Guidance for Evaluation of Volatile Emissions

Guidance for Evaluation of

Volatile Emissions

7.1 General Considerations

Volatilization is the movement of a chemical into the air from a liquid surface.

Volatilization from dredged material solids, even those that appear "dry," involves

desorption through a water film covering the solids and then from the water to the

air. Two major conditions for possible volatile losses from dredged material in

CDFs are volatilization from exposed dredged material and volatilization from

dredged material submerged under ponded water. The objective of evaluating

volatile emissions from dredged material is to determine the potential releases of

volatile and semivolatile contaminants from sediment to the atmosphere following

disposal of dredged material. Volatile emissions assessments may be necessary if

the Tier I evaluation (Chapter 3) indicates the dredged material may contain

contaminants that could result in air quality concerns in and around the CDF from

the perspective of human exposure. The volatilization pathway will be of concern

only for sediments with comparatively high concentrations of volatile organic

contaminants.

7.1.1 Volatilization Processes

Disposal and storage operations associated with dredged material disposal in

CDFs can increase the opportunity for volatile organic compound (VOC)

emissions. Sediment physical characteristics, such as aging, porosity, moisture

content, and percent oil and grease can play a significant role in controlling

volatile emissions from sediments. Contaminant chemical properties such as

Henry's Law Constant and vapor pressure are also very important in determining

contaminant flux to air. Environmental variables such as relative air humidity and

temperature can also play a part in contributing to volatile losses. Volatile

emissions pathways from CDFs can include releases from plant-covered dredged

material, exposed dredged materials, ponded water, and from effluent released

from the CDF.

The highest volatile contaminant transfer condition is in the first few hours

after the surface of the dredged material is exposed, i.e., just after a pond is

removed (USEPA 1996). After initial drying of the surface occurs, the rate of

volatile contaminant transfer is reduced to levels less than that for a ponded

7-1

Chapter 7

Guidance for Evaluation of Volatile Emissions