Section 58.01.08.537 - DESIGN STANDARDS FOR STABILIZATIONWater that is unstable due either to natural causes or to subsequent treatment must be stabilized. The expected treated water quality will be evaluated to determine what, if any, treatment is necessary.
01.Carbon Dioxide Addition. a. Recarbonation basin design must provide the following:i. A total detention time of twenty (20) minutes.ii. A mixing compartment having a detention time of at least three (3) minutes.iii. A reaction compartment.iv. The mixing and reaction compartments will have a depth sufficient to provide a diffuser submergence of not less than seven and one-half (7.5) feet and no greater than the manufacturer's recommendation.b. Where liquid carbon dioxide is used, adequate precautions must be taken to prevent carbon dioxide from entering the plant from the recarbonation process.c. Recarbonation tanks must be located outside or be sealed and vented to the outside with adequate seals and adequate purge flow of air to ensure workers safety.d. Provisions must be made for draining the recarbonation basin and removing sludge.02.Phosphates. The feeding of phosphates may be used for sequestering calcium, for corrosion control, and in conjunction with alkali feed following ion exchange softening. a. Stock phosphate solution must be kept covered and disinfected by carrying approximately ten (10) mg/1 free chlorine residual unless the phosphate is not able to support bacterial growth and the phosphate is being fed from the covered shipping container. Phosphate solutions having a pH of two point zero (2.0) or less are exempted from this requirement.b. Satisfactory chlorine residuals must be maintained in the distribution system when phosphates are used.03.Split Treatment. Raw water may be blended with lime-softened water to partially stabilize the water prior to secondary clarification and filtration. Treatment plants designed to utilize split treatment must also contain facilities for further stabilization by other methods.04.Water Unstable Due to Biochemical Action in Distribution System. Unstable water resulting from the bacterial decomposition of organic matter in water (especially in dead end mains), the biochemical action within tubercles, and the reduction of sulfates to sulfides must be prevented by the maintenance of a free or combined chlorine residual throughout the distribution system.Idaho Admin. Code r. 58.01.08.537