Transport Calculations

1 2 3 4 5 6 nAdvection

Dispersion 1 2 3 4 5 6 n

Reaction 1 2 3 4 5 6 n

ADVECTION

• Cells are numbered from 1 to N.• Index numbers (of SOLUTION,

EQUILIBRIUM_PHASES, etc) are used to define the solution and reactants in each cell

• SOLUTION 0 (or N+1) enters the column• Water is “shifted” from one cell to the next

ADVECTION

• TRANSPORT adds dispersion, stagnant zones, and heat transport

ADVECTION

• Number of cells

• Number of shifts

• If kinetics—time step

ADVECTION

• Output file– Cells to print– Shifts to print

• Selected-output file– Cells to print– Shifts to print

T.1. Exercise

1. Run the Oklahoma simulation in a 10-cell column.a. Change the log K to –15 for the following two surface complexation reactions:

Hfo_wOH + Mg+2 = Hfo_wOMg+ + H+Hfo_wOH + Ca+2 = Hfo_wOCa+ + H+

b. Initial conditions: equilibrate the following brine with calcite and dolomite.

SOLUTION_SPREAD -units mol/kgw Description Number Temp pH pe Ca Mg Na Cl C S As O2(g) -0.7 charge uMol/kgw brine 1 25 5.713 4 0.4655 0.1609 5.402 6.642 0.00396 0.004725 0.05

T.1. Exercise (continued)

c. Initial conditions: Equilibrate 1 mol of exchanger with the reacted brine and place in each cell of the column.

d. Initial conditions: Equilibrate 0.07 mol of surface complexation sites with the reacted brine. Assume 600 m^2/g specific surface area and 30 grams of sorbing material. Place the surface in each cell of the column.

e. Define evaporated rainwater with the following composition:

SOLUTION_SPREAD -units mol/kgw Description Number Temp pH pe Ca Mg Na Cl C S O2(g) -0.7 charge20xRainwater 0 25 4.6 4 0.192 0.036 0.123 0.134 0.011 0.235

T.1. Exercise (continued)

f. Assume the rainwater reacts with calcite and dolomite in the soil zone and the soil zone pCO2 = 10^-1.5. This water flows into the column.g. Replace half the pore volume of the column with the infilling water.h. Plot pH, Cl (mol/kgw) and total dissolved As (ug/kgw) versus cell number.

T.2. Questions

1. Describe the Cl- profile in the column at the end of the simulation.

2. Describe the pH profile in the column at the end of the simulation.

3. What is the pH at which arsenic appears to become a problem?

TRANSPORT

• Cell lengths

Velocity=length/time step!

• Dispersivities

TRANSPORT

• Boundary conditions

• Flow direction

• Diffusion coefficient

• Heat

TRANSPORT

• Stagnant cells/dual porosity-One stagnant cell

-Multiple stagnant cells

PHAST

• 3D Flow model• PHREEQC chemistry• Capabilities

– Specified, leaky, flux boundary conditions – Water table/confined– Wells– Rivers

• Sequential iteration– Transport all elements conservatively– Run reactions in each cell– Repeat

PHAST

• All the data for flow model—porosity, hydraulic conductivity

• All the data for solute transport model—dispersivity, boundary conditions

• All the data for chemistry– Apply initial conditions by index numbers of

PHREEQC– Associate solutions by index numbers for

boundary conditions

PHAST

• Flow and transport file– Keyword driven input– Same input style as PHREEQC

• Chemistry data file– Exactly a PHREEQC input file

FLOW ANDTRANSPORT DATA FILEGRID -uniform x 0 90000 16 -uniform y 0 48000 9 -uniform z 0 400 5MEDIA

-zone 0. 0. 0. 90000. 48000. 400. -porosity 0.22-long_dispersivity 4000. -trans_dispersivity 50. -Kx 1.373e-5 -Ky 1.373e-5 -Kz 1.373e-7 -storage 0

FLOW-AND-TRANSPORT DATA FILEFLUX_BC

-zone 30000. 3000. 400. 90000. 45000. 400. -flux -10e-5 -associated_solution 1

SPECIFIED_VALUE_BC # Lake Stanley Draper -zone 30000. 14000 300. 32000. 20000. 400.

-head 348. -associated_solution 1

LEAKY_BC -zone 0. 48000. 0. 29000. 48000. 400.

-hydraulic 1.618e-5 -thickness 30000. -head 305.0 -associated 1

CHEMISTRY_IC -zone 0. 0. 0. 90000. 48000. 400.

-solution 2 -equilibrium_phases 2 -exchange 2 -surface 2

MODELVIEWER

• Show—select items to be present in the visualization

•Solid/None

•Model features

•Grid lines

•Color bar

MODELVIEWER

• Tools—select menus by which you can change the look of the features selected by Show.

•Data

•Color bar

•Geometry

•Model features

•Crop

•Animation

Buttons

• Left mouse—3D rotate

• Shift Left mouse—2D rotate in plane of screen

• Middle mouse—Drag

• Right mouse—Grow and shrink

MODELVIEWER

T.2. Exercise

1. Run phast from a command prompt in the directory Friday\phast.ok

phast ok

2. Start ModelViewer

3. File->Open Friday\phast.ok\ok.mv

4. Use ModelViewer to make an animation of the evolution of arsenic in ground-water chemistry in Central Oklahoma