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Dear David,
	Thank you for your response and offer to look at the file. This file
contains data from the most upstream site (solution 1) and the most
downstream site (solution 2). I thank you for any assistance you can give
me. I realize WATEQ4F and PHREEQC databases do not contain Cr. I haven't
decided what to do about Cr yet but I left it in the file anyway. The only
harm it seems to cause is that I get a warning message telling me it is not
found in the database.
	Jim asked why I chose inverse modeling instead of solution/solubility. As
I told him, results of the inverse modeling examples in the PHREEQC manual
were easier for me (a biology background not a chemistry one) to interpret
and understand in relation to the questions I am trying to answer. If
another model is better suited to identifying precipitation/dissolution of
metals, or will give me the same information in a different way, I am more
than willing to listen to your advice. In fact, I have been looking at the
solution species results, but I am not sure how to take the output
(molality, activity, saturation indices and solubility constants) and say,
for example, Cd precipitates at these sites in the river, Zn precipitates
at these sites, etc. 
Thank you again!

At 11:47 AM 3/13/01 -0800, you wrote:
>I can't tell what is going on, but my first guess is that you've got too
>many phases. Though not stated, the program can only handle about 30
>possible reactants in INVERSE_MODELING. However, practically, the limit is
>much lower, somewhere between 10 and 20, probably.
>If you send me the input file, I'll take a look.
>David Parkhurst (dlpark@xxxxxxxx)
>U.S. Geological Survey
>Box 25046, MS 413
>Denver Federal Center
>Denver, CO 80225
>                    James W Ball
>                                         To:     rebecca evans
>                    03/13/01 09:17       cc:     David L
In-Reply-To: <OFAF551796.7CD0923A-ON87256A0E.006C5339@xxxxxxxx>
>                    AM                   Subject:     Re: PHREEQC(Document
link: David L Parkhurst)         
>Dear Rebecca,
>Thanks for your email describing problems you are experiencing with the
>phreeqc program. Unfortunately, although you have chosen the appropriate
>phreeqc database (wateq4f) based on your list of aqueous components, I am
>most likely not the person that can help you the most with your
>difficulties. The person I go to with my phreeqc problems is David
>Parkhurst, the main author of the phreeqc series of geochemical codes. I am
>cc'ing him your attached email in the hope he can help you. (David, can you
>help?). Just as an aside, based on your statement of your investigation I'm
>curious why you chose inverse modeling rather than just speciation/
>solubility calculations.
>On another subject, I noticed one of the metals on your list is Cr. Since I
>am presently developing a Cr section to the wateq4f model I wonder what
>your sources are for thermodynamic data and reactions for Cr?
>I wish you success in getting your modeling problems resolved. Please let
>me know if you think I can assist you further.
>James W Ball
>3215 Marine Street, Suite E-127
>Boulder, CO 80303-1066
>voice:       303-541-3035
>fax:           303-447-2505
>                    rebecca evans
>                    <evansre@xxxx        To:     jwball@xxxxxxxx
>                    l.uc.edu>            cc:
>                                         Subject:
>                    03/12/2001
>                    06:51 PM
>Dear Mr. Ball,
>           I am a graduate student working on the Little Miami River in
>Ohio. My work
>involves studying the association between water quality, water chemistry
>and bioaccumulation in benthic algae. My committee suggested I use a
>chemical speciation model to predict trace metal dissolution/precipitation
>as a lead in to developing hypotheses about what metals I might expect to
>accumulate and at what sites in the river.
>Here's what I have:
>Temp., pH, Oxygen, Total P, Al, Ca, Cd, Cl, Cr, Cu, Fe, K, Mg, Mn, Na, Se,
>Si, SO4, and Zn at eleven sites over the length of 105 miles.
>           I downloaded PHREEQC along with the WATEQ4f database. I have
>been trying
>to run inverse modeling (I chose this one because it seemed to best fit
>what I am trying to do). The program gets through the solution species and
>starts inverse modeling. It does not give me any error messages and does
>not appear to be "locked up." The log file is reported as "in use" when I
>try to open it in MS Word. However, after as long as 4 hours (when I stop
>the program by hitting the "done" icon) all that shows up in the log file
>and the output file is the solution species data for each site (currently I
>have only two sites entered until I figure out how to operate this
>correctly), and the line: "beginning of inverse modeling calcualtions."
>           I'm pretty sure the solutions balance and there are no input
>because initially I had those problems and the PHREEQC program notified me
>with error messages. However, now it seems to be working, I'm just not sure
>why I am not getting a series of results in the inverse modeling part.
>           My questions are these: 1) Is the program working and just
>something I
>have to let run for more than four hours? 2) If not, any suggestions? 3)
>Would another PHREEQC model be better for the questions I am trying to
>           I appreciate any input you can give me.
>Thank You!
>Becky Evans
temp	18.230
units	mg/L
O(0)	11.8
pH	7.848
Amm	.031
N(+5)	3.105
P	.340
Al	.112
Cd	.007
Cr	.023
Cu	.025
Fe	.044
Mn	.017
Zn	.089
Se	.073
Si	2.601
Cl	32.0
S(6)	69.2
Ca	79.609
Mg	39.695
Na	6.201
K	2.842
Alkalinity	234
temp	21.780
-units	mg/L
O(0)	9.517
pH	8.040	
Amm	.09
N(+5)	1.260
P	.543
Al	.392
Cd	.007
Cr	.020
Cu	.027
Fe	.203
Mn	.027
Zn	.069
Se	.058
Si	3.347
Cl	49.4
S(6)	38.5
Ca	66.149
Mg	22.406
Na	13.090
K	4.899
Alkalinity	180
-solutions	1 2
-uncertainty	0.10

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