Maximum flux estimation (steady state) (Cont.)

Csw = pore water concentration at sediment water interface, ng/cm3

= desorption efficiency of contaminant from sediment particles

Dbio = biodiffusion coefficient, cm2/day

obs

Rf = retardation factor =

B Kd

Lbio = depth of bioturbation, cm

Kbl = benthic boundary layer mass transfer coefficient, cm/day

Ke = evaporation mass transfer coefficient, cm/day

4/3

, cm3/day

De = effective diffusivity = Dw

Q = basin flushing rate, cm3/day

Cw = chemical concentration in the overlying water, ng/cm3

Kd = sediment water partition coefficient for chemical = Koc foc , cm3/g

Koc = organic carbon-water coefficient for chemical, cm3/g

foc = sediment fractional organic carbon content

= sediment bulk density

The overall mass transfer coefficient, Kov , can be obtained from the following

(B20)

Ke Ae

Kov

Kcap

Kbio

Kbl

An analysis of this relationship for reasonable values of Leff suggests that

1/Kov x 1/Kcap; therefore, the cap controls the flux to the overlying water, and

Equation B17 is valid.

This flux can be used to estimate concentrations in the water (Cw) or at the

sediment water interface (Csw) or multiplied by the capped area to determine total

release rate. For hydrophobic organics, the concentration in the overlying water

at steady state is defined by a balance between the flux through the cap, the rate

of evaporation to the air, and the rate of flushing of the water column. For

metals and elemental species not associated with volatile compounds, the flux

through the cap is balanced only with the flushing of the water column. The

overlying water concentration of the contaminant is given by:

B12

Appendix B Model for Chemical Containment by a Cap