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1.
The objective of this study was to investigate natural abundance and the distribution of nitrogen isotopic compositions to assess denitrification in two ~30 m thick vadose zones beneath the different land uses in the wastewater-irrigated area located in southern Shijiazhuang, China. Sediment samples were collected from cores of boreholes drilled in the vegetable growth plot and the wastewater-irrigated farmland for analyses of nitrogen isotopes, physical and chemical properties, respectively. The profile of borehole A drilled in the vegetable growth plot only applied animal wastes had lower δ15N values of mean +7.5 ‰ in the upper vadose zone, but higher values of mean +10.9 ‰ in the lower vadose zone. δ15N values in each part varied little with depth, indicating no or little denitrification occurred in the deep vadose zone below the soil zone. The profile of borehole B drilled in the wastewater-irrigated farmland had low δ15N values of mean +5.7 ‰ below the soil zone and little variations of δ15N values with depth, indicating no or little denitrification occurred in the deep vadose zone below the soil zone. This was also verified by consistent variations of NO3 ? and SO4 2? contents with Cl? contents. Our results suggested most of leachable nitrate from the soil zone was hardly subjected to biological attenuation into groundwater.  相似文献   

2.
Nitrate contamination of groundwater arises from anthropogenic activities, such as, fertilizer and animal manure applications and infiltration of wastewater/leachates. During migration of wastewater and leachates, the vadose zone (zone residing above the groundwater table), is considered to facilitate microbial denitrification. Particle voids in vadose zone are deficient in dissolved oxygen as the voids are partially filled by water and the remainder by air. Discontinuities in liquid phase would also restrict oxygen diffusion and therefore facilitate denitrification in the vadose/unsaturated soil zone. The degree of saturation of soil specimen (S r) quantifies the relative volume of voids filled with air and water. Unsaturated specimens have S r values ranging between 0 and 100 %. Earlier studies from naturally occurring nitrate losses in groundwater aquifers in Mulbagal town, Kolar District, Karnataka, showed that the sub-surface soils composed of residually derived sandy soil; hence, natural sand was chosen in the laboratory denitrification experiments. With a view to understand the role of vadose zone in denitrification process, experiments are performed with unsaturated sand specimens (S r = 73–90 %) whose pore water was spiked with nitrate and ethanol solutions. Experimental results revealed 73 % S r specimen facilitates nitrate reduction to 45 mg/L in relatively short durations of 5.5–7.5 h using the available natural organic matter (0.41 % on mass basis of sand); consequently, ethanol addition did not impact rate of denitrification. However, at higher S r values of 81 and 90 %, extraneous ethanol addition (C/N = 0.5–3) was needed to accelerate the denitrification rates.  相似文献   

3.
Assessment of chemistry of groundwater infiltrated by pit-toilet leachate and contaminant removal by vadose zone form the focus of this study. The study area is Mulbagal Town in Karnataka State, India. Groundwater level measurements and estimation of unsaturated permeability indicated that the leachate recharged the groundwater inside the town at the rate of 1 m/day. The average nitrate concentration of groundwater inside the town (148 mg/L) was three times larger than the permissible limit (45 mg/L), while the average nitrate concentration of groundwater outside the town (30 mg/L) was below the permissible limit. The groundwater inside the town exhibited E. coli contamination, while groundwater outside the town was free of pathogen contamination. Infiltration of alkalis (Na+, K+) and strong acids (Cl?, SO4 2?) caused the mixed Ca–Mg–Cl type (60 %) and Na–Cl type (28 %) facies to predominate groundwater inside the town, while, Ca–HCO3 (35 %), mixed Ca–Mg–Cl type (35 %) and mixed Ca–Na–HCO3 type (28 %) facies predominated groundwater outside/periphery of town. Reductions in E. coli and nitrate concentrations with vadose zone thickness indicated its participation in contaminant removal. A 4-m thickness of unsaturated sand + soft, disintegrated weathered rock deposit facilitates the removal of 1 log of E. coli pathogen. The anoxic conditions prevailing in the deeper layers of the vadose zone (>19 m thickness) favor denitrification resulting in lower nitrate concentrations (28–96 mg/L) in deeper water tables (located at depths of ?29 to ?39 m).  相似文献   

4.
This study describes the development of a green and sustainable strategy for the remediation of a contaminated site located in Chicago (IL, USA) to comply with the applicable federal and state environmental regulations. According to the site investigation results, many of the contaminant concentrations have been found to exceed the applicable regulatory limits that are protective of public health and local ecology. Polynuclear aromatic hydrocarbons, pesticides and heavy metals were found in the vadose zone soils throughout the site. Groundwater was found contaminated with lead or selenium in some locations. First, potential technologies to remediate the contaminated soils and groundwater at the site are identified. The most promising technologies are then systematically evaluated for sustainability based on qualitative and quantitative analyses. Sustainability considerations include greenhouse gases and other air pollutant emissions, water use, and personal injury, among others. Phytoremediation is selected to treat the majority of the site by utilizing existing and new plant species to reduce the concentrations of the contaminants. Solidification/stabilization is selected for “hot spot” treatment (high concentration area treatment) only at certain specific areas that have high concentrations of metals in the vadose zone. Monitored natural attenuation is selected for groundwater treatment.  相似文献   

5.
1,2-二氯乙烷(1,2-DCA)和1,2-二氯丙烷(1,2-DCP)是某污染场地地下水中检出最高的挥发性有机污染物。文中采用批试验方法,研究污染场地包气带中三种不同深度土壤样品对1,2-DCA和1,2-DCP的吸附-解吸特性。结果表明:土壤中有机质决定其吸附行为,三种土壤对1,2-DCA和1,2-DCP的吸附符合Henry线性等温方程,分配系数在20.49～22.43L.kg-1,1,2-DCA和1,2-DCP在三种土壤中分别具有相似的吸附能力;同一土壤中两种目标污染物的吸附能力为Kd(1,2-DCA)>Kd(1,2-DCP),但差别不大。1,2-DCA和1,2-DCP在三种土壤中的解吸可用Freundlich等温方程拟合,解吸的难易程度与土壤中黏粒含量相关,黏粒含量越高,目标污染物的解吸越困难,第三层(地下4.9～5.1m)土壤的防污能力较强;两种污染物在三种土壤中的解吸都存在明显的滞后效应,1,2-DCP的滞后指数比1,2-DCA的大。  相似文献   

6.
http://dx.doi.org/10.1016/j.gsf.2016.09.005   总被引：1，自引：1，他引：0  
We propose the nuclear geyser model to elucidate an optimal site to bear the first life.Our model overcomes the difficulties that previously proposed models have encountered.Nuclear geyser is a geyser driven by a natural nuclear reactor,which was likely common in the Hadean Earth,because of a much higher abundance of ~(235)U as nuclear fuel.The nuclear geyser supplies the following:(1)high-density ionizing radiation to promote chemical chain reactions that even tar can be used for intermediate material to restart chemical reactions,(2)a system to maintain the circulation of material and energy,which includes cyclic environmental conditions(warm/cool,dry/wet,etc.)to enable to produce complex organic compounds,(3)a lower temperature than 100℃ as not to break down macromolecular organic compounds,(4)a locally reductive environment depending on rock types exposed along the geyser wall,and(5)a container to confine and accumulate volatile chemicals.These five factors are the necessary conditions that the birth place of life must satisfy.Only the nuclear geyser can meet all five,in contrast to the previously proposed birth sites,such as tidal flat,submarine hydrothermal vent,and outer space.The nuclear reactor and associated geyser,which maintain the circulations of material and energy with its surrounding environment,are regarded as the nuclear geyser system that enables numerous kinds of chemical reactions to synthesize complex organic compounds,and where the most primitive metabolism could be generated.  相似文献   

7.
Saturation index with respect to calcite (SIc) and equilibrium CO2 partial pressure are important parameters to study groundwater in limestone aquifers. Aside from their use in time series, CO2 and SIc are used to estimate the baseline of CO2 in the vadose zone. The objective of this paper is to present conceptual examples on the use of the CO2–SIc relationship to have new information from usual parameters. Case study was considered as an example of use from Cussac site, a limestone aquifer in southwest of France. The result showed that CO2 baseline in unsaturated zone is found close to 25,000 ± 1,000 ppm.  相似文献   

8.
Industrially sourced dense non-aqueous phase liquids (DNAPLs) contaminated an alluvial aquifer in France decades ago. The location(s) and nature of the pollution source zone(s) were unknown, and the dissolved concentrations of volatile organic compounds in the monitoring wells varied greatly with time. The aquifer was in hydraulic equilibrium with an artificial canal whose water level was highly variable (up to 5 m). These variations propagated into the aquifer, causing changes in the groundwater flow direction; a transient numerical model of flow and solute transport showed that they correlate with the concentration variations because the changes in the flow direction resulted in the contaminant plume shifting. The transient hydrogeological numerical model was built, taking into account solvent biodegradation with first-order chain, since biodegradation has a significant influence on the pollutant concentration evolution. The model parameterization confirms the position of the source zones among the potential troughs in the bedrock where DNAPLs could have accumulated. The groundwater model was successfully calibrated to reproduce the observed concentration variations over several years and allowed a rapid validation of the hypotheses on the functioning of the polluted system.  相似文献   

9.
某石油化工场地土层挥发性有机物的污染特征   总被引：4，自引：0，他引：4       下载免费PDF全文
在调查华北平原一个污染年限超过35年的石油化工场地时,采用便携式仪器土层测气方法,快速、准确地测定了场地内40多个钻孔不同深度土层中挥发性有机物(VOCs)的浓度。基于对场地地质水文地质条件的认识,以及通过对大量数据的分析对比和应用空间变异分析方法,得出了对场地土层介质中VOCs污染特征的如下认识:(1)土层VOCs浓度的垂向变化可概括为污染源淋滤型、包气带扩散污染型、地下水波动带污染型和混合污染型四种污染类型;(2)在包气带砂土层和粉土层中,VOCs的扩散规律可近似用指数模型描述;(3)包气带土层中VOCs优先积聚在渗透性强的砂性土层中,砂土层中VOCs浓度是粉土层中VOCs浓度的1.5～12倍,平均3.76倍;(4)土层VOCs浓度的水平变异性表现为包气带土层的变异性要比地下水波动带土层大,且水平变异性能在25m尺度内得到充分显示;而土层VOCs浓度的垂向变异性随地而异,变化复杂,很难用统一的一个量化尺度来表征。本文对这一典型污染场地的剖析,有助于从事污染场地调查人员认识我国华北平原石油化工类场地的污染特征,并为调查与治理类似污染场地提供技术依据。  相似文献   

10.
包气带介质截留不同龄垃圾渗滤液中的有机污染物   总被引：1，自引：0，他引：1  
从渗滤液场龄和包气带岩性两方面着手,研究了不同岩性包气带介质对不同场龄渗滤液中有机污染物的截留作用规律。结果表明:新渗滤液经过以细砂、亚粘土为介质的包气带后,细砂和亚粘土中有机物的质量分数分别从0.70%和0.87%增大至0.80%和1.00%以上,而老渗滤液使细砂和亚粘土中有机物的质量分数降至0.70%和0.50%以下。新渗滤液经过包气带后,包气带介质中有机物的含量增大,而老渗滤液使包气带介质中有机物的含量降低,亚粘土较细砂更容易受到渗滤液污染的影响。即渗滤液性质对包气带介质中有机物含量具有方向性的影响作用,而包气带介质亚粘土比细砂更容易放大这种作用效果。  相似文献   

11.
This work presents the application of the ground-penetrating radar (GPR) method and electric resistivity tomography (ERT) technique in outlining a zone of contamination due to the light non-aqueous phase liquid (LNAPL) plume underground in the area of an impacted fuel station, close to Abha City. The GPR has been performed using SIR3000 unit with the 100 and 400 MHz antennas. The main objective of the GPR survey was to evaluate the lateral extension of contamination. The complex GPR signature of the plume was well characterized. Low reflectivity zone corresponds to hydrocarbon vapor phase in the vadose zone. Enhanced reflections are associated with free and residual products in the fractured saturated zone directly above the water table. An electric resistivity tomography (ERT) survey was performed on four profiles within the site to investigate the vertical and horizontal extent of the contamination plume and to define the bottom of the landfill. The 2D electric profiles show the presence of low-resistivity (4O to 37 Ω m) anomalies that refers to the presence of accumulated hydrocarbons. From the interpretation of the GPR and ERT profile, it was possible to locate the top and bottom of the contamination plume of the waste disposal site. The radar signal penetrated deep enough and enabled the identification of a second reflector at approximately 10-m deep, interpreted as the hard basement surface which causes the strong amplitude reflection in the GPR profile. The results of GPR and ERT showed good agreement.  相似文献   

12.
The effects of elevated pH, ionic strength, and temperature on sediments in the vadose zone are of primary importance in modeling contaminant transport and understanding the environmental impact of tank leakage at nuclear waste storage facilities like those of the Hanford site. This study was designed to investigate biotite dissolution under simulated high level waste (HLW) conditions and its impact on Cr(VI) reduction and immobilization. Biotite dissolution increased with NaOH concentrations in the range of 0.1 to 2 mol L-1. There was a corresponding release of K, Fe, Si, and Al to solution, with Si and Al showing a complex pattern due to the formation of secondary zeolite minerals. Dissolved Fe concentrations were an order of magnitude lower than the other elements, possibly due to the formation of green rust and Fe(OH)2. The reduction of Cr(VI) to Cr(III) also increased with increased NaOH concentration. A homogeneous reduction of chromate by Fe(II)aq released through biotite dissolution was probably the primary pathway responsible for this reaction. Greater ionic strengths increased biotite dissolution and consequently increased Fe(II)aq release and Cr(VI) removal. The results indicated that HLW would cause phyllosilicate dissolution and the formation of secondary precipitates that would have a major impact on radionuclide and contaminant transport in the vadose zone at the Hanford site.  相似文献   

13.
A modified DRASTIC model for groundwater vulnerability assessment (abbreviated as DRARCH model by combining the first letters of its six assessment indices) was proposed. It is essentially the specific application of DRASTIC model rather than a new model. Both natural hydrogeological conditions that prevent groundwater from contamination and important intrinsic hydrogeochemical properties of sediments in vadose zone that are related to the retardation of contaminants were considered as vulnerability indices. The DRARCH model consists of six indices: (1) Depth to the water table, (2) net Recharge, (3) Aquifer thickness, (4) Ratio of cumulative thickness of clay layers to total thickness of vadose zone, (5) Contaminant adsorption coefficient of sediment in vadose zone, and (6) Hydraulic conductivity of aquifer. The rating values and the weights of these vulnerability indices were obtained by contaminant transport simulation and factor analysis method respectively. Furthermore, the DRARCH model was applied to evaluate the groundwater vulnerability to arsenic contamination in Taiyuan basin, northern China, where groundwaters with high arsenic concentration occur in some localities. GIS-based mapping of groundwater vulnerability using this model indicates that the distribution of very high and high-vulnerability areas corresponds well to that of high-arsenic groundwaters. The DRARCH model is therefore reliable and useful for guiding groundwater environment management.  相似文献   

14.
The Tel Aviv metropolitan region (200 km2), located on the sandy and phreatic Mediterranean Coastal Plain aquifer in Israel, is an example of a contaminated megasite that is additionally complicated by being part of a densely populated urban environment. Despite being a major source of fresh potable water, no dedicated aquifer monitoring systems exist. The vast majority of tested water supply wells (82% of 90 wells) were found to be contaminated with one or more chlorinated volatile organic compounds (Cl-VOCs) such as trichloroethene and tetrachloroethene, originating from multiple sources, including former industrial sites. Temporal variations in Cl-VOC concentrations in water supply wells were large and unpredictable. Such aquifer contamination requires immediate action in terms of aquifer management and municipal water distribution. To cope with temporal and spatial variations in contaminant concentrations in water supply wells in an area where monitoring wells are absent, aquifer impact areas were defined based on the concentration of the Cl-VOC contaminant in pumping wells that was greatest in relation to its drinking water standard over a 3-year period. Such a map can be used to define water supply treatment and municipal well monitoring requirements, until an adequate monitoring system is established.  相似文献   

15.
Air sparging is an emerging method used to remediate saturated soils and groundwater that have been contaminated with volatile organic compounds (VOCs). During air sparging, air is injected into the subsurface below the lowest known depth of contamination. Due to buoyancy, the injected air will rise through the zone of contamination. Through a variety of mechanisms, including volatilization and biodegradation, the air will serve to remove or help degrade the contaminants. The contaminant-laden air will continue to rise towards the ground surface, eventually reaching the vadose zone, where the vapours are collected and treated using a soil vapour extraction (SVE) system.Air sparging performance and ultimately contaminant removal efficiency is highly dependent on the pattern and type of subsurface air flow. This paper presents the results of a laboratory experimental study which investigated the injected air flow pattern development within an aquifer simulation apparatus. The test apparatus consisted of a tank measuring 61 cm long by 25.4 cm wide by 38.1 cm high. The apparatus was equipped with one air injection well and two vapour extracton wells. Three different soils were used to simulate different aquifer conditions, including a sand, a fine gravel and a medium gravel. Experiments were performed with different injected air pressures combined with different vacuum and groundwater flow conditions. Experiments were also conducted by injecting air into simulated shallow aquifers with different thicknesses. The air flow patterns observed were found to depend significantly on the soil type, groundwater flow conditions and system controls, including injected air pressure, flow rate and applied vacuum. © Rapid Science Ltd. 1998  相似文献   

16.
Pharmaceuticals and personal care products (PPCPs) are a new kind of contaminant widely existing in the surface water and groundwater environment. In recent years, PPCPs have been received widely attention from many researchers. The migration and transformation of PPCPs are mainly photolysis, biodegradation, adsorption and hydrolysis in aquifer environment. The influencing factors of PPCPs migration include PPCPs' own physical and chemical properties, types and contents of organic matter, pH, lithology, geotechnical structure and the thickness of vadose zone, etc. At present, the research of PPCPs in China is still in the primary stage, especially on the contaminant in aquifer system. Therefore, the research in this field needs to be further strengthened.  相似文献   

17.
Electrical imaging (resistivity tomography) is increasingly used as a geophysical exploration technique in contaminated land research. The present work demonstrates the efficiency of electrical imaging in monitoring pollution plume evolution under both in-situ and model conditions. The in-situ campaign was done at an unlined landfill site situated in the city of Patras, Hellas. A partially saturated zone of alluvial fan deposits underlies the site, which retards leachate percolation to the underlying water table. Electrical imaging provided details of the internal structure of the waste tip, and confirmed the presence of a leachate plume beneath the base of the landfill. This field data component provided the constraints for the design of a generic model of contaminant infiltration into partially saturated sand. The aim was to study leachate plume evolution in a laboratory environment. For this purpose, a miniaturised resistivity tomography technique, developed at Cardiff University, was used to image the resistivity distribution before during and after contaminant infiltration. Comparison of resulting two-dimensional tomography with observed plume geometry at the end of the test showed the miniaturised electrical imaging technique to be highly effective. Experiment showed that contaminant evolution taking place in the model was gravity-driven, with capillary water in the vadose zone being displaced by the denser contaminant solution.  相似文献   

18.
An aquifer vulnerability of the Benin Formation aquifer (Calabar, southern Nigeria) has been assessed using a combination of DRASTIC index and GIS technology. The assessment was necessitated by the fact that uncontrolled disposal of domestic, industrial and agricultural wastes have caused groundwater contamination. Therefore, prevention of contamination, monitoring and management of the aquifer was urgently required to increase the efficient use of the current water supplies. The DRASTIC method uses seven parameters (depth to groundwater table, net recharge, aquifer media, soil media, topography, influence of vadose zone and hydraulic conductivity), which were used to produce vulnerability maps. The drastic vulnerability index ranged between 124 and 170. The vulnerability map shows that the aquifer is highly vulnerable in southeastern parts of the area covering about 22 %. The medium vulnerability area covers about 56.8 % of Calabar extending from the southwest to northern parts. 21.2 % of the area covering the central and northern parts the area lies within the low vulnerability zone. The present industrial and activities are located in the eastern and western parts, which falls within the low-medium vulnerability areas. Documented nitrate concentration in hand-dug wells and boreholes are in agreement with vulnerability zones. Sensitivity analysis was performed to evaluate the sensitivity of each parameter between map layers such that subjectivity can be reduced to an extent and new weights computed for each DRASTIC parameter. As management options sensitive areas, especially in the southern parts of Calabar area, should be protected from future development.  相似文献   

19.
Nanoscale zero-valent iron flakes for groundwater treatment   总被引：1，自引：0，他引：1  
Even today the remediation of organic contaminant source zones poses significant technical and economic challenges. Nanoscale zero-valent iron (NZVI) injections have proved to be a promising approach especially for source zone treatment. We present the development and the characterization of a new kind of NZVI with several advantages on the basis of laboratory experiments, model simulations and a field test. The developed NZVI particles are manufactured by milling, consist of 85 % Fe(0) and exhibit a flake-like shape with a thickness of <100 nm. The mass normalized perchloroethylene (PCE) dechlorination rate constant was 4.1 × 10?3 L/g h compared to 4.0 × 10?4 L/g h for a commercially available reference product. A transport distance of at least 190 cm in quartz sand with a grain size of 0.2–0.8 mm and Fe(0) concentrations between 6 and 160 g/kg (sand) were achieved without significant indications of clogging. The particles showed only a low acute toxicity and had no longterm inhibitory effects on dechlorinating microorganisms. During a field test 280 kg of the iron flakes was injected to a depth of 10–12 m into quaternary sand layers with hydraulic conductivities ranging between 10?4 and 10?5 m/s. Fe(0) concentrations of 1 g/kg (sand) or more [up to 100 g/kg (sand)] were achieved in 80 % of the targeted area. The iron flakes have so far remained reactive for more than 1 year and caused a PCE concentration decrease from 20.000–30.000 to 100–200 µg/L. Integration of particle transport processes into the OpenGeoSys model code proved suitable for site-specific 3D prediction and optimization of iron flake injections.  相似文献   

20.
王冠  熊小松  高锐  陈宣华 《中国地质》2019,46(5):1146-1160
深地震反射方法是探测地壳深部结构的先锋技术,能获取到莫霍面和上地幔的反射图像,成为揭示岩石圈结构、解决深部地质构造问题的有效手段。花海盆地位于河西走廊盆地群西部,处于不同大地构造单元的交汇部位,地层发育较全,但出露和发育程度差异较大,除白垩系为大面积连续分布外,其他各时代的地层均出露不全,常表现为被侵入岩分割破坏的残块状,为了确定深地震反射在花海盆地适合的采集参数,在采集前开展点试验,进行小、中、大炮炸药井炮激发参数对比优选,最终得到最优化的采集参数。在小炮实验中,36 kg药量取得的反射信息没有48 kg和60 kg的丰富,而且在MOHO反射的清晰度上48 kg和60 kg药量更为清晰,单井激发比组合井激发效果好;在中炮和大炮实验中,不同组合井对比差异不大,随着药量增大,激发能量增大,面波、折射波等干扰波能量也在增大,小炮干扰波能量最弱,反射信息最丰富的,中炮和大炮干扰波较发育,但通过后期去噪处理,也能得到中浅层反射信息。  相似文献   

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