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3.1 Option 1 - pH Adjustment Using Carbon Dioxide <br />Option 1 is developed to treat the approximately 35 million gallons of water currently <br />ponded in C-Pit. Option 1 will only be implemented if CEMEX is not successful in <br />dewatering the pond to its smallest practical volume by December 1, 2005. pH <br />adjustment using carbon dioxide was selected minimize the need to manage and work <br />with liquid acids which are typically classified as a hazardous material, thus reducing <br />worker health and safety concerns. Carbon dioxide treatment of the large volume <br />(approximately 35 million gallons) of water presently in C-Pit also provides ahigh-end <br />estimate of a safe and effective, but costly treatment alternative for bonding purposes. <br />The chemical process that occurs using carbon dioxide to reduce the pH of alkaline water <br />involves the dissolution of COZ liquid or gas in water to form carbonic acid (HZCO3), <br />followed by a subsequent series of dissociation reactions to produce H' ions. The H' <br />ions in turn reduce the water pH. An appealing feature of COz is that, in practice, it will <br />not lower the pH of the water below 7. The reaction mechanism is shown below. <br />COZ + HzO -. HZCO3 <br />HzCO3 -• H' + HCOa <br />HCO3- -~ H~ + CO3- <br />The pH adjustment system selected for the Option 1 conceptual design is manufactured <br />by Digital Analysis Corporation (DAC). DAC has been manufacturing pH adjustment <br />systems for over 15 years. DAC provides a complete line of pH adjustment systems that <br />can treat flows ranging from 5 to 1,000 gpm. These systems are marketed under severa] <br />product names, including pHase, batchTreat, and labTreat, and can be used with either <br />carbon dioxide or liquid acids. The labTreat system, which is capable of treating up to <br />200 gpm, was selected for the conceptual design and cost estimate for Option 1. Water <br />treated using this option will be used to support plant operations or discharged in an <br />appropriate manner. <br />The capital and operating costs to implement a labTreat system is estimated at <br />approximately $150,000. These costs include the labTreat system ($100,000), carbon <br />dioxide storage tank and equipment ($15,000), carbon dioxide ($27,000), and <br />miscellaneous equipment and materials ($8,000). The labTreat system was only selected <br />to illustrate a conceptual design and estimate costs for Option 1. Information regarding <br />CEMEX Wa[er Treatment Plan ( Revision 0 <br />