Transcript HP1: A coupled numerical code for varaibly saturated water

HP1: A coupled numerical code for
variably saturated water flow, solute
transport and biogeochemical reactions
in soils and sediments
D. Mallants, D. Jacques, J. Šimůnek, and
M.Th. van Genuchten
1
Outline
 HP1: HYDRUS1D-PHREEQC
 Possibilities of the code
 Benchmarking
 PCE-dissolution
 Migration of decay chain of adsorbing contaminants
during precipitation/evaporation
 Illustration of ‘coupled’ effects
 TNT degradation under steady state flow
 Cd leaching in an acid podzol: lysimeter experiments
 Long-term transient flow and transport of major cations and
heavy metals in a soil profile
2
 U-transport in agricultural field soils
 HP1: HYDRUS1D-PHREEQC
 Possibilities of the code
 Benchmarking
 PCE-dissolution
 Migration of decay chain of adsorbing contaminants
during precipitation/evapotranspiration
 Illustration of ‘coupled’ effects
 TNT degradation under steady state flow
 Cd leaching in an acid podzol: lysimeter experiments
 Long-term transient flow and transport of major cations and
heavy metals in a soil profile
3
 U-transport in agricultural field soils
Simulation Tool
Simulating water flow, transport and biogeochemical reactions in environmental
soil quality problems
A Coupled Numerical Code for
Variably Saturated Water Flow,
Solute Transport and
Biogeochemistry
in Soil Systems
Biogeochemical model
PHREEQC-2.4
Flow and transport model
HYDRUS-1D 2.0
4
Coupling procedure
 Coupling method: non-iterative sequential
approach (weak coupling)
 Within a single time step:
 First solve water flow equation (HYDRUS)
 Second: solve heat transport equation
 Then solve convection-dispersion equation for
solute transport for element master/primary
species (inert transport) (HYDRUS)
 Finally solve for each element, calculate
speciations, equilibrium reactions, kinetic
reactions, … (PHREEQC)
5
 HP1: HYDRUS1D-PHREEQC
 Possibilities of the code
 Benchmarking
 PCE-dissolution
 Migration of decay chain of adsorbing contaminants
during precipitation/evapotranspiration
 Illustration of ‘coupled’ effects
 TNT degradation under steady state flow
 Cd leaching in an acid podzol: lysimeter experiments
 Long term transient flow and transport of major cations and
heavy metals in a soil profile
6
 U-transport in agricultural field soils
HP1 – model features




1D FE water flow in variably-saturated media
1D FE transport of multiple solutes by CDE
1D heat transport
Mixed equilibrium / kinetic biogeochemical
reactions
 Aqueous speciation (reactions in pore-water)
 Cation exchange (on clay, organic matter, …)
 Surface complexation (e.g. iron oxyhydroxides)
 Mineral dissolution / precipitation
 Any kinetic reactions (oxidation/reduction,
(bio)degradation, dissolution/precipitation)
7
HP1 examples






Transport of heavy metals (Zn2+, Pb2+, and Cd2+)
subject to multiple cation exchange
Transport with mineral dissolution of amorphous
SiO2 and gibbsite (Al(OH)3)
Heavy metal transport in a medium with a pHdependent cation exchange complex
Infiltration of a hyperalkaline solution in a clay
sample (kinetic precipitation-dissolution of kaolinite,
illite, quartz, calcite, dolomite, gypsum, …)
Long-term transient flow and transport of major
cations (Na+, K+, Ca2+, and Mg2+) and heavy metals
(Cd2+, Zn2+, and Pb2+) in a soil profile.
Kinetic biodegradation of TNT (multiple degradation
pathways)
8
Typical application and
processes involved
 Cycling of radionuclides/metals in soilplant systems
 Heterogeneous physical/chemical properties
 Water flow under rainfall - evapotranspiration
conditions
 Root growth and water uptake
 Microbiological growth
 Degradation of organic matter with
radionuclide/metal release
 Transport/adsorption/decay
 Uptake of radionuclides/metals by plants
9
 HP1: HYDRUS1D-PHREEQC
 Possibilities of the code
 Benchmarking
 PCE-dissolution under steady-state flow conditions
 Migration of decay chain of adsorbing contaminants
during precipitation/evapotranspiration
 Illustration of ‘coupled’ effects
 TNT degradation under steady state flow
 Cd leaching in an acid podzol: lysimeter experiments
 Long-term transient flow and transport of major cations and
heavy metals in a soil profile
10
 U-transport in agricultural field soils
Test I: PCE degradation
PCE degradation pathway
(Schaerlaekens et al., Hydrological Processes, 1999)
 PCE, TCE: organic contaminant
 Solvent, degreasing agent, dry-cleaning
VC: vinylchloride: carcinogenic
Perchloroethylene
Trichloroethylene
11
Test I: PCE degradation
Comparison with analytical solution
0.25
PCE
0.8
Concentration (mole / l)
Concentration (mole / l)
1
Analytical solution
(Sun et al., 2004)
HP1
0.6
0.4
TCE
0.2
0.2
cis-DCE
0.15
0.1
0.05
trans-DCE
1,1-DCE
0
0
0
10
20
0
30
10
20
Distance (m)
Distance (m)
12
30
Test II: Migration of decay chain species
Problem definition
 Three contaminants (Cont_a, Cont_b, Cont_c)
 First-order degradation
µ1= 0.005 d-1
µ2= 0.06 d-1
µ3= 0.02 d-1
Cont_a  Cont_b  Cont_c 
nF = 1
nF = 0.9
nF = 0.8
 Linear (Cont_a)/ nonlinear Freundlich (Cont_b, Cont_c) sorption
 Homogeneous soil profile
 (Soil covered with grass (rooting depth 20 cm))
 Atmospheric boundary conditions (time dependent)
 HP1 comparison with HYDRUS-1D
13
Test II: Migration decay chain species
Water flow boundary conditions
Cumulative flux (cm / m²)
200
P
P - Ea
P - Ep
150
100
Tp
50
Ta
Ep
Ea
0
0
1
(y)
Time (d)
14
2
3
Test II: Migration decay chain species
Water content profiles
0
840 d
225 d
465 d
Depth (cm)
-20
1096 d
-40
630 d
-60
-80
-100
0.05
0.1
0.15
0.2
0.25
water content
HYDRUS-1D
HP1
15
0.3
0.35
Test II: Migration decay chain species
Concentration-depth profiles
 BC: Step-function input for Cont_a (1 M) & Cont_b (0.1 M)
Leaching
0
0
225 d
225 d
-20
-20
630 d
-40
-60
-40
630 d
-60
-80
1096 d
-100
0
0.5
840 d
Breakthrough
840 d
-80
465 d
Depth (cm)
Depth (cm)
465 d
1
1.5
2
2.5
-100
0.00
1096 d
0.02
Conta (mole / l)
0.04
0.06
0.08
Contb (mole / l)
HYDRUS-1D
HP1
16
0.10
0.12
1
Conta
Concentration-time profiles
0.8
Concentration (mol/l)
Test II: Migration decay chain species
0.6
0.4
0.2
0
0
20
40
60
80
100
Depth (cm)
0.1
 Excellent agreement between HP1
 Performance criterion for HP1
Concentration (mol/l)
and HYDRUS
Contb
0.08
0.06
1000 d
0.04
250 d
500 d
0.02
becomes more strict: Pe×Cr < 0.4
0
0
20
40
60
80
100
Depth (cm)
0.1
Contc
Concentration (mol/l)
0.08
0.06
0.04
0.02
0
17
0
20
40
60
80
Depth (cm)
HYDRUS-1D
HP1
100
 HP1: HYDRUS1D-PHREEQC
 Possibilities of the code
 Benchmarking
 PCE-dissolution under steady-state flow conditions
 Migration of decay chain of adsorbing contaminants
during precipitation/evapotranspiration
 Illustration of ‘coupled’ effects
 TNT degradation under steady-state flow
 Cd leaching in an acid podzol: lysimeter experiments
 Long-term transient flow and transport of major cations and
heavy metals in a soil profile
18
 U-transport in agricultural field soils
Transport of TNT and
its Daughter Products
4ADNT
TNT
TAT
2ADNT
•Soil profile: 100 cm, loam, Ks=1 cm/h, 10 days
•TNT in top 5 cm of soil: 1 mg/kg (6.61e-6 mol)
•TNT dissolution: rate = 4.1 mg/cm2/hour (1.8e-5 mol/cm2/hour)
•Solid 2ADNT at equilibrium with solution, 2ADNT solubility = 2,8 g/L
Degradation
•TNT -> 66% is transformed in
2ADNT and 34% is to 4ADNT
Transformation constants [1/hour]
•TNT
0.01
•2ADNT
0.006
•4ADNT
0.04
Sorption (instantaneous)
Adsorption coefficients Kd [L/kg]:
•TNT
•2ADNT
•4ADNT
•TAT
19
3
5
6
0
Transport of TNT and
its Daughter Products
0
0
2d
20
20
2d
40
4
Depth [cm]
Depth [cm]
4
6
8
60
10
40
6
8
60
10
80
80
2ADNT
TNT
100
100
0.E+00
1.E-07
2.E-07
3.E-07
4.E-07
0.E+00 2.E-09 4.E-09 6.E-09 8.E-09 1.E-08 1.E-08
Concentration [mol/L]
Concentration [mol/L]
0
0
TAT
20
2d
20
6
40
Depth [cm]
Depth [cm]
4
8
60
40
2d
60
10
80
80
4
4ADNT
100
0.E+00
3.E-09
Concentration [mol/L]
5.E-09
100
0.E+00
6
8
3.E-09
Concentration [mol/L]
10
20
5.E-09
•This example indicates
that ground water may
be more vulnerable to
leaching of TNT
daughter products
(notably TAT) than of
the parent compound
itself, and that
monitoring for the
daughter products may
provide an early warning
of possible TNT
leaching.
Cd leaching in acid podzol
Introduction
 Nothern region of Belgium: historical
contamination of soils with Cd, Pb, Cu,
Zn by atmospheric deposition
originated from the non-ferro
industry (historical contamination,
beginning 20th century)
 Risk of flooding with water containing
increased salt concentrations
21
Cd leaching in acid podzol
Objectives
 To describe the leaching of major
cations, Zn and Cd from a
lysimeter after application of an
increased salt concentration
(tracter test)
 To assess the effect of increased
salt concentrations (CaCl2) on Cd
leaching using a new coupled
reactive transport model HP1
22
Cd leaching in acid podzol
Problem definition (Seuntjens et al., 2000)
CEC (meq/kg)
24.4
11.7
83.9
62.9
14.4
7.4
 Podzol soil (Kempen) contaminated with
heavy metals (Cd, Zn, Pb)
A
 Lysimeter (80-cm-diameter, 100-cm-long)
E
 Equipped with TDR probes
Bh1
Bh2  Bottom: grid based wick sampler system
C1  Displacement exp.: boundary conditions
Time (d)
CaCl2 (mol/l)
0-27.9
0.005
C2
27.9-28.9
0.05 (tracer)
28.9-80
0.005
23
Cd leaching in acid podzol
Leaching experiment set-up
TDR probes
Cable
tester
24
Leachate collectors
Cd leaching in acid podzol
Leaching experiment modelling (1)
 Components in solution: H, Ca, Na, K,
Mg, Al, Cl, Br, Cd, Zn
 Speciation reactions in soil solution
 Complexation reactions of Zn, Cd with OH-,
Cl-:
 Cd(OH)+, Cd(OH)2, Cd(OH)3-, Cd(OH)32 Cd(Cl)+, Cd(Cl)2, Cd(Cl)3-, Cd(Cl)32-
25
Cd leaching in acid podzol
Leaching experiment modelling (2)
 Ion exchange reactions (solid phase interaction)
 Half reactions (X-: exchange complex):
H+ + X- = HX
Ca2+ + 2 X- = CaX2
 H, Ca, Na, K, Mg, Cd, Zn
 Equilibrium constants are adapted to fit the
measurements (site-specific Log_K values)
 Equilibrium with gibbsite (Al(OH)3)
26
Cd leaching in acid podzol
Multi-component modelling results (1)
6
4
3
pH
Al (mmol/l)
5
4
2
1
3
0
0
20
40
60
80
0
20
Time (d)
20
60
80
60
80
5
4
Ca (mmol/l)
15
Cl (mmol/l)
40
Time (d)
10
5
3
2
1
0
0
0
20
40
Time (d)
60
80
27
0
20
40
Time (d)
Cd leaching in acid podzol
Multi-component modelling results (2)
0.3
1
K (mmol/l)
Na (mmol/l)
0.75
0.5
0.2
0.1
0.25
0
0
0
20
40
60
0
80
20
40
Time (d)
Time (d)
28
60
80
Cd leaching in acid podzol
1x10
-2
8x10
-3
6x10
-3
4x10
-3
2x10
Zn (mmol/l)
Cd (mmol/l)
Multi-component modelling results (3)
3x10
-1
2x10
-1
1x10
-1
-3
0x10
0
0x10
0
20
40
60
0
0
80
20
40
Time (d)
Time (d)
29
60
80
Cd leaching in acid podzol
Multi-component modelling results (4)
4x100
Cd (mmol/l)
Ca (mmol/l)
3x10
0
2x100
1x10
1x10
-2
8x10
-3
6x10-3
4x10-3
0
2x10
-3
0x100
0x100
0
20
40
60
80
0
Time (d)
20
40
Time (d)
pulse 0.05 M CaCl2 - complexation/competition
30
60
80
Cd leaching in acid podzol
Cd remobilisation due to complex formation
2-n
CdCln
-2
1x10 -2
0
4x100
-3
8x10 -3
0
Cd (mmol/l)
Ca (mmol/l)
3x10
0
2x100
-3
6x10 -3
-3
4x10 -3
0
1x100
-3
2x10 -3
0
0x10 0
0
0x100
0
20
40
60
0
80
20
40
60
Time (d)
Time (d)
pulse 0.05 M CaCl2 - complexation/competition
Complexation or competition?
pulse 0.005 CaCl2 - less complexation/competition
pulse 0.05 CaBr2 - competition (no complexation)
31
Complexation!
80
Cd leaching in acid podzol
Conclusion
 Increased Cd mobilization due to
 exchange Ca-Cd
 complexation with Cl- (most important)
 Geochemical speciation models required
(instead of e.g. Kd approach)
 HP1: allows for transient flow conditions
32
 HP1: HYDRUS1D-PHREEQC
 Possibilities of the code
 Benchmarking
 PCE-dissolution
 Migration of decay chain of adsorbing contaminants
during precipitation/evapotranspiration
 Illustration of ‘coupled’ effects
 TNT degradation under steady state flow
 Cd leaching in an acid podzol: lysimeter experiments
 Long term transient flow and transport of major cations and
heavy metals in a soil profile
33
 U-transport in agricultural field soils
Geochemical transport under
transient variably-saturated flow
 Cycling of metals in soil-plant systems
 Heterogeneous physical/chemical properties
 Water flow under rainfall - evaporation conditions
 Root growth and water uptake
 Metal transport/adsorption/speciation
 Uptake of metals by plants
 Degradation of organic matter with metal release
34
Long-term transient flow and transport
Transient infiltration at surface
steady-state
A
E
Bh1
Bh2
C1
C2
Cumulative infiltration (cm)
300
actual surface
flux
= P-ETact
200
potential
surface flux
100
= P-ETpot
0
00
01
02
03
04
05
Time (year)
35
06
07
08
Long-term transient flow and transport
Effect of transient infiltration on Cd migration
Geochemical Reactions: Multisite cation exchange
Negative charge
organic matter
(meq/g soil)
0.05
0.04
Organic Matter
A-horizon
Water Phase
Air Phase
0.03
0.02
E-horizon
0.01
Site 1
0
H
K
H
Mg
H+
Ca
2
3
4
5
6
H+
NaOH
BrCd2+
K+
Cd
pH
H+
Podzol soil
Site 2
•Multi-site exchange complex
H
Na
H
H
H
Ca
H
H+
OHH+
ZnCl2
+
H+
H+
Zn
•CEC: organic matter
Site 6
•CEC=f(pH)
•Complex formation: Cl-metals
H
H
H
H
H
H
H
H
H
Cation
Exchange
•Variable infiltration
36
H+
Cl-
...
H+
H
+
CdCl+
H+
Zn2+
Na+
H+
Aqueous
Speciation
H+
Long-term transient flow and transport
Cd mobility and bio-availability as function of
, pH, Cl- (1)
Water Content
pH
0.26
0
0
4.4
-2
0.18
0.14
-4
4.2
D e pth ( c m )
D e p th ( c m )
0.22
-2
4
3.8
-4
3.6
0.1
-6
3.4
-6
0.06
3.2
1976
1977
Time (year)
1978
1975
0.02
Log(Cl) (mmol/kg soil)
0
D e p t h (c m )
1976
1977
Time (year)
1978
3
Log(Aqueous Cd) (mmol/kg soil)
-0.8
-4.2
-1.1
-2
-1.4
-4
-1.7
-3.8
0
D e p th (c m )
1975
-4.6
-2
-5
-4
-5.4
-5.8
-6
-6
1975
-2
1976
1977
Time (year)
-6.2
1975
1978
-2.3
37
1976
1977
Time (year)
1978
-6.6
Long-term transient flow and transport
Cd mobility and bio-availability as function of
, pH, Cl- (2)
5
0.32
4
0.28
3.5
0.24
0.2
Water Content
3
Cl
Cl
C2
4.5
pH
pH
0.36
10-2
10-3
1972
10-4
Cd
1974
38
1976 1978
Time (year)
10-5
1980
10-6
1982
Aqueous Cd
A
E
Bh1
Bh2
C1
Water content
0.4
Long-term transient flow and transport
Conclusions
 Temporal variability of physical soil
variables (θ) results in temporal variability
in geochemical variables (pH, Cl-,…)
 Applied to heavy metal mobility and bioavailability:
 Water content variations linearly related to pH
and inversely to Cl- variations
 pH inversely related to dissolved metal
concentration (multi-site cation exchange f(pH))
 Cl- concentration linearly related to dissolved
metal concentration (complex formation)
39
 HP1: HYDRUS1D-PHREEQC
 Possibilities of the code
 Benchmarking
 PCE-dissolution under steady-state flow conditions
 Migration of decay chain of adsorbing contaminants
during precipitation/evapotranspiration
 Illustration of ‘coupled’ effects
 TNT degradation under steady state flow
 Cd leaching in an acid podzol
 Long term transient flow and transport of major cations and
heavy metals in a soil profile
40
 U-transport in agricultural field soils
Introduction / objectives (1)
 Motivation: assessment of post-closure safety for
surface repository
 Inherent uncertainties, especially for the long-term
 Use of multiple lines of reasoning
 Complementary safety indicators for evaluating and
confirming safety: e.g., RN fluxes, U-concentration
 Objective: estimate long-term U-leaching from
agricultural soils, compare with U-fluxes from planned
surface repository
41
Introduction / objectives (2)
Multiple lines of reasoning
Individual dose
U-flux from NF


Dose limit, dose constraint
U-flux from soil, host formation
[U]radwaste

[U]concrete, mine waste
42
• Introduction
• A new biogeochemical transport code:HP1
• Problem statement: soil, geochemical
reactions, BC/IC
• Simulation results
• U-fluxes from soil vs. surface repository
• Conclusions
43
Problem statement (1)
Multilayered soil profile





depth
2 (cm)
0
7
Iron content (%)
0
0.4
0.8
1.2
1.6
A
E
Thickness
Unsaturated hydraulic properties
pH
Organic matter content
Fe2O3 content
19
Bh1
Bh2
24
28
Bh/C
50
C1
75
C2
Source: Seuntjens et al., 2001. J. Contam. Hydrol.
44
0
1
2
3
Organic matter (%)
4
5
Simulation depth: 1 m
 Dry Podzol,7 horizons
 All horizons characterized
Problem statement (2)
Geochemical equilibrium reactions
 Aqueous speciation reactions
 Chemical components: C, Ca, Cl, F, H, K, Mg,
N(5), Na, O(0), O(-2), P, S(6), U(6)
 Multi-site cation exchange reactions
 Related to amount of organic matter
 Increases with increasing pH
 Surface complexation reactions
 Specific binding to charged surfaces (FeOH)
 Related to amount of Fe-oxides
45
Problem statement (3)
Multi-site cation exchange reactions
Organic Matter
Log_K1 (HY)
Site 1
Water Phase
H
K
H
Mg
H+
BrCd2+
K+
Cd
UO22+H
Log_K2 (HY)
...
Log_K6 (HY)
Site 2
H+
NaOH
Ca
H
Na
H
H
H
Ca
Air Phase
H
+
UO2OH+
H+
OHH+
ZnCl2
+
H+
H+
Zn
Site 6
H+
Cl-
...
H
H
H
H
H
H
H
H
H
Cation
Exchange
UO22+
H
H+
+
CdCl+
H+
Zn2+
UO2Cl+
H
Na+
+
H+
Aqueous
Speciation
Because more groups of humic and fulvic acids dissociate as pH ↑
proton selectivity decreases when pH ↑
negative charge of organic matter ↑
46
Problem statement (4)
Negative charge
organic matter
(meq / g soil)
pH-dependent negative charge
0.05
Based on Appelo et al., 1998. Appl. Geoch.
0.04
A-horizon
0.03
0.02
E-horizon
0.01
0
2
3
4
pH
5
6
U-species accounted for:
• UO22+, UO2OH+, UO2Cl+, UO2F+, UO2H3PO42+, ...
adsorbs
47
Problem statement (5)
Surface complexation
• Surface complexation model
 0.875 reactive sites/mol Fe (Waite et al., 1994. G.C. Acta)
 Surface complex: FeOUO2+ (Dzombak & Morel, 1990)
• Changing processes in U adsorption with increasing pH
% U(VI) adsorbed
100
80
SC
Total
CEC
60
U-species replaced
by other cations
40
20
0
2
3
4
5
pH
Increased
deprotonation
48
Increased U-sorption
6
Problem statement (6)
Initial and Boundary conditions
 Initial condition
 No U initially present in soil profile (<> few 10 Bq/kg)
 Boundary condition
 200-year time series of synthetic meteorological
data to calculate preciptiation and potential
evaporation
 Composition rain water from measurements
 P-fertilizer (Ca(H2PO4)2): ~3000 Bq 238U/kg
 Applied each year on May 1 (1 g P/m2)
 1.610-1 mol Ca(H2PO4)2 /m² in 1 cm of rain
 =>3.810-6 mol U /m2 in 1 cm of rain (~105 Bq/ha)
49
• Introduction
• A new biogeochemical transport code:HP1
• Problem statement: soil, geochemical
reactions, BC/IC
• Simulation results
• U-fluxes from soil vs. surface repository
• Conclusions
50
Simulation results (1)
0
10
Steady-state 10
20
30
0.0x100
25
20
30
(b)
8.0x10-4 1.6x10-3
Ca (mol / 1000 cm³ soil)
50
Transient
100 year
150 year
200 year
75
40
40
50
0
Depth (cm)
0
Depth (cm)
Depth (cm)
Total Ca, P, and U depth profiles
(d)
50
(f)
100
0.0x100 1.0x10-3 2.0x10-3 3.0x10-3 0.0x100
P (mol / 1000 cm³ soil)
2.0x10-9
4.0x10-9
U (mol / 1000 cm³ soil)
• Ca, P, U accumulation in Bh-horizon (rich in o.m. & Fe-ox.)
• U-breakthrough after 100 y
• U moved faster under transient than under steady-state
51
Simulation results (2)
Transient flow conditions =>
transient geochemical conditions
4.2
Steady-state
pH
4
3.8
Atmospheric
3.6
5 cm depth
3.4
150
151
152
153
154 155 156
Time (year)
157
158
159
160
• Water content variations induce pH variations (dry soil => low pH)
• pH variations => variations in sorption potential (low pH => low sorption)
52
Simulation results (3)
K = adsorbed U (mol/l) / aqueous U (mol / l)
∆pH results in time variations of
U-mobility
1x104
Atmospheric
Steady-state
1x10
25 cm depth
3
5 cm depth
1x102
1x101
3.4
3.6
3.8
4
4.2
pH
•At least one order of magnitude variation in K
53
U flux (Bq year-1 ha-
1x10
6
1x10
3
1x10
0
1x10
Simulation results (4)
1x10
0
7 cm
1x10
-3
50 cm
1x10
0
U flux (Bq year-1 ha-1)
3
1x10
U-fluxes: steady-state
vs. transient
1x10-6
100
50
150
-3
1x10-6
0
200
1x10
6
1x10
6
1x10
3
1x10
3
1x10
0
1x10
0
19 cm
▲
100
50
: steady-state
E-horizon
0
50
100
150
1x10-6
0
200
150
100 cm
50
100
150
Time (year)
1x10
6
1x10
3
Long-term U flux = U application rate:~105 Bq/ha/y
54
1x10
0
200
▬ : transient
1x10-3
1x10-3
1x10-6
q year-1 ha-1 )
6
200
• Introduction
• A new biogeochemical transport code:HP1
• Problem statement: soil, geochemical
reactions, BC/IC
• Simulation results
• U-fluxes from soil vs. surface repository
• Conclusions
55
Comparison of U-fluxes
(1) Drums & monolith
(2) Module
(3) Soil cover
(4) Drainage gallery
 Planned Belgian
surface repository :
 70 000 m3 LILW;
~71012 Bq long-lived alphas
 Flux from NF, optimistic scenario: ~3 Bq/ha/y 238U
 Flux from NF, realistic scenario: ~103 Bq/ha/y 238U
 Fertilizer application: ~103 -104 Bq/ha/y
56
238U
• Introduction
• A new biogeochemical transport code:HP1
• Problem statement: soil, geochemical
reactions, BC/IC
• Simulation results
• U-fluxes from soil vs. surface repository
• Conclusions
57
Conclusions (1)
 New biogeochemical transport code HP1
provides useful insight into complex U-migration
processes
 U migration under atmospheric boundary
conditions faster than under steady-state flow
conditions
 Due to changing flow and geochemical
conditions (∆ pH =>∆ sorption)
 Atmospheric boundary conditions important
when assessing U-flux to groundwater
58
Conclusions (2)
 Calculated U-fluxes from soil same order of
magnitude as U-flux from surface repository
 Limitations of the study






No interactions U-nitrate
CO2 transport not accounted for
More typical agricultural soils
Include plant uptake
Need verification experiments
...
59
Use of Geochemical Transport Models
 Process Coupling and Interactions
Tools for investigating the impacts of multiple coupled
biogeochemical reactions in the presence of complex flow
fields and spatial heterogeneity. Enable extrapolation to
environmentally relevant temporal and spatial scales.
 Interpretation of Laboratory and Field Data
Provide a useful framework for interpreting experimental
results. Serve as a tool for understanding qualitative and
quantitative trends and relationships present in the data.
 Sensitivity Analysis
Permit the systematic evaluation of the impact of model
parameters (both reactive and hydrogeological), initial
conditions, and boundary conditions upon the model output.
 Integration and Synthesis
Tool for integrating all of the knowledge obtained from
simulation, sensitivity analyses, and laboratory and field
60
experimentation.
Find out more about HP1!
www.sckcen.be/hp1
61