Section 58.01.08.532 - DESIGN STANDARDS FOR SOFTENINGThe softening process selected must be based upon the mineral qualities of the raw water and the desired finished water quality in conjunction with requirements for disposal of sludge or brine waste (see Section 540), cost of plant, cost of chemicals, and plant location. Applicability of the process chosen must be demonstrated.
01.Lime or Lime-Soda Process. Rapid mix, flocculation, and sedimentation processes must meet the requirements of Section 520. In addition the following requirements must be met: a. When split treatment is used, an accurate means of measuring and splitting the flow must be provided.b. Rapid mix basins must provide not more than thirty (30) seconds detention time with adequate velocity gradients to keep the lime particles dispersed.c. Equipment for stabilization of water softened by the lime or lime-soda process is required, see Section 537.d. Mechanical sludge removal equipment will be provided in the sedimentation basin.e. Provisions must be included for proper disposal of softening sludges; see Section 540.f. The plant processes must be manually started following shut-down.02.Cation Exchange Process. a. Pre-treatment is required when the content of iron, manganese, or a combination of the two, is one milligram per liter (1 mg/L) or more.b. The units may be of pressure or gravity type, of either an upflow or downflow design. Automatic regeneration based on volume of water softened will be used unless manual regeneration is justified and is approved by the Department. A manual override will be provided on all automatic controls.c. Rate-of-flow controllers or the equivalent will be used to control the hydraulic loading of cation exchange units.d. The bottoms, strainer systems and support for the exchange resin will conform to the criteria provided for rapid rate gravity filters in Section 521.e. Backwash, rinse and air relief discharge pipes will be installed in such a manner as to prevent any possibility of back-siphonage.f. A bypass must be provided around softening units to produce a blended water of desirable hardness. Totalizing meters must be installed on the bypass line and on each softener unit. The bypass line must have a shutoff valve.g. When the applied water contains a chlorine residual, the cation exchange resin must be a type that is not damaged by residual chlorine.h. Smooth-nose sampling taps must be provided for the collection of representative samples. The taps will be located to provide for sampling of the softener influent, effluent, blended water, and on the brine tank discharge piping. The sampling taps for the blended water will be at least twenty (20) feet downstream from the point of blending. Petcocks are not acceptable as sampling taps.i. Brine and salt storage tanks must meet the following requirements:i. Salt dissolving or brine tanks and wet salt storage tanks must be covered and must be corrosion-resistant.ii. The make-up water inlet must be protected from back-siphonage.iii. Wet salt storage basins must be equipped with manholes or hatchways for access and for direct dumping of salt from truck or rail car. Openings must be provided with raised curbs and watertight covers having overlapping edges similar to those required for finished water reservoirs.iv. Overflows, where provided, must be protected with twenty-four (24) mesh or similar non-corrodible screens, and must terminate with either a turned downed bend having a proper free fall discharge or a self-closing flap valve.v. The salt will be supported on graduated layers of gravel placed over a brine collection system.vi. Alternative designs which are conducive to frequent cleaning of the wet salt storage tank may be considered.vii. An eductor may be used to transfer brine from the brine tank to the softeners. If a pump is used, a brine measuring tank or means of metering will be provided to obtain the proper dilution.j. Suitable disposal must be provided for brine waste; see Section 540. Where the volume of spent brine must be reduced, consideration may be given to using a part of the spent liquid concentrate for a subsequent regeneration.k. Pipes and contact materials must be resistant to the aggressiveness of salt. Plastic and red brass are acceptable piping materials. Steel and concrete must be coated with a non-leaching protective coating which is compatible with salt and brine.l. Bagged salt and dry bulk salt storage will be enclosed and separated from other operating areas in order to prevent damage to equipment.Idaho Admin. Code r. 58.01.08.532