Geoscience Reference
In-Depth Information
Figure 12.6
Contaminant transport with water and sediment.
sediment particles also contributes to the variation of the sorbed contaminant concen-
tration. Adopting the linear sorption/desorption isotherm and the first-order kinetics
yields the following transport equations for the dissolved and sorbed contaminants in
the water column in the 1-D and depth-averaged 2-D models:
J
d
,
aw
h
DC
dw
Dt
=
+
q
dw
−
k
ad
,
w
r
sw
,
w
C
dw
+
k
de
,
w
C
sw
−
k
dw
C
dw
q
d
,
ex
h
k
dbw
h
(
+
C
db
−
C
dw
)
+
(12.102)
DC
sw
Dt
q
s
,
ex
h
=
q
sw
+
k
ad
,
w
r
sw
,
w
C
dw
−
k
de
,
w
C
sw
−
k
sw
C
sw
+
(12.103)
where
C
dw
and
C
sw
are the cross-section-averaged or depth-averaged concentra-
tions of the dissolved and sorbed contaminants in the water column, respectively;
k
ad
,
w
and
k
de
,
w
are the sorption and desorption rate coefficients, respectively;
r
sw
,
w
is the sediment-to-water ratio;
k
dw
and
k
sw
are the decay coefficients of the dis-
solved and sorbed contaminants, respectively;
q
dw
and
q
sw
are the loading rates
of the dissolved and sorbed contaminants per unit volume, respectively;
J
d
,
aw
is
the flux across the water surface per unit surface area;
C
db
is the concentration
of contaminant dissolved in the bed surface layer;
k
dbw
is the diffusional transfer
coefficient of the dissolved contaminant across the bed surface; and
q
d
,
ex
and
q
s
,
ex
are
the exchange rates of the dissolved and sorbed contaminants due to sedimentation,
respectively.
In the 3-D and width-averaged 2-D models, the mass transfers at the water and bed
surfaces are handled through boundary conditions, so the transport equations of the
