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41.
Palut JM Montarnal P Gautschi A Tevissen E Mouche E 《Journal of contaminant hydrology》2003,61(1-4):203-218
A long-term single borehole diffusion experiment using tritiated water as tracer was carried out in Opalinus clay, an argillaceous rock formation that is accessible at the Mont Terri Underground Research Laboratory, situated in the Swiss Jura. The tracer was diluted in reconstituted formation water and introduced into a packed-off section of a borehole located in saturated rock. Pressure in this interval was maintained equal to the pore pressure of the surrounding rock in order to prevent any hydraulic gradient around the borehole and to avoid advective transport processes. The evolution of the tracer concentration in the injection system was monitored over time. After 1 year of diffusion, the claystone surrounding the interval was retrieved by overcoring the whole borehole and packer system, and by an adjacent oblique borehole. Compressed air was used as drilling fluid to reduce rock disturbances. The recovered overcore was sampled along profiles perpendicular to the borehole wall with a view to determining the tracer-concentration profiles in the rock. To avoid further evaporation of tritiated water, subsamples were immediately transferred into polyethylene bottles and disaggregated by adding a known amount of tracer-free water. Fifteen profiles were determined and showed a decreasing tracer concentration with distance into the rock. The pore-water contents were constant along those profiles, confirming that only very little water was lost during overcoring operations. The evolution of tritium-tracer concentration in the injection system over time and in situ profiles were interpreted with a 3-D numerical simulation of the experiment. That allowed for the identification of the transport parameters (orthotropic diffusion tensor and porosity) by minimising the relative quadratic error between the experimental and simulated data. The fitting is good and the results are consistent with data obtained on drill-core samples. The result of tritiated water is discussed regarding (1) the potential effect of mechanical and/or chemical disturbances around the injection borehole and (2) the specific behaviour of tritiated water. 相似文献
42.
In situ methods are needed to evaluate the effectiveness of chemical amendments at enhancing reductive dechlorination rates in groundwater that is contaminated with the priority pollutant, trichloroethene (TCE). In this communication, a method that utilizes single-well, “push–pull” tests to quantify the effects of chemical amendments on in situ reductive dechlorination rates is presented and demonstrated. Five push–pull tests were conducted in each of five monitoring wells located in a TCE-contaminated aquifer at the site of a former chemical manufacturing facility. Rates for the reductive dechlorination of the fluorinated TCE-surrogate, trichlorofluoroethene (TCFE), were measured before (test 1) and after (test 5) three successive additions (tests 2–4) of fumarate. Fumarate was selected to stimulate the growth and activity of indigenous microorganisms with the metabolic capability to reduce TCFE and TCE. In three wells, first-order rate constants for the reductive dechlorination of TCFE increased by 8.2–92 times following fumarate additions. In two wells, reductive dechlorination of TCFE was observed after fumarate additions but not before. The transformation behavior of fumarate was also monitored following each fumarate addition. Correlations between the reductive dechlorination of TCFE and the reduction of fumarate to succinate were observed, indicating that these reactions were supported by similar biogeochemical conditions at this site. 相似文献
43.
The purpose of this paper is to develop a set of associated statistical tests for spatial clustering. In particular, a set
of three associated tests will be developed; these will correspond to the three types of tests set out by Besag and Newell
(general tests, focused tests, and tests for the detection of clustering). The associated tests draw primarily, though not
exclusively, upon existing tests and results. The principal contributions are based upon the score statistic for focused tests,
which has been an important approach to testing for clustering around environmental hazards. The first contribution consists
of the formulation of a global statistic for general tests that corresponds to focused score statistics, along with an assessment
of the distribution of the statistic under the null hypothesis of no raised incidence. The local score statistics used for
focused tests will have the property of summing to the global statistic used for the corresponding general test. Attention
is also given to the maximum local score statistic for the “test for the detection of clustering”. The critical values of
this statistic which are required for testing the null hypothesis are described. Application of the methods is made to leukemia
data for central New York State. 相似文献
44.
An agricultural system is sustainable if productive output is maintained economically over time when assessed in relation to environmental concern. This paper considers ways of statistically evaluating measures of sustainability illustrated by reference to extensive data from the Classical Experiments at Rothamsted. 相似文献
45.
46.
为防止空调系统内霉菌、细菌的过度孳生,本文以空调系统内常见的黑曲霉(A. niger)、大肠埃希氏菌(E. coli)、金黄色葡萄球菌(S. aureus)、枯草芽孢杆菌(B. subtilis)为典型霉菌、细菌,基于纸片扩散法药敏试验,研究了空调除湿常用工质LiCl溶液对上述典型菌种的抑制作用及浓度影响规律.结果表明:在常见除湿浓度范围(35%~40%)内,LiCl溶液对上述4种典型菌种均有抑制作用;特别是对A. niger抑制效果最强,在15%的低浓度下即可产生明显抑制;其次为E. coli,而对S. aureus和B. subtilis的抑制相对较弱.此外,所得抑制效果随LiCl溶液浓度的提高而明显增强,特别是对A. niger和E. coli,溶液浓度与抑菌圈直径呈显著的正相关性. 相似文献
47.
Regine Keymeulen Mikls Grgnyi Kroly Hberger Anda Priksane Herman Van Langenhove 《Atmospheric environment (Oxford, England : 1994)》2001,35(36)
Concentrations of benzene, toluene, ethyl benzene and xylenes (BTEX) in ambient air and in 1 yr old Pinus sylvestris pine needles were monitored along a busy road, petrol station and rural area of Belgium, Hungary and Latvia in a 1 yr period. To test P. sylvestris as a possible biomonitor for the BTEX concentrations, samples were taken in the four seasons. As the distribution of data was not normal, the level of pollution on different sites and seasons was compared and evaluated by non-parametric tests. The measured air concentrations did not differ significantly from one season to another throughout the year. There were, however, differences between sampling places. The C2-alkylbenzene and toluene concentrations in the needles were similar in the autumn/winter and spring/summer periods but a significant decrease in their concentration was observed in every place between winter and spring. This effect was less obvious for toluene. 相似文献
48.
Forecasting the behaviour of a flammable or toxic cloud is a critical challenge in quantitative risk analysis. Recent literature shows that empirical and integral models are unable to model complex dispersion scenarios, like those occurring in semi-confined spaces or with the presence of physical barriers. Although CFD simulators are promising tools in this regard, they still need to be fully validated with comprehensive datasets coming from experimental campaigns designed ad-hoc. In this paper, we present an experimental campaign carried out by a joint venture between University of São Paulo and Universitat Politècnica de Catalunya to investigate CFD tools performance when used to analyse clouds dispersion. The experiments consisted on propane cloud dispersion field tests (unobstructed and with the presence of a fence obstructing the flow) of releases up to 0.5 kg s−1 of 40 s of duration in a discharge area of 700 m2. We provide a full 1-s averaged propane concentration evolution dataset of two experiments, extracted from 29 points located at different positions within the cloud, with which we have tested FLACS® CFD-software performance. FLACS reproduces successfully the presence of complex geometry, showing realistic concentration decreases due to cloud dispersion obstruction by the existence of a fence. However, simulated clouds have not represented the whole complex accumulation dynamics due to wind variation. 相似文献
49.
What do significance tests really tell us about the environment? 总被引:8,自引:0,他引:8
Routine application of significance tests does not extract the maximum information from environmental data and can lead to misleading conclusions. Reasons leading to this are: a significant result can often be reached merely by collecting enough samples; a statistically significant result is not necessarily practically significant; and reports of the presence or absence of statistically significant differences for multiple tests are not comparable unless identical sample sizes are used. These problems are demonstrated by application to pH data for grazed and retired fields, and by discussion of significance tests used in recent US regulations for groundwater quality. The advantages of equivalence tests, where the tester must state the difference of practical difference, are discussed and applied to the field pH problem. We recommend that environmental managers and scientists pay more attention to statistical power and decide on what is a practical difference. Confidence intervals for the size of the differences, accompanied where necessary by equivalence tests, are the preferred means of addressing the question: “is there a difference of practical significance?” 相似文献
50.
O. Thas L. Van Vooren J. P. Ottoy 《Journal of the American Water Resources Association》1998,34(2):347-357
ABSTRACT: In this paper four nonparametric tests for monotonic trend detection are compared with respect to their power and accuracy. The importance of comparing powers at equal empirical significance levels rather than nominal levels is stressed. Therefore, an appropriate graphical method is presented. The effect of the sampling frequency is also assessed using Monte Carlo simulations and a trajectory representation that visualizes the dynamics of the trade-off between the type I and type II errors. These methods are applied to compare four nonparametrical tests (seasonal Mann. Kendall, modified seasonal Mann-Kendall, covariance eigenvalue and covariance inversion) under several conditions. It is concluded with respect to the power that it is not worthwhile for the modified seasonal Mann-Kendall test applied to the AR(1) process considered in this paper to increase the sampling frequency from monthly to biweekly for detecting a monotonic trend of 5 percent, 10 percent, or 15 percent of the process variance. Under these conditions the seasonal Mann-Kendall test is highly liberal, while the covariance inversion and the covariance eigenvalue test are conservative. This research is situated in the development of an efficient sampling design for the Flemish water quality monitoring network. 相似文献