An experiment in which a continuous beam of high‐energy electrons is emitted from a satellite (e.g. to produce an artificial aurora or to map the geomagnetic field) will be jeopardized if the satellite potential becomes so high that the beam electrons cannot escape. The potential acquired by the satellite is determined by the condition that it collect from the ambient ionosphere a current equal to the emitted current. The geomagnetic field severely limits the current that may be emitted. For example, a spherical satellite of radius 1.5 meters in the F layer cannot emit more than about 40 ma of kilovolt electrons.

We have developed a simplified analytical indoor air model that describes the concentrations as a function of position and time in a room following a short‐term release of airborne particles or gases. The indoor dispersion model considers the two main physical processes of (1) point‐source dispersion with reflection from all walls and (2) the general concentration decay in a room due to room ventilation and surface deposition of pollutants. Comparison of model predictions with experimental indoor measurements conducted by other researchers showed excellent agreement. This model should prove useful for human‐health risk estimations in which the inhalation dose resulting from an indoor, short‐term release of a contaminant needs to be calculated.

No abstract

The establishment of health-protective soil remediation levels often relies on the results of a risk assessment, which provides a way to equate a permissible risk to a target soil contaminant concentration. Inherent in such risk assessments is the assumption that the target concentrations are representative averages. Unfortunately, soil cleanup levels thus calculated are typically misapplied on a point by point basis rather than on an average. This is not costeffective because it results in post-remedy conditions that overshoot the target risk goals. Because environmental contamination is characterized by a distribution of concentrations, some exceedances of target averages, average risk, or average concentration can be allowed in the post-remediation distribution. This work presents a mathematical model for calculating this allowable higher than average concentration, termed the confidence response goal (CRG), which places a limit on concentrations requiring remediation while ensuring that target average concentrations are satisfied overall. The CRG is sitespecific becauses it depends on the contaminant concentration distribution. The strength of the approach lies in its ability to handle typical data uncertainties quantitatively because it relies on the upper confidence limit as a measure of the mean concentration (in a manner similar to its use in risk assessment), hence the term "confidence" in the CRG. The advantages of the approach are significant. An example is given of a Superfund site where excavation volumes were reduced by 66% and $40 million was saved, about half of which could be attributed to the CRG approach.

Experiments have been carried out to examine the spectrum of internal gravity waves excited in a stratified incompressible fluid during stabilization following the buoyant rise of a miscible fluid. The rise time of the buoyant fluid to its stabilization height in the stratified fluid was observed to be about 0.85 of the Brunt-Väisälä period for the stratified fluid. The motion of specific fluid elements in the wave field was observed using neutrally buoyant marker particles, and the particle trajectories were found to be in close accord with theoretical predictions. Observations on the internal waves generated by the forced oscillation of a spherical body suspended in the stratified medium showed the wave pattern to be well behaved and similar to that described by Mowbray & Rarity. However, the gravity wave field generated by the motion of the buoyant fluid was observed to be inhomogeneous and transient in nature. Wave periods from one to four times the Brunt-Väisälä period were clearly observed and at later times it appeared that the motion tended towards vertical oscillations a t the Brunt- Väisälä frequency.

No abstract

Gas production from solid and liquid hydrocarbon fuels was once a major industry. The gas manufacturing process produced a variety of wastes including tars, oils, and wastewater. An important issue in insurance litigation over who pays the cost of cleaning up these wastes is whether contamination was "expected and intended" or whether it resulted from accidental spills and leaks. After presenting a review of gas manufacturing processes and the historical development of this industry, we present 13 known intentional disposal practices for tar and oil and wastewater at manufactured gas plants (MGPs). We then introduce the concept of differential diagnosis, a method used in medicine and in medical/legal settings, and show how this method can be used to help determine if the cause of contamination at MGP sites was accidental or intentional.

This paper describes risk assessment methods for two chronic exposure pathways involving arsenic contaminated soil, namely inhalation of fugitive dust emissions over a lifetime, and inadvertent soil/house dust ingestion. The endpoint in the first case is assumed to be lung cancer and in the second case skin cancer. In order to estimate exposures, inhalation rates and soil/dust ingestion rates are estimated for different age groups; indoor/outdoor time budgets for different age groups are developed; and indoor surface dust and air arsenic concentrations are estimated based on outdoor concentration measurements. Differences observed in indoor/outdoor ratios and arsenic containing dust particle size among different types of communities are noted, as well as possible relationship of particle size to bioavailability. Calculations of risk are presented using cancer potency factors developed by the U.S. Environmental Protection Agency, and uncertainties in these toxicity estimates are described based on: (1) evidence that arsenic may be neither a cancer initiator nor promotor, but may act instead as a late stage carcinogen and (2) evidence that the arsenic dose-response relationship for ingestion may be nonlinear at low doses due to increasing methylation of inorganic arsenic. The first of these considerations influences the relative importance ascribed to arsenic doses in different age groups. The latter consideration indicates that the risk estimates described here are probably very conservative.