In the long term, however, protection of groundwater resources is
of direct practical importance because, once pollution of groundwater has been allowed to occur, the scale and persistence
of such pollution makes restoration technically difficult and costly. In order to maintain basin aquifer as a source of water
for the area, it is necessary to find out, whether certain locations in this groundwater basin are susceptible to receive
and transmit contamination. This study aims to: (1) assess the vulnerability of the aquifer to contamination in Khanyounis
governorate, (2) find out the groundwater vulnerable zones to contamination in the aquifer of the study area, and (3) provide
a spatial analysis of the parameters and conditions under which groundwater may become contaminate. To achieve that, DRASTIC
model within geographic information system (GIS) environment was applied. The model uses seven environmental parameters: depth
of water table, net recharge, aquifer media, soil media, topography, impact of vadose zone, and hydraulic conductivity to
evaluate aquifer vulnerability. Based on this model and by using ArcGIS 9.3 software, an attempt was made to create vulnerability
maps for the study area. According to the DRASTIC model index, the study has shown that in the western part of the study area
the vulnerability to contamination ranges between high and very high due to the relatively shallow water table with moderate
to high recharge potential, and permeable soils. To the east of the previous part and in the south-eastern part, vulnerability
to contamination is moderate. In the central and the eastern part, vulnerability to contamination is low due to depth of water
table. Vulnerability analysis of the DRASTIC Model indicates that the highest risk of contamination of groundwater in the
study area originates from the soil media. The impact of vadose zone, depth to water level, and hydraulic conductivity imply
moderate risks of contamination, while net recharge, aquifer media, and topography impose a low risk of aquifer contamination.
The coefficient of variation indicates that a high contribution to the variation of vulnerability index is made by the topography.
Moderate contribution is made by the depth to water level, and net recharge, while impact of vadose zone, hydraulic conductivity,
soil media, and Aquifer media are the least variable parameters. The low variability of the parameters implies a smaller contribution
to the variation of the vulnerability index across the study area. Moreover, the “effective” weights of the DRASTIC parameters
obtained in this study exhibited some deviation from that of the “theoretical” weights. Soil media and the impact of vadose
zone were the most effective parameters in the vulnerability assessment because their mean “effective” weights were higher
than their respective “theoretical” weights. The depth of water table showed that both “effective” and “theoretical” weights
were equal. The rest of the parameters exhibit lower “effective” weights compared with the “theoretical” weights. This explains
the importance of soil media and vadose layers in the DRASTIC model. Therefore, it is important to get the accurate and detailed
information of these two specific parameters. The GIS technique has provided an efficient environment for analysis and high
capabilities of handling large spatial data. Considering these results, DRASTIC model highlights as a useful tool that can
be used by national authorities and decision makers especially in the agricultural areas applying chemicals and pesticides
which are most likely to contaminate groundwater resources. 相似文献
7.
The effectiveness of aquifer remediation is typically expressed in terms of a reduction in contaminant concentrations relative
to a regulated maximum contaminant level (MCL), and is usually confirmed by sparse monitoring data and/or simple model calculations.
Here, the effectiveness of remediation is re-examined from a more thorough risk-based perspective that goes beyond the traditional
MCL concept. A methodology is employed to evaluate the health risk to individuals exposed to contaminated household water
that is produced from groundwater. This approach explicitly accounts for differences in risk arising from variability in individual
physiology and water use, the uncertainty in estimating chemical carcinogenesis for different individuals, and the uncertainties
and variability in contaminant concentrations within groundwater as affected by transport through heterogeneous geologic media.
A hypothetical contamination scenario is developed as a case study in a saturated, alluvial aquifer underlying an actual Superfund
site. A baseline (unremediated) human exposure and health risk scenario, as induced by contaminated groundwater pumped from
this site, is predicted and compared with a similar estimate based upon pump-and-treat exposure intervention. The predicted
reduction in risk in the remediation scenario is not an equitable one—that is, it is not uniform to all individuals within
a population and varies according to the level of uncertainty in prediction. The importance of understanding the detailed
hydrogeologic connections that are established in the heterogeneous geologic regime between the contaminated source, municipal
receptors, and remediation wells, and its relationship to this uncertainty is demonstrated. Using two alternative pumping
rates, we develop cost-benefit curves based upon reduced exposure and risk to different individuals within the population,
under the presence of uncertainty. 相似文献
8.
将土壤或含水层的介质参数视为随机分布,建立了饱和非饱和水流运动的随机微分方程,利用随机数值求解方法,得到各种随机参数对水头分布和含水量空间变异性的影响。分析结果表明,随着渗透系数空间变异性和相关尺度的增大,含水层水头分布的变异性增大;对于区域内有抽水井分布的问题,在井点附近区域,z向水流速度空间变异性大,而在井点处变异性较小。当采用Gardner-Russo模型描述非饱和水分特征时,其非饱和土壤介质参数α的变异性对土壤负压和含水量变异性的影响大于饱和渗透系数,土壤含水量越小,含水量的空间变异性越大。初步讨论了根据随机数值方法研究地下水运动问题的可靠性分析方法。 相似文献
9.
Hydrochemical framework of the aquifer in and around East Kolkata Wetlands,West Bengal,India 总被引：1，自引：0，他引：1
The area lies between Hugli river in the northwest and Bidyadhari river in the east and includes the East Kolkata Wetlands.
The East Kolkata Wetlands is included in the List of Wetlands of International Importance (“Ramsar List”), as per the Convention
on Wetlands signed in Ramsar, Iran, in 1971. This wetland has been declared as a Ramsar site on the 19th August 2002 (Ramsar
site no. 1208) and therefore has acquired an international status. The area is a part of the lower deltaic plain of the Bhagirathi–Ganga
river system and is generally flat in nature. The sub-surface geology of the area is completely blanketed by the Quaternary
fluviatile sediments comprising a succession of clay, silty clay, sand and sand mixed with occasional gravel. The Quaternary
aquifer is sandwiched between two clay sequences. The confined aquifer is made up of moderately well sorted sand and reflects
fluviatile environment of deposition. The regional groundwater flow direction is from east to west. Detailed geochemical investigations
of 40 groundwater samples along with statistical analysis (for example, correlation and principal component analysis) on these
chemical data reveal: (i) four types of groundwater quality, for example, good, poor, very poor and water unsuitable for drinking
purpose, (ii) four hydrochemical facies which may be assigned to three broad types such as “fresh”, “blended”, and “brackish”
waters, (iii) the evolution of the “blended” water is possibly due to hydraulic mixing of “fresh” and “brackish” waters within
the aquifer matrix and/or in well mixing, and (iv) absence of Na–Cl facies indicates continuous flushing of the aquifer. 相似文献
10.
11.
P. F. Hudak 《Environmental Geology》1997,31(1-2):21-26
Simplified approaches are often used to model the removal of groundwater contamination. These approaches can yield poor remediation
schemes because they incorrectly portray the effects of multiple pumping wells. In this study, a pumping configuration designed
by graphically overlaying capture zones having an identical, quasi-elliptical shape was evaluated with a numerical mass transport
model. After a 3-year period (within which the hypothetical aquifer was to be remediated) the contaminant mass had been reduced
by 77%. Due to stagnation zones which developed between extraction wells, approximately 15 years of pumping was required to
remediate the aquifer with the overlay configuration. An alternative design, consisting of an extraction well between two
injection wells along the long axis of the plume, removed the contaminant within the 3-year design period.
Received: 23 October 1995 · Accepted: 18 June 1996 相似文献
12.
Variation in time-to-compliance for pump-and-treat remediation of mass transfer-limited aquifers with hydraulic conductivity heterogeneity 总被引：2，自引：2，他引：0
In this study, the impact of correlation length (λ) of hydraulic conductivity (K) heterogeneity on pump-and-treat (P&T) remediation period (time-to-compliance) for a mass transfer-limited aquifer is evaluated.
Additionally, impacts of variance (σ
2), different distributions of high and low K zones and different initial contaminant masses are explored. Two different P&T policies including different number of wells
pumping at different rates are employed for the investigation. Simulation–optimization approach in which a genetic algorithm
(GA) is linked with a groundwater flow and contaminant transport model is used. Results show that K heterogeneity, in terms of λ
ln K
, sln K2 \sigma_{\ln \,K}^{2} and respective locations of low and high K zones, significantly impacts the time-to-compliance. Contaminant presence at low K zones can increase the time required to clean up the aquifer. Lower variation is observed in time-to-compliance for the remediation
design utilizing higher number of wells pumping at slower rates compared to the design with a single well pumping at a higher
rate. Higher number of wells increases the robustness of P&T remediation system when aquifer is heterogeneous in K. 相似文献
13.
Groundwater pollution risk mapping for the Eocene aquifer of the Oum Er-Rabia basin, Morocco 总被引：2，自引：0，他引：2
Said Ettazarini 《Environmental Geology》2006,51(3):341-347
Sustainable development requires the management and preservation of water resources indispensable for all human activities. When groundwater constitutes the main water resource, vulnerability maps therefore are an important tool for identifying zones of high pollution risk and taking preventive measures in potential pollution sites. The vulnerability assessment for the Eocene aquifer in the Moroccan basin of Oum Er-Rabia is based on the DRASTIC method that uses seven parameters summarizing climatic, geological, and hydrogeological conditions controlling the seepage of pollutant substances to groundwater. Vulnerability maps were produced by using GIS techniques and applying the “generic” and “agricultural” models according to the DRASTIC charter. Resulting maps revealed that the aquifer is highly vulnerable in the western part of the basin and areas being under high contamination risk are more extensive when the “agricultural” model was applied. 相似文献
14.
It occurs worldwide that the organic components of non-aqueous phase liquid (NAPL) enter the porous medium and become the source of contaminants in the subsurface. The transport of the organic components through NAPL interphase into the aqueous phase and the subsurface determines the extent of contamination, the persistence of residual NAPL phases and the techniques of remediation. During the transport process the NAPL interphase may experience "aging", a physical and chemical change when NAPL is exposed to aqueous and or gaseous phases. This aging process alters vice versa the mass transfer behaviour of the organic contaminants in the porous medium. 相似文献
15.
针对非水相流体污染含水层的表面活性剂强化修复过程,在多相流数值模拟模型以及径向基函数人工神经网络替代模型的基础上,应用Sobol法对影响修复效果的变量进行全局灵敏度分析。当替代模型的训练集包含12组和22组数据时,替代模型与模拟模型拟合的确定性系数分别为0.977 8和0.981 6,表明随着训练集数据的增多,替代模型与模拟模型的近似精度逐渐增加。灵敏度分析结果表明：对修复效果贡献最大的决策变量为总抽水量(总灵敏度为0.491 2),其次为修复时间(总灵敏度为0.468 5),表面活性剂浓度对修复效果的贡献最小(总灵敏度为0.124 2);各个变量之间存在着相互作用,但相互作用对输出响应的影响不大。 相似文献
16.
Samuel Boateng 《Hydrogeology Journal》2001,9(6):543-554
A variably saturated flow model is coupled to a first-order reliability algorithm to simulate unsaturated flow in two soils.
The unsaturated soil properties are considered as uncertain variables with means, standard deviations, and marginal probability
distributions. Thus, each simulation constitutes an unsaturated probability flow event. Sensitivities of the uncertain variables
are estimated for each event. The unsaturated hydraulic properties of a fine-textured soil and a coarse-textured soil are
used. The properties are based on the van Genuchten model. The flow domain has a recharge surface, a seepage boundary along
the bottom, and a no-flow boundary along the sides. The uncertain variables are saturated water content, residual water content,
van Genuchten model parameters alpha (α) and n, and saturated hydraulic conductivity. The objective is to evaluate the significance of each uncertain variable to
the probabilistic flow. Under wet conditions, saturated water content and residual water content are the most significant
uncertain variables in the sand. For dry conditions in the sand, however, the van Genuchten model parameters α and n are the most significant. Model parameter n and saturated hydraulic conductivity are the most significant for the wet
clay loam. Saturated water content is most significant for the dry clay loam.
Electronic Publication 相似文献
17.
Victor Ryzhik 《Computational Geosciences》2007,11(1):1-8
Spreading of a non-aqueous phase liquid (NAPL) denser than water (DNAPL) lens (mound) in the unsaturated zone of double-porosity
aquifer above an impervious plane boundary is investigated. The double-porosity aquifer is conceptualized as a fracture network
surrounding pervious blocks. Vertical gravity equilibrium is assumed to prevail in each one of the two media, fractures and
blocks. Through vertical integration, two coupled partial differential equations for the DNAPL content in each medium are
obtained. The mass exchange rate between high- and low-permeability media is considered as a function of NAPL content. The
dominant effect is gravity, whereas capillary forces are negligible. Analytical solutions for one-dimensional and axisymmetric
problems of mound spreading are obtained. 相似文献
18.
M. Draoui J. Vias B. Andreo K. Targuisti J. Stitou El Messari 《Environmental Geology》2008,54(3):455-463
This paper presents the results of a comparative study relating to the application of four vulnerability mapping methods,
GOD, AVI, DRASTIC and SINTACS, in a pilot detritic aquifer situated in NW Morocco, known as the Martil–Alila aquifer. The
principal objective of this work is to determine the most suitable such methods for this aquifer type within a Mediterranean
context, and to show the effect of the rainfall variations that are characteristic of the Mediterranean climate on the degree
of vulnerability. The methods applied distinguish five classes of vulnerability, these being irregularly divided up in space,
with the division varying according to the method in question. The vulnerability maps obtained by the different methods strongly
suggest that the eastern half of the aquifer is more vulnerable to contamination than the western half, for all hydrological
situations. The effect of climatic conditions on the degree of vulnerability is well represented by the DRASTIC, according
to which the aquifer is moderately to strongly vulnerable during humid hydrological years and weakly to moderately vulnerable
during dry ones. For the other methods, this climatic effect is limited to the area occupied by the two predominant classes
(“High” and “Low” for GOD and “High” and “Moderate” for SINTACS) while it is null for AVI. In conclusion, DRASTIC appears
the most suitable for mapping the vulnerability to contamination of Mediterranean coastal detritic aquifers such as the Martil–Alila
aquifer. 相似文献
19.
膨胀土强度影响因素与规律的试验研究 总被引：11，自引：1，他引：10
针对同一种膨胀土,通过直剪试验和三轴试验研究了土体由无裂隙天然非饱和状态到无裂隙饱和状态再到裂隙充分发展的饱和状态的过程中强度的影响因素和变化规律。试验结果表明,含水率、密度以及裂隙是影响膨胀土强度的三个因素,其中含水率和裂隙对强度的影响较大,密度对强度的影响较小。膨胀土强度指标的确定应考虑裂隙的开展。建议用试样做5次干湿循环后的强度指标作为膨胀土裂隙发育区的强度指标。通过膨胀土残余强度试验分析表明,所得指标与裂隙充分发展的膨胀土强度指标是接近的,故也可用其作为裂隙发育区的强度指标近似值。 相似文献
20.
Samuel Wildemeersch Philippe Orban Ingrid Ruthy Olivier Grière Philippe Olive Abdelkhalek El Youbi Alain Dassargues 《Environmental Earth Sciences》2010,60(8):1753-1769
Located in the Mid-Atlas (Morocco), the Oulmes plateau is famous for its mineral water springs “Sidi Ali” and “Lalla Haya”
commercialised by the company “Les Eaux minérales d’Oulmès S.A”. Additionally, groundwater of the Oulmes plateau is intensively
exploited for irrigation. The objective of this study, essentially performed from data collected during isotopic (summer 2004)
and piezometric and hydrogeochemical field campaigns (spring 2007), is to improve the understanding of the Oulmes hydrogeological
system. Analyses and interpretation of these data lead to the statement that this system is constituted by a main deep aquifer
of large extension and by minor aquifers in a perched position. However, these aquifers interact enough to be in total equilibrium
during the cold and wet period. As highlighted by isotopes, the origin of groundwater is mainly infiltration water except
a small part of old groundwater with dissolved gas rising up from the granite through the schists. 相似文献