F.3 Volatile Exposure Evaluation

where

Dm = mass (ng) of compound collected on the trap in time Dt (hr)

Ac = area of the sediment-air interface, cm2

NA(t) is expressed in ng/cm2/hr.

An example of actual fluxes obtained from a contaminated dredged material

is given in Figure F-3. These fluxes represent phenanthrene emissions over a

17-day sampling period. Continuous sampling was conducted, meaning that a

trap was attached to the chamber for the entire sampling period. The first five

points on the graph represent samples of 6, 24, 72, 168, and 240 hr with

corresponding sampling times of 6, 18, 48, 96, and 72 hr. This figure gives a

representative pattern for organic compound (PCBs, PAHs) emissions from a

contaminated dredged material.

Figure F-3. Phenanthrene fluxes from a contaminated dredged material

F.3 Volatile Exposure Evaluation

F.3.1 Site exposure concentration

To estimate the exposure concentration at the site:

a. A control volume of air overlying the site should be designated as a

mixing volume for the contaminant flux. This control volume would

extend over the entire area of volatilization locale to a height

characteristic of worker exposure (typically, about 2 m or 6 ft) and its

volume should be estimated in cubic meters.

b. Next, the air residence time of the control volume for low, medium, and

high wind speeds should be estimated by dividing the length of the site

by the wind speed.

Appendix F Laboratory Evaluation of Volatile Emissions and Volatile Dispersion Modeling