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2 Geochemical Modeling <br />To evaluate the possible treatment options, several additives were evaluated using an <br />equilibrium geochemical reaction model, PHREEQC, to determine their effectiveness in <br />adjusting the pH of the ponded water. The pH of the ponded water is approximately 12.0 <br />to 123 and is the primary environmental issue for wildlife or groundwater posed by the <br />pond. The geochemical modeling results provide an estimate of the effectiveness of each <br />amendment and quantity required to adjust the pH of the C-Pit water. Model results can <br />also be used to develop a treatment plan and estimate the approximate cost of treatment <br />for bonding purposes. <br />2.1 Modellnput <br />Evaluation of the effectiveness of the additives in adjusting the pH of the ponded water <br />was performed using PHREEQC Version 2.8. PHREEQC is a computer code that <br />models the geochemical mixing reaction between the C-Pit water and a reactive <br />amendment to predict the quantity of additive required to adjust the pH of the ponded <br />water. Comparison of the PHREEQC results for various amendments allows selection of <br />an effective additive. Once the amendment is selected, the conceptual design and cost of <br />a treatment remedy can be evaluated. <br />PHREEQC input includes the chemical composition of the C-Pit water and the additive. <br />The chemical composition of C-Pit water used in the model was obtained from a <br />synthetic precipitation leaching procedure (SPLP) analysis of CKD presented in Banks <br />and Gesso (1999). The whole water analysis performed by the Colorado Division of <br />Mines and Geology (DMG) for a sample collected on June 24, 2004 was incomplete and <br />could not be used. Use of the SPLP leachate composition provides a likely worst case <br />analysis of the quantity of amendment needed to adjust the pH. <br />The additive compositions used in the model were based on their stoichiometric formulas <br />(e.g., sulfuric acid as H2SOn). Five amendments were evaluated to determine their <br />effectiveness in adjusting the pH of the C-Pit water to a pH of approximately 8. <br />Additives evaluated included sulfuric acid (H2SOa), hydrochloric acid (HCl), carbon <br />~ Parkhurst, D. L. and C. A. J. Appelo, 1999, User's Guide to PHREEQC (Version 2) - A Computer <br />Program for Specia[ion, Balch-Reaction, One-Dimensional Transport, and Inverse Geochemical <br />Calculations, U. S. Geological Survey Water-Resources Investigations Report 99-4259, 326 pp. <br />CEMEX Water Treatment Plan 2 Revision 0 <br />