> 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. Unfortuately, for gas reactions, PHREEQC is more like a batch reactor than a transport code. We have made some tentative efforts with a stagnant liquid and a diffusive gas, but we have not attempted a fully coupled gas and liquid transport model. The national labs programs (Lichtner, Steefel, others), MIN3P from Waterloo (actually Mayer is at the Univ of British Columbia now I think), and perhaps Hydrogeochem (I'm not sure about this one) address this class of problems. 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?)? I think in concept you could do this, but it would be messy. You would have to generate kinetic reactions (one for each gas) that remove or add a net number of moles for each cell. You would have to have some way of determining how a plausible formulation to redistribute the gas. The put and get functions are available to each cell, so you can pass information through these functions. Ideally, you would solve the diffusion equation to redistribute the gas, but that would be pretty unwieldy in Basic I think. The time scale of gas transport is so much faster than the liquid transport that time stepping gets to be a problem. You sound like you have some idea of how you would like to transport the gas, so maybe you have a reasonable simplification. The other complication is that you would have to do all this through kinetic reactions, so you would have to generate rates that transfer the right number of moles. In this case the rate should be the net amount of a gas to transfer to a cell divided by the time step. Sorry I don't have a good answer for you at this time. David David Parkhurst (dlpark@xxxxxxxx) U.S. Geological Survey Box 25046, MS 413 Denver Federal Center Denver, CO 80225 Project web page: https://wwwbrr.cr.usgs.gov/projects/GWC_coupled
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