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1.
Transport of BTEX Vapours Through Granular Soils with Different Moisture Contents in the Vadose Zone
The single-ring aromatic hydrocarbons benzene, toluene, ethylbenzene and m-xylene (BTEX) are common and dangerous pollutants in subsurface environments. The diffusive transport of BTEX vapours through
the unsaturated zone of the ground is a potential health hazard to humans, living in the vicinity of petroleum fuel contaminated
sites. Past studies have shown that gas transport through the vadose zone can be influenced by moisture content due to variations
in gaseous permeability, phase partitioning and aerobic biodegradation. In this particular study laboratory soil column experiments
were employed to compare the diffusive transport of BTEX vapours through a sand layer of high moisture content, where biodegradation
of BTEX compounds occurred, with diffusion through air-dried sand. The presence of a thin soil layer of high moisture content
reduced the gaseous concentrations of benzene and toluene and stopped the migration of ethylbenzene and m-xylene vapours, demonstrating its efficiency as a barrier on the diffusive transport of BTEX vapours in unsaturated soil. 相似文献
2.
In CO2 geological storage (CGS) context, the evolution of the caprock sealing capacity has received increasing attention, particularly on a geological time span (thousands of years). At this time scale, geochemical reactions may enhance or weaken the caprock quality. It is widely recognized that, for the reservoir, geological heterogeneities affect the concentration and spatial distribution of CO2, and then affect the extent of gas–water–rock interactions, which in turn alters the hydrogeological properties of the reservoir. However, much less attention of these effects has been paid to the caprock. In this study, we presented and applied a novel approach to evaluate the effects of permeability and porosity heterogeneities on the alteration of minerals, the associated evolution of the caprock sealing efficiency and the containment of supercritical CO2 (scCO2) within the caprock. Even though this is a generic study, several conditions and parameters such as pressure, permeability, and mineral composition, were extracted from a caprock layer of the Shiqianfeng Formation in the Ordos Basin demonstration site in China. For the sake of simplification, a 2-dimensional model was designed to represent the caprock domain. We firstly generated an appropriate heterogeneous random field of permeability with the average permeability taken from the uppermost mudstone layer of the Shiqianfeng Formation, and then the heterogeneity in porosity was incorporated using a joint normal distribution method based on the available data. Homogeneous mineral compositions of the reservoir and caprock were used in all simulations. Simulations of three cases were performed, including a homogeneous case, a case with only permeability heterogeneity and a case with both permeability and porosity heterogeneities. The results demonstrate dramatic influences of permeability and porosity heterogeneities on the migration of scCO2 within the caprock, the alteration of minerals, and therefore the evolution of the caprock sealing quality. Specific to the data used in this study, hydrogeological heterogeneities facilitated the overall penetration of scCO2 within the caprock and promoted the alteration of minerals, thereby weakening the caprock sealing efficiency over the simulation time. 相似文献
3.
Assessment of natural attenuation of aromatic hydrocarbons in groundwater near a former manufactured-gas plant, South Carolina, USA 总被引：1，自引：0，他引：1
J. E. Landmeyer F. H. Chapelle M. D. Petkewich P. M. Bradley 《Environmental Geology》1998,34(4):279-292
Shallow, anaerobic groundwater near a former manufactured-gas plant (MGP) in Charleston, South Carolina, USA, contains mono-
and polycyclic aromatic hydrocarbons (MAHs and PAHs, respectively). Between 1994 and 1997, a combination of field, laboratory,
and numerical-flow and transport-model investigations were made to assess natural attenuation processes affecting MAH and
PAH distributions. This assessment included determination of adsorption coefficients (K
ad
) and first-order biodegradation rate constants (K
bio
) using aquifer material from the MGP site and adjacent properties. Naphthalene adsorption (K
ad
=1.35×10–7 m3/mg) to aquifer sediments was higher than toluene adsorption (K
ad
=9.34×10–10 m3/mg), suggesting preferential toluene transport relative to naphthalene. However, toluene and benzene distributions measured
in January 1994 were smaller than the naphthalene distribution. This scenario can be explained, in part, by the differences
between biodegradation rates of the compounds. Aerobic first-order rate constants of 14C-toluene, 14C-benzene, and 14C-naphthalene degradation were similar (–0.84, –0.03, and 0.88 day–1, respectively), but anaerobic rate constants were higher for toluene and benzene (–0.002 and –0.00014 day–1, respectively) than for naphthalene (–0.000046 day–1). Both areal and cross-sectional numerical simulations were used to test the hypothesis suggested by these rate differences
that MAH compounds will be contained relative to PAHs. Predictive simulations indicated that the distributions of toluene
and benzene reach steady-state conditions before groundwater flow lines discharge to an adjacent surface-water body, but do
discharge low concentrations of naphthalene. Numerical predictions were "audited" by measuring concentrations of naphthalene,
toluene, and benzene at the site in early 1997. Measured naphthalene and toluene concentrations were substantially reduced
and the areal extent of contamination smaller than was both observed in January 1994 and predicted for 1997. Measured 1997
benzene concentrations and distribution were shown to be relatively unchanged from those measured in 1994, and similar to
predictions for 1997.
Received: 26 June 1997 · Accepted: 25 August 1997 相似文献
4.
Geological storage of CO2 is considered a solution for reducing the excess CO2 released into the atmosphere. Low permeability caprocks physically trap CO2 injected into underlying porous reservoirs. Injection leads to increasing pore pressure and reduced effective stress, increasing the likelihood of exceeding the capillary entry pressure of the caprocks and of caprock fracturing. Assessing on how the different phases of CO2 flow through caprock matrix and fractures is important for assessing CO2 storage security. Fractures are considered to represent preferential flow paths in the caprock for the escape of CO2. Here we present a new experimental rig which allows 38 mm diameter fractured caprock samples recovered from depths of up to 4 km to be exposed to supercritical CO2 (scCO2) under in situ conditions of pressure, temperature and geochemistry. In contrast to expectations, the results indicate that scCO2 will not flow through tight natural caprock fractures, even with a differential pressure across the fractured sample in excess of 51 MPa. However, below the critical point where CO2 enters its gas phase, the CO2 flows readily through the caprock fractures. This indicates the possibility of a critical threshold of fracture aperture size which controls CO2 flow along the fracture. 相似文献
5.
Despite its location on sediment-free basalt, vent fluids from the Main Endeavour Field (MEF) contain chemical species that indicate fluids have interacted with sediments during circulation. We report on the distribution and isotopic abundances of organic compounds (C1-C3 alkanes and alkenes, benzene and toluene) in fluids collected from the Main Endeavour Field (MEF) in July, 2000, to understand the processes that regulate their abundances and characterize fluid sources. Aqueous organic compounds are derived from the thermal alteration of sedimentary organic matter and subsequently undergo further oxidation reactions during fluid flow. Fluid:sediment mass ratios calculated using ΣNH4 concentrations indicate that the sediments are distal to the MEF, resulting in a common reservoir of fluids for all of the vents. Following the generation from sediment alteration, aqueous organic compounds undergo secondary alteration reactions via a stepwise oxidation reaction mechanism. Alkane distributions and isotopic compositions indicate that organic compounds in MEF fluids have undergone a greater extent of alteration as compared to Middle Valley fluids, either due to differences in subsurface redox conditions or the residence time of fluids at subsurface conditions. The distributions of the aromatic compounds benzene and toluene are qualitatively consistent with the subsurface conditions indicated by equilibration of aqueous alkanes and alkanes. However, benzene and toluene do not achieve chemical equilibrium in the subsurface. Methane and CO2 also do not equilibrate chemically or isotopically at reaction zone temperatures, a likely result of an insufficient reaction time after addition of CO2 from magmatic sources during upflow. The organic geochemistry supports the assumption that the sediments with which MEF fluids interact has the same composition as sediments present in Middle Valley itself, and highlight differences in subsurface reaction zone conditions and fluid flow pathways at these two sites. 相似文献
6.
W. Tala S. Chantara S. Thiansem M. Rayanakorn 《International Journal of Environmental Science and Technology》2016,13(7):1685-1696
A simple and low-cost passive sampler for collection of volatile organic compounds, specifically benzene, toluene, ethylbenzene and xylene (BTEX), from the ambient air has been developed by using cow bone char (CBC) as an adsorbent with desorption by solvent extraction prior to analysis by gas chromatography–mass spectrometry (GC–MS). The laboratory-made CBC was prepared by calcination process in a partially oxidative atmosphere. The developed passive sampler was tested for a suitable amount of CBC used, diffusion tube type and size, and sampling duration, in a closed chamber saturated with each of the BTEX vapors. With the optimum amount of 250 mg CBC packed in a glass bottle (82.6 mm height × 11.1 mm i.d.) and the exposure time of 168 h, detection limits (µg/m3) for BTEX determination using this developed sampler together with GC–MS were 0.28 (benzene), 0.79 (toluene), 0.58 (ethylbenzene), 0.28 (p-xylene) and 0.54 (o-xylene). The proposed method was applied to sampling BTEX from selected petrol stations, traffic congestion areas and a rural area in Chiang Mai Province, Thailand. The BTEX concentrations detected were well correlated with their sources as they were the highest at the petrol station sites, lower at the traffic congestion area sites and the lowest at the rural area site. The laboratory-made passive sampler containing CBC has thus opened up a possibility of having a simple and effective device for sampling of BTEX in the ambient air. 相似文献
7.
《Applied Geochemistry》2003,18(10):1641-1651
Compound-specific H isotope analysis has been used to monitor bioremediation of petroleum hydrocarbons. However, the success of this approach requires a full evaluation of the isotopic effects resulting from evaporation, because light petroleum hydrocarbons undergo both biodegradation and evaporation under natural conditions. The authors determined the H isotope fractionation of common volatile petroleum hydrocarbons, including the C10–C14 n-alkanes, MTBE (tert-butyl methyl ether), and BTEX (benzene, toluene, ethylbenzene, p-xylene and o-xylene) during progressive vaporization under simulated experimental conditions. A decrease in δD values for n-alkanes of up to 33.3‰ and up to 44.5‰ for BTEX compounds when 99% of these substances had evaporated was observed. The results also show that H isotope fractionation increases with n-alkane chain length. Such fractionation patterns are interpreted in terms of competition between the decreased intermolecular binding energy in D-enriched species, and the isotope effect due to the mass difference. In contrast to hydrocarbons, methanol and ethanol show H isotopic enrichment during vaporization, indicating that H-bonding, when present in organic molecules, plays a controlling role on the vapor pressure of different isotope species. 相似文献
8.
污染河流中苯系物对浅层地下水影响的室内模拟试验 总被引：1，自引：0，他引：1
为了研究污染河流中苯系物对浅层地下水的影响，室内试验选用3种天然砂土作为渗透介质，以生活污水模拟污染河流，68d以后发现，苯、甲苯和苯系物总量的总去除率在粗砂中分别为32．06％、21．39％和27．13％。在两种中砂中总去除率2号柱为76．26％、81．40％和87．99％，3号柱为68．94％、74．41％和81．69％，粗砂小于中砂，并且由于2号柱的粘粒物质含量大，其总去除率大于3号柱和1号柱。苯系物各组分浓度随深度呈递减趋势，苯系物的净化作用主要发生在地表以下0．4m范围内。水动力特征的改变影响污染物的迁移和转化特征，苯系物的去除机理为挥发、吸附和生物降解，其中最主要的是厌氧条件下的微生物降解。 相似文献
9.
Perfluorocarbon compounds (PFCs) have high chemical and thermal stability, low background levels in natural systems, and easy detectability. They are proposed as tracers for monitoring potential CO2 leakage associated with geological carbon sequestration (GCS). The fate of the PFCs in porous media, and in particular, the transport of these compounds relative to CO2 gas in geological formations, has not been thoroughly studied. We conducted column tests to study the transport of perfluoro-methylcyclo-pentane (PMCP), perfluoro-methylcyclo-hexane (PMCH), ortho-perfluoro-dimethylcyclo-hexane (ortho-PDCH), and perfluoro-trimethylcyclo-hexane (PTCH) gas tracers in a variety of porous media. The influence of water content and sediment minerals on the retardation of the tracers was tested. The transport of PFC tracers relative to 13CO2 and the conservative tracer sulfur hexafluoride (SF6) was also investigated. Results show that at high water content, the PFCs and SF6 transported together. In dry and low-water-content sediments, however, the PFCs were retarded relative to SF6 with the degree of retardation increasing with the molecular weight of the PFC. When water was present in the medium, the transport of CO2 was greatly retarded compared to SF6 and the PFC tracers. However, in dry laboratory sediments, the migration of CO2 was slightly faster than all the tracers. The type of minerals in the sediments also had a significant impact on the fate of the tracers. In order to use the PFC tracer data obtained from the ground surface or shallow subsurface in a GCS site to precisely interpret the extent and magnitude of CO2 leakage, the retardation of the tracers and the interaction of CO2 with the reservoir overlying formation water should be carefully quantified. 相似文献
10.
汽油污染含水层中芳香烃的自然去除与生物降解特征 总被引：7，自引：0，他引：7
石油烃污染地下水是一个普遍而严重的环境问题.用砂卵石、中粗砂、细砂、粉砂和粘土等在实验室内按照自然界沉积物层序制作了一个含水层物理模型,具有给水、排水、监测、抽提、淋滤与注入等功能.利用该模型开展石油烃污染地下水的特征研究结果表明,苯、甲苯、乙苯和二甲苯(benzene,toluene,ethylbenzene,xylene;BTEX)各溶解组分能够被自然去除,其中甲苯自然衰减的速率系数为0.057 5～0.150 4 d-1,二甲苯为0.068 3～0.104 6 d,乙苯大约为0.047 8 d,苯为O.017 8～0.040 6 d.甲苯与二甲苯容易被去除,然而苯的去除则需要较长的时间.作为BTEX去除反应的电子受体,溶解氧、硝酸盐在需氧或厌氧条件下具有优先利用的机会,而硫酸盐则缺乏优先利用的机会.BTEX溶解组分浓度的降低,加上电子受体浓度的降低,可以表明含水层存在需氧条件与硝酸盐还原条件下的内在生物降解作用.其意义在于通过增加含水层中电子受体的浓度,将有助于内在生物降解能力的增强,从而能够提高含水层中污染物去除的效果. 相似文献
11.
Experiment simulation study on removal mechanism of BTEX in using river filtration system 总被引：1，自引：1，他引：0
River filtration system is a natural purification process to remove the pollutants in river water and make use of surface water. In this study, a series of experiments were set up with soil column test and static adsorption experiments to simulate the environmental behaviors of BTEX in the river filtration system. It was found that the environmental behaviors of BTEX in the river filtration system included adsorption and microbial degradation. Among the four components of BTEX used in the experiments, the removal rate of xylene was the highest, ethyl-benzene was second, toluene was third, and that of benzene was the lowest. The stability of the structure of benzene was the major contributor for the relatively lower degradation efficiency, and the low removal rate of toluene was due to the impact of adsorption on degradation. By comparison of the results of soil column test and static adsorption experiments, it was found that the soil–water partition coefficient K d of each component of BTEX was higher, the degradation ratio was lower. Compared with the previous study, the results of this experiment showed that when the initial concentration of the each component of BTEX reached 80 mg/L, the mixed pollution of BTEX could be removed by the river filtration system efficiently, and the average removal rate could be over 65 %. As a natural purification, river filtration system could efficiently remove the BTEX mixed pollution in a quite high concentration and protect the ground water from being contaminated. However, its purification efficiency was limited in a certain time range and concentration. It was shown in the later stage of the leaching experiment that the exudation concentration of BTEX increased, at the same time both the concentrations of the two electron acceptors increased to about the initial concentration and kept stable state until the end of the experiment, which revealed that due to accumulation of the concentration of BTEX in the soil column, the microbial activity was inhibited and then the denitrification and sulfate reduction terminated. When the adsorption saturation was achieved and microbial activity was inhibited, BTEX contamination would penetrate through the unsaturated zone and threaten the security of the ground water. 相似文献
12.
Mobilization of Ti-Nb-Ta during subduction: Evidence from rutile-bearing dehydration segregations and veins hosted in eclogite, Tianshan, NW China 总被引：15，自引：0，他引：15
Field evidence from the western Tianshan subduction complex in northwestern China indicates that the high field strength elements Ti, Nb, and Ta were mobilized and thereby fractionated from Zr and Hf during the dehydration process that transformed blueschist into eclogite. Both a segregation with a depletion halo, thought to represent initial mobilization during dehydration, and a transport vein, indicative of the long distance transport were investigated. In each case, centimeter-sized rutile grains grew as needle-like crystals in the segregation and as prismatic crystals in the vein. Within the host rock of the segregation, the Ti contents of garnet and omphacite, the modal abundances of rutile and titanite and the bulk rock Ti, Nb, and Ta contents decrease towards the segregation. These observations are consistent with transport of Ti, Nb, and Ta from the host rock into the segregation. Textural and geochemical data for the eclogite-facies vein minerals indicate that Ti-Nb-Ta-rich fluids were transported over long-distances (at minimum meter-scale) during fracture-controlled fluid flow. Complex forming ligands (e.g., Na-Si-Al polymers and F−) may have enhanced the solubility of Ti, Nb, and Ta in the fluid. Changes in fluid composition (e.g., XCO2) may both precipitate rutile and fractionate Ti, Nb, and Ta from LILE and REE. 相似文献
13.
Hailong Tian Tianfu Xu Fugang Wang Vivek V. Patil Yuan Sun Gaofan Yue 《Acta Geotechnica》2014,9(1):87-100
Geochemical interactions of brine–rock–gas have a significant impact on the stability and integrity of the caprock for long-term CO2 geological storage. Invasion of CO2 into the caprock from the storage reservoir by (1) molecular diffusion of dissolved CO2, (2) CO2-water two-phase flow after capillary breakthrough, and (3) CO2 flow through existing open fractures may alter the mineralogy, porosity, and mechanical strength of the caprock due to the mineral dissolution or precipitation. This determines the self-enhancement or self-sealing efficiency of the caprock. In this paper, two types of caprock, a clay-rich shale and a mudstone, are considered for the modeling analyses of the self-sealing and self-enhancement phenomena. The clay-rich shale taken from the Jianghan Basin of China is used as the base-case model. The results are compared with a mudstone caprock which is compositionally very different than the clay-rich shale. We focus on mineral alterations induced by the invasion of CO2, feedback on medium properties such as porosity, and the self-sealing efficiency of the caprock. A number of sensitivity simulations are performed using the multiphase reactive transport code TOUGHREACT to identify the major minerals that have an impact on the caprock’s self-sealing efficiency. Our model results indicate that under the same hydrogeological conditions, the mudstone is more suitable to be used as a caprock. The sealing distances are barely different in the two types of caprock, both being about 0.6 m far from the interface between the reservoir and caprock. However, the times of occurrence of sealing are considerably different. For the mudstone model, the self-sealing occurs at the beginning of simulation, while for the clay-rich shale model, the porosity begins to decline only after 100 years. At the bottom of the clay-rich shale column, the porosity declines to 0.034, while that of mudstone declines to 0.02. The sensitive minerals in the clay-rich shale model are calcite, magnesite, and smectite-Ca. Anhydrite and illite provide Ca2+ and Mg2+ to the sensitive minerals for their precipitation. The mudstone model simulation is divided into three stages. There are different governing minerals in different stages, and the effect of the reservoir formation water on the alteration of sensitive minerals is significant. 相似文献
14.
Zhangshuan Hou Mark L. Rockhold Christopher J. Murray 《Environmental Earth Sciences》2012,66(8):2403-2415
Numerical models are essential tools in fully understanding the fate of injected CO2 for commercial-scale sequestration projects and should be included in the life cycle of a project. Common practice involves modeling the behavior of CO2 during and after injection using site-specific reservoir and caprock properties. Little has been done to systematically evaluate and compare the effects of a broad but realistic range of reservoir and caprock properties on potential CO2 leakage through caprocks. This effort requires sampling the physically measurable range of caprock and reservoir properties, and performing numerical simulations of CO2 migration and leakage. In this study, factors affecting CO2 leakage through intact caprocks are identified. Their physical ranges are determined from the literature from various field sites. A quasi-Monte Carlo sampling approach is used such that the full range of caprock and reservoir properties can be evaluated without bias and redundant simulations. For each set of sampled properties, the migration of injected CO2 is simulated for up to 200 years using the water–salt–CO2 operational mode of the STOMP simulator. Preliminary results show that critical factors determining CO2 leakage rate through caprocks are, in decreasing order of significance, the caprock thickness, caprock permeability, reservoir permeability, caprock porosity, and reservoir porosity. This study provides a function for prediction of potential CO2 leakage risk due to permeation of intact caprock and identifies a range of acceptable seal thicknesses and permeability for sequestration projects. The study includes an evaluation of the dependence of CO2 injectivity on reservoir properties. 相似文献
15.
Soonyoung Yu Pyeong-Koo Lee Seong-Taek Yun Sang-Il Hwang Gitak Chae 《Environmental Earth Sciences》2017,76(9):338
Volatile organic compounds (VOCs) detected in stormwater were compared with VOCs present in emission sources, air, groundwater, and influent to sewage treatment plants in Seoul to understand their fate and transport in the urban hydrological system. Stormwater is a carrier of non-point source pollutants and contains VOCs from land surfaces and air. Samples of stormwater and influent to sewage treatment plants were collected and analyzed for 61 VOCs, while the VOCs in emission sources, air and groundwater were investigated through literature reviews for comparison. The results showed that the most frequently detected VOCs in stormwater were similar to those in air. However, the atmospheric concentrations of benzene, toluene, ethylbenzene, and xylenes (BTEX), and methyl tertiary-butyl ether (MTBE) were too low to explain their frequent detection and high concentrations in stormwater. As a result, land surfaces seem to be a primary source of these VOCs in stormwater. Comparison of the VOCs in stormwater and groundwater showed that toluene and MTBE were frequently detected in both media, but more often and at higher concentrations in stormwater. This finding indicates that stormwater recharge is a source of toluene and MTBE in groundwater. Regarding groundwater, land surfaces seem to be a primary source of toluene, while urban air is the primary source in the case of MTBE. Specifically, the MTBE values in air were sufficiently high to explain its levels in groundwater, which had continually increased and remained low afterward. Furthermore, the high ratios of TEX (toluene, ethylbenzene, and xylenes) to benzene and MTBE in stormwater indicated that TEX had additional sources other than vehicles, most likely hydrocarbon solvents. These solvents seem to be a primary source of TEX and other frequently detected VOCs in stormwater. However, trichloroethylene (TCE), tetrachloroethylene (PCE) and their dechlorination intermediates were far more frequently detected and at higher concentrations in groundwater than in stormwater. Additionally, their concentrations frequently exceeded the water-quality criteria. It seems that halogenated solvents had produced contamination plumes of these chlorinated VOCs in the Seoul aquifer. Based on VOCs detected in Seoul, stormwater was mixed with groundwater in combined sewers and flowed into sewage treatment plants. The results imply that organic solvents should be handled with extreme care to protect groundwater quality. 相似文献
16.
Hydrothermal vent fluids from Middle Valley, a sediment-covered vent field located on the northern Juan de Fuca Ridge, were sampled in July, 2000. Eight different vents with exit temperatures of 186-281 °C were sampled from two areas of venting: the Dead Dog and ODP Mound fields. Fluids from the Dead Dog field are characterized by higher concentrations of ΣNH3 and organic compounds (C1-C4 alkanes, ethene, propene, benzene and toluene) compared with fluids from the ODP Mound field. The ODP Mound fluids, however, are characterized by higher C1/(C2 + C3) and benzene:toluene ratios than those from the Dead Dog field. The aqueous organic compounds in these fluids have been derived from both bacterial processes (methanogenesis in low temperature regions during recharge) as well as from thermogenic processes in higher temperature portions of the subsurface reaction zone. As the sediments undergo hydrothermal alteration, carbon dioxide and hydrocarbons are released to solution as organic matter degrades via a stepwise oxidation process. Compositional and isotopic differences in the aqueous hydrocarbons indicate that maximum subsurface temperatures at the ODP Mound are greater than those at the Dead Dog field. Maximum subsurface temperatures were calculated assuming that thermodynamic equilibrium is attained between alkenes and alkanes, benzene and toluene, and carbon dioxide and methane. The calculated temperatures for alkene-alkane equilibrium are consistent with differences in the dissolved Cl concentrations in fluids from the two fields, and confirm that subsurface temperatures at the ODP Mound are hotter than those at the Dead Dog field. Temperatures calculated assuming benzene-toluene equilibrium and carbon dioxide-methane equilibrium are similar to observed exit temperatures, and do not record the hottest subsurface conditions. The difference in subsurface temperatures estimated using organic geochemical thermometers reflects subsurface cooling processes via mixing of a hot, low salinity vapor with a cooler, seawater salinity fluid. Because of the disparate temperature dependence of alkene-alkane and benzene-toluene equilibria, the mixed fluid records both the high and low temperature equilibrium conditions. These calculations indicate that vapor-rich fluids are presently being formed in the crust beneath the ODP Mound, yet do not reach the surface due to mixing with the lower temperature fluids. 相似文献
17.
Monitored natural attenuation can be a viable option for remediation of groundwater contamination by BTEX compounds. Under
the field conditions, the rate of contaminant mass attenuation through natural processes, such as biodegradation, to a large
extent affected by the groundwater flow regime, which is primarily controlled by the aquifer heterogeneity. Numerical simulation
techniques were used to describe quantitatively the relationship between biodegradation rate of BTEX and aquifer heterogeneity.
Different levels of aquifer heterogeneity were described by random hydraulic conductivity fields (K) having different statistical
parameters, the coefficient of variation (CV) and the correlation length (h). The Turning Bands Algorithm was used to generate
such K fields. Visual MODFLOW/RT3D was used to simulate the fate and transport of dissolved BTEX plume within heterogeneous
aquifers. The multispecies reactive transport approach described BTEX degradation using multiple terminal electron-accepting
processes. First-order biodegradation rate constants were calculated from simulated BTEX plumes in heterogeneous flow fields.
The results showed that aquifer heterogeneity significantly affected biodegradation rate; it decreased with increasing CV
when h was in the range of up to 12 m, whereas it increased with increasing CV when h was greater than about 12 m. For well characterized aquifers, this finding could be of great value in assessing the effectiveness
of natural attenuation during feasibility studies at BTEX contaminated sites. 相似文献
18.
反硝化增强去除乙醇对多孔介质渗透性的影响 总被引：1，自引：0，他引：1
随着乙醇混合汽油的不断推广应用,乙醇将成为地下水中与苯、甲苯、乙苯及二甲苯的同分异构体（BTEX）共存的一种新型污染物。通过4 个含水砂柱实验,研究了乙醇存在及其强化去除对含水介质渗透性能的影响。结果表明：在有限溶解氧与反硝化增强修复条件下,乙醇去除率达92% 以上;生物过程对介质渗透能力影响程度随乙醇初始浓度、消耗速率与补充频率而变化：乙醇初始浓度接近1 000 mg/L 和3 000 mg/L 时,乙醇消耗快,补充频率高,渗透系数下降总体上有连续性,最大下降幅度达一个数量级（×10-1 cm/s）;乙醇初始浓度达到5 000 mg/L 时,渗透性下降显著,可下降两个数量级,但乙酸的积累可影响生物活性,并使得渗透性变化出现反复;当不含乙醇时,汽油溶解组分对介质渗透性能的影响相对不明显。 相似文献
19.
C1-C7 volatile organic compounds were analyzed in three gravity cores taken from Walvis Bay shelf. The compounds detected included alkanes (methane, ethane, propane, i- and n-butane, and i- and n-pentane, and heptane), alkenes (2-methyl-2-butene, dimethylcyclopentenes, cyclohexene), oxygen containing compounds (2- and 3-methylfuran, 2,5-dimethylfuran, 2- and 3-methylbutanal and 3-pentanone), sulfur compounds (dimethylsulfide, thiophene, 2- and 3-methylthiophene) and aromatic compounds (benzene and toluene). In situ biological and low temperature chemical (less than 15°C) formation processes are proposed, possibly from marine terpene precursors. Subsequent to this work, these compounds were found to be widely distributed in surface gravity cores from other areas. Many of these compounds do not survive deeper burial. Furans, ketocompounds, and alkenes are generally not found in more than trace quantities in deeper (?10m subbottom) DSDP cores we have examined from other areas. 相似文献
20.
为了解石油烃类污染物在地下水中的自然衰减规律,以苯、萘、菲作为目标污染物,采用实验场地4种天然砂土作为含水层介质进行了室内模拟实验。结果表明：在单组分和混合组分溶液中,苯、萘和菲在地下含水层介质中的自然衰减均符合一级动力学方程;在不同含水层介质中,苯和萘的衰减速率大小顺序为粉砂>中砂≈粗砂>砾砂,而菲的自然衰减速率大小顺序为粉砂≈中砂≈粗砂>砾砂;微生物降解在苯和萘的自然衰减中起重要作用,而固相吸附在菲的自然衰减中起重要作用。3种物质共存时,苯和萘的自然衰减加快,菲的自然衰减减慢。 相似文献