A Tracer Study of Headspace Ventilation in a Collector Sewer

ABSTRACT

A field-scale tracer test was conducted to evaluate in-situ ventilation rates in a major collector sewer. The sewer under study was ~11 km long and ranged from 0.61 to 2.1 m in diameter. For the purposes of the tracer testing, the collector was divided into four reaches, each of which was tested individually. The tracer test involved injecting a measured volume of CO gas into a manhole over a short time period. CO concentrations were then measured in the collector headspace at selected manholes along the length of the reach.

The technique employed successfully measured average headspace velocities over extended lengths of the collector. In a section that had a relatively stagnant headspace, ~1.1 km of sewer could be evaluated, with substantial tracer loss attributed to losses to manholes. In a section of the sewer with elevated headspace velocities, a section ~7.0 km long was successfully tested with one injection of tracer gas. The velocities observed in the collector varied substantially with time and location in the collector. The lowest velocities measured were in the upstream sections, with a minimum observed value of 3.8 m/min. The highest velocities were observed in the downstream sections, with a maximum value of 31.5 m/min. The presence of a substantial drop structure appeared to reduce the headspace velocity in the upstream reach. In general, there was an increasing trend in gas-phase flows with distance along the length of the collector. Flows at the discharge end of the collector were almost 2 orders of magnitude greater than those at the beginning.     

KAPPA-G,A Non-Gaussian Plume Dispersion Model: Description and Evaluation Against Tracer Measurements

This paper presents a mixed methodology for the simulation of atmospheric disperson phenomena in which vertical diffusion is computed using an analytical solution of the K-theory equation, while horizontal diffusion is simulated by the Gaussian formula. This new formulation, while maintaining a simple analytical form for the concentration field, incorporates the effects of power-law vertical profiles of both wind speed and eddy diffusivity. The performance of this approach, which has been implemented into a full computer package (KAPPA-G), is evaluated by comparison with data from SF₆ tracer experiments.     

Tracer Study In an Urban Valley

Results of a series of nighttime tracer experiments conducted during the Autumn of 1966 in the industrialized valley of Johnstown, Pa., are discussed. Quite atypical meteorology and dispersion occur within a classical drainage flow framework. An urban heat island effect is observed creating uniform temperature and wind structures within a layer of air flowing through the valley. Dispersion in the valley at night is comparable to that of neutral conditions over open country.     

Tracer Study In an Urban Valley

Results of a series of nighttime tracer experiments conducted during the Autumn of 1966 in the industrialized valley of Johnstown, Pa., are discussed. Quite atypical meteorology and dispersion occur within a classical drainage flow framework. An urban heat island effect is observed creating uniform temperature and wind structures within a layer of air flowing through the valley. Dispersion in the valley at night is comparable to that of neutral conditions over open country.     

Conceptual Design of a Massive Aerometric Tracer Experiment (MATEX)

A hypothetical field experiment is evaluated that relates, through tracer releases, reactive pollutant emissions to long range transport and deposition. The feasibility of such an approach is established provided certain requirements can be met. The experiment must: (a) trace emissions from several sources simultaneously and repetitively over an extended period of time, (b) link a tracer to the chemical behavior of emissions, and (c) apply a statistically sound method of guidance for deducing empirical source-receptor relationships (SRRs) while accounting for natural variability. One design approach would use perfluoro-carbon tracers (PFTs), which are nonreactive in the atmosphere, to simulate the transport and dispersion of reactive species such as sulfur and nitrogen oxides. Conversion and loss factors would be calibrated using isotopic sulfur and nitrogen compounds with PFTs, in combination with aerometric and deposition observations. An experimental concept is described that determines SRRs for deposition from observations and their interpolation, synthesized by an empirical model. If implemented, the experiment would be very expensive and has high design risk for achieving its goals given present knowledge.     

Dispersion climatology in a coastal zone

A crosswind integrated K-model with wind- and K-profiles described by Monin-Obukhov similarity expressions is solved for a continuous surface release to yield the vertical spread of the plume as a function of the surface roughness z₀ and the Monin-Obukhov length L for a given downwind distance. The vertical spread of the plume is translated into σ_z, and lines were traced in a (z₀, L⁻) plane for which the σ_z of the K-model matched the corresponding σ_z of Pasquill's system. By this technique a new classification scheme is constructed. Knowing z₀ and L, the scheme tells which σ_z curve in the Pasquill system should be used to describe the dispersion.This dispersion classification scheme is used to organize 3 years of data from two meteorological masts, one placed directly at a shoreline and the other roughly 1 km inland. Differences in the dispersion climatology over land and water are studied by averaging the data selectively. The large differences for water and land surfaces between the seasonal and diurnal variation of the dispersion class distributions are illustrated. It is found that the water surface influences the dispersion climatology as far as 20 km inland.     

A Modification of the Gaussian Dispersion Equation to Accommodate Restricted Lateral Dispersion in Deep River Valleys

The last decade has seen a rapid increase in statutory requirements to regulate the disposal of hazardous wastes and clean up the legacies of their past indiscriminate disposal. The ability to accomplish this depends on the development of innovative technologies and the transfer of technical information on their performance to U.S. Environmental Protection Agency staff, state and local governments, and the private sector. This is a key responsibility of the Office of Solid Waste and Emergency Response, in concert with the Office of Research and Development. This paper describes the evolution of a program to transfer critically needed technologies to the field. A series of Agency evaluations that revealed institutional and communications problems impeding technology transfer led to the development of a systematic strategy that clearly defined roles and responsibilities and provided the impetus for improvement. Some of the major improvements resulting from this approach are briefly described.     

A Multivariable Model for Atmospheric Dispersion Predictions

In conjunction with a 15-month air quality survey of Jacksonville, Fia., a mathematical model has been developed to describe the dispersion of atmospheric pollutants. The source inventory used with the model was compiled, in part, from the data obtained from the sampling of all major sources within the area. The major sources were considered separately from the one-mile square area sources which accounted for the remainder of the emissions. Meteorological data was recorded continuously in the city including vertical temperature observations to 750 ft. The model was compiled in FORTRAN and can be used for both gaseous and particulate pollutants, by utilizing proper decay rates. The variant nature of meteorological parameters and emission rates are considered. The ground level concentrations of several pollutants which were determined for 24 hr periods at 11 sites and continuously at two other sites were used to check the model. A limited tracer study was carried out in conjunction with the project.     

A Wind Tunnel Study of Gaseous Pollutants in City Street Canyons

Steady state mean concentrations of tracer gas were measured in a 400:1 scale model of an idealized city with variable geometry placed within a wind tunnel at various orientations to the mean flow for a free stream velocity of 6.8 ft/sec. The tracer gas was released from two parallel line sources to simulate lanes of traffic in an effort to quantify the persistence of pollution as well as the mean values realized at street levels. An aerodynamically rough turbulent boundary layer of neutral thermal stratification was employed to simulate the atmosphere. Values of concentration measured in the model city were converted to prototype concentrations in ppm and compared to National Ambient Air Quality Standards. It was shown that single isolated structures may cause favorable mixing of pollution downwind but very high concentrations exist in the immediate leeward vicinity of the building. Two favorable geometries for city blocks tested were found to reduce pedestrian exposure to pollution both near heavy traffic congestion and downwind. It was concluded that the pollutant dilution was controlled by the mean flow rather than by turbulent diffusion and that the lateral spread of the plume was slight as one proceeded downwind of the line source. The combination of favorable geometry and higher dilution velocities may bring pollution levels down to existing Air Quality Standards. The body of information presented in this paper should interest city planners and air quality monitoring personnel, as well as those researchers attempting to study and model flow in city street canyons. It provides order of magnitude estimates on pedestrian and office worker exposure to pollutants under a wide range of conditions.     

Evaluation of a Puff Dispersion Model in Complex Terrain

California's Pacific Gas and Electric Company has many power plant operations situated in complex terrain, prominent examples being the Geysers geothermal plant in Lake and Sonoma Counties, and the Diablo Canyon nuclear plant in San Luis Obispo County. Procedures ranging from plant licensing to emergency response require a dispersion modeling capability in a complex terrain environment. This paper describes the performance evaluation of such a capability, the Pacific Gas and Electric Company Modeling System (PGEMS), a fast response Gaussian puff model with a three-dimensional wind field generator.

Performance of the model was evaluated for ground level and short stack elevated release on the basis of a special intensive tracer experiment in the complex coastal terrain surrounding the Diablo Canyon Nuclear Power Plant in San Luis Obispo County, California. The model performed well under a variety of meteorological and release conditions within the test region of 20-kilometer radius surrounding the nuclear plant, and turned in a superior performance in the wake of the nuclear plant, using a new wake correction algorithm for ground level and roof-vent releases at that location.     

Use of Tracer Gas for Direct Calibration of Emission-Factor Measurements in a Traffic Tunnel

ABSTRACT

Pollutant measurements in traffic tunnels have been used to estimate motor-vehicle emissions for several decades. The objective in this type of study is to use the traffic tunnel as a tool for characterizing motor vehicles rather than seeking a tunnel design with acceptably low pollutant concentrations. In the past, very simple aerodynamic models have been used to relate measured concentrations to vehicle emissions. Typically, it is assumed that velocities and concentrations are uniform across the tunnel cross section. In the present work, a vehicle emitting a known amount of sulfur hexafluoride (SF₆) was driven repeatedly through a 730-m-long traffic tunnel in Vancouver, Canada. Comparing the measured SF₆ concentrations to the known emission rates, it is possible to directly assess the accuracy of the simple tunnel aerodynamic models typically used to interpret tunnel data. Correction factors derived from this procedure were then applied to measurements of carbon monoxide and other pollutants to obtain gram-per-kilometer emission factors for vehicles. Although the specific correction factors measured here are valid only for the tunnel tested, the magnitude of the factors (up to two or more) suggests that the phenomena observed here should be considered when interpreting data from other tunnels.     

A Modified Power Law Representation of the Pasquill-Gifford Dispersion Coefficients

Abstract

To broaden the beneficial reuse of sewage sludge, small amounts of nanomaterial were considered as additives to evaluate influences of nanomaterials on microstructures of sludge cement paste. Paste specimens were manufactured using different mix designs and cured for various ages. Tests such as scanning electron microscope, X-ray diffraction, transmission electron microscope, and mercury intrusion porosimetry were then performed. Results obtained indicated that the quantities of crystallization in hydrates rose with the increased amounts of nanomaterial added. Moreover, nanomaterial additives could make crystallizations denser, pore sizes smaller, and the number of pores decreased. Consequently, the strength of sludge cement paste became better as more amounts of nanomaterial were added.     

A Simple Method of Calculating Dispersion from Urban Area Sources

A simple but physically realistic model is shown to be adequate for estimating pollutant concentrations due to area sources in cities. In this model, the surface concentration is directly proportional to the local area source strength and inversely proportional to the wind speed. The model performs nearly as well as much more complex models that require the use of digital computers.     

Dispersion from tall stacks into a shore line environment

A method is presented to model the dispersion of pollutants from a tall stack into the thermal internal boundary layer which develops at a land and water interface for onshore flows. It is assumed that dispersion within the boundary layer proceeds independently of the stable layer aloft in view of the different turbulent characteristics of each layer. The diffusion parameters (σ_y, σ_z), used in the model, are shown to depend on the self-generated turbulence of the plume in the stable layer and the convective turbulence in the internal boundary layer.     

Plume Dispersion in a Mountainous River Valley during Spring

The dispersion of hot plumes emitted from a smelter complex located In the Columbia River Valley, British Columbia, was evaluated under stable and neutral conditions during two mornings In spring. Spatial measurements of SO₂ and temperature within the plume were obtained by immersion probing using fast response helicopter and automobile mounted Instrumentation. In addition, meteorological measurements of vertical wind and temperature profiles at, and downwind from, the smelter were obtained from minisonde balloon releases. With weak down-valley winds, it was found that the plume axis elevations were generally lower during both stable and neutral conditions than would be predicted by Briggs plume-rise formulae. In contrast, plume dispersion, although confined in the horizontal by the steep valley walls during both stability regimes, was significantly enhanced by exceptionally good lateral mixing, particularly close to the source.     

Aircraft Release of Sulfur Hexafluoride as an Atmospheric Tracer

Abstract

The effect of temperature on polyvinylchloride (PVC) combustion using a downstream tubular furnace was investigated for the formation of polycylcic aromatic hydrocarbons (PAHs) and chlorinated compounds. As the temperature increased, higher levels of PAHs were generated. Chlorinated compounds reached a peak at 600°C, with low emissions recorded at 300 and 900°C. There was a close correlation (R² = 0.97) among polychlorinated bi-phenyls (PCBs), hexachlorobenzene, pentachloroben-zene, and polychlorinated dibenzo-p-dioxins and poly-chlorinated dibenzofurans (PCDD/Fs). PAHs at all temperatures were analyzed in the gas phase. PCDD/Fs and PCBs were emitted as a solid phase at 300 and 600°C and as a gas phase at 900°C. For some PAHs, chloroben-zenes, and PCDD/Fs, a mathematical equation between the gas and solid phase and the reciprocal temperature in semilog proportion was derived. The proposed equation, which is log (amount in gas phase/amount in solid phase) = ?A/T + B, where T is the temperature of the furnace and A and B are constants, for these species relating their gas/solid distributions showed a good relationship.