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  • 1
    Electronic Resource
    Electronic Resource
    Vertical Heterogeneity in Horizontal Components of Specific Discharge: Case Study Analysis (1993)
    Oxford, UK : Blackwell Publishing Ltd
    Ground water 31 (1993), S. 0 
    Details
    ISSN: 1745-6584
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Notes: Ground-water management decisions are usually taken under uncertainty, since they depend on unknown parameters of the aquifer such as hydraulic conductivity and specific discharge. This study applies a number of analytical techniques to a case study in order to demonstrate the potential effect of vertical heterogeneity in the horizontal component of specific discharge on evaluating contaminant travel time in an aquifer. The modified point dilution technique developed by Ronen et al. (1986) is applied to study the vertical variability of the horizontal component of specific discharge in a deep unconfined sandy aquifer. This technique, used under natural flow conditions, employs a multilayer sampler, a tracer, and a mathematical diffusion model. Also analyzed are data from a very large unplanned tracer test where the “tracer”, sewage effluent with a high chloride content, was infiltrated into the aquifer for about 30 years. To date, based on available sedimentological evidence and pumping tests, the aquifer has been regarded as homogeneous. However, information from analysis of the tracer test data by two different flow models, and findings obtained by the modified point dilution technique, indicate the existence of zones of high hydraulic conductivity with specific discharges one order of magnitude higher than expected. As a consequence, chloride breakthrough in a pumping well downstream of effluent infiltration was detected after 10 years, at least 70 years earlier than could have been estimated from previously available data. The results demonstrate that consideration must be given to vertical heterogeneity when evaluating contaminant transport and show that detailed site-specific field studies are needed in order to prevent or control aquifer contamination.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1745-6584.1993.tb00825.x
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  • 2
    Electronic Resource
    Electronic Resource
    Unsaturated Zone and Ground-Water Contamination by Organic Pollutants in a Sewage-Effluent-Irrigated Site (1993)
    Oxford, UK : Blackwell Publishing Ltd
    Ground water 31 (1993), S. 0 
    Details
    ISSN: 1745-6584
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Notes: This study describes the distribution of organic pollutants from the ground surface, through the unsaturated zone, to the water table at a citrus grove irrigated by sewage effluent for about 20 years. The citrus grove, located in Israel, overlies an unconfmed Coastal Plain aquifer about 2 km inland from the Mediterranean Sea. The distribution of organic compounds at the citrus grove is compared with two control sites receiving moisture from nonpolluted water sources (one in another citrus grove irrigated by ground water and the other in an uncultivated area receiving only precipitation). Overall, 10 analyses were performed. At the effluent-irrigated site, organic pollutants from the sewage had migrated through the 20 meter thick unsaturated zone to the water table; included in these were several pollutants, such as toluene and phthalates, that are considered to be biodegradable. Pollutant concentrations generally increased with depth. On the other hand, pollutant concentrations at the two control sites decreased significantly with depth through the unsaturated zone. The downward mobility of organic pollutants may be enhanced by the sewage itself. Because sewage effluent is considered to be a readily available source of irrigation water in many parts of the world, the results of this study suggest that what may seem to be a relatively simple solution to water scarcity problems may have potentially long-term and dangerous effects on ground-water quality.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1745-6584.1993.tb00588.x
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  • 3
    Electronic Resource
    Electronic Resource
    Multilayer Sampling in the Water-Table Region of a Sandy Aquifer (1991)
    Oxford, UK : Blackwell Publishing Ltd
    Ground water 29 (1991), S. 0 
    Details
    ISSN: 1745-6584
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Notes: Depth profiles of organic pollutants, metals, and anions were obtained using a ground-water multilayer sampler (MLS) in a sandy unconfined aquifer contaminated by liquid fuels. The sampler incorporates dialysis membranes and is capable of obtaining vertical profiles with a resolution on the order of few centimeters. Of the eight solutes examined (metals, organics, and anions), all except sulfate exhibited microscale heterogeneities in their concentration over a vertical interval of 200 cm. Chloride, manganese, and iron showed a long linear concentration gradient versus depth which is probably the result of vertical mixing by rainfall input. Maximum concentrations of toluene, xylene, and xylidine at the water table were 17.1, 8.3, and 17.1 mg/l, respectively, decreasing with depth. For toluene and xylene the maximum concentrations found at the water table with the MLS are 40 and 4 times higher, respectively, than those detected at depths greater than 200 cm in water samples obtained with a pump.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1745-6584.1991.tb00510.x
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  • 4
    Electronic Resource
    Electronic Resource
    An In Situ Multilevel Sampler for Preventive Monitoring and Study of Hydrochemical Profiles in Aquifers (1987)
    Oxford, UK : Blackwell Publishing Ltd
    Ground water monitoring & remediation 7 (1987), S. 0 
    Details
    ISSN: 1745-6592
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Notes: AbstractA modular multilevel sampler was developed and utilized for sampling undisturbed ground water chemical profiles and gases in both the saturated and the unsaturated zone. Sampling at 3cm depth intervals is based on the dialysis-cell method and has no depth limitations. The sampler may be used for the development of early warning monitoring systems and research.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1745-6592.1987.tb00965.x
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  • 5
    Electronic Resource
    Electronic Resource
    In situ microcosms in aquifer bioremediation studies (1997)
    Oxford, UK : Blackwell Publishing Ltd
    FEMS microbiology reviews 20 (1997), S. 0 
    Details
    ISSN: 1574-6976
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The extent to which aquifer microbiota can be studied under laboratory or simulated conditions is limited by our inability to authentically duplicate natural conditions in the laboratory. Therefore, extrapolation of laboratory results to real aquifer situations is often criticized, unless validation of the data is performed in situ. Reliable data acquisition is critical for the estimation of chemical and biological reaction rates of biodegradation processes in groundwater and as input data for mathematical models. Typically, in situ geobiochemical studies relied on the injection of groundwater spiked with compounds or bacteria of interest into the aquifer, followed by monitoring the changes over time and space. In situ microcosms provide a more confined study site for measurements of microbial reactions, yet closer to natural conditions than laboratory microcosms. Two basic types of in situ aquifer microcosm have been described in recent years, and both originated from in situ instruments initially designed for geochemical measurements. Gillham et al. [Ground Water 28 (1990) 858–862] constructed an instrument that isolates a portion of an aquifer for in situ biochemical rate measurements. More recently Shati et al. [Environ. Sci. Technol. 30 (1996) 2646–2653] modified a multilayer sampler for studying the activity of inoculated bacteria in a contaminated aquifer. Keeping in mind recent advances in environmental microbiology methodologies such as immunofluorescence direct counts, oligonucleotide and PCR probes, fatty acid methyl esther analysis for the detection and characterization of bacterial communities, measurement of mRNA and expression of proteins, it is evident that much new information can now be gained from in situ work. Using in situ microcosms to study bioremediation efficiencies, the fate of introduced microorganisms and general geobiochemical aquifer processes can shed more realistic light on the microbial underworld. The aim of this paper is to emphasize the importance of in situ studies and to describe two different concepts of construction and application of in situ microcosms for studying microbial activity in aquifers. The overall goal is to promote the development and utilization of these valuable and largely unexplored tools.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1574-6976.1997.tb00332.x
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  • 6
    Electronic Resource
    Electronic Resource
    Contaminated aquifers are a forgotten component of the global N 2 O budget (1988)
    [s.l.] : Nature Publishing Group
    Nature 335 (1988), S. 57-59 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Water samples were collected in the Netherlands and Israel (1) at the Veluwe region (52°15; N, 5°40' W), where a shallow 9 m-deep sandy aquifer under woodland is contaminated by acid rain, ammonia volatilization and the disposal of manure on small land enclaves6; (2) in the Jerusalem area ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/335057a0
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  • 7
    Electronic Resource
    Electronic Resource
    On the Structure and Flow Processes in the Capillary Fringe of Phreatic Aquifers (1997)
    Springer
    Transport in porous media 28 (1997), S. 159-180 
    Details
    ISSN: 1573-1634
    Keywords: capillary fringe ; network modeling ; saturated-unsaturated interface ; multiphase flow.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract The water distribution in the capillary fringe (CF) reflects the interaction of a strongly wetting fluid in a heterogeneous porous medium. Field profiles of gravimetric water content of the CF for a 30m deep, sandy, phreatic aquifer in Israel are critically analyzed in the context of the possible wetting and drainage processes in these sediments. A highly plausible explanation of the profiles is based on the spatial configuration of the CF surface determined from a model of the movement of water within the porous medium. The structural types of CF that can arise from a number of competing pore-scale displacement mechanisms, in the presence of gravity, are characterized by the model. We differentiate between two generic types of CF structures: a tenuous invasion-percolation type and a compact type. Flow, in response to a horizontal pressure gradient, associated with each structure is analyzed. Our interpretation of the field data supports the compact structure with a spatial variation in the height of the CF surface, above the water table, on the order of 1m. In this compact structure horizontal flow is characterized by stagnant regions in the CF above a critical height h c and flow only for regions below h c . The field water content (at h c ) may be used to predict the onset of lateral water flow in the CF.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1006583410617
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  • 8
    Electronic Resource
    Electronic Resource
    The development and influence of gas bubbles in phreatic aquifers under natural flow conditions (1989)
    Springer
    Transport in porous media 4 (1989), S. 295-306 
    Details
    ISSN: 1573-1634
    Keywords: Gas/air bubbles ; phreatic aquifers ; hydraulic conductivity ; bacterial activity ; entrapment
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract In a phreatic aquifer, bubbles may result from the entrapment of air during groundwater recharge and/or bacterial metabolism. The calculated critical depth of about 1 m at which bubbles are most likely to be found in a granular aquifer, coincides with the depth of 0.60 m of an almost stagnant water layer (specific discharge 1 × 10-6 cm sec-1) found at the water table region under natural flow conditions. Bubbles clog pores and therefore reduce the hydraulic conductivity without significantly reducing the volumetric water content. Stagnation at the water table region results since prevailing pressures (in the order of 10-1 atmospheres) are not sufficiently large to move bubbles through porous media in a water environment.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00138041
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  • 9
    Electronic Resource
    Electronic Resource
    Penetration of pesticides and industrial organics deep into soil and into groundwater (1993)
    New York, NY [u.a.] : Wiley-Blackwell
    Archives of Insect Biochemistry and Physiology 22 (1993), S. 487-499 
    Details
    ISSN: 0739-4462
    Keywords: organic contaminants ; xenobiotics ; herbicides ; effluent irrigation ; mass spectrometric analysis ; Chemistry ; Food Science, Agricultural, Medicinal and Pharmaceutical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology
    Notes: We report on two different cases of penetration of organic pollutants deep into the soil and into groundwater. In one event a point source of pollution from a pesticides plant has been studied by a long-term follow-up of a polluted well close to the plant. A typical pattern of pollution has been observed in this well, which was studied for four years. There was a similar organic pollution pattern in soil samples close to the plant. The second case involved an agricultural area long irrigated with effluents. In this area there was an accumulation of organic pollutants deep in the soil (5-20 m depth) and in the groundwater. The mobilizing effect of effluents in promoting the penetration of micropollutants into the depth of soil has been shown. This effect presumably is due to the presence of surface active components. The reported results demonstrate the facile transport of a wide range of xenobiotic organics deep into the soil and into deep groundwater, and advises caution in the use of reclaimed wastewaters for irrigation. © 1993 Wiley-Liss, Inc.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/arch.940220314
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