Plume stability

Extent of contamination/plume stability Hydrocarbon type Chromatographic evidence Hydrocarbon concentration Soil pH... 

Hydrogeologic factors for consideration include aquifer type, hydrogeologic gradient, permeability, recharge capability, depth to groundwater, moisture content/field capacity, dissolved oxygen (DO), depth to contamination, extent of contamination, and plume stability. 

Plume stability Plume is stable asymptotic conditions reached... 

Substantial research on environmental pollution plume persistence and dispersion in air has produced a classification system called Pasquill s stability classes for plume stability in air. Unfortunately, the system does not apply as directly as we might wish since it applies at the much larger scale of stack exhausts and the like. However, some insight from the system is available. 

The data evaluation step in Tier 1 identifies the constituents of potential concern and the concentrations at which they occur in impacted media as determined by investigations conducted at the site. Most states do not require evaluation of historical data as part of the Tier 1 evaluation, although they may require submission of these data in the RBCA report as a basis for comparison (e.g., to demonstrate the decrease in constituent concentrations over time and/or demonstrate plume stability). However, the data that best represent the current environmental conditions at the site should be used in the risk-based decision-making approach. 

This solution describes a plume with a Gaussian distribution of poUutant concentrations, such as that in Figure 5, where (y (x) and (y (x) are the standard deviations of the mean concentration in thejy and directions. The standard deviations are the directional diffusion parameters, and are assumed to be related simply to the turbulent diffusivities, and K. In practice, Ct (A) and (y (x) are functions of x, U, and atmospheric stability (2,31—33). 

In addition to short-term emission estimates, normally for hourly periods, the meteorological data include hourly wind direction, wind speed, and Pasquill stability class. Although of secondary importance, the hourly data also include temperature (only important if buoyant plume rise needs to be calculated from any sources) and mixing height. 

As an example of the use of the Gaussian plume equations using the Pasquill-Gifford dispersion parameters, assume that a source releases 0.37 g s of a pollutant at an effective height of 40 m into the atmosphere with the wind blowing at 2 m s . What is the approximate distance of the maximum concentration, and what is the concentration at this point if the atmosphere is appropriately represented by Pasquill stability class B ... 

Plume rise observations based on single-stack operation were regressed into the above expression and empirically fitted to the following expression, which incorporates atmospheric stability classes into the coefficients ... 

Plume height is based on the assumed F stability and 2.5 m/s wind speed, and the dispersion parameter (o, ) incorporates the effects of buoyancy induced dispersion. If x , is less than 200 m, then no shoreline fumigation calculation is made, since the plume may still be influenced by transitional rise and its interaction with the TIBL is more difficult to model. 

Having determined tlie stability class. Figs. 12.6.2. and 12.6.3. may be used to evaluate ay and a as a function of downwind distance from tlie source. Figures 12.6.2. and 12.6.3. apply strictly to open, level country and probably underestimate tlie plume dispersion potential from low level sources in built-up areas. Altliough tlie vertical spread may be less than tlie values for class F witli... 

A proposed source is to emit 72 g/s of a toxic pollutant from a stack 30 meters liigh with a diameter of 1.5 meters. Tlic effluent gases are emitted at a temperature of 250 F (394K) with an exit velocity of 13 m/s. Using Holland s plume rise equation, obtain the plume rise as a function of wind speed for stability classes B and D. Assume that the design atmospheric pressure is 970 mbar and that the design ambient air temperature is 20 C (293K). 

Plume containment involves stabilization of the dissolved plume hydraulically downgradient. Containment can be achieved by several means, including natural-gradient renovation with minimal pumping and treatment directly within the source area pump-and-treat scenarios, which rely on aquifer hydraulics and solute transport mechanisms and consist of the select placement of extraction wells or natural flushing with capture. 

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