Virginia Administrative Code › Title 12 - HEALTH › Agency 5 - DEPARTMENT OF HEALTH › Chapter 590 - WATERWORKS REGULATIONS › Section 12VAC5-590-920 - Iron and manganese control

Current through Register Vol. 40, No. 24, July 15, 2024
A.
				Iron and manganese control, as used in this section, refers solely to treatment
				processes designed specifically for this purpose. The treatment process used
				will depend upon the character of the source water. The selection of one or
				more treatment processes shall meet specific local conditions as determined by
				engineering investigations, including chemical analyses of representative
				samples of water to be treated, and receive the approval of the department. The
				department may require that pilot studies be conducted.
B. Iron and manganese removal by oxidation
				and filtration.
1. Oxidation shall be
				accomplished by aeration or by chemicals, such as chlorine, potassium
				permanganate, sodium permanganate, or a combination thereof.
2. The design shall consider:
a. pH adjustment to promote rapid
				oxidation;
b. A pre-settling tank
				located ahead of the filters to remove oxidized iron and increase filter run
				times;
c. A manganese-oxide coating
				on the filter media, such as manganese greensand. The total depth of media
				shall not be less than 30 inches. Media shall have an effective size from 0.3
				to 0.35 mm and a uniformity coefficient of no more than 1.6. Following initial
				placement of the media, care shall be taken to remove fines by backwashing and
				skimming the surface; and
d. An
				anthracite cap layer over the manganese-oxide coated media having a depth of
				six to 18 inches.
3.
				Aeration shall be designed in accordance with
				12VAC5-590-910.
4. Flow proportional chemical feeders shall
				be provided, and the feed rate shall be adequately controlled by using feeders
				that are paced by water meters to prevent an over-dosage of chemical. A flow
				switch in place of a flow proportional feeder may be permissible.
5. Sample taps shall be provided before the
				application of the oxidant, immediately ahead of filtration, and at the filter
				effluent.
6. Pressure filters shall
				include provisions for:
a. Pressure gauges on
				the inlet and outlet pipes of each filter or a differential pressure gauge on
				each filter;
b. An easily readable
				meter or flow indicator on each battery of filters. A flow indicator is
				recommended for each filtering unit;
c. Filtration, backwashing, and
				filter-to-waste of each filter individually:
(1) Backwash water shall be evenly
				distributed in an adequate quantity to achieve at least a 30% media bed
				expansion during backwashing. The backwash rate shall be based on the
				media;
(2) The top of the backwash
				water collection trough shall be at least 18 inches above the media
				surface;
(3) An underdrain system
				to efficiently collect the filtered water and to distribute an adequate
				quantity of backwash water to achieve at least a 30% media bed expansion during
				backwashing;
d. Flow
				indicators and controls are located so that they are easily readable while
				operating the control valves;
e. An
				air release valve on the highest point of each filter;
f. An accessible manhole to facilitate
				inspections and repairs for filters greater than 36 inches in
				diameter;
g. A means to observe the
				wastewater during backwashing; and
h. Construction to prevent
				cross-connection.