Analysis of a vertical dipole tracer test in highly fractured rock

The results of a vertical dipole tracer experiment performed in highly fractured rocks of the Clare Valley, South Australia, are presented. The injection and withdrawal piezometers were both screened over 3 m and were separated by 6 m (midpoint to midpoint). Due to the long screen length, several fracture sets were intersected, some of which do not connect the two piezometers. Dissolved helium and bromide were injected into the dipole flow field for 75 minutes, followed by an additional 510 minutes of flushing. The breakthrough of helium was retarded relative to bromide, as was expected due to the greater aqueous diffusion coefficient of helium. Also, only -25% of the total mass injected of both tracers was recovered. Modeling of the tracer transport was accomplished using an analytical one-dimensional flow and transport model for flow through a fracture with diffusion into the matrix. The assumptions made include: streamlines connecting the injection and withdrawal point can be modeled as a dipole of equal strength, flow along each streamline is one dimensional, and there is a constant Peclet number for each streamline. In contrast to many other field tracer studies performed in fractured rock, the actual travel length between piezometers was not known. Modeling was accomplished by fitting the characteristics of the tracer breakthrough curves (BTCs), such as arrival times of the peak concentration and the center of mass. The important steps were to determine the fracture aperture (240 microm) based on the parameters that influence the rate of matrix diffusion (this controls the arrival time of the peak concentration); estimating the travel distance (11 m) by fitting the time of arrival of the centers of mass of the tracers; and estimating fracture dispersivity (0.5 m) by fitting the times that the inflection points occurred on the front and back limbs of the BTCs. This method works even though there was dilution in the withdrawal well, the amount of which can be estimated by determining the value that the modeled concentrations need to be reduced to fit the data (approximately 50%). The use of two tracers with different diffusion coefficients was not necessary, but it provides important checks in the modeling process because the apparent retardation between the two tracers is evidence of matrix diffusion and the BTCs of both tracers need to be accurately modeled by the best fit parameters.     

气候变化研究方法,研究区域和历史模拟引论

气候变化研究方法、研究区域和历史模拟引论ＷｉｌｌｉａｍＥ．Ｅａｓｔｅｒｌｉｎｇ，ＮｏｒｍａｎＪ．Ｒｏｓｅｎｂｅｒｇ，ＭａｒｙＳ．ＭｃｋｅｎｎｅｙａｎｄＣ．ＡｌｌａｎＪｏｎｅｓ￥／／１引言科学家们都很清楚，持续增强的温室效应将有可能导致气候前所未有的变...     

高耸建筑动态变形的GPS监测

利用全球定位系统（ＧＰＳ）进行高耸建筑的动态形监测，已经成为可能。对位于加拿大艾伯塔西部的卡尔加里高塔进行这种监测的结果，证明该塔因风荷引起南─北、东─西方向的振动频率，均约为０．３Ｈｚ，没有超出允许的０．１－１０Ｈｚ这一范围。本文在扼要阐述利用加速计、激光干涉仪、光电测距仪等方法测振的优缺点后，描述了利用ＧＰＳ测量塔体振动的方法。相信在得到进一步证实后，可将ＧＰＳ作为一种标准的建筑物振动测量方法。     

Plume and lithologic profiling with surface resistivity and seismic tomography

Improved surface-based geophysical technologies that are commercially available provide a new level of detail that can be used to guide ground water remediation. Surface-based multielectrode resistivity methods and tomographic seismic refraction techniques were used to image to a depth of approximately 30 m below the surface at the Natural and Accelerated Bioremediation Research Field Research Center. The U.S. Department of Energy (DOE) established the research center on the DOE Oak Ridge Reservation in Oak Ridge, Tennessee, to conduct in situ field-scale studies on bioremediation of metals and radionuclides. Bioremediation studies are being conducted on the saprolite, shale bedrock, and ground water at the site that have been contaminated with nitrate, uranium, technetium, tetrachloroethylene, and other contaminants (U.S. DOE 1997). Geophysical methods were effective in imaging the high-ionic strength plume and in defining the transition zone between saprolite and bedrock zones that appears to have a significant influence on contaminant transport. The geophysical data were used to help select the location and depth of investigation for field research plots. Drilling, borehole geophysics, and ground water sampling were used to verify the surface geophysical studies.