Rural releases

Figure 5-10 Dispersion coefficients for Pasquili-Gifford plume model for rural releases.

The Chemical Emergency Preparedness and Prevention Office has estimated the zone of vulnerability under worst-case scenario conditions for facilities containing different hazardous substances. They conclude that for a facility containing toxic substances, the median distance from the facility to the outer edge of its vulnerable zone is 1.6 miles. Flammable substances have a worst-case scenario vulnerability zone whose median distance reaches 0.4 miles from the facility. However, many facilities reported vulnerability zones extending 14 miles from the facility (primarily for urban area releases of chlorine stored in 90-ton rail tank cars) and 25 miles (for rural releases of chlorine stored in 90-ton rail tank cars). Other chemicals for which the reported vulnerability zone equaled or exceeded 25 miles include anhydrous ammonia, hydrogen fluoride, sulfur dioxide, chlorine dioxide, oleum (fuming sulfuric acid). 

Distance Downwind, km FIGURE 2.27. Dispersion coefficients for a continuous release or plume. The top two graphs apply onjy for rural release conditions and the bottom two graphs appiy only for urban release conditions. 

FIGURE 2.29. Dispersion coefficients for an instantaneous release or puff. These apply only for rural release conditions and are developed based on limited data. 

FIGURE 2.31. Dimensionless Gaussian dispersion model output for the distance to a particular concentration. This applies for rural release only. 

The Britter and McQiiaid model was developed by performing a dimensional analysis and correlating existing data on dense cloud dispersion. The model is best suited for instantaneous or continuous ground-level area or volume source releases of dense gases. Atmospheric stability was found to have little effect on the results and is not a part of the model. Most of the data came from dispersion tests in remote, rural areas, on mostly flat terrain. Thus, the results would not be apphcable to urban areas or highly mountainous areas. 

SIMPLE TERRAIN INPUTS SOURCE TYPE EMISSION RATE (G/S) FLARE STACK HEIGHT (H) TOT HEAT RLS (CAL/S) RECEPTOR HEIGHT (M) UR6AN/RURAL OPTION EFF RELEASE HEIGHT (H) BUILDING HEIGHT (M)... 

Site characteristics Releases occurred in settings ranging from rural to very congested industrial areas. 

Population Characterization. An important part of any exposure assessment is the development of a detailed and up-to-date human demographic data base for the area being studied. These data can provide the basis for estimates of subpopulations associated with different exposure pathways. In national exposure assessments it is common to use an average population density for the total U.S. or to simply distinguish between rural and urban densitites. In a geographic exposure assessment in which site-specific data on pollutant releases, environmental fate and ambient levels are measured or estimated, it is important to have equally detailed population data. Population breakdowns by age, sex, housing and... 

The Britter-McQuaid model is a dimensional analysis technique, based on a correlation developed from experimental data. However, the model is based only on data from flat rural terrain and is applicable only to these types of releases. The model is also unable to account for the effects of parameters such as release height, ground roughness, and wind speed profiles. 

On an overcast day a stack with an effective height of 60 m is releasing sulfur dioxide at the rate of 80 g/s. The wind speed is 6 m/s. The stack is located in a rural area. Determine... 

Cresols are widely distributed natural compounds. As discussed above, they are formed as metabolites of microbial activity and are excreted in the urine of mammals (Fiege and Bayer 1987) and humans (Needham et al. 1984). Cresols from human urine are probably biodegraded at municipal sewage treatment facilities prior to release to ambient waters. However, for combined septic and storm sewage systems, cresols may be released to surface waters during periods of precipitation when influent volumes exceed treatment plant capacities. Also, in rural and suburban areas where septic tanks are used (o- and m-cresols can resist anaerobic digestion), human excrement may be a nonpoint source release of cresols to groundwater. 

Nickel releases to the atmosphere are mainly in the form of aerosols that cover a broad spectrum of sizes. Particulates from power plants tend to be associated with smaller particles than those from smelters (Cahill 1989 Schroeder et al. 1987). Atmospheric aerosols are removed by gravitational settling and dry and wet deposition. Submicron particles may have atmospheric half-lives as long as 30 days (Schroeder et al. 1987). Monitoring data confrrm that nickel can be transported far from its source (Pacyna and Ottar 1985). Nickel concentrations in air particulate matter in remote, rural, and U.S. urban areas are 0.01-60, 0.6-78, and 1-328 ng/m, respectively (Schroeder et al. 1987). 

The most simple and widely used spatial increment approach compares concentration levels measured in different environments, assuming that the actual level at a given site is the sum of emissions released on regional, urban, and local scales (cf. Fig. 2). Hence, by calculation of the spatial increments (e.g. traffic-urban background, urban background-rural background) basic assessments of the shares of emissions from the different source areas can be obtained. This approach constitutes the first step within a source apportionment method first proposed by Lenschow et al. [3]. 

Miner 1969a). Barium enters the environment naturally through the weathering of rocks and minerals. Anthropogenic releases are primarily associated with industrial processes. Barium is present in the atmosphere, urban and rural surface water, soils, and many foods. 

Emissions versus Deposition. Several workers have compared estimates of atmospheric emissions with measured deposition fluxes for PCDD/Fs a selection are summarized in Table 8. Whilst the database on which such comparisons are founded is limited, the tentative conclusions which may be derived are of potentially great significance. In particular, it has been observed that most such comparisons, including several of those referred to in Table 8, indicate that current deposition exceeds atmospheric emissions from primary sources.44 Whilst there are significant sources of potential error involved in such calculations (e.g. in addition to those mentioned in earlier sections, like the failure to consider releases from secondary sources, there is the possibility that estimates of representative depositional inputs may overestimate the true figure, owing to the fact that measurements of rural depositional inputs are extremely scarce), the obvious conclusion is that we have yet to discover all sources of the current depositional inputs of PCDD/Fs. 

Older exterior paints and floor finishes can release PCBs, furniture finishes can release phthalates as well as more volatile solvents and paint pigments can release new PCBs (e.g. PCB 11) as pigment by-products (Rudel and Perovich, 2009 Hu et al, 2008). Road sealants can contain extremely high concentrations of PAH that are released over time (Mahler et al, 2005 Van Metre and Mahler, 2005 Van Metre et al, 2009). Pesticides are widely used outdoors in urban areas and use of phenoxy herbicides such as 2,4-D and prometon in urban areas exceeds that in rural areas (Templeton et al., 1998 Struger et al, 1994). 

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