Tracer Concentration Data Research Articles

Characterization of Regional Transport and Dispersion Using Project MOHAVE Tracer Data

ABSTRACT Perfluorocarbon tracers were released continuously from several surface locations and one power plant stack location during the winter (30 days) and summer (50 days) intensive studies as part of Project MOHAVE. Tracers were released in winter from the Mohave Power Plant (MPP) and Dangling Rope, UT, located on the shore of Lake Powell near Page, AZ; and in summer from MPP, the Tehachapi Pass between the Mojave Desert and the Central Valley in California, and El Centro, CA, on the California-Mexico border. At the Tehachapi tracer release site six-hour pulses of a separately identifiable perfluorocarbon tracer were released every four days in order to assess the time for the tracer to clear the monitoring network. Daily 24-hr integrated samples were collected at about 30 sites in four states. Limited tracer concentration data with higher time resolution is also available. Graphical displays and analyses identify several regional transport paths, including a convergence zone in the Mojave Desert, the importance of terrain channeling, especially in winter, and a relationship between 24-hr maximum influence function and distance that may prove useful as a scoping tool and to test regional scale air quality models. In winter, Dangling Rope tracer was routinely transported through the entire length of the Grand Canyon, while in summer, MPP tracer was routinely transported over most of Lake Mead.

Multicell Model for Ground Water Recharge Analysis: The Ibi River Basin, Japan

A coupled water quantity/quality model was developed and applied to estimate ground water recharge and simulate tracer concentrations in the Ibi River Basin of Japan. The ground water basin was divided into five sub-basins, each of which contains a surface reservoir and up to three subsurface reservoirs. The reservoirs exchange water and solute mass among themselves and contribute direct runoff and base flow to adjacent streams. The simulation model is parameterized in terms of 14 water quantity and three water quality parameters. A parameter calibration procedure was implemented wherein streamflow and tracer concentration data were used in parameter estimation. Prior information on the parameters can be used to initialize and constrain calibrated parameters. The calibrated model was validated successfully and used to simulate Na+ and Ca2+ and to estimate ground water recharge in the sub-basins and the Ibi River Basin as a whole. Ground water recharge varied substantially among sub-drainage basins, reflecting the predominant role of precipitation variability in determining deep percolation to the first confined aquifer. It was determined that about 10% of the gross precipitation becomes ground water recharge over the entire Ibi River Basin. Analysis of ground water recharge to a large pulse of precipitation demonstrated the important effect of impermeable clay layers in controlling the magnitude and timing of deep ground water recharge. The validation results indicate that the equilibrium concentrations of Na− and Ca2+ in the first confined aquifer have negligible sensitivity to their initial concentrations in the simulation model. Similar behavior was observed for the equilibrium concentrations of these two tracers in reservoir 3, and to a lesser extent in reservoir 2. The top reservoir exhibited large fluctuations in tracer concentrations due to the effect of direct rainfall input.

Parameter space methods in joint parameter estimation for groundwater flow models

The joint estimation of model parameters using hydraulic head and tracer concentration data is examined using methods based on parameter space analysis. Response surfaces and confidence regions can indicate how multiple data sets interact to reduce parameter uncertainty. Each data set produces a unique response surface and confidence region. If these surfaces are oriented differently for the two data sets, parameter uncertainties are significantly reduced when the second data set is included in the inversion. If these surfaces are similar for the two data sets, the second data set will not reduce the parameter uncertainty significantly. The axes of the linearized confidence ellipsoid are analyzed to determine the difference in orientation of the confidence regions for the two data sets. The use of confidence regions can be extended to predict the value of a second data set in reducing the uncertainty of parameter estimates, before the data are collected. Parameter space approaches are also introduced for selecting the relative weights for the individual data sets in joint parameter estimation. The conventional method based on the analysis of data residuals is compared to three other methods: with the weights selected to maximize parameter stability, to minimize the volume of the confidence region, or to minimize the longest axis of the confidence region. Each criterion can lead to substantially different weights applied to each of the data sets. The application of these methods is demonstrated using hydraulic head measurements and 14C concentrations to calibrate a model of groundwater flow in the San Juan Basin, New Mexico.

Optimal estimation of residual non–aqueous phase liquid saturations using partitioning tracer concentration data

Stochastic methods are applied to the analysis of partitioning and nonpartitioning tracer breakthrough data to obtain optimal estimates of the spatial distribution of subsurface residual non–aqueous phase liquid (NAPL). Uncertainty in the transport of the partitioning tracer is assumed to result from small‐scale spatial variations in a steady state velocity field as well as spatial variations in NAPL saturation. In contrast, uncertainty in the transport of the nonpartitioning tracer is assumed to be due solely to the velocity variations. Partial differential equations for the covariances and cross cpvariances between the partitioning tracer temporal moments, nonpartitioning tracer temporal moments, residual NAPL saturation, pore water velocity, and hydraulic conductivity fields are derived assuming steady flow in an infinite domain [Gelhar, 1993] and the advection‐dispersion equation for temporal moment transport [Harvey and Gorelick, 1995]. These equations are solved using a finite difference technique. The resulting covariance matrices are incorporated into a conditioning algorithm which provides optimal estimates of the tracer temporal moments, residual NAPL saturation, pore water velocity, and hydraulic conductivity fields given available measurements of any of these random fields. The algorithm was tested on a synthetically generated data set, patterned after the partitioning tracer test conducted at Hill AFB by Annable et al. [1997]. Results show that the algorithm successfully estimates major features of the random NAPL distribution. The performance of the algorithm, as indicated by analysis of the “true” estimation errors, is consistent with the theoretical estimation errors predicted by the conditioning algorithm.

Observed Downwash Concentrations Compared to ISCST Predictions in Urban Core

An atmospheric tracer (SF 6 ) was released from an industrial stack in an urban core during nocturnal neutral to stable atmospheric conditions in an effort to determine the dispersive characteristics and the atmospheric transport of stack effluent under these conditions. Tracer concentration data are compared to predictions made by the Environmental Protection Agency's Industrial Source Complex Short Term (ISCST) model. ISCST is the regulatory air-pollution model typically recommended in situations where structure-induced plume downwash is a possibility. Under the meteorological conditions and stack parameters sampled in the present study, the downwash algorithm causes the ISCST model to overpredict surface concentrations below 3.5 m/s or below a wind speed/exit velocity ( u /V e) ratio of 0.25. Model performance was better in neutral than in stable atmospheric conditions. The stack effluent temperature was >450°K, and the model overprediction may be due in part to the treatment of thermal buoyancy in the model treatment of building wake downwash.

Application of a generalized scavenging model to thorium isotope and particle data at equatorial and high‐latitude sites in the Pacific Ocean

A generalized trace metal scavenging model has been applied to particle cycle and 234Th data at three equatorial Pacific sites, and to dissolved and particulate 228Th, 230Th, and 234Th profiles at a single high‐latitude station. The one‐dimensional (and here steady state) model consists of two particle classes, small (suspended) and large (sinking). It is driven by particle primary production and parameterized from particle and tracer concentration and flux data. The model has been used to determine, as functions of depth, (1) rates of particle remineralization; (2) aggregation and disaggregation of the small and large‐particle classes, respectively, and (3) adsorption and desorption rate constants of thorium. The results are insensitive to die assumed large particle sinking rate of 150 m d−1. The profiles of all three tracers at Station P are described satisfactorily by a single set of model parameters. The adsorption rate constant, normalized for the effect of particle concentration, is enhanced in the upper 100 m of the water column by a factor of 2 or greater at all sites. Values of this and the other major model parameters are consistent with earlier results for a variety of oceanic environments.

Generalized Lagrangian Model for Buoyant Jets in Current

A general Lagrangian jet model formulation is presented for an inclined buoyant jet in a current, with a three‐dimensional trajectory. The shear‐induced entrainment is computed as a function of the local densimetric Froude number and jet orientation, while the forced entrainment is taken as the ambient flow intercepted by the “windward” side of the buoyant jet. Model predictions are compared with both trajectory and tracer concentration data for a wide range of discharge and ambient flow conditions: horizontal buoyant jets in a coflow; vertical jets, oblique jets, and dense plumes in a cross flow; buoyant jets in a stagnant uniform or stratified fluid; and a horizontal buoyant jet in a perpendicular cross flow. The model is also consistent with the concept of asymptotic flow regimes, and reproduces the correct behavior in both the near and far field of a vertical momentum of buoyancy‐dominated jet in a cross flow. The connection of the model with traditional integral jet models is also discussed.

Simulation of Tracer Concentration Data in the Brush Creek Drainage Flow Using an Integrated Puff Model

Abstract During the 1984 ASCOT field study in Brush Creek Valley, two perfluorocarbon tracers were released into the nocturnal drainage flow at two different heights. The resulting surface concentrations were sampled at 90 sites, and vertical concentration profiles at 11 sites. These detailed tracer measurements provide a valuable dataset for developing and testing models of pollutant transport and dispersion in valleys. In this paper, we present the results of Gaussian puff model simulations of the tracer releases in Brush Creek Valley. The model was modified to account for the restricted lateral dispersion in the valley, and for the gross elevation differences between the release site and the receptors. The variable wind fields needed to transport the puffs were obtained by interpolation between wind profiles measured using tethered balloons at five along-valley sites. Direct turbulence measurements were used to estimate diffusion. Subsidence in the valley flow was included for elevated releases. Two te...

Spatial and temporal patterns of root activity in a species-rich alluvial grassland.

The time and depth of activity of a number of co-existing grassland plants was measured using a technique involving the simultaneous injection to different depths in soil of 3 chemical tracers - Li, Rb and Sr. Root activity at a particular depth was assessed from the concentration of each tracer in leaf tissue.The seven most constant species showed very similar patterns of root activity, which was greater at 5 than at 15 or 25 cm except towards the end of the growth period in late June. Maximum root activity generally occurred earlier than maximum shoot productivity but there was little evidence of differentiation between species. When root activity was assessed as a proportion of total community root activity, by combining tracer concentration and biomass data, seasonal differences between species were more obvious. Using both root activity and productivity data, species were grouped into two main guilds, one active in spring (April-May) and one in summer (June).Correlations of above-ground biomass with root activity at different depths revealed that species of the spring guild were more active in the 5-15 cm horizons and those of the summer guild at 15-25 cm.These patterns suggest that rooting depth and time of activity are strongly linked: early-active species tend to be less productive and shallower-rooted and this combination of characters allows them to escape from competition with more productive species, by being active at a time when deeper soil layers are less hospitable.

Trend Surface Analysis of Sand Tracer Distributions on a Carbonate Beach, Bimini, B.W.I.

Two-dimensional trend surface analyses were performed on areally distributed tracer-concentration data for three different fluorescent sand tracers recovered from four depth intervals of the foreshore. The tracers had been affected by the swash, breakers, and longshore currents of one tidal cycle. Analysis of the statistical significance of trend surfaces for each depth interval showed that only the upper 2.5 cm. of the sand column evidenced definite trend components. Differential sorting of tracers of different shapes and mean grain sizes was probably negligible, as deduced from the similarity in direction of orthogonals to the trend surface contours for the various tracer data. The advantage of the trend surface method of describing sand movement patterns on beaches lies in its ability to represent, in an objective manner, the average movement of sand grains by means of a single representative equation. Furthermore, for time scales of the order of minutes to several hours, the motion of sand is seldom p...