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Re: phreeqc question

> My thesis involves modeling the sorption, gas phase partitioning, and
biodegradation of organics in a column.  I'm starting with benzene to make
simple.  Instead of calling benzene C6H6, I am calling it "benzene."  I
created something called "benzdp" which is the benzene daughter product,
product of a first-order biodegradation decay.  The database accepts the
entry of the two under solution species.  However, whenever I try to
the two in the database (Benzene = Benzdp, log_k -20 or with an equation
Benzene + H2O = Benzdp + H2O), the error says the elements aren't balanced.

Do you have any advice on this?

To connect them in SOLUTION_SPECIES would require aqueous equilibrium. You
don't really want to do this I don't think. You should leave them separate
and use KINETICS to transfer from the Benzene pool to the Benzdp pool as
you have done. (If you do want aqueous equilibria, you wouldn't define two
separate "elements", just 1 element with two species.)

> My second question involves the gas phase partitioning.  I want the
to move from cell to cell, each time encountering a new surface and gas
bubble to which it will partition (sorption is working fine this way).

You should be able to do this, although the gas phases do not move, which
is a limitation. Just looking at your kinetics file, it seems ok except for
the RATE definition.

40    rate = e^(-5.55e-5*6.3E8)#4.8day-1

"e" is interpreted as a variable that is initialized to zero, so I think
your rate is always zero.

"exp(-5.55e-5*6.3E8)" would be exponentiation. I think the following form
is probably closer to what you want for first-order decay.

10 benz = TOT("Benzene")
20 k = 4.8/(60*60*24)  # day-1 to sec-1
30 rate = benz*k       # mol/kgw/sec
40 moles = rate*TIME
50 SAVE moles


David Parkhurst (dlpark@xxxxxxxx)
U.S. Geological Survey
Box 25046, MS 413
Denver Federal Center
Denver, CO 80225

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