Environmental Engineering Reference
In-Depth Information
No dispersion, adsorption or advection
Dispersion only
Dispersion
+
Adsorption
Dispersion
+
Adsorption
+
Reaction
Time
FIGURE 6.54
Effects of dispersion, adsorption, and reaction on the movement of a pollutant
in the subsurface.
TABLE 6.13
Typical
κ
Values for Porous Media
Media
κ
(cm/s)
Gravel
0.03-3
9
×
10
−
5
Sand (coarse)
−
0.6
2
×
10
−
5
Sand (fine)
−
0.02
10
−
7
Silt
1
×
−
0.003
10
−
11
10
−
7
Clay
8
×
−
2
×
10
−
11
10
−
7
Shale
1
×
−
2
×
Source:
FromBedient,P.B.,Rifai,H.S.,andNewell,
C.L. 1994.
Groundwater Contamination
.
Englewood Cliffs, NJ: Prentice-Hall PTR.
E
XAMPLE
6.27 T
IME TO
B
REAKTHROUGH FOR A
C
ONTAMINANT
P
LUME IN
G
ROUNDWATER
Estimate the concentration of chlorobenzene in the groundwater at a well 1 km from
a source after 500 years. The Darcy velocity is 5 m/y. The soil has an organic carbon
content of 2%, a porosity of 0.4, and a density of 1.2 g/cm
3
.
For chlorobenzene, log
K
ow
=
2.91. Hence log
K
oc
=
(
0.92
)(
2.91
)
−
0.23
=
2.45.
K
sw
=
K
oc
f
oc
=
(
10
2.45
)(
0.02
)
=
5.6 L/kg.
R
F
= ε +
(
1
− ε
)
ρ
s
K
sw
=
4.4.
D
w
=
8.7
×
10
−
6
cm
2
/s.
α
D
=
0.017
X
1.5
=
530 m
=
5.3
×
10
4
cm.
U
D
=
5 m/y
=
1.6
×
s
10
−
5
cm/s.
D
=
2.5
×
10
−
6
+
0.85
=
0.85 cm
2
/s. Note that
Pe
=
1.8 and hence both
advection and dispersion are important.
continued
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