Volatilization to Air

Framework for Dredged Material Management

May 2004

regarding potential for human health effects and for beneficial uses of the site or dredged

material. Levels of contaminants in the biomass are compared with Federal criteria for

food or forage. Risk assessment may also be performed to evaluate the potential effects

of plant and animal uptake on sensitive species subject to primary or secondary exposure

(Cura, Wickwire, and McArlde in preparation).

From the test results, appropriate management strategies can be formulated

regarding where to place dredged material to minimize plant or animal uptake or how to

control and manage the species on the site so that desirable species that do not take up

and accumulate contaminants are allowed to colonize the site, while undesirable species

are removed or eliminated.

5.3.8 Volatilization to Air

Contaminant transport from in situ sediment to air is a relatively slow process,

because most contaminants must first be released to the water phase prior to reaching the

air. Potential for volatilization should be evaluated in accordance with regulatory

requirements of the Clean Air Act. Thibodeaux (1989) discusses volatilization of organic

chemicals during dredging and disposal and identifies four locales where volatilization

may occur:

Dredged material exposed directly to air.

Dredging site or other water area where suspended solids are elevated.

Ponded CDF with a quiescent, low-suspended solids concentration.

Dredged material covered with vegetation.

In cases where highly contaminated sediments are disposed, airborne emissions

must be considered to protect workers and others who could inhale contaminants released

through this pathway.

Rate equations based on chemical vapor equilibrium concepts and transport

phenomena fundamentals have been used to predict chemical flux (Thibodeaux 1989;

Semmler 1990). Computerized programs have been developed utilizing these rate

equations for the evaluation of volatile emissions from dredged material (Myers,

Schroeder and Estes in preparation (b)). Since the original publication of this document,

considerable effort has also been directed to testing procedures for direct measurement of

volatile emissions (Price et al. 1997; Price et al. 1998; Price et al. 1999, USACE 2003).

Emission rates are primarily dependent on the chemical concentration at the

source, the surface area of the source, and the degree to which the dredged material is in

direct contact with the air. The magnitude of release from exposed dredged material is

initially higher than for ponded conditions. This is of limited duration however.

Volatilization from ponded areas occurs at a lower rate, but is continuous, and may result

in a higher mass flux over time.