共查询到20条相似文献，搜索用时 31 毫秒
1.
为了研究硝酸盐在不同Eh条件下通过弱透水层的迁移机理及转化形式,用天然黏土作为渗透介质弱透水层,在高渗透压条件下进行室内实验,模拟地下水中硝酸盐通过弱透水层的迁移转化过程。结果表明：单位质量黏土截污容量为1.45 mg/g,阻截率R=92%,不同Eh条件下（Eh分别为0、-100、-200 mV）弱透水层对硝酸盐的阻截能力都很强;低氧化还原电位有利于弱透水层吸附硝酸盐。弱透水层中硝酸盐的转化途径表明,弱透水层对硝酸盐的阻截能力很强,是微孔隙截留作用、机械过滤、离子吸附、协同吸附以及较弱的微生物共同作用的结果。 相似文献
2.
考虑非达西流的弱透水层固结计算 总被引：13，自引：1，他引：12
由于成岩作用的影响,深部弱透水层中的黏性土较为坚硬、致密,在这种黏土层中的孔隙渗流规律有偏离达西定律的现象,而在现有的地面沉降研究中,对深部弱透水层的固结变形计算始终沿用以达西定律为基础的固结方程进行,这显然是与实际情况不相符的。鉴于此,以孔隙渗流为非达西流为基础,对太沙基一维固结方程进行了重新推导,并采用半解析法对非达西流-太沙基一维固结方程进行了求解。分别采用达西流-太沙基固结方程和非达西流-太沙基固结方程对同一固结问题进行了计算,结果表明,考虑非达西流后土层达到某一固结度所需的固结时间较之不考虑非达西流时明显增加了,而且固结时间增长的趋势与实测的增长趋势较为一致。 相似文献
3.
Samantha Murphy Thomas Ouellon Jean-Marc Ballard Ren�� Lefebvre Ian D. Clark 《Hydrogeology Journal》2011,19(1):195-207
Tritium?Chelium groundwater dating was carried out in a trichloroethylene (TCE)-contaminated valley-fill aquifer system in Quebec, Canada, where a numerical groundwater flow model was developed. Forty seven discrete groundwater and dissolved gas samples were obtained along two flow paths originating from known TCE source zones whose related plumes converge down gradient to form a single plume. Sampling points in monitoring wells were projected onto vertical sections showing particle tracks along the two flow paths. At these points, simulated advective ages obtained from particle tracking were matched to tritium?Chelium ages using different porosity values; the best match was 0.35. Ages were also obtained above and below a prodeltaic silty aquitard in a portion of the aquifer where some source zones are located, which provide groundwater and TCE transit times through the aquitard as well as a mean vertical hydraulic conductivity that agrees with previous estimates used in the model. In certain locations, anomalously old ages associated with high terrigenic 4He indicate areas where groundwater from the underlying proglacial unit flows upward into the deltaic sand aquifer through aquitard windows. Upflow locations correspond with increased TCE concentrations, suggesting significant TCE provenance through the proglacial unit originating from a previously unrecognized TCE source zone. 相似文献
4.
Investigation of a 17 m vertical profile of a silt and clay aquitard at a natural gas well site in Alberta, Canada revealed a contaminant plume of gas condensate, along with high concentrations of acetate, propionate and butyrate. The pattern of the distribution of these short-chain fatty acids in groundwater and sediment samples suggested that they have been produced by microorganisms in a process associated with degradation of the condensate hydrocarbons. It is suggested that, in certain zones, under water-saturated and/or anaerobic conditions, these acids were actively consumed by SO4-reducing bacteria. Analyses of DNA extracts by denaturing gel gradient electrophoresis (DGGE) indicated that, compared to sediment samples collected from outside the condensate plume, contaminated samples tended to have fewer, but more strongly developed bands of DNA, which typically had closest affinities to known anaerobes, including species of Fe-reducing Geobacter, and SO4-reducing Desulfosporosinus. 相似文献
5.
The Lower Murrumbidgee alluvial fan at the eastern edge of the Murray Basin is comprised of high‐yielding coarse‐grained aquifers and interlayered fine‐grained deposits that exert an important control on recharge and vertical leakage of contaminants such as salt. Concerns over increasingly saline shallow groundwater, particularly in irrigation areas, has focused investigations on the depositional origin and spatial distribution of these fine‐grained deposits (aquitard units), which may constitute both a source of leachable salt and a barrier to leakage. Detailed laboratory analysis of a minimally disturbed core to 83m depth, obtained from a drillhole adjacent to an irrigation bore, was augmented with geophysical investigations from this and other boreholes near the apex of the alluvial fan. Previously mapped clay units (aquitards) are redefined as clayey silts based on clay content variation between 10% and 30%. Mineralogical and lithostratigraphic evidence for three clayey silt units is presented: a lower unit (75–83m), a middle unit (45–64m) and an upper unit (0–16m). Electrical image surveys indicate that the upper unit is discontinuous, interrupted by large palaeodrainage features probably containing sands and gravels. These palaeodrainage channels are buried beneath a veneer of clay and significantly increase recharge and leakage. Some evidence suggests an aeolian component near the surface and within the middle clayey silt unit. However, mixing with fluvial deposits and subsequent weathering has also occurred. The clayey silt units are extensively weathered and oxidised, with the degree of oxidation increasing towards the surface and adjacent to aquifers saturated with oxygenated groundwater. Post‐depositional weathering of the middle and lower units may also have been associated with leaching of salts. No salt remains in the middle and lower units, but 10.2kg/m2 is stored within 15m of the surface at the Tubbo site. The upper clayey silt unit is a significant source of leachable salt, which is associated with increasing shallow groundwater salinity at some sites. 相似文献
6.
黏性土孔隙水的地球化学行为对于弱透水层水质水量研究、污染物在黏性土中的迁移、核废物储存场址评价及油气储层的盖层评价等均具有重要作用。受低渗透性限制,传统方法提取黏性土孔隙水非常困难。通过实验测定黏性土的物化特性,利用PHREEQC软件模拟计算了孔隙水组成。通过浸提实验,利用阴离子可通过孔隙度（50%总孔隙度）确定模型中孔隙水的Cl-和SO2-4含量;根据岩土的阳离子交换量及各离子的交换选择系数,矿物沉淀 溶解平衡,确定了孔隙水的主要化学组分。结果显示,模拟的孔隙水化学组分与压榨液（相当于原位孔隙水）相近,不同于浸提液。传统的浸提方法不可直接换算为孔隙水,受矿物可交换点阳离子的释出与矿物溶解影响,各离子含量被明显高估。模拟所得天津滨海区黏性土阳离子交换量为13.4~37.8 meq/100g土,可交换离子以Na、Mg、Ca为主。所得孔隙水为还原环境,且随着深度增加,还原性增强。模型中所选矿物均为平衡状态,溶液中可能存在的矿物大部分为未饱和或平衡状态,仅部分含Fe、Al矿物过饱和。由结果可知Fe含量偏高,对控制Fe元素的矿物需进一步精确测定。本方法在低渗透,超固结,低含水量介质的孔隙水相关研究中将发挥重要作用。 相似文献
7.
为探索低浓度乙醇溶液中氯苯(Chlorobenzene,简称CB)在土壤中的迁移行为,以武汉市某化工厂受CB污染土壤为研究对象,设计正交试验,开展了淋洗条件筛选、最佳条件的验证和解吸动力学研究3组实验.优化出的最佳淋洗条件为常温、液土比(mL/g)为25∶1、淋洗液中乙醇体积浓度为10%、淋洗时间为2 h;在最优淋洗条件下,CB的提取率为90%;且CB解吸规律符合Freundlich吸附模型.以低浓度乙醇为淋洗剂修复受CB污染土壤,不仅可实现污染土壤修复的目标,同时还能够保留土壤功能,避免造成二次污染. 相似文献
8.
Geostatistical regionalization of glacial aquitard thickness in northwestern Germany, based on fuzzy kriging 总被引：1，自引：0，他引：1
In many instances hydrogeological parameters obtained by conventional methods for selected localities within an aquifer or an aquitard are not sufficient for adequate regionalization at the scale of the entire layer. Here, we demonstrate an application of the fuzzy kriging method in regionalization of hydrogeological data, in which the set of conventional, crisp values is supplemented by imprecise information subjectively estimated by an expert. It is believed that such an approach eventually may reflect the real-world conditions more closely than a traditional crisp-value approach, because the former does not impose exactness artificially on phenomena which are diffuse by their nature. Spatial interpolation was done for the thickness of one of the major aquitards (till and glaciolacustrine clay) in northwestern Germany. The dataset consists of 329 crisp values from boreholes supplemented by 172 imprecise values defined as fuzzy numbers. It is demonstrated that the reliability of regionalization was higher, compared to regionalization performed with the crisp dataset only. Fuzzy kriging was performed with FUZZEKS (Fuzzy Evaluation and Kriging System) developed at the Ecosystem Research Center at the University of Kiel. 相似文献
9.
The drainage of the aquitard and its implication for groundwater exploitation in Hengshui City 
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下载免费PDF全文 SU Chen WANG Ying ZHENG Zhao-xian CHENG Zhong-shuang CHEN jiang HAO Qi-chen 《地下水科学与工程》2018,6(2):84-91
The deformation and the drainage of the aquitard is the main concern in the North China Plain(NCP), and the water released from aquitard compaction may be a large portion of the exploited groundwater. The skeletal specific storage of aquitard is the element parameter to the drainage of aquitard, and the undisturbed core samples are the best choice for the measurement of the physical parameters. In this study, the consolidation test was employed to analyze the skeleton specific storage of the clay sample drilled from Hengshui City, and the contribution from the drainage of aquitard to the groundwater exploitation. The results suggest the consolidation test can be utilized to understand the skeletal specific storage of aquitard, which is about 3.92×10-4 m-1 in the Hengshui. The water-saturation content of the aquitard was less than 100%, and the amount of the drainage of the aquitard was about 69% of the volume of land subsidence. The water released from aquitard compaction was about 35% of the groundwater exploitation to the deep aquifers. 相似文献
10.
N. M. Sushchevskaya O. V. Levchenko E. P. Dubinin B. V. Belyatsky 《Geochemistry International》2016,54(3):237-256
The study of magmatism and tectonic structure of the East Indian or Ninetyeast Ridge (NER) reveals the geochemical similarity of mantle sources for the NER and Kerguelen Plateau melts. Magmas related to the Kerguelen plume were derived from an enriched mantle source, whereas the NER tholeiitic basalts originated from a source contaminated by a depleted material. While, depleted basalt varieties were not found within the NER basalts. It was shown that magmatic rocks forming the NER were generated by high degrees (30%) of partial melting within the ancient Wharton spreading ridge due to the activity of the Kerguelen plume, which was located at this time in the vicinity of the ridge. The most significant impact of the plume on the NER structures was recorded at 70–50 Ma ago. 相似文献
11.
Diesel transport monitoring in simulated unconfined aquifers using miniature resistivity arrays 总被引：2，自引：0，他引：2
The principal aim of this study is to assess the scope of monitoring diesel plume migration in a scaled aquifer model with
a miniaturised electrical resistivity array. Respectively 1000 and 500 ml of diesel were injected in both the unsaturated
and water-saturated zones of a sand body overlying a clay aquitard, and diesel migration was monitored with a miniature electrode
array and an off-the-shelf resistivity meter. Inverted time-lapse electrical resistivity tomography (ERT) data reflect downward
and lateral spreading of the diesel plume away from the injection point in the unsaturated zone. Diesel was also imaged to
spread upwards and laterally away from the injection point in the saturated zone, as controlled by capillary rise. In both
cases later-time ERT images reflected preferential pooling of diesel on the water table, as well as vertical smearing of pooled
diesel in response to simulated water-table fluctuations. Repeat fluid electrical conductivity (EC) and dissolved oxygen (DO)
measurements validate the observed changes in bulk resistivity caused by both diesel injections. Artefacts introduced by 2D
inversion of 3D contaminant transport were abound. Time-lapse ERT imaging of diesel transport is therefore inferred to be
feasible and well-suited to complementing conventional techniques of intrusive site investigation, although time-lapse 3D
or 4D ERT imaging is strongly advocated. 相似文献
12.
采用高渗透压渗流试验装置,模拟已被污染的浅层地下水越流通过弱透水层污染深层地下水的过程,研究不同矿化度、不同pH条件下有机污染物（菲）通过饱和黏性土弱透水层时的质量浓度变化特征。结果表明：矿化度的增加有利于弱透水层吸附截留渗滤液中的菲;高矿化度水中的Na+交替土层中的Ca2+、Mg2+,使水中的Ca2+、Mg2+质量浓度增加,与HCO-3、菲组合形成络合物;不同pH条件下,Ca2+、Mg2+、HCO-3对菲的迁移有阻滞作用,SO2-4参与还原反应并可与菲形成络合物,对菲迁移有促进作用。菲在弱透水层中的迁移能力很弱,衰减率达82％～96％,高渗透压下菲的污染锋面迁移速度为0.714 m/d,pH=8时菲通过弱透水层的迁移质量浓度最小。控制渗滤液的pH、组分可有效阻止菲在弱透水层中的迁移。 相似文献
13.
弱透水层与含水层相互作用是国际水文地质学界关注的热点问题,特别是黏性土弱透水层与孔隙含水层的相互作用。近年来,在自然沉积、过量开采地下水、现代化农业机械与建筑业重型机械应用等自然与人为活动影响下,黏土弱透水层会发生有效应力增加、孔隙结构变形和孔隙度减少、渗透性降低、溶解氧和贮水能力减少以及侧向和垂向排水等的压实作用,导致地下水污染、地面沉降等环境问题的发生。本文重点介绍了黏性土弱透水层压实作用的原理,分析了地下水系统中4种不同状态下沉积物压实与孔隙流体压力的关系,基于压实物理模拟和数值模拟两个方面对压实作用的研究方法与技术进行了系统总结,随后探讨了压实作用下黏性土弱透水层对地下水水量与水质的影响,并对此研究的发展趋势及其在地球科学、环境科学等研究领域的潜在应用提出了展望。 相似文献
14.
Land subsidence due to aquifer-system compaction accompanying groundwater extraction is a global hazard. Rising urban construction and groundwater demand necessitate increased awareness and better understanding of the geological problem. Motivated by the lack of laboratory-scale studies on this issue, an experimental investigation on the newly developed Tongchuan region, China, is presented. The study addresses the deformation behaviors of three soil samples, with the lithology of silty clay, silt, and fine sand, under the conditions of groundwater withdrawal and recharge using the GDS Consolidation Testing System. Results indicate that all three samples were characterized by elastic–plastic deformation under the conditions of withdrawing and recharging. The vertical deformation of the silty clay in the aquitard above the first confined aquifer was larger than those of the other two samples, and its deformation is a gradual and long process; thus, considerable attention should be paid to deformation in this aquitard due to the apparent creep effect and tiny rebound deformation. However, the settlement of the fine sand in the second confined aquifer cannot be ignored due to the great thickness of the aquifer. For the same soil, as the pore-water pressure declined, the unit rate of vertical deformation decreased gradually, whereas the creep effect of deformation in the later declining stage of pore-water pressure was more apparent than that in the former declining stage. These observations are highly important to the local government, which is developing measures to prevent and control subsidence. 相似文献
15.
The major sources of cassiterite in Nigeria are the alluvial and eluvial deposits from the biotite granites within the Jurassic alkaline ring complex (the Younger Granites) of the Jos Plateau. Less than 5% of the total production has been recovered from pegmatites within the largely Precambrian basement complex consisting of migmatites, gneisses, the Pan-African (Older) Granites and pegmatites, but with the rapidly depleting reserves of the former source new reserves have to be found.This study presents the first report on an important new source of cassiterite in basement-complex gneisses, migmatites, pegmatites and aplites in the Gurum area near Jos. The cassiterite, which has been economically concentrated by the leaching and weathering of these rocks, is generally finer grained and darker than the alluvial cassiterite derived from the Jurassic biotite granites. This new find has important petrogenetic and economic implications, suggesting that the basement complex could be a suitable parent rock for the Younger Granites and a significant potential source of cassiterite in Nigeria. 相似文献
16.
连云港市位于苏北沿海地区,地面沉降灾害面积较大,多地沉降速率超过20 mm/a,徐圩的沉降现状尤为严重。为了能够对徐圩地区的地面沉降进行精细化观测,文章采用BOTDR分布式光纤感测技术,对徐圩镇127 m深的钻孔地层进行了两年多的全断面精细化监测。结果表明:徐圩镇共有四个承压含水层组,I-1隔水层和I-2隔水层土体沉降量分别占总沉降量的70.29 %、24.59 %,抽水层的土体最大沉降量仅占比1.38 %。I-1隔水层和I-2隔水层的地层岩性包括淤泥质黏土（L2）、亚黏土（L3）、亚砂土夹粉砂（L4）,总厚度为44 m,由于抽水过程中隔水层向含水层失水,导致该隔水层土体固结压缩。同时,工程建设附加荷载对地面沉降的影响也不可忽视。徐圩地区现阶段的沉降仍在继续发生,但沉降速率有减小的趋势。BOTDR技术可有效获取地面沉降钻孔全断面的土层变形分布信息,为地面沉降评价提供了一种精细化的分布式监测手段。 相似文献
17.
A series of patterns in the chemical and isotopic composition of the groundwater of the Cerro Prieto area have been recognized. These patterns were used to define four hydrochemical and isotopical zones in the area. One of these areas located at the east side was found to be the source of recharge, while another in the central part is where an older aquifer exist in lacustrine deposits. The low permeability of the area causes the aquifer to act as an aquitard, which at least is partly surrounded by an interface zone where mixing of waters occurs. Tritium and radiocarbon method revealed that the aquitard is an isolate system whose residence time is of 32 ka. 相似文献
18.
Garth van der Kamp 《Hydrogeology Journal》2001,9(1):5-16
Shallow clay-rich aquitards limit groundwater recharge to underlying aquifers, but they also protect the aquifers from contamination.
The bulk hydraulic conductivity of such shallow aquitards can range from less than 1 mm/year to more than 100 m/year and may
be much greater than the hydraulic conductivity of small intact samples of the aquitard material. This enhanced hydraulic
conductivity diminishes the qualities of the aquitards for the protection of underlying aquifers but allows a higher rate
of recharge. For aquifers that are overlain by aquitards, management and protection of groundwater resources may be critically
dependent on reliable determinations of aquitard permeability.
A variety of methods for determining bulk hydraulic conductivities of shallow clay aquitards is available; each has drawbacks
and advantages, and each is based on simplifying assumptions. These methods include slug tests, pumping tests, response of
the aquitard to mechanical loading, and analysis of natural pore-pressure fluctuations. Several of the commonly used methods
require an independent measurement of specific storage. Laboratory methods for determining specific storage are probably not
representative of in situ conditions and may lead to overestimation of aquitard permeability. Much of the theory developed
to date depends on the assumption that horizontal displacement of the solid material is negligible, and this may not be a
valid assumption for highly deformable media such as clay aquitards. However, with judicious selection of the most suitable
methods for a particular site, good test design, careful instrumentation, and respect for the underlying assumptions, reliable
determinations of aquitard permeability can be obtained.
Electronic Publication 相似文献
19.
Geochemical and hydrologic controls on the mobilization of arsenic derived from herbicide application 总被引：1，自引：0，他引：1
Arthur G. Fitzmaurice A. Azra Bilgin Peggy A. O&#x;Day Virginia Illera David R. Burris H. James Reisinger Janet G. Hering 《Applied Geochemistry》2009,24(11):2152-2162
The fate and transport of As was examined at an industrial site where soil- and groundwater contamination are derived from the application of As2O3 as a herbicide. Application of arsenical herbicides was discontinued in the 1970s and soils in the source area were partially excavated in 2003. Arsenic contamination (up to 280 mg/kg) remains in the source area soils and a plume of As-contaminated groundwater persists in the surficial aquifer downgradient of the source area with maximum observed As concentrations of 1200 μg/L near the source area. The spatial extent of As contamination as defined by the 10 μg/L contour appears to have remained relatively stable over the period 1996–2006; the boundary of the 1000 μg/L contour has retreated over the same time period indicating a decrease in total As mass in the surficial groundwater.In column experiments conducted with source area soil, the As concentrations in the column effluent were comparable to those observed in groundwater near the source area. A substantial fraction of the As could be leached from the source area soil with ammonium sulfate and ammonium phosphate. Exhaustive extraction with background groundwater removed most of the total As. These results indicate that As in the source area soils is geochemically labile. Source area soils are low in extractable Fe, Mn and Al, and characterization by X-ray absorption spectroscopy and electron microscopy indicated that As is present primarily as arsenate sorbed to (alumino)silicate minerals. Batch sorption experiments showed much less sorption on surficial aquifer sediments than on sediments from the Jackson Bluff Formation (JBF), a presumed confining layer. This limited capacity of the surficial aquifer sediments for As sorption is consistent with the similar As contents observed for these sediments within and upgradient of the As plume. The apparent stability of the As plume cannot be explained by sequestration of As within the surficial aquifer. Sorption to JBF sediments may contribute to As sequestration, but As enrichment in JBF sediments within the plume (i.e., as compared with JBF sediments upgradient) was not observed. These results indicate that neither the persistence of As in the source area soils or the apparent stability of the plume of As-contaminated groundwater at this site can be explained by geochemical controls on As mobility. The absence of demonstrable geochemical bases for such observations suggests that possible hydrologic controls should be further investigated at this site. 相似文献
20.
Ahzegbobor P. Aizebeokhai Kehinde D. Oyeyemi Emmanuel S. Joel 《Arabian Journal of Geosciences》2016,9(7):496
Geoelectrical resistivity techniques are increasingly being applied in addressing a wide range of hydrological, environmental, and geotechnical problems. This is due to their effectiveness in near-surface characterization. In the present study, a suite of vertical electrical soundings (VESs) was integrated with 2D geoelectrical resistivity and time-domain induced polarization (IP) imaging to characterize the near-surface and delineate the underlying aquifer in a sedimentary terrain. The geophysical survey was conducted as part of preliminary studies to evaluate the potential of groundwater resource in Iyana-Iyesi and Canaan Land area of Ota, southwestern Nigeria. A high-yield confined sandy aquifer overlain by a low-yield aquitard was delineated; overlying the aquitard is a very resistive and thick layer that is predominantly composed of kaolinitic swelling clay intercalated with phosphate mineral. 相似文献