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 Physical characteristics
The long-term average water flushing rate should be measured onsite to
evaluate water-side mass transfer resistances. Cap material properties are
dependent on the specific materials available and should be measured using
standard analytical methods.
Mass transfer coefficients
A turbulent mass transfer correlation (Thibodeaux 1996) can be used to
estimate the value of Kbl in the water above the cap:
0.036 Re 0.8 Sc 1/3
Sh
(B37)
where
Kbl
x
Sh = Sherwood number =
Dw
x
u
Re = Reynolds number =
Sc = Schmidt number =
Dw
= kinematic viscosity of water, 0.01 cm2/sec at 20 C
u = benthic boundary layer water velocity, cm/s
As is taken
x = length scale for the contaminated region - here x
where As is area of contaminated region, cm
As indicated previously, however, the benthic boundary layer mass transfer
coefficient is rarely significant in the estimation of contaminant flux through the
cap.
Transport by bioturbation has often been quantified by an effective diffusion
coefficient based on particle reworking rates. A bioturbation mass transfer
coefficient can then be estimated from the following relation assuming linear
partitioning between the sediment and water in the bioturbation layer
Dbio
b Kd
Kbio
(B38)
Lbio
where is a desorption efficiency of the chemical once the particle carrying it
has been reworked to the sediment-water interface. would tend to be small for
more hydrophobic compounds that tend to desorb slowly at the surface and
large for compounds that are more soluble. In the absence of experimental
B19
Appendix B Model for Chemical Containment by a Cap
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