Dr. Parkhurst I emailed you earlier today with a question which I subsequently figured out the answer to (message below). I now know I should have been using the incremental reaction step. I tried to recall my earlier message but just in case it gets to you I wanted to let you know I was no longer in need of a response. Thank-you, Cheryl Ross -----Original Message----- From: Ross, Cheryl Sent: Thursday, March 08, 2001 11:01 AM To: 'dlpark@xxxxxxxx' In-Reply-To: <BE020C49D751D3119E0B009027305015010A657C@xxxxxxxxxxxxxxxxxxx> Subject: Pyrite Oxidation Phreeqc Question Dr. Parkhurst, I was hoping you might be able to provide some insight for a warning message I am getting running a pyrite oxidation simulation. I am modeling injecting oxygenated water into a basalt aquifer containing 0.1% pyrite to simulate what may occur during aquifer storage and recovery operations. For my initial simulation I have not included possible precipitation of ferrihydrite. There is no iron in my initial solution so the only source of iron is what is released due to the oxidation of pyrite. At the point in the simulation where iron concentrations plateau as oxygen is depleted I get the following warning: WARNING: Element Fe has negative moles in solution, -2.943717e-005. Erroneous mole balance occurs as moles are added to produce zero moles. Caused by KINETICS or REACTION. May be due to large time steps in early part of KINETICS simulation. Using solution 2. Richland Water (9/25/00) Using kinetics 2. Kinetics defined in simulation 2. The final iron concentration in solution however is equal to the total amount of pyrite that has dissolved during the simulation as would be expected. Since I have no reactions that would remove iron, I'm not sure how I could have negative moles in solution. I have tried decreasing my time step but this does not seem to help. Any help would be greatly appreciated. Cheryl Ross _____________________________ Cheryl Ross, M.Sc. Hydrogeochemist Golder Associates Inc. 18300 NE Union Hill Rd., Suite 200 Redmond, WA 98052 Office: 425-883-0777 Fax: 425-882-5498
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