Section NR 811.57 - Softening The softening process selected shall be based upon the chemical qualities of the raw water, the desired finished water quality, the requirements for disposal of sludge or brine waste, the cost of plant and chemicals, and plant location. The applicability of the process chosen shall be demonstrated and discussed in detail in an engineering report. For very hard water, the sodium levels in cation exchange softened water shall be considered in selecting the treatment process. Following are requirements for specific processes:
(1) LIME-SODA PROCESS. The applicable design standards for lime-soda softening of groundwater are the same as those for conventional clarification-filtration surface water treatment plants, except that the minimum settling time may be reduced to 2 hours. Where softening is included in the surface water treatment process, the clarification criteria shall govern. In addition: Note: See s. NR 811.47 for criteria pertaining to softening with solids contact units and s. NR 811.49 for filtration requirements.
(a) Mechanical sludge removal equipment shall be provided in the sedimentation basin.(b) Determinations shall be made for the carbon dioxide content of the raw water. Note: When concentrations exceed 10 mg/l, the economics of removal by aeration as opposed to removal with lime should be considered. See s. NR 811.45 for aeration requirements.
(c) Equipment for stabilization of water softened by the lime-soda process is required. Note: See s. NR 811.58 for stabilization requirements.
(d) Provisions shall be included for proper disposal of softening sludges. Note: See s. NR 811.858 for design requirements.
(e) The use of excess lime may not be substituted for chlorination or any other approved method of disinfection. Note: See s. NR 811.48.
(2) CATION EXCHANGE PROCESS. Iron, manganese or a combination of both in the oxidized state or unoxidized state may cause resin fouling in the ion exchange process. Pretreatment shall be required whenever the content of iron, manganese, or a combination of both is one milligram per liter or more. In specific instances, the department may also require pretreatment when lesser amounts exist. All of the following requirements shall be satisfied unless the department determines sufficient justification for alternative operational parameters is provided by the vessel manufacturer or demonstrated through pilot testing under s. NR 811.44: (a) The units shall be of pressure or gravity type, of either an upflow or downflow design, using automatic or manual regeneration. Automatic regeneration is suggested for small plants. A manual override shall be provided for all automatic controls.(b) The design capacity for hardness removal may not exceed 20,000 grains per cubic foot when resin is regenerated with 0.3 pounds of salt per kilograin of hardness removed.(c) The depth of the exchange material may not be less than 3 feet.(d) The rate of softening may not exceed 7 gallons per square foot per minute, and the backwash rate shall be 6 to 8 gallons per square foot per minute.(e) The freeboard design shall be based upon the specific gravity of the media and the direction of water flow.(f) The bottoms, strainer systems, and support for the exchange materials shall conform to criteria provided for rapid rate gravity filters in s. NR 811.49.(g) Facilities shall be included for even distribution of the brine over the entire surface of both upflow or downflow units. Backwash, rinse, and air relief discharge pipes shall be installed in such a manner as to prevent back-siphonage.(h) A bypass shall be provided around softening units to produce a blended water of desirable hardness. Meters shall be installed on the bypass line and on each softener unit. An automatic proportioning or regulating device and shut-off valve shall be provided on the bypass line. The department may require treatment of the bypassed water to obtain acceptable levels of iron or manganese in the finished water.(i) Waters having 5 units or more of turbidity may not be applied directly to the cation exchange softener. Silica gel materials may not be used for waters having a pH above 8.4 or when iron is present. When the applied water contains a chlorine residual, the cation exchange material shall be a type that is not damaged by residual chlorine. Phenolic resin may not be used.(j) Brine storage tanks shall conform to the following requirements: 1. The wet storage tank shall be designed to hold at least 1.5 times the volume of salt delivered to permit refill before the tank is completely empty. The volume of both salt and brine storage to be provided depends upon the size of the plant, the proximity and assuredness of the salt source, and the method of delivery.2. It shall be isolated from possible sources of contamination.3. It shall be properly covered and equipped with manholes having overlapping watertight covers to prevent entry of surface runoff where applicable.4. Overflows and vents shall be designed in accordance with s. NR 811.64 (4) and (8), respectively, where applicable.5. The water for filling the tank shall be distributed over the entire surface of the tank by pipes at least 2 pipe diameters above the maximum liquid level in the tank or be protected from back-siphonage.6. The underdrain collection system shall be covered with a screen or perforated plate to allow brine but not salt to pass through.7. A sampling tap shall be provided on the brine discharge line in order that the concentration of brine can be determined. A suitable means for measuring the volume of brine used for regeneration shall be provided.8. Pipes and contact materials shall be resistant to the aggressiveness of salt. Steel and concrete shall be coated with a non-leaching protective coating that is compatible with salt and brine and is certified by ANSI/NSF standard 61, dated March 15, 2022, which is incorporated by reference. Note: A copy of ANSI/NSF standard 61 dated March 15, 2022 is available for inspection at the Legislative Reference Bureau and may be obtained for personal use from NSF International, https://www.nsf.org.
9. Bagged salt and dry bulk salt storage shall be enclosed and separated from other operating areas to prevent damage to equipment.(k) The requirements for brine wastes are found in s. NR 811.854.(l) Smooth-end sampling taps shall be provided for control purposes. Taps shall be located on each raw water source, each treatment unit influent and each treatment unit effluent. Testing equipment shall be provided to adequately control the treatment process at all plants.(m) Water from ion exchange treatment plants shall be stabilized as required in s. NR 811.58 (4), except where it can be shown that the treated water will be non-corrosive.Wis. Admin. Code Department of Natural Resources NR 811.57
CR 09-073: cr. Register November 2010 No. 659, eff. 12-1-10.Amended by, CR 22-074: am. (2) (intro.), (j) 3., 4., cr. (2) (j) 8., 9. Register January 2024 No. 817, eff. 2/1/2024