Environmental Engineering Reference
In-Depth Information
HP1
HYDRUS-1D was coupled with the PHREEQC geochemical code (Parkhurst and
Appelo
1999
) to create a new comprehensive simulation tool, HP1 (acronym for
HYDRUS1D-PHREEQC) (Jacques and Šimunek
2005
; Jacques et al.
2003
,
2008a
,
2008b
). The combined code contains modules simulating (1) transient water flow in
variably-saturated media, (2) the transport of multiple components, (3) mixed equi-
librium/kinetic biogeochemical reactions, and (4) heat transport. HP1 is a significant
expansion of the individual HYDRUS-1D and PHREEQC programs by preserving
most of their original features and capabilities. The code still uses the Richards
equation for simulating variably-saturated water flow and advection-dispersion type
equations for heat and contaminant transport. However, the program can now sim-
ulate also a broad range of low-temperature biogeochemical reactions in water,
the vadose zone and in ground water systems, including interactions with miner-
als, gases, exchangers, and sorption surfaces, based on thermodynamic equilibrium,
kinetics, or mixed equilibrium-kinetic reactions.
Jacques et al. (
2003
,
2008a
,
2008b
) and Jacques and Šimunek (
2005
) demon-
strated the versatility of the HP1 model on several examples such as:
the transport of heavy metals (Zn
2+
,Pb
2+
, and Cd
2+
) subject to multiple cation
exchange reactions;
•
•
transport with mineral dissolution of amorphous SiO
2
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 (this example consid-
ers kinetic precipitation-dissolution of kaolinite, illite, quartz, calcite, dolomite,
gypsum, hydrotalcite, and sepiolite);
long-term transient flow and transport of major cations (Na
+
,K
+
,Ca
2+
, and
Mg
2+
) and heavy metals (Cd
2+
,Zn
2+
, and Pb
2+
) in a soil profile
•
•
cadmium leaching in acid sandy soils;
•
radionuclide transport following phosphorus fertilization (U and its aqueous
complexes);
•
the fate and subsurface transport of explosives (TNT and its daughter products
2ADNT, 4ADNT, and TAT) (Šimunek et al.
2006b
).
To illustrate the capabilities of HP1 and the importance of coupling in an inte-
grated manner all relevant physical and contaminant transport processes when
analyzing the fate and transport of contaminants in variably saturated field soils, the
next section discusses the leaching of cadmium from a podsol soil under transient
boundary conditions.
Applications to Unsaturated Flow and Geochemical Transport Modeling
In this example (Jacques et al.
2008a
) we discuss a hypothetical HP1 applica-
tion involving the transport of major cations and heavy metals in a soil during
transient flow over a period of 30 years. Results will show that variations in water
Search WWH ::
Custom Search