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Chapter 3: SESOIL Model Description
The New SESOIL User’s Guide
The user is cautioned regarding the use of literature values for the biodegradation
rates since these values are quite variable and in many cases are not applicable
to site field conditions. In most cases, biodegradation rates are very site-specific
and uncertainty in these rates must be recognized. The user-supplied first-order
decay rate constants (for moisture and solids) should be values measured for the
pollutant in a soil culture test under conditions similar to the site being modeled.
The SESOIL hydrolysis algorithm allows the simulation of neutral, acid- or
base-catalyzed reactions and assumes that both dissolved and adsorbed
pollutant are susceptible to hydrolysis (Lyman et al., 1982). Since hydrolysis is
the reaction of the pollutant with water, this reaction may occur at any depth as
the pollutant moves through the soil column. The hydrolysis subroutine requires
user-supplied rate constants for the neutral, acid and base hydrolysis reactions of
the pollutant, and the pH for each soil layer. The model does not correct for the
temperature of the modeled soil.
0 Side Note:
The hydrolysis
algon?hm
has been
verified but has not been
As for the biodegradation process, the algorithm for hydrolysis uses Eq. (15)
except the rates b, and k,,Jare both replaced by the rate constant k,, defined as
(from Bonazountas and Wagner, 1984):
validated.
k,, = k, + k,-,[H’]
+ kOH [OH -1
(16)
where:
k,
=
the
k,
=
rate constant
(day-‘),
k,
=
rate constant
for acid-catalyzed
drolysis
(days-‘mol-‘L),
pi’]
=
10mpH,the
(mollL),
kOH
=
rate constant
for base-catalyzed
drolysis
(days“mol-‘L),
and
[OH-]
=
10pH-14, the
(mol/L).
hydrolysis
rate
constant
for neutral
hydrogen
hydroxyl
(day-‘),
hydrolysis
hy-
ion concentration
hy-
ion concentration
If cation exchange is considered, the following formula is used:
where the parameters are as defined for Eqs. (9), (14), (15), and (16).
Wisconsin
Department
of Natural Resources
page
27