SECTION 252:626-9-10. Softening

  Select the softening process based on mineral qualities of raw water, desired finished water quality, requirements for disposal of residuals or brine waste, cost of plant, cost of chemicals and plant location.

(1)   Lime or lime-soda process.

(A)   Residuals removal. Provide mechanical residuals removal equipment in the sedimentation basin.

(B)   Rapid mix. In addition to the rapid mix requirements of OAC 252:626-9-8(a)(1), the design of a softening plant must allow for the recycling of previously formed calcium carbonate crystals (lime residuals) to the rapid mix basin.

(C)   Filtration. In addition to the requirements for filter design as set forth in OAC 252:626-9-9, equip filters with a mechanical surface sweep to assist filter backwashing.

(D)   Stabilization. Equipment for stabilization of water softened by the lime or lime-soda process is required.

(2)   Cation exchange process.

(A)   Pre-treatment. Pre-treatment is required when the content of iron, manganese, or a combination of the two, is 1 mg/l or more.

(B)   Design. Automatic regeneration based on volume of water softened is required unless manual regeneration can be justified and is approved by the DEQ. Provide a manual override on all automatic controls.

(C)   Exchange capacity. Do not exceed the resin manufacturer's recommended design capacity for hardness removal and regeneration.

(D)   Depth of resin. The depth of the exchange resin must be at least 3 feet.

(E)   Flow rates. Do not exceed 7 gal/min/ft flow rate for softening of bed area. Provide for backwash flow rate of 6 B 8 gal/min/ft of bed area.

(F)   Freeboard. The freeboard will depend upon the specific gravity of the resin and the direction of water flow. Washwater collector shall be twenty-four inches (24") above the top of the resin on downflow units.

(G)   Underdrains and supporting gravel. Design the bottoms, strainer systems and support for the exchange resin to conform to criteria provided for rapid rate gravity filters.

(H)   Brine distribution. Provide for even distribution of the brine over the entire surface of both upflow and downflow units.

(I)    Blending configuration. Provide piping around softening units to produce blended water of desirable hardness. Provide an automatic proportioning or regulating device and shut-off valve on each line. Install totalizing meters on the bypass line and on each softener unit. Treatment of the water will be required when iron and/or manganese levels in the blended water exceed the levels for secondary standards found in 40 CFR, Part 143.

(J)   Additional limitations. Do not apply water with turbidity of 5 NTU or more directly to the cation exchange softener. Do not use silica gel resins for waters having a pH above 8.4 or containing less than 6 mg/l of silica. When the applied water contains a chlorine residual, the cation exchange resin must be a type that is not damaged by chlorine.

(K)   Sampling taps. Provide smooth-nose sampling taps for the collection of representative samples. Locate the taps to provide sampling of the softener influent, effluent, and blended water. Install sampling taps for the blended water at least 20 feet downstream from the point of blending.

(L)   Brine and salt storage tanks. Cover brine measuring or salt dissolving tanks and wet salt storage facilities and construct them of corrosion-resistant material. The make-up water inlet must have a free fall discharge of two pipe diameters above the maximum liquid level of the unit or obtain DEQ approval of other methods of protection from back-siphonage. Support the salt on graduated layers of gravel with a suitable means of collecting the brine. Equip wet salt storage basins with manhole or hatchway openings having raised curbs and watertight covers with overhanging edges similar to those required for finished water reservoirs. Overflow, where provided, must have a free fall discharge and terminate at an approved brine waste disposal facility.

(M)   Salt storage capacity. Design salt storage large enough to accommodate a 30-day supply.

(N)   Stabilization. Provide stabilization for corrosion control.

(O)   Waste disposal. Provide a DEQ approved disposal plan for brine waste. If disposal is to an impoundment, then the impoundment must be lined with a synthetic liner in accordance with the requirements contained in OAC 252:656.

(P)   Construction material. Pipes and contact materials must be resistant to the aggressiveness of salt.

(Q)   Housing. Enclose and separate salt storage from other operating areas.

(3)    New technology. Other forms of softening not covered in this subchapter shall be considered for approval under the conditions of OAC 252:626-3-8 until data from a sufficient number of installations demonstrate their ability to perform satisfactorily.

(4)   Water quality test equipment. Provide test equipment for pH, alkalinity and total hardness to determine treatment effectiveness.

[Source: Added at 18 Ok Reg 1612, eff 6-1-01; Amended at 25 Ok Reg 2304, eff 7-11-08]