Mapping a Brine Plume Using Surface Geophysical Methods in Conjunction with Ground Water Quality Data

Oil field brine was applied to a gravel roadbed at an instrumented study site in Newark, Ohio, to simulate the use of brine as a deicer on roads in certain areas of Ohio. Brine was applied on a weekly basis eight times during the winter of 1988 as part of the deicing simulation. Eleven wells were installed at the site prior to brine application to permit collection of ground water quality samples. Surface geophysical methods — electrical resistivity and electromagnetic conductivity — were used to map the resulting brine plume. The accuracy of the methods was evaluated by comparing geophysical and ground water quality data. The presence of brine in ground water resulted in a decrease in resistivity and an increase in conductivity. Specific conductance measured in the field was used as a general indicator of the presence of the brine plume in ground water. Chloride concentration was an indicator of brine in the ground water. Results of the surface geophysical surveys correlated best with chloride and dissolved solids concentrations, and with specific conductance in ground water. The surface geophysical methods were found to be useful for qualitative interpretations of ground water quality changes resulting from the application of brine on roads.     

Differences between Mean Sea Levels for the Pacific,Atlantic and Indian Oceans From Topex/Poseidon Altimetry

Geopotential values W of the mean equipotential surfaces representing the mean ocean topography were computed on the basis of four years (1993 - 1996) TOPEX/POSEIDON altimeter data: W = 62 636 854.10m ² s ^–2 for the Pacific (P), W = 62 636 858.20m ² s ^–2 for the Atlantic (A), W = 62 636 856.28m ²s^–2 for the Indian (I) Oceans. The corresponding mean separations between the ocean levels were obtained as follows: A – P = – 42 cm, I– P = – 22 cm, I – A = 20 cm, the rms errors came out at about 0.3 cm. No sea surface topography model was used in the solution.     

The hydrological effects of fire in South African mountain catchments

Streamflow and its storm-flow elements in four catchments were analyzed by the paired catchment method for a response to fire. Prior to burning two of the catchments were vegetated with over-mature fynbos (the indigenous scrub vegetation of the southwestern Cape, South Africa), one was afforested with Pinus radiata and the fourth with Eucalyptus fastigata. One of the fynbos catchments was burned in a prescribed fire in the late dry season. The other catchments burned in wildfires.

Neither of the fynbos catchments showed a change in storm-flow. Annual total flow increases of around 16% were in agreement with model predictions, being related to the reductions in transpiration and interception. The manner of streamflow generation appeared to have remained unaltered despite the presence of some water repellency in the soils and consequent overland flow on some steep midslope sites.

The two timber plantation catchments experienced large and significant increases in storm-flows and soil losses, while total flow increased by 12% in the pine catchment and decreased marginally in the eucalypt catchment. The pattern of the storm-flow increases was similar in both cases. After fire, storm hydrographs were higher and steeper though their duration was little changed. The respective first year increases in the pine and eucalypt catchments were 290% and 1110% for peak discharge, 201% and 92% for quick-flow volume, and 242% and 319% for storm response ratio. These fire effects are considered to be due to changes in storm-flow generation consistent with an increased delivery of overland flow (surface runoff) to the stream channel. This was caused, in part, by reduced infiltration resulting from water repellency in the soils of the burned catchments. Overall the hydrological effects of fire are related to numerous interactive factors, including the degree of soil heating, the vegetation type and soil properties.     

Kinetics of Cd sorption, desorption and fixation by calcite: A long-term radiotracer study

Time-dependent sorption and desorption of Cd on calcite was studied over 210 days utilizing ¹⁰⁹Cd as a tracer to distinguish between ‘labile’ and ‘non-labile’ forms of sorbed Cd. Stabilizing the calcite suspensions for 12 months under atmospheric P_CO2 and controlled temperature was necessary to reliably follow Cd dynamics following initial sorption. Results revealed time-dependant Cd sorption and marked desorption hysteresis by calcite under environmentally relevant conditions. Data obtained were fitted to a first-order kinetic model and a concentric shell diffusion model. Both models described the progressive transfer of Cd²⁺ to a less reactive form within calcite and subsequent desorption of Cd subject to different initial contact times. The kinetic model provided a better fit to the combined sorption and desorption data (R² = 0.992). It differentiates between two ‘pools’ of sorbed Cd²⁺ on calcite, ‘labile’ and ‘non-labile’, in which labile sorbed Cd is in immediate equilibrium with the free Cd²⁺ ion activity in solution whereas non-labile Cd is kinetically restricted. For the diffusion model (R² = 0.959), the rate constants describing Cd dynamics in calcite produced a half-life for Cd desorption of ∼175 d, for release to a ‘zero-sink’ solution. Results from this study allow comment on the likely mechanisms occurring at the calcite surface following long-term Cd sorption.     

Fractal analysis of long-range paleoclimatic data: Oxygen isotope record of pacific core V28-239

R/S analysis of the oxygen isotope curve of Pacific core V28-239 yields a fractal dimension of 1.22. This value is considered to characterize global climatic change over the last 2 million years as expressed by changing O¹⁸ ratios and confirms that climatic variations are characterized by long-term persistence. The fractal dimension of 1.22 compares favorably with the approximate fractal dimension of 1.26 for annual precipitation records for nine major cities in the United States. Although the precipitation and oxygen isotope data are measured in different physical units and recorded at different time scales, fractal analysis allows for a mathematical comparison of the two phenomena. Additionally, since the fractal dimensions of the oxygen isotope and precipitation records are similar, it is implied that such fractal dimensions are characteristic of climate change over the spectral range of 10 to 10⁶ years. Given this temperature curves based on fractal parameters of long-term O¹⁸ data could be constructed which would allow examination of characteristics of temperature variation over tens and hundreds of years. Such studies may allow the establishment of limits on natural temperature variation and document the persistence of temperature trends through time. If these trends and limits can be resolved, long-range climatic prediction is feasible.     

A Method for Estimating Field-Scale Mass Transfer Rate Parameters and Assessing Aquifer Cleanup Times

A general method for estimating ground-water solute mass transfer rate parameters from field test data is presented. The method entails matching solute concentration and hydraulic head data collected during the recovery phase of a pumping test through application of a simulation-regression technique. Estimation of hydraulic conductivity and mass transfer rate parameter values is performed by fitting model simulations to the data. Parameter estimates are utilized to assess cleanup times for pump-and-treat aquifer remediation scenarios. Uncertainty in the cleanup time estimate is evaluated using statistical information obtained with the parameter estimation technique. Application of the method is demonstrated using a hypothetical ground-water flow and solute transport system. Simulations of field testing, parameter estimation, and remedial time frames are performed to evaluate the usefulness of the method. Sets of random noise that signify potential field and laboratory measurement errors are combined with the hypothetical data to provide rigorous testing of the method. Field tests are simulated using ranges of values for data noise, the mass transfer rate parameters, the test pumping rates, and the duration of recovery monitoring to evaluate their respective influence on parameter and cleanup time estimates. The demonstration indicates the method is capable of yielding accurate estimates of the solute mass transfer rate parameters. When the parameter values for the hypothetical system are well estimated, cleanup time predictions are shown to be more accurate than when calculated using the local equilibrium assumption.