On the Displacement of NAPL Lenses and Plumes in a Phreatic Aquifer

The movement of an LNAPL lens above a sloping or horizontal water table, and a DNAPL lens above an impermeable surface is discussed. The governing equations are derived, using the vertical equilibrium approach and assuming the water mobility to be much greater than that of the NAPL. Analytical solutions are obtained for onedimensional movement of a lens along a sloping water table. They describe the lens movement with the formation of a jump at the leading front (large-scale approximation), and the distribution of NAPL in the transition zone near the jump (smallscale approximation). A model,describing the movement of a lens, taking into account NAPL retention,is proposed. Approximate onedimensional solutions for the movement of a NAPL lens along sloping or horizontal surfaces under such conditions are presented for this model. Some approximate analytical solutions for twodimensional lens (plume) formation and movement are obtained for the case of a point source at a sloping surface.     

An analysis of perturbation based methods for the treatment of parameter uncertainty in numerical groundwater models

Monte Carlo methods are robust approaches for the estimation of prediction uncertainty in groundwater flow and transport modelling under uncertain model parameters. However Monte Carlo procedures estimate the prediction statistics by generating a population of solutions from random realisations of the model parameters which are consistent with the parameter statistics, and as a result are computationally demanding. Taylor series based procedures offer an alternative to Monte Carlo methods for calculating the prediction statistics. Two such approaches, the first-order second moment and McLaughlin and Wood's perturbation method, are based on using a Taylor series to derive approximate expressions for the model predictions first and second statistical moments. In this paper the perturbation method presented by McLaughlin and Wood is rederived using Vetter matrix notation. This is compared with the first-order second moment (FOSM) method and while the steady state expressions for these two approaches are shown to be equivalent, the transient forms are considerably different. A new form of the FOSM is derived, which is simpler and has a lower computational burden. However, the transient McLaughlin and Wood expression is found to have a significantly lower computational overhead than either of the FOSM methods presented.     

Modeling Three-Dimensional Groundwater Flows by the Body-Fitted Coordinate (BFC) Method: I. Stationary Boundary Problems

Based on the body-fitted coordinate (BFC) method, a three-dimensional finite difference computer code, BFC3DGW, was developed to simulate groundwater flow problems. Methodology and solution procedures of the BFC method for simulating groundwater flows, particularly when the flow domain is stationary as in the case of confined aquifers, are described. The code was verified by comparing numerical results with analytical solutions for well-flow problems in an isosceles right-triangular aquifer. An example simulation is made to demonstrate capability of the code for solving flow problems in anisotropic aquifers where directions of anisotropy change continuously. The method differs from the conventional finite difference method (FDM) in the ability to use a flexible, nonorthogonal, and body-fitted grid. The main advantages of the method are the convenience of grid generation, the simplified implementation of boundary conditions, and the capability to construct a generalized computer code which can be consistently applied to problem domains of any shape.     

计算近场地震作用下隔震结构支座破坏易损性曲线的概率凸集混合模型

用凸集模型模拟隔震结构参数的不确定性,而用随机模型模拟地震动输入的不确定性,提出了计算近场地震作用下在考虑双不确定性因素时隔震结构支座发生破坏的易损性曲线计算新方法;计算结果将给隔震支座力学参数的设计提供参考;通过计算对比可知,若不考虑结构参数不确定性将低估隔震支座破坏的地震易损性;对计算实例中基底最大位移敏感度分析发现,隔震支座的力学参数(如屈服力、屈服后刚度等)对基底最大位移影响较大,上部结构质量的影响次之,而上部结构的刚度对其影响不大;此外,本文的研究内容也为考虑结构参数和输入地震动双不确定性因素的情况下,计算各类结构地震易损性曲线提供了一种新的思路和途径。     

Deuterium as Natural Tracer in Groundwater from Neighbouring Area of Danube Delta Biosphere Reserve

Abstract

Measurements of deuterium content of the groundwater from neighbouring area of Danube Delta Biosphere Reserve show that the waters are meteoric in origin, but at the same time the results showed that the water for three sampling points could not originate from local groundwater and have their recharge area at high altitude and a considerable distance.

According to the δD values the following categories of waters were delineated:

• (1) waters that belong to an confined aquifer in limestone and have their recharge in high altitude region, higher than 1000m (δD < -80‰)

  (2) waters tributary to the Danube river that have a small variability in time of δD values (δD > - 75‰)
  (3) local infiltration waters, situated in the West of the investigated area towards the continental platform of the Dobroudja, with high variability in time of δD values, due to seasonal effect (δD > - 70‰)
  (4) waters originated in mixing processes between the waters with different isotopic content. The one endmember is heavier isotopic water that belongs to local recharged waters (local infiltration waters and waters tributary to Danube river) and the other endmember is the isotopically light water.

     

Two-step synthesis of ethylene glycol-D6 via isotope exchange of glycolic acid

Tracers can be used to monitor emissions of leachate from landfills in order to detect hydrological pathways and to evaluate environmental pollution. We investigated the stable carbon isotope ratio (δ¹³C–Σ CO ₂) in dissolved inorganic carbon and tritium (³H) in water, in addition to the tracers of pollution commonly found in relatively high concentrations in leachate, such as chloride (Cl), organic matter (COD), nitrogen (total and NH₄–N), iron (Fe), electrical conductivity (EC) and pH. The sampling was performed at seven landfills in the south-eastern part of Norway during a period of 5 years. The objective was to evaluate the potential for tracing leachate in the environment with emphasis on groundwater pollution. By measuring the δ¹³C–Σ CO ₂ in leachates, groundwaters and surface waters, the influence of leachate can be identified. The value of δ¹³C–Σ CO ₂ varied from?5.5 to 25.9 ‰ in leachate, from?25.4 to 14.7 ‰ in groundwater and from?19.7 to?13.1 ‰ in creeks. A comparison of the carbon isotope ratio with COD, EC and the concentrations of total and NH ₄–N, Cl and Fe showed that δ¹³C–Σ CO ₂ is a good tracer for leachate due to higher sensitivity compared to other parameters. The mean concentrations of all the studied parameters were higher in the leachate samples; however, only the carbon isotope ratio showed significant differences between all the groups with strong and middle pollution and samples with low pollution, showing that it can be used as a convenient tracer for leachate in groundwater and surface water. The carbon isotope ratio showed strong correlation between nitrogen, EC and bicarbonate, but not with pH. Tritium was only sporadically found in measureable concentrations and is not considered as a suitable tracer at the sampled locations.     

Kontamination und Schutz Des Grundwassers in Der Nähe Von Atomkraftwerken

Abstract

The influence of diffusion, dispersion, retardation and their correlation with groundwater velocities, porosity and radioactivity is discussed in relation to nuclear power plants and their potential influence on groundwater pollution.     

Radioactivity of sand,groundwater and wild plants in northeast Sinai,Egypt

The radioactivity levels are poorly studied in non-coastal arid regions. For this reason, 38 locations covering an area of about 350 km² in northeast Sinai, Egypt, were investigated by γ-ray spectroscopy. Moderately significant correlations among ²³⁸U, ²³⁴Th, and ²²⁶Ra isotopes and low significant correlations between the concentrations of ²³⁸U-series and ²³²Th in sand were obtained. No evidence of correlation was found between the concentrations of radioisotopes and pH, grain size, total organic matter content, bicarbonate or calcium carbonate concentrations of the sand samples. The mean values of soil-to-plant transfer factor were 0.15, 0.18, 1.52 and 0.74 for ²²⁶Ra, ²³²Th, ⁴⁰K, and ¹³⁷Cs, respectively. The range of concentrations of ²²⁶Ra, ²³²Th, and ⁴⁰K in water samples collected from five wells were<0.4–0.16,<0.4–0.13, and<0.15–1.62 Bq l^?1, respectively. The mean absorbed dose rate in outdoor air at a height of 1 m above the ground surface for the sand samples was 19.4 nGy h^?1. The Ra_eq activities of the sands are lower than the recommended maximum value of 370 Bq kg^?1 criterion limit for building materials.     

Insights from stable isotopes of water and hydrochemistry to the evolutionary processes of groundwater in the Subei lake basin,Ordos energy base,Northwestern China

ABSTRACT

Changes in groundwater evolutionary processes due to aquifer overexploitation show a world-wide increase and have been of growing concern in recent years. The study aimed to improve the knowledge of groundwater evolutionary processes by means of stable water isotopes and hydrochemistry in a representative lake basin, Ordos energy base. Groundwater, precipitation, and lake water collected during four campaigns were analysed by stable isotopes and chemical compositions. Results showed that temperature effect predominated the isotope fractionation in precipitation, while evaporation and inadequate groundwater recharge were the key factors explaining high salinity and isotopic enrichment in lake water. Additionally, the Kuisheng Lake was a preferential area of groundwater recharge, while the Subei Lake received less sources from underlying aquifer due to the combined effects of low permeable zone and upstream groundwater captured by the production wells. The homogeneous isotope signatures of groundwater may be ascribed to the closely vertical hydraulic connectivity between the unconfined and the confined aquifers. Isotopically enriched groundwater pumping from well field probably promoted isotopic depletion in groundwater depression cone. These findings not only provide the conceptual framework for the inland basin, but also have important implications for sustainable groundwater management in other groundwater discharge basins with arid climate.     

Groundwater of the Crimean peninsula: a first systematic study using stable isotopes

ABSTRACT

Karst springs in the Main Range of the Crimean Mountains and the Crimean Piedmont show a restricted range of values (δ¹⁸O?=?–10.5 to –8.0 ‰, δ²H?=?–72 to –58 ‰), somewhat more negative than the weighted mean of meteoric precipitation. This suggests preferential recharge at higher elevations during winter months. Groundwater tapped by boreholes splits in three groups. A first group has isotopic properties similar to those of the springs. The second group shows significantly lower values (δ¹⁸O?=?–13.3 to –12.0 ‰, δ²H?=?–95 to –82 ‰), suggesting recharge during colder Pleistocene times. The third group has high isotope values (δ¹⁸O?=?–2.5 to +1.0 ‰, δ²H?=?–24 to –22 ‰); the data points are shifted to the right of the Local Meteoric Water Line, suggesting water–rock exchange processes in the aquifer. These boreholes are located in the Crimean Plains and discharge mineralized (ca. 25 g L^?1) thermal (65°C) water from a depth of 1600–1800 m. Groundwater associated with mud volcanoes on the Kerch peninsula have distinct isotope characteristics (δ¹⁸O?=?–1.6 to +9.4 ‰, δ²H?=?–30 to –18 ‰). Restricted δ²H variability along with variable and high δ¹⁸O values suggest water–rock interactions at temperatures exceeding 95 °C.