Natural Gradient Tracer Test to Evaluate Natural Attenuation of MTBE Under Anaerobic Conditions   总被引：1，自引：0，他引：1  

Illa Amerson  Richard L. Johnson 《Ground Water Monitoring & Remediation》2003,23(1):54-61

A natural gradient tracer test using perdeuterated MTBE was conducted in an anaerobic aquifer to determine the relative importance of dispersion and degradation in reducing MTBE concentrations in ground water. Preliminary ground water chemistry and hydraulic conductivity data were used to place the tracer within an existing dissolved MTBE plume at Port Hueneme, California. Following one year of transport, the tracer plume was characterized in detail.
Longitudinal dispersion was identified as the dominant mechanism for lowering the perdeuterated MTBE concentrations. The method of moments was used to determine the longitudinal and lateral dispersion coefficients (0.85 m²/day and 0.08 m²/day, respectively). A mass-balance analysis, carried out after one year of transport, accounted for 110% of the injected mass and indicated that no significant mass loss occurred. The plume structure created by zones of higher and lower hydraulic conductivity at the site was complex, consisting of several localized areas of high tracer concentration in a lower concentration plume. This is important because the aquifer has generally been characterized as exhibiting fairly minor heterogeneity. In addition, the tracer plume followed a curved flowpath that deviated from the more macroscopic direction of ground water flow inferred from local ground water elevation measurements and the behavior of the existing plume. Understanding the mass balance, plume structure, curvature of the tracer plume, and consequently natural attenuation behavior required the detailed sampling approach employed in this study. These data imply that a detailed understanding of site hydrogeology and an extensive sampling network may be critical for the correct interpretation of monitored natural attenuation of MTBE.  相似文献   

Relative size of fluvial and glaciated valleys in central Idaho   总被引：2，自引：1，他引：1  

Byron E. Amerson  David R. Montgomery  Grant Meyer 《Geomorphology》2008,93(3-4):537-547

Quantitative comparisons of the morphometry of glaciated and fluvial valleys in central Idaho were used to investigate the differences in valley relief and width in otherwise similar geologic and geomorphic settings. The local relief, width, and cross-sectional area of valleys were measured using GIS software to extract information from USGS digital elevation models. Hillslope gradients were also measured using GIS software. Power-law relationships for local valley relief, width, and cross-sectional area as a function of drainage area were developed. Local valley relief in glaciated valleys relates to drainage area with a power-law exponent similar to fluvial valleys, but glaciated valleys are deeper for a given drainage area. Local valley width in glaciated valleys is greater than in fluvial valleys, but the exponent of the power-law relationship to drainage area is similar in both valley types. Local valley cross-sectional area in glaciated valleys increases with drainage area with a power-law exponent similar to fluvial valleys, however, glacial valleys have roughly 80% greater cross-sectional area. Steep valley walls in glaciated basins increase the potential for bedrock landsliding relative to fluvial basins. Both the Olympic Mountains of Washington and valleys in central Idaho show relationships in which glaciated valleys are up to 30% deeper than fluvial valleys despite differences in lithology, tectonic setting, and climate.  相似文献