Environmental Engineering Reference
In-Depth Information
Table 18.3
K
d
variability based on statistical analysis of literature data (excerpt from Thibault
et al.
1990
)
σ
∗
Range of
K
d
values - L Kg
−
1
Parameter
Soil texture
Number of observations
Cd
1.6
Silt
7-962
8
1.5
Sand
2.7
−
625
14
0.9
Clay
112
−
2,450
10
Cr
2.9
Silt
2.2
−
1,000
4
2.1
Sand
1.7
−
1,729
15
-
Clay
1,500 (exp(
μ
))
−
Pb
1.4
Silt
3,500-59,000
3
2.3
Sand
19-1,405
3
-
Clay
550 (exp(
μ
))
−
Zn
2.4
Silt
3.6-11,000
12
2.6
Sand
0.1-8,000
22
1.4
Clay
200-100,000
23
∗
Standard deviation of the logarithms of the observed values
in this section can be loosely categorized as
static properties
and dynamic
proper-
ties
. Static properties include porosity, bulk density, compositional properties such
as particle size fractions, water retention properties, soil pH, cation exchange capac-
ity (CEC) and such distribution coefficients as the linear
K
d
, the Freundlich
K
f
and
the Langmuir
K
d
. Dynamic properties include the soil water diffusivity, hydraulic
conductivity, contaminant breakthrough curves, dispersivity and contaminant con-
centrations (Jury
1985
). The following sections summarize salient aspects of some
of the static and dynamic properties from these compilations, supplemented with
recent data on spatial variability.
Static Properties
Jury's (1985) compilations suggest that the range of the coefficient of variation
(CV
standard deviation/mean) for static properties is surprisingly small given the
variety of soils and field sizes where the experiments were conducted. For instance,
the CV for porosity ranged between 9.6-11.4% and soil bulk density varied between
2.3-26%. In some studies, replicate measurements of the volumetric or gravimetric
water content in equilibrium with an imposed suction of 0.1 bar showed CV's rang-
ing from 4.3 to 20%; however, when the imposed suction was raised to 15 bars, the
CV was higher and had a range of 14-45%. This is similar to observations reported
by Mallants et al. (
1996c
) who obtained a CV of 23% at 2.3 pF compared to 7% at
0 pF, although the trend reversed at higher pFs.
From Jury's (1985) compilations, soil pH was generally found to be quite uni-
form with a maximum CV of 15%. For the
K
d
values they reported only one study
based on batch and column measurements, which showed a low CV of 31% on soil
samples taken across a sandy field of 0.64 ha.
Thibault et al. (
1990
) presented a comprehensive compilation of
K
d
values for
various soil textures and elements. Table
18.3
only presents the values for some
=
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