Agriculture Reference
In-Depth Information
9.6.2 MRTM Simulations
To illustrate the influence of mixing soils having different properties
on the mobility and retention of reactive chemicals in soils or geologi-
cal media, two examples are presented. The results shown are based on
MRTM simulations for the respective parameters of each medium. In the
first example, one assumes here a soil A which is mixed with a sand mate-
rial (soil B), which is considered much less reactive compared to soil A.
For simplicity, soil B is considered as a nonreactive material where all the
retention coefficients such as
K
e
, k
1
, k
2
, . . ., and
k
irr
are set to zero. For soil A,
the retention coefficients selected for these simulations are
K
e
= 1 mg L
-1
,
n
= 0.75,
k
1
= 0.1 h
-
,
k
2
= 0.01 h
-1
,
n
=0.5, and
k
irr
= 0.005 h
-1
. The influence of
mixing a fraction
(f)
of the sand material on solute transport in this mixed
medium is exhibited by the set of BTCs shown in Figure 9.15. When the
fraction of the added sand in the mixed soil was 25% or
f
of 0.25, a right
shift of the BTC along with an increase in concentration is observed when
compared with the BTCs where no sand was added (
f
= 0). As
f
increases,
BTC simulations indicate earlier arrival time, that is, early breakthrough of
the solute in the effluent solution, along with an increased concentration of
peak maxima. In addition, as
f
increased, a slower release or tailing during
leaching is observed.
In Figure 9.15, simulations for
f
of 0 and 1 represent those for the respective
soils A and B and illustrate the dominance of soil properties of each fraction
on the resulting BTC.
1.0
f =
0
Mixed Soil
0.8
f =
0.25
Soil A = Reactive
Soil B = Nonreactive
0.6
f =
0.50
f =
0.75
0.4
f =
1.00
0.2
0.0
0
1
2
3
4
5
6
7
Pore Volume (V/V
o
)
FIGURE 9.15
Miscible displacement of a solute pulse in a mixed medium made up of a mixture of two soils.
Solute retention properties of soil A include irreversible, nonlinear kinetic, and nonlinear equi-
librium reactions. Soil B is considered nonreactive.
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