1
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
2
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 U-transport in agricultural field soils
Outline
3
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 U-transport in agricultural field soils
4
Simulation Tool
A Coupled Numerical Code forVariably Saturated Water Flow,
Solute Transport andBiogeochemistryin Soil Systems
Simulating water flow, transport and bio-geochemical reactions in environmental soil quality problems
Biogeochemical modelPHREEQC-2.4
Flow and transport modelHYDRUS-1D 2.0
5
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)
6
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 U-transport in agricultural field soils
7
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)
HP1 – model features
8
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 pH-dependent 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)
9
Cycling of radionuclides/metals in soil-plant 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
Typical application and processes involved
10
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 U-transport in agricultural field soils
11
Test I: PCE degradationPCE degradation pathway
(Schaerlaekens et al., Hydrological Processes, 1999)
PCE, TCE: organic contaminant Solvent, degreasing agent, dry-cleaning
VC: vinylchloride: carcinogenic
Perchloroethylene Trichloroethylene
12
Test I: PCE degradationComparison with analytical solution
0 10 20 30D istance (m )
0
0.2
0.4
0.6
0.8
1
Con
cent
ratio
n (m
ole
/ l)
A nalytica l so lu tion(Sun e t a l., 2004)H P 1
PCE
TC E
0 10 20 30D istance (m )
0
0.05
0.1
0.15
0.2
0.25
Con
cent
ratio
n (m
ole
/ l)
cis-DC E
trans-D C E
1,1-DC E
13
Test II: Migration of decay chain species
Problem definition Three contaminants (Cont_a, Cont_b, Cont_c)
First-order degradation
Cont_a Cont_b Cont_c
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
nF = 1 nF = 0.9 nF = 0.8
µ1= 0.005 d-1 µ2= 0.06 d-1 µ3= 0.02 d-1
14
Test II: Migration decay chain species
Water flow boundary conditions
0 1 2 3T im e (d )
0
50
100
150
200
Cum
ulat
ive
flux
(cm
/ m
²)P
T p
E p
T a
E a
P - E p
P - E a
(y)
15
Test II: Migration decay chain speciesWater content profiles
0.05 0.1 0.15 0.2 0.25 0.3 0.35w ater content
-100
-80
-60
-40
-20
0
Dep
th (c
m)
H YD R US -1DH P1
225 d 465 d
630 d
840 d
1096 d
16
Test II: Migration decay chain speciesConcentration-depth profiles
0 0.5 1 1.5 2 2.5C onta (m ole / l)
-100
-80
-60
-40
-20
0
Dep
th (c
m)
225 d
465 d630 d
840 d
1096 d
0.00 0.02 0.04 0.06 0.08 0.10 0.12C ontb (m ole / l)
-100
-80
-60
-40
-20
0
Dep
th (c
m)
225 d
465 d
630 d
840 d
1096 d
H YD R US-1DH P1
BC: Step-function input for Cont_a (1 M) & Cont_b (0.1 M)Leaching
Breakthrough
17
0 20 40 60 80 100D e p th (cm )
0
0.2
0.4
0.6
0.8
1
Con
cent
ratio
n (m
ol/l)
0 20 40 60 80 100D e p th (cm )
0
0.02
0.04
0.06
0.08
0.1
Con
cent
ratio
n (m
ol/l)
0 20 40 60 80 100D e p th (cm )
0
0.02
0.04
0.06
0.08
0.1
Con
cent
ratio
n (m
ol/l)
H Y D R US -1DH P 1
Conta
Contb
Contc
250 d500 d
1000 d
Test II: Migration decay chain species
Concentration-time profiles
Excellent agreement between HP1 and HYDRUS Performance criterion for HP1 becomes more strict: Pe×Cr < 0.4
18
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 U-transport in agricultural field soils
19
Transport of TNT and its Daughter Products
•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 Sorption (instantaneous)
Adsorption coefficients Kd [L/kg]:•TNT 3•2ADNT 5•4ADNT 6•TAT 0
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
4ADNTTNT TAT
2ADNT
20
Transport of TNT and its Daughter Products
0
20
40
60
80
1000.E+00 1.E-07 2.E-07 3.E-07 4.E-07
Concentration [mol/L]
Dep
th [c
m]
2 d
4
6
8
10
0
20
40
60
80
1000.E+00 2.E-09 4.E-09 6.E-09 8.E-09 1.E-08 1.E-08
Concentration [mol/L]
Dep
th [c
m]
2 d
4
6
8
10
2ADNT
0
20
40
60
80
1000.E+00 3.E-09 5.E-09
Concentration [mol/L]
Dep
th [c
m]
2 d4
6
8
10
4ADNT
0
20
40
60
80
1000.E+00 3.E-09 5.E-09
Concentration [mol/L]
Dep
th [c
m] 2 d
4 6 810
TAT
TNT
•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.
21
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
22
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
23
Cd leaching in acid podzol Problem definition (Seuntjens et al., 2000)
Podzol soil (Kempen) contaminated with heavy metals (Cd, Zn, Pb)
Lysimeter (80-cm-diameter, 100-cm-long)
Equipped with TDR probes Bottom: grid based wick sampler system Displacement exp.: boundary conditions
Time (d) CaCl2 (mol/l)0-27.9 0.00527.9-28.9 0.05 (tracer)28.9-80 0.005
Bh2
AE
C1
C2
CEC (meq/kg)24.411.783.962.914.47.4
Bh1
24
Cd leaching in acid podzol Leaching experiment set-up
Leachate collectors
TDR probes
Cable
tester
25
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)3
2-
Cd(Cl)+, Cd(Cl)2, Cd(Cl)3-, Cd(Cl)3
2-
Cd leaching in acid podzol Leaching experiment modelling (1)
26
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)
Cd leaching in acid podzol Leaching experiment modelling (2)
27
Cd leaching in acid podzol Multi-component modelling results (1)
0 20 40 60 80T im e (d)
3
4
5
6
pH
0 20 40 60 80T im e (d)
0
1
2
3
4
Al (m
mol/l)
0 20 40 60 80T im e (d)
0
5
10
15
20
Cl (m
mol/
l)
0 20 40 60 80T im e (d)
0
1
2
3
4
5
Ca (m
mol/l)
28
Cd leaching in acid podzol Multi-component modelling results (2)
0 20 40 60 80T im e (d)
0
0.25
0.5
0.75
1
Na
(mm
ol/l)
0 20 40 60 80T im e (d )
0
0.1
0.2
0.3
K (m
mol
/l)
29
Cd leaching in acid podzol Multi-component modelling results (3)
0 20 40 60 80T im e (d )
0x10 0
2x10 - 3
4x10 - 3
6x10 - 3
8x10 - 3
1x10 - 2
Cd
(mm
ol/l)
0 20 40 60 80T im e (d)
0x10 0
1x10 - 1
2x10 - 1
3x10 - 1
Zn (m
mol
/l)
30
Cd leaching in acid podzol Multi-component modelling results (4)
0 20 40 60 80T im e (d )
0x10 0
2x10 - 3
4x10 - 3
6x10 - 3
8x10 - 3
1x10 - 2
Cd
(mm
ol/l)
0 20 40 60 80T im e (d )
0x10 0
1x10 0
2x10 0
3x10 0
4x10 0
Ca
(mm
ol/l)
pulse 0 .05 M CaC l2 - com plexation/com petition
31
Cd leaching in acid podzol Cd remobilisation due to complex
formation
0 20 40 60 80T im e (d )
0x10 0
2x10 - 3
4x10 - 3
6x10 - 3
8x10 - 3
1x10 - 2
Cd
(mm
ol/l)
0 20 40 60 80T im e (d )
0x10 0
1x10 0
2x10 0
3x10 0
4x10 0
Ca
(mm
ol/l)
pulse 0 .05 M CaC l2 - com plexation/com petition
0 20 40 60 80T im e (d)
0x10 0
2x10 - 3
4x10 - 3
6x10 - 3
8x10 - 3
1x10 - 2
Cd
(mm
ol/l)
0 20 40 60 80T im e (d)
0x10 0
1x10 0
2x10 0
3x10 0
4x10 0
Ca
(mm
ol/l)
pulse 0 .05 M CaC l2 - com plexation/com petitionpulse 0 .005 C aC l2 - less com plexation/com petition
0 20 40 60 80T im e (d )
0x10 0
2x10 - 3
4x10 - 3
6x10 - 3
8x10 - 3
1x10 - 2
Cd
(mm
ol/l)
0 20 40 60 80T im e (d )
0x10 0
1x10 0
2x10 0
3x10 0
4x10 0
Ca
(mm
ol/l)
pulse 0 .05 M CaC l2 - com plexation/com petitionpulse 0 .005 CaC l2 - less com plexation/com petitionpulse 0 .05 C aBr2 - com petition (no com plexation)
CdCln2-n
Complexation or competition?
Complexation!
32
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
33
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 U-transport in agricultural field soils
34
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
35
steady-state
actual surface flux
= P-ETact
potential surface flux
= P-ETpot
0 0 0 1 0 2 0 3 0 4 0 5 0 6 0 7 0 8T im e (year)
0
100
200
300
Cum
ulat
ive
infil
trat
ion
(cm
)
Long-term transient flow and transport Transient infiltration at surface
Bh1
AE
Bh2C1
C2
36
Long-term transient flow and transport Effect of transient infiltration on Cd migration
Site 1
Site 2
Site 6
...
O rganic M atter
C ation Exchange
Aqueous Specia tion
W ater P hase A ir Phase
HKHM g
C a
C d
HN aHH
C a
Zn
H
HHHHHHHHH
H +
H +
ZnC l2
H +
H +
H +N a +
C d 2+
H +
B r -
O H -
H +
C l-
C dC l+
H +
N aO H
H +
H +H +
H +
K +
H +
H +
Z n 2+
Geochemical Reactions: Multisite cation exchange
2 3 4 5 6p H
0
0.01
0.02
0.03
0.04
0.05
Neg
ativ
e ch
arge
orga
nic
mat
ter
(meq
/g s
oil) A -horizon
E-horizon
Podzol soil•Multi-site exchange complex•CEC: organic matter•CEC=f(pH)•Complex formation: Cl-metals•Variable infiltration
37
Long-term transient flow and transport Cd mobility and bio-availability as function of
, pH, Cl- (1)
pH
1975 1976 1977 1978Time (year)
-6
-4
-2
0
De
pth
(c
m)
3
3.2
3.4
3.6
3.8
4
4.2
4.4
Time (year)
Water Content
1975 1976 1977 1978
-6
-4
-2
0
De
pth
(c
m)
0.02
0.06
0.1
0.14
0.18
0.22
0.26
Log(Aqueous Cd) (mmol/kg soil)
1975 1976 1977 1978Time (year)
-6
-4
-2
0
De
pth
(c
m)
-6.6
-6.2
-5.8
-5.4
-5
-4.6
-4.2
-3.8Log(Cl) (mmol/kg soil)
1975 1976 1977 1978Time (year)
-6
-4
-2
0
De
pth
(c
m)
-2.3
-2
-1.7
-1.4
-1.1
-0.8
38
Long-term transient flow and transport Cd mobility and bio-availability as function of
, pH, Cl- (2)
Bh1Bh2
AE
C1
C2
0.2
0.24
0.28
0.32
0.36
0.4
Wat
er c
onte
nt3
3.5
4
4.5
5
pH
pH
Water Content
1972 1974 1976 1978 1980 1982Time (year)
Cl
Aqu
eou s
Cd
Cd
Cl10-4
10-5
10-6
10-2
10-3
39
Long-term transient flow and transportConclusions
Temporal variability of physical soil variables (θ) results in temporal variability in geochemical variables (pH, Cl-,…)
Applied to heavy metal mobility and bio-availability: 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)
40
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 U-transport in agricultural field soils
41
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
Introduction / objectives (1)
42
Introduction / objectives (2) Multiple lines of reasoning
[U]radwaste
[U]concrete, mine waste
U-flux from NF
U-flux from soil, host formation
Individual dose
Dose limit, dose constraint
43
• Introduction
• A new biogeochemical transport code:HP1
• Problem statement: soil, geochemical reactions, BC/IC
• Simulation results
• U-fluxes from soil vs. surface repository
• Conclusions
44
Problem statement (1)Multilayered soil profile
Dry Podzol,7 horizons All horizons characterized
Thickness Unsaturated hydraulic properties pH Organic matter content Fe2O3 content
AE
Bh1Bh2
Bh/C
C 1
C 2
07
19
2428
50
75
depth(cm )
Sim
ulat
ion
dept
h: 1
m
0 0 . 4 0 . 8 1 . 2 1 . 6 2I r o n c o n t e n t ( % )
0 1 2 3 4 5O rganic matter (%)Source: Seuntjens et al., 2001. J. Contam. Hydrol.
45
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
Problem statement (2)Geochemical equilibrium reactions
46
Problem statement (3)Multi-site cation exchange reactions
Because more groups of humic and fulvic acids dissociate as pH ↑proton selectivity decreases when pH ↑
negative charge of organic matter ↑
Site 1
Site 2
Site 6
...
O rganic M atter
C ation Exchange
A queous S peciation
W ater Phase A ir Phase
HKHM g
C a
C d
HN aHH
C a
Zn
H
HHHHHHHHH
H +
H +
ZnC l2
H +
H +
H +N a +
C d 2+
H +
B r -
O H -
H +
C l-
C dC l+
H +
N aO H
H +
H +H +
H +
K +
H +
H +
Zn 2+
Log_K1 (HY)
Log_K2 (HY)
Log_K6 (HY)
...
UO22+
UO22+
UO2Cl+
UO2OH+
47
Problem statement (4)pH-dependent negative charge
2 3 4 5 6p H
0
0.01
0.02
0.03
0.04
0.05N
egat
ive
char
geor
gani
c m
atte
r(m
eq /
g so
il) A -horizon
E-horizon
U-species accounted for:• UO2
2+, UO2OH+, UO2Cl+, UO2F+, UO2H3PO42+, ...
Based on Appelo et al., 1998. Appl. Geoch.
adsorbs
48
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
2 3 4 5 6pH
0
20
40
60
80
100
% U
(VI)
adso
rbed Tota l
C EC
SC
Increased deprotonationIncreased U-sorption
U-species replaced by other cations
49
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) 1.610-1 mol Ca(H2PO4)2 /m² in 1 cm of rain =>3.810-6 mol U /m2 in 1 cm of rain (~105 Bq/ha)
Problem statement (6)Initial and Boundary conditions
50
• Introduction
• A new biogeochemical transport code:HP1
• Problem statement: soil, geochemical reactions, BC/IC
• Simulation results
• U-fluxes from soil vs. surface repository
• Conclusions
51
0.0x10 0 8.0x10 - 4 1.6x10 - 3
C a (m o l / 1 0 0 0 cm ³ so il)
5 0
4 0
3 0
2 0
1 0
0
Dep
th (c
m)
0.0x10 0 1.0x10 - 3 2.0x10 - 3 3.0x10 - 3
P (m o l / 10 0 0 cm ³ so il)
5 0
4 0
3 0
2 0
1 0
0
Dep
th (c
m)
0.0x10 0 2.0x10 - 9 4.0x10 - 9
U (m o l / 1 00 0 cm ³ so il)
100
75
50
25
0
Dep
th (c
m)
100 year150 year200 year
(b) (d) (f)
Simulation results (1)Total Ca, P, and U depth profiles
Steady-state
Transient
• 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
52
Simulation results (2)Transient flow conditions =>
transient geochemical conditions
150 151 152 153 154 155 156 157 158 159 160Tim e (ye a r)
3.4
3.6
3.8
4
4.2pH
S teady-sta te
A tm ospheric
5 cm depth
• Water content variations induce pH variations (dry soil => low pH)• pH variations => variations in sorption potential (low pH => low sorption)
53
Simulation results (3)∆pH results in time variations of
U-mobility
3.4 3.6 3.8 4 4.2p H
1x10 1
1x10 2
1x10 3
1x10 4
K =
ads
orbe
d U
(mol
/l) /
aque
ous
U (m
ol /
l)
A tm osphericS teady-sta te 25 cm depth
5 cm depth
•At least one order of magnitude variation in K
54
Simulation results (4)U-fluxes: steady-state vs. transient
0 50 100 150 2001x10 - 6
1x10 - 3
1x10 0
1x10 3
1x10 6
U fl
ux (B
q ye
ar-1
ha-
1 )
0 50 100 150 2001x10 - 6
1x10 - 3
1x10 0
1x10 3
1x10 6
U fl
ux (B
q ye
ar-1
ha-
1 )
0 50 100 150 200Tim e (ye a r)
1x10 - 6
1x10 - 3
1x10 0
1x10 3
1x10 6
U fl
ux (B
q ye
ar-1
ha-
1 )
0 50 100 150 2001x10 - 6
1x10 - 3
1x10 0
1x10 3
1x10 6
0 50 100 150 200T im e (year)
1x10 - 6
1x10 - 3
1x10 0
1x10 3
1x10 6
7 cm
19 cm
29 cm
50 cm
100 cm
▲ : steady-state▬ : transient
Long-term U flux = U application rate:~105 Bq/ha/y
E-horizon
55
• Introduction
• A new biogeochemical transport code:HP1
• Problem statement: soil, geochemical reactions, BC/IC
• Simulation results
• U-fluxes from soil vs. surface repository
• Conclusions
56
Comparison of U-fluxes
Planned Belgian surface repository :
70 000 m3 LILW; ~71012 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 238U
(1) Drums & monolith(2) Module(3) Soil cover(4) Drainage gallery
57
• Introduction
• A new biogeochemical transport code:HP1
• Problem statement: soil, geochemical reactions, BC/IC
• Simulation results
• U-fluxes from soil vs. surface repository
• Conclusions
58
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
59
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 ...
60
Use of Geochemical Transport Models
Process Coupling and InteractionsTools 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 DataProvide a useful framework for interpreting experimental results. Serve as a tool for understanding qualitative and quantitative trends and relationships present in the data.
Sensitivity AnalysisPermit the systematic evaluation of the impact of model parameters (both reactive and hydrogeological), initial conditions, and boundary conditions upon the model output.
Integration and SynthesisTool for integrating all of the knowledge obtained from simulation, sensitivity analyses, and laboratory and field experimentation.
61
Find out more about HP1!
www.sckcen.be/hp1