Virginia Administrative Code › Title 12 - HEALTH › Agency 5 - DEPARTMENT OF HEALTH › Chapter 590 - WATERWORKS REGULATIONS › Section 12VAC5-590-900 - Cation exchange softening

Current through Register Vol. 40, No. 24, July 15, 2024
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.
Statutory Authority: §§
											32.1-12
					 and
					 32.1-170 of the Code
					 of Virginia.