simulation of degassing and subsequent gas-transport in PHREEQC

• To: dlpark@xxxxxxxx
• Subject: simulation of degassing and subsequent gas-transport in PHREEQC
• From: "Boris M. van Breukelen" <breb@xxxxxxxxx>
• Date: Mon, 30 Jun 2003 16:55:26 +0200

```Dear David Parkhurst,

I have simulated instantaneous degassing of methane from a landfill leachate
plume using a 1D horizontal PHREEQC flowpath model and simulating formation
of a gas-phase if the total gas pressure exceeded the hydrostatic pressure
(see my PhD thesis at: http://www.geo.vu.nl/users/breb/). The formed
gas-phase was removed in order to simulate the loss of gas from the plume
(chapter 5 thesis).

I simulated methane degassing as well in another 1D vertical transport model
of the rising plume fringe (chapter 6 in thesis). However, I do not know how
to simulate detailed/real gas-transport towards the atmosphere in PHREEQC.
Methane gas could for example re-dissolve in aerobic water above the
leachate plume...This would be interesting to add to the model. Therefore my
question:

Is it possible to transfer a gasphase from a lower cell to an upper cell
using BASIC statements in the RATES command? For example, a PHREEQC vertical
column model has 100 cells, where cell 100 is the deepest cell and cell 1 is
at the groundwater table. A gas-phase is formed in cell 40 because the gas
pressure exceeds hydrostatic pressure. Is it possible to transfer the
gas-phase from cell 40 to the upper cell 39? On its turn a gas-phase may
form in cell 39 because of transfer of the gas-phase from lower cell 40
and/or by reactions in cell 39, so the gas-phase from cell 39 is then
transported to cell 38, etc. I think you need to formulate a RATES/KINETICS
statement for each cell where the gas-phase from the neighboring lower cell
is added to the the current cell where is may dissolve or not... This model
would then assume that gas-transport and degassing/re-dissolution is a fast
equilibrium process. Is this possible in PHREEQC (with PUT and GET
functions, CEL_NO?)?

Sincerely,
Boris van Breukelen

--
Dr. Boris M. van Breukelen
http://www.geo.vu.nl/users/breb/
phone 31-20-4447265 | fax. 31-20-4449940 | e-mail:
boris.van.breukelen@xxxxxxxxxx
Department of Hydro(geo)logy, Faculty of Earth and Life Sciences, Vrije
Universiteit
De Boelelaan 1085 (room C420), 1081 HV Amsterdam, the Netherlands
--

```

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