12 Va. Admin. Code § 5-590-900

Current through Register Vol. 40, No. 22, June 17, 2024

Section 12VAC5-590-900 - Cation exchange softening

A. The softening design selected shall be based upon the mineral qualities of the source water and the desired finished water quality in conjunction with requirements for disposal of sludge or brine water, cost of the plant, cost of the chemicals, and the plant location.

B. Iron, manganese, or a combination of the two, in the oxidized state or unoxidized state, shall not exceed 0.3 mg/L in the water applied to the cation exchange material.

C. The units shall be of pressure or gravity type of either an upflow or downflow design, using automatic or manual regeneration.

D. The design capacity for hardness removal shall not exceed 20,000 grains/ft³ when the resin is regenerated with 0.3 pounds of salt per kilograin of hardness removed.

E. The depth of the cation exchange material shall not be less than three feet.

F. The hydraulic loading rate should not exceed seven gpm/ft² and the backwash rate should be six to eight gpm/ft. ²

G. The freeboard shall depend upon the specific gravity of the media and the direction of the water flow.

H. The bottoms, strainer systems, and support for the cation exchange material shall conform to criteria provided for rapid rate gravity filters. See also 12VAC5-590-874.

I. Facilities shall be included for even distribution of brine over the entire surface of both upflow and downflow units. Backwash, rinse, and air relief discharge pipes shall be installed in a manner as to prevent any possibility of backsiphonage.

J. A bypass shall be provided around the cation exchange units to produce a blended water of desirable hardness. Meters shall be installed to measure total water delivered to the distribution system and on each softener unit. An automatic proportioning or regulating device and shutoff valve should be provided on the bypass line. In some installations, it may be necessary to treat the bypassed water to obtain acceptable levels of iron and manganese in the finished water.

K. Waters having turbidity of five NTUs or more shall not be applied directly to the cation exchange softener. Silica gel materials should be used for water having a pH above 8.4 and should not be used 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 the chlorine residual. Phenolic resin shall not be used.

L. Sampling taps shall be provided for the collection of representative samples for both bacteriological and chemical analyses. The taps shall be located to provide for sampling of the softener influent, softener effluent, and the blended water. The sampling taps for the blended water shall be at least 20 ft downstream from the point of blending.

M. Brine measuring or salt-dissolving tanks and wet salt storage facilities shall be covered. The makeup water inlet shall have a free fall discharge of two pipe diameters but not less than two inches above the maximum liquid level of the unit or be protected from backsiphonage. Water for filling the tank should be distributed over the entire surface by pipes above the maximum brine level in the tank. The salt shall be supported on graduated layers of gravel under which is a suitable means of collecting the brine. Wet salt storage basins must be equipped with manhole or hatchway openings having raised curbs and watertight covers with overhanging edges similar to those required for finished water reservoirs. Overflows, where provided, shall be turned down, have a proper free fall discharge and be protected with noncorrodible screens or self-closing flap valves.

N. Wet salt storage basins shall have sufficient capacity to store at least a 30-day operating supply.

O. Stabilization of the finished water for corrosion control shall be considered.

P. Suitable disposal must be provided for the brine waste.

Q. Pipes and contact materials shall be resistant to the aggressiveness of the salt.

12 Va. Admin. Code § 5-590-900

Derived from VR355-18-009.06 § 3.27, eff. August 1, 1991; Amended, Virginia Register Volume 37, Issue 20, eff. 6/23/2021.

Statutory Authority: §§ 32.1-12 and 32.1-170 of the Code of Virginia.