Article 3. Processes and Devices [Repealed]
12VAC5-590-850. Appropriate treatment.
A. The design of water treatment facilities shall depend upon the evaluation of the nature and quality of the particular source water to be treated and the required quality of the finished water. Treatment process selection shall follow the requirements of 12VAC5-590-680.
B. The design of water treatment facilities shall address safety considerations as required in 12VAC5-590-560.
Statutory Authority
§§ 32.1-12 and 32.1-170 of the Code of Virginia.
Historical Notes
Derived from VR355-18-009.01 § 3.22, eff. August 1, 1991; amended, Virginia Register Volume 9, Issue 17, eff. June 23, 1993; Volume 37, Issue 20, eff. June 23, 2021.
12VAC5-590-860. Chemical application.
A. Plans and specifications shall be submitted for evaluation and approval, as required in Part I (12VAC5-590-200 through 12VAC5-590-220), and shall include:
1. Descriptions of feed equipment, including maximum and minimum feed ranges;
2. Location of feeders, piping layout, and points of application;
3. Chemical storage and handling facilities;
4. Specifications for chemicals to be used;
5. Operating and control features; and
6. Descriptions of testing equipment and procedures.
B. Chemicals shall be applied to the water at such points and by such means as to:
1. Assure maximum efficiency of treatment;
2. Provide maximum protection to the consumer;
3. Provide maximum safety to operators;
4. Assure satisfactory mixing of the chemicals with the water;
5. Provide maximum flexibility of operation through various points of application, when appropriate;
6. Prevent backflow or backsiphonage between multiple points of feed through common manifolds; and
7. Provide for the application of pH-affecting chemicals to the source water before the addition of the coagulant in turbidity removal processes.
C. Feed equipment.
1. Where chemical feed is necessary for the treatment of the source water, such as chlorination, coagulation, or other essential processes, a standby feeder or combination of feeders shall be available to provide the required chemical dose with the largest feeder out of service.
2. Feeders shall be of such design and capacity to meet the following requirements:
a. Feeders shall be able to supply the necessary amounts of chemical at an accurate rate throughout the range of feed at all times.
b. Proportioning of chemical feed to the rate of flow shall be provided where the water flow is not constant or where specifically required by the department.
c. Positive displacement type solution feed pumps, or gravity feed through rotameters, shall be used to feed liquid chemicals, but should not normally be used to feed chemical slurries.
d. Chemical contact materials and surfaces shall be resistant to the aggressiveness of the chemical solution.
e. Dry chemical feeders shall:
(1) Measure chemicals volumetrically or gravimetrically;
(2) Provide effective solution of the chemical in the solution pot;
(3) Provide gravity feed from solution pots; and
(4) Completely enclose chemicals to prevent emission of dust to the room.
f. No direct connection shall exist between any sewer and a drain or overflow from the feeder or solution chamber or tank.
g. A separate chemical waste tank should be considered.
3. Chemical feed equipment:
a. Shall be located near points of application to minimize length of feed lines;
b. Shall be readily accessible for servicing and repair, and observation of operation; and
c. Shall be located within a protective curbing so that chemicals resulting from equipment failure, spillage, or accidental drainage shall not enter the water in conduits or treatment or storage basins.
4. Control.
a. Feeders shall be capable of both manual and automatic control with the automatic control reverting to manual control as necessary;
b. Feeders shall be manually started following shutdown, unless otherwise approved by the department; and
c. Automatic chemical dose controls with residual analyzers shall provide alarms for critical values and shall include indicating and recording equipment.
5. Solution tanks. All solution tanks shall be manufactured of materials suitable for food contact or that meet the requirements of 12VAC5-590-810.
a. Means shall be provided to maintain uniform strength of solution, consistent with the nature of the chemical solution. Continuous agitation shall be provided to maintain slurries in suspension.
b. Solution tanks shall be of sufficient number and capacity to assure continuous chemical application during tank servicing, and the access openings shall be curbed and fitted with tight covers.
c. Each tank exceeding 30 gallons in capacity or fixed in place shall be provided with a drain unless other means of dewatering the tank are provided.
(1) Direct connection between any tank or drain and a sewer is prohibited.
(2) All drains shall terminate at least two pipe diameters, but not less than two inches, above the rim of the receiving sump, conduit, or waste receptacle.
d. Means shall be provided to indicate the solution level in the tank.
e. Process water shall enter the tank above the rim at a distance of two pipe diameters but not less than two inches.
f. Chemical solutions shall be kept covered.
g. Buried or subsurface chemical storage or solution tanks are prohibited.
h. Overflow pipes, when provided, shall:
(1) Be turned downward, and when located outside, be provided with an appropriately sized screened end to prevent entry of insects and small animals;
(2) Have free discharge;
(3) Be located where noticeable; and
(4) Be directed so as not to contaminate the water or be a hazard to operating personnel.
6. Weighing scales.
a. Shall be provided for weighing cylinders at all water treatment plants utilizing chlorine gas; for large water treatment plants, indicating and recording type are desirable;
b. Shall be provided for fluorosilicic acid feed systems in conjunction with a loss-of-weight recorder;
c. Shall be considered for volumetric dry chemical feeders; and
d. Shall be accurate to measure increments of 0.5% of load.
7. Feed lines.
a. Shall be as short as possible in length of run and be:
(1) Of durable, corrosion-resistant material;
(2) Easily accessible throughout the entire length;
(3) Protected against freezing; and
(4) Readily cleanable;
b. Shall slope upward from chemical source to feeder, when conveying gases.
c. Shall introduce corrosive chemicals in a manner as to minimize potential for corrosion.
d. Shall be designed consistent with scale forming solids depositing properties of the water, chemical solution, or mixture conveyed.
e. Shall not carry chlorine gas beyond the chlorine feeder room unless the chlorine is under vacuum.
f. Shall be designed so that liquid alum does not mix with water before the point of application.
8. Process water.
a. Water used for dissolving dry chemicals, diluting liquid chemicals, or operating chemical feeders shall be:
(1) From a safe, approved source;
(2) Protected from contamination by appropriate means;
(3) Ample in supply and adequate in pressure;
(4) Provided with means for measurement when preparing specific solution concentrations by dilution; and
(5) Properly treated for hardness when necessary.
b. Where a booster pump is required, a spare pump shall be provided.
c. Backflow prevention shall be achieved by appropriate means such as:
(1) An air gap between the fill pipe and overflow rim of the solution or dissolving tank, and equivalent to two pipe diameters but not less than two inches;
(2) An approved reduced pressure zone backflow preventer, consistent with the degree of hazard, aggressiveness of chemical solution, back pressure sustained, location, and available means for maintaining and testing the device; or
(3) A satisfactory vacuum relief device.
D. Chemicals.
1. Storage.
a. Space shall be provided where at least 30 days of chemical supply can be stored, based on the average dose and average annual water treatment plant flow rate. Storage shall be at a location that is convenient for efficient handling and safety. Lesser storage capacity may be approved if the owner can demonstrate that the local suppliers or other conditions will provide an uninterrupted source of chemicals.
b. Cylinders of chlorine gas shall be:
(1) Isolated from operating areas;
(2) Restrained in position to prevent upset; and
(3) Stored in rooms separate from ammonia storage.
c. Liquid chemical storage tanks shall:
(1) Have a liquid level indicator; and
(2) Have an overflow and a receiving basin or drain capable of receiving accidental spills or overflows.
d. Special precautions shall be taken with sodium chlorite to eliminate any danger of explosion.
e. Activated carbon. The following special precautions shall be taken in areas where activated carbon is stored, handled, and fed.
(1) Isolated, cool, and dry areas free from sources of ignition shall be provided for activated carbon storage;
(2) Electrical equipment, devices, and materials shall comply with applicable codes;
(3) Ventilation in areas associated with the storage, handling, and feeding of activated carbon shall be localized so as not to cause dust or material to be drawn into other areas; and
(4) Activated carbon shall not be stored with strong oxidants such as ozone, liquid chlorine (i.e., compressed chlorine gas), and permanganate.
f. Chemicals shall be stored in covered or unopened shipping containers, unless the chemical is transferred into an approved covered storage unit.
g. Solution storage or day tanks supplying feeders directly should have sufficient capacity for one day of operation.
h. Acid storage tanks shall be vented to the outside atmosphere, but not through vents in common with day tanks.
2. Handling.
a. Provisions shall be made for measuring quantities of chemicals used to prepare feed solutions.
b. Storage tanks and pipelines for liquid chemicals shall be specific to the chemicals and not for alternates.
c. Chemicals that are incompatible shall not be fed, stored, or handled together.
d. Provisions shall be made for the proper transfer of dry chemicals from shipping containers to storage bins or hoppers to mitigate the quantity of dust that may enter the room in which the equipment is installed. Control shall be provided by use of:
(1) Vacuum pneumatic equipment or closed conveyor systems;
(2) Facilities for emptying shipping containers in special enclosures; or
(3) Exhaust fans and dust filters that put the hoppers or bins under negative pressure.
e. Precautions shall be taken with electrical equipment to prevent explosions and other hazards.
f. Acids shall:
(1) Be kept in closed, acid-resistant shipping containers or storage units; and
(2) Not be handled in open vessels, but should be pumped in undiluted form from original containers, through a suitable hose, to the point of treatment or to a covered day tank.
g. Carts, elevators, and other appropriate means shall be provided for lifting chemical containers to mitigate excessive lifting by operators.
h. Provisions shall be made for disposing of empty containers by an approved procedure that will mitigate exposure to the chemical.
E. Housing.
1. Structures, rooms, and areas accommodating chemical feed equipment shall provide convenient access for servicing, repair, and observation of operation.
2. Floor surfaces shall be smooth and impervious, slip-proof, and well drained.
3. Open basins, tanks, and conduits shall be protected from chemical spills or accidental drainage.
F. Operator safety. Safety provisions shall protect people at the waterworks from chemical exposures in accordance with VOSH laws and regulations.
1. Gases from feeders, storage, and equipment exhausts shall be conveyed to the outside atmosphere, above grade, and remote from air intakes.
2. See 12VAC5-590-1000 and 12VAC5-590-1001 for special provisions for handling and storing chlorine.
3. A plastic bottle of hydrochloric acid (muriatic acid in commercial form) shall be available for ammonia leak detection where ammonia gas is used or stored.
4. At least one pair of rubber gloves with long gauntlets, a dust respirator of a type that complies with VOSH laws and regulations for toxic dusts, and an apron or other protective clothing shall be provided for each operator in any shift who will handle dry chemicals.
5. Facilities such as emergency eye wash and showers shall be provided for washing of the face, gloves, and protective equipment.
Statutory Authority
§§ 32.1-12 and 32.1-170 of the Code of Virginia.
Historical Notes
Derived from VR355-18-009.02 § 3.23, eff. August 1, 1991; amended, Virginia Register Volume 9, Issue 17, eff. June 23, 1993; Volume 37, Issue 20, eff. June 23, 2021.
12VAC5-590-865. Conventional filtration treatment.
A. Conventional filtration treatment is generally used for surface water sources. It is defined as a series of four processes: coagulation, flocculation, sedimentation, and filtration. The specific design parameters shall consider the water supply characteristics and variability in quality due to seasonal and climatic events.
B. Conventional filtration treatment plants shall provide staged, multiple treatment process units to allow individual units to be taken out of service without disrupting operation.
C. The department may require presedimentation of waters containing high turbidity or organics (as measured by TOC).
1. Presedimentation basins utilizing a coagulant feed shall have hoppered bottoms or shall be provided with continuous sludge removal equipment. The minimum hydraulic detention time shall be three hours. The department may require greater detention times depending on the source water quality and the level of pretreatment required.
2. Presedimentation basins without coagulant feed shall provide a minimum hydraulic detention time of 24 hours. The design shall address future needs for solids removal and handling.
3. Incoming water shall be dispersed across the full width of the line of travel as quickly as possible. Short circuiting shall be minimized. The department may require baffling on large basins.
4. Provisions for bypassing presedimentation basins shall be provided.
5. Surface runoff shall be prevented from entering presedimentation basins or reservoirs.
6. Dikes shall be structurally sound and protected against wind action and erosion.
Statutory Authority
§§ 32.1-12 and 32.1-170 of the Code of Virginia.
Historical Notes
Derived from Virginia Register Volume 37, Issue 20, eff. June 23, 2021.
12VAC5-590-870. (Repealed.)
Historical Notes
Derived from VR355-18-009.03 § 3.24, eff. August 1, 1991; amended, Virginia Register Volume 9, Issue 17, eff. June 23, 1993; repealed, Virginia Register Volume 37, Issue 20, eff. June 23, 2021.
12VAC5-590-871. Coagulation and flocculation.
A. Rapid mixing is the rapid dispersion of chemicals throughout the water to be treated, usually by violent agitation, to promote coagulation.
1. Rapid mix basins or inline static mixers shall be provided.
2. Basins shall be equipped with mechanical mixing devices. Other arrangements, such as baffling, may be acceptable under special conditions and only when approved by the department. Where mechanical mixing devices are utilized, duplicate units or spare mixing equipment shall be provided.
3. Rapid mix basins with mechanical mixers should be based upon the mean temporal velocity gradient "G" (expressed as units of seconds-1). The owner's engineer shall submit the basis for the selected velocity gradient considering the chemicals to be added and water temperature. Typical values for G and T are:
TABLE 871.1 Rapid Mix Basin GT Values | |
T (seconds) | G (seconds-1) |
20 | 1,000 |
30 | 900 |
40 | 700 |
60 | 600 |
a. The point of application of the coagulant shall be at the point of maximum mixing intensity;
b. The physical configuration of the mixing basin shall be designed to eliminate vortexing; and
c. Mechanical mixers should be designed to allow speed variation with a highest speed of at least three times the lowest speed.
B. Flocculation mixing is the agitation of treated water at low velocity gradients for sufficient time to agglomerate coagulated particles.
1. Basin inlet and outlet design shall prevent short circuiting and destruction of floc. A drain and overflow shall be provided. Multiple units shall be provided for continuous operability, and each basin shall be designed so that individual basins may be isolated without disrupting plant operation. Basins shall be arranged to allow for either series or parallel operation.
2. Design parameters:
a. The minimum detention time shall be 30 minutes for water treatment plants employing rapid rate gravity filters, and 20 minutes for water treatment plants using high rate gravity filters. Basin flow-through velocity should not be less than 0.5 ft/min or greater than 1.5 ft/min.
b. The design of the flocculation units shall be based upon the value of GT, which is ordinarily in the range of 20,000 to 200,000. The owner's engineer should establish the value of GT through experimentation.
c. Agitators shall be driven by variable speed drive units with peripheral tip speed of the paddles ranging from 0.5 to 3.0 ft/sec.
d. To control short circuiting in mechanical flocculators, at least three successive compartments should be provided. In addition, special attention should be given to the ports between compartments to further suppress short circuiting.
e. To accomplish maximum power input and reduce particle shearing, tapered flocculation should be provided.
f. In basins utilizing vertical shaft flocculators, wing walls, or stators shall be provided to prevent vortexing.
3. Flocculation and sedimentation basins shall be as close together as possible. The velocity gradient of the flocculated water through pipes or conduits to settling basins shall not be greater than the velocity gradient utilized in flocculating the water. Where velocity gradient is not used as a design parameter, the linear velocity in pipes and conduits from the flocculators to the settling basin shall not exceed 0.5 ft/sec unless otherwise approved by the department. Allowances shall be made to minimize turbulence at bends and changes in direction.
4. Baffling may be used for flocculation in small water treatment plants only when approved by the department. The design should allow the velocity gradients noted in subdivision B 3 of this subsection to be maintained.
Statutory Authority
§§ 32.1-12 and 32.1-170 of the Code of Virginia.
Historical Notes
Derived from Virginia Register Volume 37, Issue 20, eff. June 23, 2021.
12VAC5-590-872. Sedimentation.
A. The water treatment plant capacity, source water quality, and filtration process used shall be considered in determining the number and design of sedimentation basins.
B. The minimum settling time shall be four hours for water treatment plants employing rapid rate gravity filters, and a minimum of three hours for water treatment plants using high rate gravity filters. Reduced settling times may be approved by the department where effective settling is demonstrated. Effective settling time shall be calculated using the volume of the basins from the stilling wall to the submerged effluent orifice or weir, including the volume under launders or finger weirs.
C. Inlets shall be designed to distribute the water equally and at uniform velocities. Open ports, submerged ports, stilling walls, and similar entrance arrangements are required. Port velocities should be in the range of 0.5 to 1.5 ft/sec. Where stilling walls are not provided, a baffle shall be constructed across the basin close to the inlet and shall project several feet below the water surface to dissipate inlet velocities and provide uniform flows across the basin.
D. Outlet weirs or submerged orifices shall be designed to maintain settling velocities in the basin and minimize short circuiting. Outlet weirs and submerged orifices shall be designed as follows:
1. The rate of flow over the outlet weir shall not exceed 20,000 gpd/ft of the outlet launder.
2. Submerged orifices shall not be located lower than three feet below the normal water surface.
3. The entrance velocity through the submerged orifices shall not exceed 0.5 ft/sec.
E. The linear velocity in pipes and conduits from settling basins shall not exceed 1.0 ft/sec.
F. Rectangular sedimentation basins shall be designed with a length-to-width ratio of at least 4:1.
G. Surface overflow rates shall be within the range of 0.25 to 0.38 gpm/ft2 in water treatment plants using rapid rate filters, and a maximum of 0.5 gpm/ft2 for water treatment plants using high rate filters. Increased surface overflow rates and reduced settling times may be approved by the department where effective settling is demonstrated. The length and area between launders and finger weirs may be included in determining length-to-width ratio and overflow rates.
H. Basins shall be provided with a means for dewatering. Basin bottoms shall slope toward the drain not less than one foot in 12 feet unless mechanical sludge collection equipment is provided.
I. In areas where settling basins are subject to high and frequent cross winds, windbreaks shall be considered. Covers or enclosures shall be considered in locations subject to freezing.
J. The velocity through settling basins shall not exceed 1.0 ft/min. The basins shall be designed to minimize short circuiting. Baffles shall be provided as necessary to minimize short circuiting.
K. Multiple basins shall be provided for continuous operability, and each basin shall be designed so that individual basins may be isolated without disrupting plant operation.
L. Mechanical sludge collecting equipment shall be considered for all plants.
M. Sedimentation basins with tube or plate settlers shall meet the following design requirements:
1. Inlet and outlets shall be designed to maintain velocities suitable for settling in the basin and minimize short circuiting. Plate units shall be designed to ensure even flow distribution across the units.
2. Drain piping from the settler units shall be sized to facilitate a quick flush of the basin and to prevent flooding other portions of the plant.
3. Where units are located outdoors, adequate freeboard shall be provided above the top of the settlers to prevent freezing.
4. The maximum loading for tube settlers shall be two gpm/ft2 of cross-sectional area unless higher rates are demonstrated through pilot plant or in-plant demonstration studies.
5. The maximum loading for plate settlers shall be 0.5 gpm/ft2 based upon 80% of the projected horizontal plate area.
6. Flushing lines shall be provided to facilitate maintenance and shall be properly protected against backflow or backsiphonage.
Statutory Authority
§§ 32.1-12 and 32.1-170 of the Code of Virginia.
Historical Notes
Derived from Virginia Register Volume 37, Issue 20, eff. June 23, 2021.
12VAC5-590-873. Solids contact treatment units.
A. Solids contact units shall be acceptable for combined flocculation and clarification where source water characteristics are not variable and flow rates are uniform. When approved, these units shall be designed for the maximum uniform rate and shall be adjustable to changes in flow that are less than the design rate and for changes in water characteristics.
B. A minimum of two units shall be provided.
C. A rapid mix device designed in accordance with 12VAC5-590-871 A shall be provided. Mixing devices shall be constructed to:
1. Provide good mixing of the source water with previously formed sludge particles; and
2. Prevent deposition of solids in the mixing zone.
D. Flocculation equipment designed in accordance with 12VAC5-590-871 B shall:
1. Be equipped with an adjustable drive mechanism;
2. Ensure that coagulation occurs in a separate chamber or baffled zone within the unit; and
3. Provide a flocculation period of at least 20 minutes.
E. The sludge equipment shall provide either internal or external sludge concentrators in order to obtain a concentrated sludge with a minimum of waste water. Sludge removal systems shall provide:
1. Sludge pipe sizes of not less than three inches in diameter;
2. Piping arrangements to prevent clogging and to facilitate cleaning;
3. Valves that are located outside the tank for accessibility;
4. A means to observe or sample sludge being withdrawn from the unit;
5. A time clock with proportional timer with automatic blowoff; and
6. Suitable controls for sludge withdrawal.
F. Cross-connections.
1. Blowoff outlets and drains shall terminate and discharge at a place satisfactory to the department; and
2. Cross-connection control shall be included for the potable water mains used to flush sludge lines.
G. The detention time shall be established on the basis of the source water characteristics and other local conditions that affect the operation of the unit. The minimum detention time shall be two hours for suspended solids contact clarifiers.
H. Orifices shall produce uniform rising rates over the entire area of the tank and shall provide for an exit velocity not to exceed 1.0 ft/sec.
I. Upflow rates shall not exceed 1.0 gpm/ft² of area at the sludge separation line.
Statutory Authority
§§ 32.1-12 and 32.1-170 of the Code of Virginia.
Historical Notes
Derived from Virginia Register Volume 37, Issue 20, eff. June 23, 2021.
12VAC5-590-874. Gravity filtration.
A. At least two gravity filter units shall be provided in conventional filtration treatment plants and direct filtration treatment plants.
B. Filter loading rates shall not exceed 2.0 gpm/ft2 of filter area for rapid rate filters and shall not exceed 4.0 gpm/ft2 for high rate filters, during normal operation. Alternative loading rates may be approved by the department when effective filtration is demonstrated.
C. The filter structure shall be so designed as to comply with the following:
1. The walls within the filter shall be vertical;
2. The filter walls shall not protrude into the filter media;
3. There shall be no common wall between filtered or finished water and any lesser quality water;
4. The filter shall be covered by a superstructure if determined necessary under local climatic conditions;
5. There shall be head room to allow normal inspection and operation;
6. A curb at least four inches high shall surround each filter to prevent floor drainage into the filter;
7. The maximum velocity gradient of treated water in pipes and conduits to the filters shall not exceed that used in flocculation. Where velocity gradient is not used as a design parameter, the linear velocity in pipes and conduits from settling basins to filters shall not exceed 1.0 ft/sec;
8. Influent pipes or conduits, where solids loading is heavy, shall be straight and equipped with cleanouts;
9. Backwash water drain capacity shall be sufficient to carry the maximum flow;
10. Access in the form of walkways not less than 24 inches in width shall be provided to each filter; and
11. The normal operating water surface on a filter shall be at the same hydraulic grade level as the sedimentation basin, if no intermediate treatment process is provided.
D. Backwash water troughs shall be so designed as to provide:
1. Bottom elevation of the trough above the maximum level of expanded media during backwashing;
2. At least a two-inch freeboard inside the trough at the maximum rate of wash;
3. A level top or edge;
4. Spacing so that each trough serves an equal area of each filter; and
5. Maximum horizontal travel of suspended particles to reach the trough not to exceed 3.0 ft.
E. Filter media shall be free from detrimental chemical or bacterial contaminants. Acceptable filter media shall include anthracite coal, silica sand, garnet sand, and GAC. Other natural or synthetic media may be approved by the department when pilot-scale or full-scale demonstration studies demonstrate that the media is capable of meeting the filter effluent turbidity treatment technique requirements in Part II (12VAC5-590-395) of this chapter.
1. Filters may be of single media, dual media, or multimedia design depending upon the water to be treated and the specific filtration process employed. A total media depth of not less than 27 inches shall be provided after cleaning and scraping.
2. Types of filter media:
a. Anthracite coal. A sieve analysis shall be provided. Anthracite media shall have:
(1) An effective size from 0.45 to 0.55 mm with a uniformity coefficient not greater than 1.65 when used alone.
(2) An effective size from 0.8 to 1.2 mm with a uniformity coefficient not greater than 1.85 when used in dual or multimedia filters.
b. Silica sand. A sieve analysis shall be provided. The media shall be clean silica sand having an effective size from 0.35 to 0.55 mm and a uniformity coefficient not greater than 1.65.
c. Garnet sand. A sieve analysis shall be provided. The media shall have an effective size from 0.15 to 0.35 mm.
d. Granular activated carbon (GAC) may be used as a media for filtration. The department may require pilot studies where precursor or organics removal is a treatment objective. The design shall include the following:
(1) GAC media shall meet the basic specifications for filter media contained in this section, except the uniformity coefficient shall not be greater than 2.0. The department may allow larger size media based upon pilot-scale or full-scale demonstration testing. The department may require that a layer of sand media be placed below the GAC.
(2) Provisions shall be made for periodic treatment of GAC filter material for the control of bacteria and other growths.
(3) Provisions shall be made for GAC media replacement or regeneration.
(4) Only materials suitable for use with GAC media filters shall be utilized.
F. Support media.
1. Sand. A sieve analysis shall be provided. A three-inch layer of sand shall be used as a supporting media for the filter media where supporting gravel is used and shall have an effective size from 0.8 to 2.0 mm and a uniformity coefficient not greater than 1.7.
2. Gravel. When used as the supporting media, gravel shall consist of hard, rounded particles and shall not include flat or elongated particles. The coarsest gravel shall be 2-1/2 inches in size when the gravel rests directly on the strainer system and shall extend above the top of the perforated laterals or strainer nozzles. Not less than four layers of gravel shall be provided in accordance with the size and depth distribution specified in Table 874.1.
3. Changes of gravel depths and sizes may be considered by the department where proprietary filter bottoms are proposed.
TABLE 874.1 | |
SIZE | DEPTH |
2-1/2 - 1-1/2 inches | 5 - 8 inches |
1-1/2 - 3/4 inches | 3 - 5 inches |
3/4 - 1/2 inches | 3 - 5 inches |
1/2 - 3/16 inches | 2 - 3 inches |
3/16 - 3/32 inches | 2 - 3 inches |
G. Filter bottoms and strainer systems. The department may allow deviations from requirements of this subdivision for high rate filters and for proprietary filter bottoms. Porous plate bottoms shall not be used where iron, manganese, or hard water may result in clogging. The design of manifold-type collection systems shall:
1. Minimize loss of head in the manifold and laterals;
2. Assure even distribution of backwash water and an even rate of filtration over the entire area of the filter;
3. Provide a ratio of the area of the final openings of the strainer systems to the area of the filter of about 0.003;
4. Provide a total cross-sectional area of the laterals at about twice the total area at the final openings; and
5. Provide a manifold that has a cross-sectional area which is 1-1/2 to two times the total area of the laterals.
H. Surface wash or air scouring of filters shall be provided.
1. All rotary surface wash devices shall be designed with:
a. Provisions for water pressures of at least 45 psig;
b. A vacuum breaker or other device or assembly to prevent backsiphonage; and
c. Adequate surface wash water to provide 0.5 - 1.0 gpm/ft2 of filter area.
2. Air scouring shall provide for:
a. An air flow rate of three to five scfm/ft2 of filter area when air is introduced in the underdrain. A lower air flow rate shall be used when the air scour distribution system is placed above the underdrain.
b. A method for avoiding loss of filter media during backwashing.
c. A fluidization backwash following air scour sufficient to restratify the filter media. The backwash water delivery system shall be in accordance with this section except the rate of flow should not exceed 8.0 gpm/ft2 unless operating experience demonstrates that a higher rate is necessary to remove scoured particles from the filter media.
I. Turbidity monitoring.
1. Indicating and recording turbidimeters meeting the requirements of 12VAC5-590-770 B shall be provided for:
a. The source water;
b. The settled water from each sedimentation basin;
c. The filter effluent from each filter; and
d. The CFE.
2. Finished water indicating and recording turbidimeters shall be considered if chemical pH adjustment occurs following filtration.
3. The location of the turbidity sample tap shall allow turbidity to be monitored for both the filtered water and the filter-to-waste water.
4. The design may incorporate an operator selected filter effluent high turbidity alarm.
J. Appurtenances.
1. A sampling tap shall be placed between each filter and the effluent rate-of-flow controller to sample filtered water and filter-to-waste water. The location of sample taps shall allow turbidity to be monitored of both the filtered water and the filter-to-waste water.
2. Indicating and recording loss-of-head gauges shall be provided on all filters having a capacity of greater than 100 gpm. An indicating loss-of-head gauge shall be provided on all filters having a capacity of 100 gpm or less.
3. Indicating and recording rate-of-flow gauges shall be provided on all filters having a capacity of greater than 100 gpm. An indicating and totalizing water meter may be used instead of an indicating and recording gauge on filters having a capacity of 100 gpm or less.
4. Effluent rate-of-flow controllers of the direct acting, indirect acting, or constant rate types shall be provided on each filter.
a. All control devices used shall incorporate an auxiliary shutoff valve in the filter effluent line. Indirect and direct acting effluent rate-of-flow control devices shall start operation from the closed position. Failure of indirect acting controllers shall not result in any increase in the rate of flow.
b. Filter effluent rate-of-flow control that simply maintains a constant water level on the filter is prohibited.
c. Control devices shall be configured to prevent exceeding the design filter hydraulic loading rate when any filter is taken out of service.
5. Provisions for draining the filter-to-waste (rewash) with appropriate backflow prevention and rate control shall be provided on each filter. The filter-to-waste design flow rate shall be equal to the filtration rate.
6. A high pressure hose and hose rack shall be provided to allow washing down filter walls.
K. Backwash provisions.
1. Filtered or finished water shall be applied uniformly across the filter in an upflow direction to provide at least 50% media expansion during all operating conditions. This will normally require backwash flow rates of up to 20 gpm/ft2 depending on media size, media specific gravity, uniformity coefficient, and water temperature.
2. The backwash water shall be provided at the required rate by backwash pumps, backwash water tanks, the high service main, or a combination of these methods. Consideration should be given to including provisions to obtain backwash water from the distribution system or other sources and to supply backwash water during plant start-up or during catastrophic events.
3. At least two backwash water pumps shall be installed unless an alternate means of obtaining backwash water is available.
4. The volume of backwash water provided shall be sufficient to backwash one filter at the design backwash flow rate and duration during the warmest water temperature. This backwash water volume shall be in addition to any other water storage requirements.
5. A backwash water controller or valve shall be provided on the main backwash water supply line to obtain the desired rate of filter wash with the backwash water valves on the individual filters open wide.
6. Consideration shall be given to provide for seasonal adjustments of the backwash flow rate to ensure proper backwashing while preventing media loss and to conserve water.
7. The rate-of-flow indicator on the main backwash water supply line shall be located so that it may easily be read by the operator during the backwashing process.
8. Where backwash water pumps are provided, a means for air release shall be installed between the backwash water pump and the backwash water valve.
L. Other design considerations.
1. Roof drains shall not discharge into the filter or basins and conduits preceding the filters.
2. Provision shall be made for continuous operation of all other filtering units while one filtering unit is out of operation.
3. High rate filtration shall be provided with precise coagulation control. A multiple six-gang stirring machine for performing jar tests shall be provided in addition to one or more of the following means of controlling the coagulation process:
a. Zeta potential, as measured by microelectrophoresis.
b. Pilot filters. Where dual pilot filters are used, two units shall be provided. Each pilot filter shall consist of a small filter (about six inches in diameter) containing the same type and depth of media as the plant filters. The pilot filter shall be equipped with recording turbidimeters on the effluent to measure the filterability of the water as reflected by turbidity monitoring.
c. Streaming current monitor, defined as a continuous sampling instrument that measures the electric current generated when water flows past suspended particles contained in the water.
4. High rate filtration shall be provided with indicating and recording pH monitoring equipment for:
a. The source water;
b. The rapid mix effluent; and
c. The finished water leaving the treatment plant.
Statutory Authority
§§ 32.1-12 and 32.1-170 of the Code of Virginia.
Historical Notes
Derived from Virginia Register Volume 37, Issue 20, eff. June 23, 2021.
12VAC5-590-875. Direct filtration.
A. Direct filtration is defined as a series of treatment processes, including coagulation and filtration but excluding sedimentation. Direct filtration shall be considered only for treatment of high quality and seasonally consistent surface water sources or GUDI sources.
B. An in-plant demonstration study or pilot study shall be required to demonstrate acceptable performance of direct filtration. The study shall be conducted over a sufficient time to treat all expected source water conditions throughout the year. The pilot plant filter shall be of a similar type and operated in the same manner as proposed for full-scale operation.
C. The department may require presedimentation meeting the requirements of 12VAC5-590-865 C to be provided (in the treatment sequence) to direct filtration treatment plants.
D. Rapid mix coagulation and flocculation shall be provided, meeting the requirements of 12VAC5-590-871.
E. Filters shall be dual media or multimedia gravity filters. Design of filtration units shall meet requirements for rapid rate or high rate gravity filters in 12VAC5-590-874, including filter structure, filter media, support gravel, backwash provisions, rate-of-flow control, surface wash, or air scour. Alternative designs may be considered by the department.
F. Turbidity monitoring.
1. Indicating and recording turbidimeters meeting the requirements of 12VAC5-590-770 B shall be provided for:
a. The source water;
b. The filter effluent from each filter; and
c. The CFE.
2. Finished water indicating and recording turbidimeters shall be considered if chemical softening occurs following filtration.
G. Where automatic unit process control is provided, manual override of all automatic features shall be provided.
1. Automatic start-up of treatment plant unit processes is prohibited.
2. Valve actuators shall be provided with manual override capability.
H. The plant design should allow for the future installation of sedimentation basins.
Statutory Authority
§§ 32.1-12 and 32.1-170 of the Code of Virginia.
Historical Notes
Derived from Virginia Register Volume 37, Issue 20, eff. June 23, 2021.
12VAC5-590-880. Diatomaceous earth filtration.
A. Diatomaceous earth filtration shall be limited to treatment of a surface water source, a GUDI source, or both with low turbidity and low bacterial contamination, and may be used for iron removal from groundwater.
B. Pilot plant study. Installation of a diatomaceous earth filtration system shall be preceded by a pilot plant study on the water to be treated.
C. Types of filters. Pressure or vacuum diatomaceous earth filtration units will be considered for approval.
D. Treated water storage. Treated water storage capacity in excess of normal requirements shall be provided to:
1. Allow operation of the filters at a uniform rate during all conditions of system demand at or below the approved filtration rate, and
2. Guarantee continuity of service during adverse source water conditions without bypassing the system.
E. Number of units. At least two filtering units shall be provided at plants having a rated capacity of more than 100 gpm.
F. Precoat.
1. Application. A uniform precoat shall be applied hydraulically to each septum by introducing a slurry to the tank influent line and employing a filter-to-waste or recirculation system.
2. Quantity. Diatomaceous earth in the amount of 0.2 lb/ft2 of filter area.
G. Body feed. A body feed system to apply additional amounts of diatomaceous earth slurry during the filter run is required.
1. Quantity. Rate of body feed is dependent on source water quality and characteristics and must be determined in the pilot plant study.
2. Adequate accessibility to the feed system and slurry lines is required.
3. Continuous mixing of the body feed slurry is required.
4. Consideration should be given to providing a coagulant coating (alum or suitable polymer) of the body feed.
H. Rate of filtration. The hydraulic loading rate shall not exceed 1.5 gpm/ft2 of filter area. The filtration rate shall be controlled.
I. Head loss. The head loss shall not exceed 30 psi for pressure diatomaceous earth filters, or a vacuum of 15 inches of mercury for a vacuum system.
J. Recirculation. A recirculation or holding pump shall be employed to maintain a differential pressure across the filter when the unit is not in operation to prevent the filter cake from dropping off the filter elements. A minimum recirculation rate of 0.1 gpm/ft§ filter area shall be provided.
K. Septum or filter element. The filter elements shall be structurally capable of withstanding maximum pressure and velocity variations during filtration and backwash cycles, and shall be spaced so that no less than one inch is provided between elements or between any element and a wall. Means shall be provided to check the septum for cleanliness or damage. Consideration should be given to providing septum assemblies where an individual septum can be removed, cleaned, repaired, and replaced.
L. Inlet design. The filter influent shall be designed to prevent scour of the diatomaceous earth from the filter element.
M. Backwash. Provision shall be made for periodic backwashing of the filter. A satisfactory method to thoroughly remove and dispose of spent filter cake shall be provided.
N. Appurtenances. The following shall be provided for every filter:
1. Sampling taps for source and filtered water;
2. A loss-of-head or a differential pressure gauge;
3. A rate-of-flow indicator, preferable with totalizer; and
4. A throttling valve used to reduce rates below normal during adverse source water conditions.
O. Turbidity monitoring. Indicating and recording turbidimeters meeting requirements of 12VAC5-590-770 B shall be provided for:
1. The source water;
2. The effluent from each filter unit; and
3. The CFE.
P. An operation and maintenance manual shall be provided for all diatomaceous earth filtration units. The manual shall include the following:
1. A detailed description of the treatment units and the control of each unit for optimal performance;
2. A preventative maintenance schedule;
3. The manual adjustment and override procedures for all automatic control features; and
4. A troubleshooting guide for typical problems.
Q. The owner shall require the equipment manufacturer to provide onsite start-up and follow-up training.
Statutory Authority
§§ 32.1-12 and 32.1-170 of the Code of Virginia.
Historical Notes
Derived from VR355-18-009.04 § 3.25, eff. August 1, 1991; amended, Virginia Register Volume 9, Issue 17, eff. June 23, 1993; Volume 37, Issue 20, eff. June 23, 2021.
12VAC5-590-881. Slow sand filtration.
A. Slow sand filters shall be approved only after a pilot study demonstrates that the water supply contains sufficient nutrients for use of this treatment technology.
B. At least two filters shall be provided. In all cases, the filters shall be capable of meeting the design maximum daily water demand with one filter out of service.
C. Sand shall be clean silica sand that meets the following criteria:
1. The effective size shall be between 0.15 mm and 0.35 mm;
2. The uniformity coefficient shall not exceed 2.5; and
3. The sand depth shall not exceed 55 inches. A minimum depth of 30 inches is required for normal operation.
D. Supporting media gravel shall meet the requirements of 12VAC5-590-874 F.
E. Structural details.
1. All slow sand filters shall be covered.
2. Sufficient head room shall be provided for normal movement on the filter by operating personnel for periodic sand removal operations.
3. Adequate manholes and access ports shall be provided for moving sand off and onto the filter.
4. There shall be no common wall between the finished water and any water of lesser quality.
5. All filters shall be protected from freezing.
F. General design requirements.
1. Filter to waste shall be provided for all slow sand filters.
2. Water entering the filter shall be distributed in a manner so that the surface of the filter shall not be disturbed in any way.
3. The nominal rate of filtration range shall be from 45 to 150 gpd/ft2 (0.031 to 0.10 gpm/ft2) of sand area.
4. The minimum depth of water over the filters shall be three feet. The maximum depth of water over the filters shall not exceed five feet. An overflow capable of handling the maximum flow to the filter shall be provided at the maximum filter water level.
5. Underdrains shall be provided to assure an even rate of filtration across the filter surface. The maximum velocity of water in the lateral underdrains shall be 0.75 ft/sec. The underdrain spacing shall not exceed three feet.
6. Each filter shall be capable of being filled with water from the bottom up.
7. Each filter shall be equipped with a loss-of-head gauge; a rate-of-flow control device such as an orifice, weir, or butterfly valve; a weir or effluent pipe designed to assure that the water level over the filter never drops below the sand surface; and filtered water sample taps.
8. Monitoring, indicating, and recording turbidimeters meeting the requirements of 12VAC5-590-770 B shall be provided for:
a. The source water;
b. The filter effluent from each filter unit; and
c. The CFE.
9. The filters shall be designed to operate to waste after scraping or replacement of the sand, until the ripening process is complete and the turbidity meets the requirements of 12VAC5-590-395 A 2 b (3).
Statutory Authority
§§ 32.1-12 and 32.1-170 of the Code of Virginia.
Historical Notes
Derived from Virginia Register Volume 37, Issue 20, eff. June 23, 2021.
12VAC5-590-882. Membrane filtration.
A. Applicability. This section pertains to the use of membrane filtration as follows:
1. For pathogen and turbidity log removal credits in accordance with Table 500.1 in 12VAC5-590-500, the use of MF and UF are allowed.
2. For softening, total dissolved solids (TDS) removal, organics removal, and other treatment purposes, reverse osmosis (RO) and nanofiltration (NF) are allowed in accordance with 12VAC5-590-680 G.
B. Membrane filtration systems shall meet all requirements contained in 12VAC5-590-401 E 6 b to be granted removal credit for Giardia lamblia and Cryptosporidium.
C. A demonstration study shall be conducted on the water to be treated before the installation of a membrane filtration system unless the owner can demonstrate to the satisfaction of the department that the source water quality range over all four seasons of a year will be adequately treated by the proposed design.
D. All membrane treatment units for pathogen and turbidity removal shall employ MF or UF using hollow fiber, positive pressure-driven membrane filtration technology. They may employ either an inside-to-outside or outside-to-inside flow direction.
E. The number of membrane units shall be a function of the overall treatment facility capacity, waterworks capacity, and water demand. Multiple membrane units shall be provided where the treatment facility design capacity exceeds 0.5 MGD.
F. Approved materials and chemicals.
1. All membrane materials, associated piping, and other components in contact with the water shall be in accordance with 12VAC5-590-810.
2. Chemicals used in any membrane cleaning process shall be in accordance with 12VAC5-590-515.
G. Turbidity monitoring. Continuous indicating and recording equipment meeting the requirements of 12VAC5-590-770 B shall be provided for the following locations:
1. Source water;
2. Pretreated water, such as by coagulation, flocculation, and sedimentation (if applicable);
3. Filtrate from each membrane unit; and
4. Combined filter effluent, where more than one membrane unit is installed.
H. Indicating and recording equipment for entry point chlorine residual monitoring shall be provided. Indicating and recording equipment for filtered water temperature monitoring shall be provided.
I. Pressure monitoring:
1. Indicating equipment shall be provided for monitoring the pressure drop across any prefilter.
2. Indicating and recording equipment shall be provided for monitoring the pressure drop across membrane modules, (i.e., transmembrane pressure).
3. Integrity monitoring. Indicating and recording equipment for direct integrity test monitoring shall be provided and shall document the date, time, and results of every test performed on each unit.
J. Flow measurement. Equipment shall be provided for measuring or calculating the following flows:
1. Source water, gpm and totalized;
2. Filtrate from each unit, gpm and totalized;
3. Flux from each unit, gpd/sf;
4. Recirculation to each unit, gpd or percent of feed flow, if applicable;
5. Entry point, gpm and totalized; and
6. Waste.
K. An alarm system shall be provided that will report alarm conditions and shut down the treatment plant and entry point flow as necessary.
1. All alarms shall be reported to a location manned 24 hours per day or to a person on call and shall report alarm conditions audio-visually at the water treatment plant.
2. At a minimum, the following points shall be monitored by the alarm system. Alarm and shut down set point conditions will be determined by the department on an individual basis.
a. Feed water flow;
b. Feed water turbidity, if required by the department;
c. Filtrate turbidity from each unit exceeding operational control criteria;
d. Membrane direct integrity test initiation, failure, and exceeding operational control criteria; and
e. Entry point disinfectant residual.
L. Sample taps shall be provided to monitor the following:
1. Source water;
2. Source water storage tank effluent;
3. Feed water after prefiltration;
4. Filtrate from each membrane unit;
5. Combined filtrate from all units;
6. Entry point; and
7. Additional sample taps to monitor the presence of cleaning solutions used in either the backwash or cleaning operations.
M. Equipment shall be provided, using variable frequency drive or other suitable means to adjust the feed pump output in order not to exceed the design flux in the event modules are taken off line.
N. Pressure gauges.
1. A portable, pocket-type pressure gauge of the correct range and accuracy for the application and with the capability of being calibrated shall be provided to check the pressure readings of the pressure transducers installed on the membrane units.
2. At each location of a pressure transducer, a 1/4-inch diameter pressure gauge with American National Standard Taper Threads (NPT) connection shall be provided to facilitate the connection of a portable, pocket-type test gauge.
O. Clean-in-place systems, including tanks, piping, all joints, and valves, shall be compatible with the cleaning solution and shall be corrosion resistant.
P. An operation and maintenance manual shall be provided for all membrane filtration treatment units. The operation and maintenance manual shall include the following:
1. A maintenance schedule for each piece of equipment.
2. Operation procedures, including software user instructions.
3. A troubleshooting guide.
4. Identification of specific proprietary equipment or software not available to the owner or operator.
5. A service call number.
6. DIT requirements.
7. Chemical cleaning instructions.
8. A detailed description of the treatment units and the control of each unit for optimal performance.
Q. A means shall be provided to isolate a compromised module or fiber or both. A means to visually inspect modules while simultaneously conducting the DIT shall be provided. Alternatively, sonic testing equipment that provides a relative accelerometer reading shall be provided where visual inspection cannot be performed.
Statutory Authority
§§ 32.1-12 and 32.1-170 of the Code of Virginia.
Historical Notes
Derived from Virginia Register Volume 37, Issue 20, eff. June 23, 2021.
12VAC5-590-883. Bag and cartridge filtration.
A. Bag or cartridge filtration shall be limited to treating a surface water source, a GUDI source, or both with low turbidity.
B. A pilot plant study shall be conducted on the water to be treated before the installation of a bag or cartridge filter system.
C. Bag and cartridge filtration systems shall be granted removal credit for Giardia lamblia and Cryptosporidium in accordance with 12VAC5-590-401 E 6 a, provided that they meet the requirements of this section.
D. General design requirements.
1. All system components such as housing, bags, cartridges, gaskets, O-rings, and other components in contact with water shall be in accordance with 12VAC5-590-810. All cartridge filter housing shall be certified by the ASME certification program, or equivalent, for pressure vessels and stamped with the appropriate certification mark.
2. Indicating and recording turbidimeters meeting requirements of 12VAC5-590-770 B shall be provided for the source water and the CFE. The department may require indicating and recording effluent turbidimeters for each filter unit.
3. The maximum flux rate across the final filter shall not exceed 0.2 gpm/ft2.
4. Maximum differential pressure across the cartridge filter shall not exceed 20 psi.
5. Pressure gauges and sampling taps shall be provided before and after each bag or cartridge filter.
6. Provisions to accomplish filter-to-waste shall be provided.
7. Automatic start-up of bag or cartridge filters is prohibited.
8. An alarm system shall be provided that will report alarm conditions and shut down the treatment plant and entry point flow.
a. All alarms shall be reported to a location manned 24 hours per day or to a person on call and shall report alarm conditions audio-visually at the water treatment plant.
b. The following shall be monitored by the alarm system:
(1) Source water turbidity;
(2) Feed water flow;
(3) If applicable, filtrate turbidity from each unit exceeding operational control criteria;
(4) Combined filter effluent turbidity exceeding operational control criteria;
(5) Differential pressure at each unit; and
(6) Entry point disinfectant residual.
9. At least two filtering units shall be provided at plants having a rated capacity of greater than 100 gpm.
E. Operation and maintenance documents shall be provided for all bag or cartridge filter units and shall include:
1. Detailed description of the bag or cartridge treatment units and the control of each unit for optimal performance.
2. Procedural criteria, such as pressure differential, turbidity, and other parameters, and expected frequency of bag or cartridge filter replacement.
3. A preventative maintenance schedule.
4. Manual adjustment and override procedures for any automatic control features.
5. Troubleshooting guide for typical problems.
F. The owner shall require the equipment manufacturer to provide onsite start-up and follow-up training.
Statutory Authority
§§ 32.1-12 and 32.1-170 of the Code of Virginia.
Historical Notes
Derived from Virginia Register Volume 37, Issue 20, eff. June 23, 2021.
12VAC5-590-890. (Repealed.)
Historical Notes
Derived from VR355-18-009.05 § 3.26, eff. August 1, 1991; amended, Virginia Register Volume 9, Issue 17, eff. June 23, 1993; repealed, Virginia Register Volume 37, Issue 20, eff. June 23, 2021.
12VAC5-590-895. Pre-engineered package treatment units.
A. Pre-engineered package treatment units are defined as predesigned, factory built, and transported virtually assembled to the operation site. The provisions of 12VAC5-590-290 shall apply.
B. General design considerations.
1. A rapid mix unit process shall be provided. The design shall meet requirements of 12VAC5-590-871 A.
2. Flocculation units shall meet requirements of 12VAC5-590-871 B or as identified and justified in the approved PER.
3. Sedimentation units shall meet requirements of 12VAC5-590-872 or as identified and justified in the approved PER.
4. Filters shall be dual media or multimedia gravity filters. Design of filtration units shall meet the requirements of 12VAC5-590-874 or as identified and justified in the approved PER.
5. Indicating and recording turbidimeters meeting requirements of 12VAC5-590-770 B shall be provided for the:
a. Source water;
b. Applied water to each filter;
c. Filter effluent from each filter; and
d. CFE.
6. Sufficient overflows and drains shall be provided to maintain a maximum water level within the plant, including the depth of water over the filters, and to facilitate complete draining of the package unit.
7. Where automatic unit process control is provided, operator adjustment of chemical feed rates, times, and sequences shall be provided as well as a manual override of all automatic features.
a. Automatic start-up of water treatment unit processes is prohibited.
b. Valve actuators shall be provided with manual override capability.
8. Treatment units installed at ground level shall be provided with stairways, walkways, or other suitable means to allow access for operation and maintenance and observation of all treatment process units. Filters shall be adequately accessible to facilitate evaluation of the entire filter bed for media condition and placement, fluidization during backwashing, and evaluation of compaction during filtration.
C. An operation and maintenance manual shall be provided for all pre-engineered package treatment units. The operation and maintenance manual shall include the following:
1. A detailed description of the treatment units and the control of each unit for optimal performance.
2. A preventative maintenance schedule.
3. Manual adjustment and override procedures for any automatic control features.
4. A troubleshooting guide for typical problems.
D. The owner shall require the equipment manufacturer to provide onsite start-up and follow-up training.
Statutory Authority
§§ 32.1-12 and 32.1-170 of the Code of Virginia.
Historical Notes
Derived from Virginia Register Volume 37, Issue 20, eff. June 23, 2021.
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 feet 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.
Historical Notes
Derived from VR355-18-009.06 § 3.27, eff. August 1, 1991; amended, Virginia Register Volume 37, Issue 20, eff. June 23, 2021.
12VAC5-590-910. Aeration.
A. Aeration treatment is acceptable for oxidation, separation of gases, or for taste and odor control. General design requirements include the following:
1. The aerated water shall be chlorinated following aeration.
2. The equipment shall incorporate materials resistant to deterioration and corrosion and shall be designed to eliminate the potential for fouling problems from calcium carbonate and iron precipitation and from algae, slime, and bacteriological growth. Disinfection capability shall be provided before the aeration treatment units.
3. The equipment shall be easily accessed and serviced.
4. The air introduced into the treatment units shall be filtered and shall be free of insects, obnoxious fumes, dust, dirt, and other contaminants. If blowers are located inside a building, then the air intakes shall extend to the outside and be furnished with appropriate air filters.
5. Air exhaust outlets shall be located to avoid induced contaminants, particularly at or near occupied areas or blower intakes.
6. Duplicate blowers, motors, or multiple treatment units shall be required for treatment processes designed to meet the drinking water quality standards in 12VAC5-590-340.
B. Natural, forced, or induced draft aeration units shall be designed to provide an adequate liquid distribution and countercurrent of air through the enclosed aeration column, and adequately seal the water outlet to prevent unwanted loss of air.
C. Pressure aeration means the injection of compressed air into the water to be treated, typically for oxidation. Pressure aeration shall not be approved for removal of dissolved gases. Filters following pressure aeration shall have adequate exhaust devices for the release of air. Pressure aeration devices shall be designed to provide thorough mixing of compressed air with the water being treated.
D. Packed tower aeration (air stripping) is suitable for removing VOCs, THMs, carbon dioxide, and radon.
1. Justification shall be provided for the selected design parameters (e.g., height and diameter of the unit, air-to-water ratio, packing depth, surface loading rate, and other features). The design shall consider the effects of temperature change and the resulting impact in contaminant removal efficiency. Pilot plant studies may be required to substantiate the design.
2. The packing material used shall be resistant to the aggressiveness of the water, dissolved gases, and cleaning materials, and shall meet requirements of 12VAC5-590-810.
3. Water shall be evenly distributed at the top of the tower using spray nozzles or orifice-type distributor trays that will prevent short circuiting. A mist eliminator above the water distribution system may be required.
4. A means to allow for discharge and wasting of water or chemicals used to clean the tower shall be provided.
5. Sample taps shall be provided in the influent and effluent piping.
6. The design shall prevent freezing of the influent riser and effluent piping.
7. An overflow pipe discharging 12 to 24 inches above the ground and over a drainage inlet structure or splash pad shall be provided.
8. A sufficient number of access ports with a minimum diameter of 24 inches shall be provided to facilitate inspection, media replacement, media cleaning, and maintenance of the unit interior.
9. A positive air flow sensing device and a pressure gauge shall be installed on the air influent line. If the aeration unit is designed to remove a contaminant with a PMCL, then the positive air flow sensing device shall be an integral part of an automatic control system that will turn off the influent water if positive air flow is not detected.
E. Other methods of aeration shall be designed to meet the particular needs of the water to be treated and are subject to the approval of the department.
Statutory Authority
§§ 32.1-12 and 32.1-170 of the Code of Virginia.
Historical Notes
Derived from VR355-18-009.07 § 3.28, eff. August 1, 1991; amended, Virginia Register Volume 37, Issue 20, eff. June 23, 2021.
12VAC5-590-920. Iron and manganese control.
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.
C. Iron and manganese removal by ion exchange shall only be approved for removing low concentrations (less than 0.5 mg/L) of combined iron and manganese. The department may require pilot studies be conducted to determine post-exchange pH/alkalinity adjustment. See 12VAC5-590-900 for general ion exchange design requirements.
D. Sequestering iron and manganese.
1. Sequestration with polyphosphates shall be considered for polishing filtered water; however, it shall not be used where the residual iron, manganese, or combination thereof exceeds 1.0 mg/L.
2. Phosphate feed rates shall be determined by the product manufacturer and shall not exceed 10 mg/L.
3. Feed equipment shall be in accordance with the requirements of 12VAC5-590-860.
4. Stock phosphate solution shall be disinfected in accordance with manufacturer recommendations unless the phosphate solution is fed directly from the covered shipping container.
5. Sodium silicate or other silicate-based chemicals for the sequestration of iron and manganese shall be approved by the department on an individual basis. Operational data from actual full-scale facilities treating waters of similar quality or pilot tests may be required.
E. Sampling taps shall be provided for control purposes. Taps shall be located on each source water, each treatment unit influent, and each treatment unit effluent.
F. Iron and manganese testing equipment shall be provided. Iron testing equipment shall be capable of accurately measuring iron concentration as low as 0.1 mg/L. Manganese testing equipment shall be capable of accurately measuring manganese concentration as low as 0.05 mg/L.
G. The department may approve proprietary treatment processes for the removal of iron and manganese on an individual basis. Operational data from actual full-scale facilities treating waters of similar quality or pilot tests may be required. The provisions of 12VAC5-590-290 may apply.
Statutory Authority
§§ 32.1-12 and 32.1-170 of the Code of Virginia.
Historical Notes
Derived from VR355-18-009.08 § 3.29, eff. August 1, 1991; amended, Virginia Register Volume 37, Issue 20, eff. June 23, 2021.
12VAC5-590-930. Fluoridation.
A. The board recommends that all community waterworks in Virginia be optimally fluoridated. Fluoridation feed systems shall be designed to deliver the optimum fluoride ion concentration as determined by the U.S. Department of Health and Human Services.
B. Fluoride compounds. Commercial sodium fluoride, sodium fluorosilicate (also called sodium silicofluoride), and fluorosilicic acid (also called hydrofluorosilicic acid) shall conform to the applicable AWWA standards or NSF/ANSI/CAN Standard 60-2020, as appropriate.
C. Fluoride compound storage. Fluoride chemicals shall be isolated from other chemicals to prevent cross contamination. Compounds shall be stored in covered or unopened shipping containers in a separate room (except sodium fluoride saturators) with the chemical feeder.
D. Chemical feed installations.
1. Scales and loss-of-weight recorders for dry chemical feeders and hydrofluorosilicic acid feeders shall be provided.
2. Fluoride metering pumps shall have an accuracy so that the actual feed rate will be within 5.0% of the intended feed rate.
3. The point of application shall be located to provide adequate mixing.
4. All fluoride feed lines shall be provided with adequate anti-siphon devices.
5. Design of fluoride saturators shall consider:
a. The source water hardness. The water applied to the sodium fluoride saturator feeders shall be softened if the hardness exceeds 50 mg/L.
b. The fluoride source. Use only sodium fluoride in the saturators.
c. A flow restrictor with a maximum flow of 2.0 gpm on all upflow saturators.
6. Adequate fluoride feed rate control and mixing shall be provided.
7. Provisions shall be made for venting fluorosilicic acid carboys to the outside of the building when the carboys are in use.
E. Suitable protective equipment shall be provided which includes gloves, aprons, dust mask, and goggles.
F. Suitable equipment shall be provided for wet mopping and hosing dust that might accumulate in the plant. Dry feeders shall be equipped with bag loading hoppers.
G. Equipment shall be provided for measuring the quantity of fluoride ion in the water. Testing equipment shall be colorimetric or electrode type as approved by the department.
Statutory Authority
§§ 32.1-12 and 32.1-170 of the Code of Virginia.
Historical Notes
Derived from VR355-18-009.09 § 3.30, eff. August 1, 1991; amended, Virginia Register Volume 37, Issue 20, eff. June 23, 2021.
12VAC5-590-940. Fluoride removal.
A. Fluoride removal may be accomplished by blending with a different quality water or by removal treatment. Where fluoride removal is required, the treatment units shall be designed to achieve a finished water fluoride concentration that is below the SMCL.
B. Blending. Blended water shall result in all water delivered to the distribution system being of the same quality.
C. Treatment.
1. Treatment shall include ion exchange, activated alumina, bone char, RO, or electrodialysis. The selected design shall be supported by pilot studies, unless at least two pilot studies or two prototype plants have demonstrated that the selected design is feasible. These studies or prototypes shall be for waters having characteristics similar to the water that is to be treated.
2. Water pH shall be adjustable to an optimum level to achieve the best fluoride removal.
3. With any one unit out of service, the remaining units shall be capable of treating the maximum plant flow rate.
4. Filter clogging constituents such as iron having a concentration greater than 1.0 mg/L shall be removed before fluoride removal.
5. Test equipment shall be provided and must be accurate to at least 0.1 mg/L.
6. An operation and maintenance manual shall be provided.
Statutory Authority
§§ 32.1-12 and 32.1-170 of the Code of Virginia.
Historical Notes
Derived from VR355-18-009.10 § 3.31, eff. August 1, 1991; amended, Virginia Register Volume 37, Issue 20, eff. June 23, 2021.
12VAC5-590-950. Corrosion control or stabilization.
A. Water that is unstable due either to natural causes or to the treatment applied to the water shall be stabilized.
B. Deposition of calcium carbonate film. The desired calcium carbonate film may be obtained by using either soda ash or caustic soda when the alkalinity of the water exceeds about 35 mg/L. Soft waters should be treated with lime to provide the required calcium. Soft waters that also have a low carbon dioxide content may need a mixture of lime and soda ash to provide both calcium and carbonate for the calcium carbonate film.
C. Phosphates or other corrosion inhibitors may be used for corrosion control when applied in accordance with manufacturer recommendations and when they meet the requirements of 12VAC5-590-515. Stock phosphate solution shall be disinfected in accordance with manufacturer recommendations unless the phosphate solution is fed directly from the covered shipping container.
D. Cathodic protection shall be acceptable for preventing or reducing corrosion of the inner surfaces of water storage tanks and standpipes and the outer surface of metal pipe.
E. Laboratory equipment shall be provided for determining the effectiveness of stabilization treatment and the concentration of chemicals in the treated water.
Statutory Authority
§§ 32.1-12 and 32.1-170 of the Code of Virginia.
Historical Notes
Derived from VR355-18-009.11 § 3.32, eff. August 1, 1991; amended, Virginia Register Volume 37, Issue 20, eff. June 23, 2021.
12VAC5-590-960. Taste and odor control.
A. The continuous or periodic treatment of source waters with copper sulfate and other copper compounds to kill algae or other growths shall be controlled to prevent a copper concentration in excess of 1.0 mg/L, as copper, in the finished water leaving the treatment plant.
B. Surface water aerators or diffused aeration systems shall be acceptable for de-stratifying reservoirs, reducing or eliminating seasonal turnover, and releasing compounds in the anaerobic or anoxic zones.
C. Addition of chemical oxidants at the source water intake, in the source water pump station discharge line, at the head of the treatment plant, or within the treatment train shall be acceptable for treating tastes and odors. Effective oxidants include chlorine, chlorine dioxide, potassium permanganate, and ozone. If breakpoint chlorination is proposed, then the actual breakpoint of the water shall be determined accurately. "Breakpoint chlorination" means the addition of chlorine to water until the chlorine demand has been satisfied, chlorine and ammonia nitrogen reactions are near completion, and further additions of chlorine result in a free chlorine residual that is directly proportional to the amount of chlorine added.
D. Powdered activated carbon (PAC). When taste and odor problems are anticipated on an intermittent basis, the addition of PAC shall be considered, and a pilot study shall be conducted to determine the optimum dosage. Multiple PAC feed locations shall be evaluated to provide maximum contact time, including the rapid mixer, the flocculation basins, and at the midpoint of the sedimentation basins.
1. PAC shall not be applied near the point of chlorine or other oxidant application.
2. Continuous agitation or resuspension equipment shall be required to keep the PAC from depositing in the slurry or storage tank.
3. All mechanisms for handling dry PAC shall be tightly sealed. Dust collection is required at all installations.
4. The PAC feed lines to the application points shall be sized to handle the PAC suspension and should be equipped with flushing provisions.
E. GAC media shall be acceptable in conventional gravity filters or in separate contactors to reduce taste and odor.
F. Ozonation shall be acceptable for taste and odor control.
Statutory Authority
§§ 32.1-12 and 32.1-170 of the Code of Virginia.
Historical Notes
Derived from VR355-18-009.12 § 3.33, eff. August 1, 1991; amended, Virginia Register Volume 37, Issue 20, eff. June 23, 2021.
12VAC5-590-970. (Repealed.)
Historical Notes
Derived from VR355-18-009.13 § 3.34, eff. August 1, 1991; amended, Virginia Register Volume 9, Issue 17, eff. June 23, 1993; Volume 12, Issue 2, eff. November 15, 1995; repealed, Virginia Register Volume 37, Issue 20, eff. June 23, 2021.
12VAC5-590-975. Removal of radionuclides.
A. Processes for the removal of radionuclides specified as BAT are identified in 40 CFR 141.66. The specific process and equipment proposed for removal of radionuclides shall to the satisfaction of the department have a demonstrated history of successful performance with similar water quality characteristics and performance requirements. Otherwise, the procedures of 12VAC5-590-290 shall apply.
B. When manganese greensand filter systems are utilized, the design shall meet the requirements of 12VAC5-590-920 B. In addition, a chemical contact tank with a minimum detention time of 30 minutes shall be provided. Laboratory or pilot studies may be required to demonstrate compliance with the radium standard when using a filtering treatment system for groundwater with total radium greater than 10 pCi/L.
C. Waste handling, disposal, and permitting shall be given special consideration early in the design process.
D. Occupational exposure shall be considered in the project design.
E. Provisions for operational control monitoring of the radionuclides requiring removal or of acceptable surrogates shall be included in the project design.
Statutory Authority
§§ 32.1-12 and 32.1-170 of the Code of Virginia.
Historical Notes
Derived from Virginia Register Volume 37, Issue 20, eff. June 23, 2021.
12VAC5-590-980. (Repealed.)
Historical Notes
Derived from VR355-18-009.14 § 3.35, eff. August 1, 1991; amended, Virginia Register Volume 9, Issue 17, eff. June 23, 1993; repealed, Virginia Register Volume 37, Issue 20, eff. June 23, 2021.
12VAC5-590-985. GAC contactors.
A. Granular activated carbon (GAC) contactors may be used to adsorb natural organic compounds, taste and odor compounds, and SOCs. The most common applications of GAC contactors in drinking water treatment plants are (i) post-filtration adsorption and (ii) filtration-adsorption, in which some or all of the filter media in a granular media filter is replaced with GAC.
B. General requirements.
1. A demonstration study using bench-scale or pilot-scale tests shall be conducted to determine the GAC media effectiveness, adsorption efficiency, and regeneration frequency.
2. GAC contactors shall be sized for the optimum empty bed contact time.
3. A minimum of two contactor units shall be provided.
4. Bypassing the GAC facility may be permissible under certain circumstances to accommodate seasonal water quality fluctuations and allow for blending water.
C. Hydraulic configuration.
1. Pressure vessel installation may be configured in parallel or in series.
2. For pressure contactors, pre-filter and post-filter pressure gauges shall be installed at each individual contactor unit.
3. The rate of flow through the contactors shall be controlled either manually or automatically to ensure equal flow through each contactor.
D. Design details.
1. For pressure contactors, the maximum pressure loss through the vessels shall be as determined by the product manufacturer.
2. Sample taps, isolation valves, and bypass piping shall be provided before and after each individual contactor unit.
3. Pipes, tanks, and appurtenances shall be corrosion resistant.
4. The GAC facility shall provide the ability to filter-to-waste to prevent carbon fines in the effluent water.
5. Unless otherwise approved by the department, disinfection shall be accomplished following the GAC contactors.
6. If backwashing of GAC specific units is required, then unchlorinated filtered water shall be used.
7. Turbidity monitoring of contactor effluent shall be considered.
8. The facility design shall include provisions for spent carbon disposal, GAC delivery, and storage.
Statutory Authority
§§ 32.1-12 and 32.1-170 of the Code of Virginia.
Historical Notes
Derived from Virginia Register Volume 37, Issue 20, eff. June 23, 2021.
12VAC5-590-990. Waterworks waste.
A. With the exception of sanitary sewage and flows recycled through the water treatment system, the wastes generated during the operation of water filtration plants constitute industrial wastes and are subject to the State Water Control Law (Chapter 3.1 (§ 62.1-44.2 et seq.) of Title 62.1 of the Code of Virginia).
Industrial wastes generated by water treatment facilities include the following:
1. Filter backwash water;
2. Coagulant residuals;
3. Softening residuals;
4. Iron and manganese residuals;
5. Settled solids from presedimentation units; and
6. Brine wastes.
B. After receipt and review of plans and specifications from the consulting engineer for the water treatment facilities, the department will advise DEQ of any proposal to treat and discharge industrial wastes into state waters. The department will submit a letter or report to DEQ that includes the following:
1. Capacity of the proposed treatment facilities;
2. Location of the proposed facilities;
3. Proposed final disposition of the treated waste effluent;
4. Name and address of the consulting engineer; and
5. Name and address of the owner.
C. Except for recycle flows as described in 12VAC5-590-395 C, the owner will need to satisfy DEQ's requirements for the final disposal of these wastes.
D. The sanitary wastes from water treatment plants must receive treatment. Wastes from these facilities shall be discharged either directly to a sanitary sewer system or to an individual waste disposal facility providing suitable treatment approved by the State Water Control Board.
Statutory Authority
§§ 32.1-12 and 32.1-170 of the Code of Virginia.
Historical Notes
Derived from VR355-18-009.15 § 3.36, eff. August 1, 1991; amended, Virginia Register Volume 9, Issue 17, eff. June 23, 1993; Volume 19, Issue 20, eff. July 16, 2003; Volume 37, Issue 20, eff. June 23, 2021.
12VAC5-590-1000. Disinfection.
A. The objective of disinfection is to prevent the occurrence of waterborne diseases from the consumption of drinking water.
B. Primary disinfection shall be provided for all surface water sources, all spring sources, all GUDI sources, and all well sources determined to be of questionable bacteriological quality as required by the department. Consideration shall be given to minimizing the formation of DBPs when designing a disinfection process. Waterworks with groundwater sources requiring disinfection under this section shall meet the requirement of 12VAC5-590-421 A 1 d.
C. All pipes, tanks, and equipment that convey, store, or treat potable water shall be disinfected with chlorine before being placed in service in accordance with the following AWWA standards where applicable: C651-14, C652-19, and C653-20.
D. All residual disinfectant determinations shall be made using methods identified in 12VAC5-590-440.
1. The project documents shall outline the procedures and include the disinfectant dosage, contact time, and method of testing the results of the procedure.
2. Methods of disinfection other than chlorination may be considered by the department on an individual basis.
Statutory Authority
§§ 32.1-12 and 32.1-170 of the Code of Virginia.
Historical Notes
Derived from VR355-18-009.16 § 3.37, eff. August 1, 1991; amended, Virginia Register Volume 9, Issue 17, eff. June 23, 1993; Volume 37, Issue 20, eff. June 23, 2021.
12VAC5-590-1001. Chlorination.
A. General design requirements.
1. Chlorine feed capacity shall be capable of meeting the disinfection requirements under all operating conditions.
a. Chlorine feed systems for primary disinfection at a waterworks using a surface water source, a GUDI source, or both shall provide sufficient capacity to achieve the required microbial log inactivation specified in Table 500.1.
b. Chorine feed systems for primary disinfection at a waterworks using groundwater sources shall provide sufficient capacity to achieve 4-log virus inactivation and removal.
c. Chlorine feed systems for secondary disinfection at a waterworks shall provide sufficient capacity to achieve a minimum chlorine residual at the entry point of 0.2 mg/L for more than 4 hours.
2. Chlorine feed systems for disinfection at a waterworks using a surface water source, a GUDI source, or both shall be sized to deliver the required dose with the largest unit out of operation. Small hypochlorination installations for groundwater source waterworks shall have a spare metering pump, unless it can be demonstrated to the satisfaction of the department that spare equipment is readily available from a local supplier. Spare parts shall be available for all chlorinators to replace parts that are subject to wear and breakage.
3. Consideration shall be given to providing multiple chlorine feed points at all waterworks. For conventional filtration treatment plants, chlorine feed points shall be provided for the source water, applied water to the filters, and filter effluent.
4. The piping providing the water for preparing the chlorine solution shall be designed to prevent contamination of the "bulk treated" finished water.
a. At all facilities treating surface water, pre-filtration and post-filtration disinfection systems shall operate independently of each other to prevent possible siphoning of partially treated water into the clearwell.
b. The water piping to each ejector shall have a separate shutoff valve. A master shutoff valve is prohibited.
5. Provisions shall be made to ensure uniform mixing of the chlorine with the water near the point of application.
6. Residual and contact time.
a. The owner of a waterworks using a surface water source, a GUDI source, or both shall provide a minimum residual (C) and contact time (T) as calculated in accordance with 12VAC5-590-500.
b. The owner of a waterworks using a groundwater source that is required to disinfect shall provide a minimum residual (C) and contact time (T) to achieve 4-log virus inactivation and removal based on maximum design flow rate. Provisions shall be made to prevent short circuiting. The contact basin shall be designed utilizing the appropriate baffle factors referenced in Table 500.15 of 12VAC5-590-500.
7. Automatic proportioning chlorinators shall be provided where the rate of flow is not reasonably constant.
8. Equipment shall be provided for measuring the chlorine residual, employing any method specified in 12VAC5-590-440. The equipment shall be capable of a chlorine residual measurement to the nearest 0.1 mg/L.
9. Continuous chlorine residual analyzers shall be provided at all waterworks that are required to filter and that serve 3,300 or more persons or at any waterworks required by the department. Where a continuous chlorine residual analyzer is provided, the department may require that the design incorporate an operator-selected high or low chlorine residual alarm.
B. Gas chlorine feed systems.
1. Equipment.
a. An ample supply of potable water shall be available for operating the chlorinator. Where a booster pump is required, duplicate equipment shall be provided, and when necessary, standby power shall be provided as well. Equipment for backflow prevention shall be provided. A pressure gauge shall be provided on each chlorinator mixing water piping.
b. Scales for weighing cylinders shall be provided at all waterworks using chlorine gas. At large waterworks, scales of the indicating and recording type shall be considered. Scales shall be recessed unless they are of the low-platform type.
c. Where a manifold of several cylinders is required to evaporate sufficient chlorine, consideration shall be given to the installation of gas evaporators.
d. Automatic switch-over of chlorine cylinders shall be provided to assure continuous disinfection.
2. Chlorine gas leak detection.
a. Automatic chlorine gas leak detection with strategically located sensors and related alarm equipment shall be provided for all installations.
b. A bottle of ammonia hydroxide solution shall be provided for detecting chlorine gas leaks.
3. Emergency cylinder repair kits shall be provided.
4. Consideration shall be given to the provision of caustic soda solution reaction tanks for absorbing the contents of leaking one-ton cylinders where the cylinders are in use.
5. Piping and connections for chlorine gas.
a. Pressure gauges shall be installed on the piping to each chlorinator. Piping systems shall be well supported and adequately sloped to allow drainage. Suitable allowance shall be made for pipe expansion due to changes in temperature.
b. Fittings and appurtenances shall be suitable for handling dry chlorine.
6. Building design.
a. Any building to house chlorine equipment or containers shall be designed and constructed to protect all components of the chlorine system from fire hazards. See 12VAC5-590-720.
b. If gas chlorination equipment and chlorine cylinders are to be in a building used for other purposes, a gas-tight partition shall separate this room from any other portion of the building. Doors to this room shall open only to the outside of the building and shall be equipped with panic hardware. These rooms shall be at ground level and should be separated from the feed area.
c. At least two means of exit shall be considered from each separate room or building in which chlorine is stored, handled, or used. All exit doors shall open outward.
d. A clear glass, gas-tight window shall be installed in an interior wall of the chlorinator room to permit the chlorinators to be viewed without entering the room.
e. Feed lines shall not carry chlorine gas beyond the chlorine feeder room unless the chlorine is under vacuum.
f. Chlorinator rooms shall be provided with a means of heating so that a temperature of at least 60°F can be maintained, but the room should be protected from excess heat. Cylinders shall be kept at essentially room temperature for at least 24 hours before use unless an evaporator is employed.
g. Forced, mechanical ventilation that provides one complete air change per minute shall be installed in all chlorine feed rooms and rooms where chlorine cylinders are stored. The inlet to the air exhaust duct from the room shall be near the floor, and the point of discharge shall be located so as not to contaminate the air inlet to any building or inhabited areas. Air inlets shall be located so as to provide cross ventilation with air and at a temperature that will not adversely affect the chlorination equipment. The vent hose shall run without traps from the chlorinator and shall discharge to the outside atmosphere above grade.
h. The electrical controls for the fans and lights shall automatically operate when the door is opened and can be manually operated from the outside without opening the door.
C. Calcium hypochlorite and sodium hypochlorite feed systems.
1. Both calcium hypochlorite and sodium hypochlorite shall be acceptable for disinfection.
2. Hypochlorite solution feeders of the positive displacement type shall be provided.
3. Adequate mixing of the calcium hypochlorite or sodium hypochlorite solutions shall be provided.
4. Special design considerations for bulk delivery systems:
a. Bulk sodium hypochlorite storage tanks shall be constructed of corrosion-proof materials. Pumps, piping, materials, and appurtenances exposed to the sodium hypochlorite shall be suitable for such use.
b. Sodium hypochlorite storage facilities shall be designed to keep ambient temperature and lighting low. Sodium hypochlorite fumes are corrosive and tanks shall be vented to the outside. Tanks shall be designed for ease of filling, draining, and transfer of contents.
c. Piping, valves, pumps, and pipe accessories shall be designed and configured so as not to allow accumulation of gases that could cause air locking or loss of prime in chemical feed piping or pumps.
d. The design shall provide a system of local or general exhaust features to keep employee exposures below the airborne exposure limits, as described in the Safety Data Sheet for the chemical used, in accordance with federal occupational safety and health standards (29 CFR § 1910.1200 (g)). Local exhaust ventilation is generally preferred because it controls contaminant emissions at the source and thus, preventing dispersion into the general work area which could result in corrosion or exposure. Exhaust equipment and accessories shall be corrosion proof.
e. An eye wash fountain and quick-drench facilities in the immediate work area shall be provided.
Statutory Authority
§§ 32.1-12 and 32.1-170 of the Code of Virginia.
Historical Notes
Derived from Virginia Register Volume 37, Issue 20, eff. June 23, 2021.
12VAC5-590-1002. Chloramination.
A. Chloramines shall be acceptable for secondary disinfection. Chloramines are formed by the reaction of ammonia and chlorine. Multiple chemical species may be created; however, monochloramine is the desired form.
B. The process shall be controlled to minimize formation of dichloramine and nitrogen trichloride, which can create objectionable taste and odors. Control should be sufficient to limit free ammonia leaving the chloramination facility to no more than 0.1 mg/L as nitrogen.
C. pH adjustment facilities shall be provided to maintain pH in the range of 7 to 8.
D. When use of chloramines is proposed, the potential increase of lead leaching within the distribution system shall be considered. Additional distribution system monitoring may be required by the department.
E. The owner shall inform the public before initiating any disinfection process involving chloramines, as directed by the department.
Statutory Authority
§§ 32.1-12 and 32.1-170 of the Code of Virginia.
Historical Notes
Derived from Virginia Register Volume 37, Issue 20, eff. June 23, 2021.
12VAC5-590-1003. Chlorine dioxide addition.
A. Chlorine dioxide may be considered as a pre-oxidant to control tastes and odors, reduce color, oxidize iron and manganese, and reduce DBPPs. Chlorine dioxide may be used for primary disinfection. Where chlorine dioxide is used, consideration shall be given to the formation of the byproducts chlorite and chlorate.
B. Chlorine dioxide is generated onsite from sodium chlorite and either chlorine gas or hypochlorite solution. Chlorine dioxide generation equipment shall be factory assembled, pre-engineered units with a minimum efficiency of 95%. The excess free chlorine shall not exceed 3.0% of the theoretical stoichiometric concentration required.
C. The owner shall inform the public before using chlorine dioxide, as directed by the department.
Statutory Authority
§§ 32.1-12 and 32.1-170 of the Code of Virginia.
Historical Notes
Derived from Virginia Register Volume 37, Issue 20, eff. June 23, 2021.
12VAC5-590-1004. Ozonation.
A. Ozone may be considered as a pre-oxidant to control tastes and odors, reduce color, oxidize iron and manganese, reduce DBPPs, and used for primary disinfection. Where ozone is used, consideration shall be given to the level of bromide and formation of brominated byproducts.
B. Ozone systems are typically comprised of four basic subsystems: ozone generation, feed gas preparation, ozone contactors, and off-gas disposal.
C. The PER shall evaluate water and gas flow rates, oxygen source, generator selection and sizing, contactor design, treatment process location, exhaust gas collection and destruction, and operator requirements.
D. Treatability studies using bench-scale or pilot-scale tests may be required as part of the PER to address the following:
1. Alternate points of ozone application;
2. Ozone demand tests, applied dose, transferred dose, and decay rates; and
3. Ozone byproducts, including bromide and bromate analyses.
E. Ozone systems shall be granted disinfection credit for Giardia lamblia, Cryptosporidium, and viruses, in accordance with 12VAC5-590-401 E 7 and 12VAC5-590-500, provided that they meet the requirements of this section.
1. Ozone residual levels shall be monitored continuously and recorded. For waterworks that claim inactivation credit for ozone, a minimum of two dedicated, online monitors per ozone contactor shall be provided. The location of the monitors shall be acceptable to the department. A portable ozone monitor shall be provided as a backup.
2. Ozone systems using multiple, consecutive contact chambers with gaseous ozone injected in the initial chambers, shall be designed to measure the ozone residual and compute log inactivation of Giardia and virus using the CeffluentT10 Method or the Log Integration CT10 Method, as described in the "Long Term 2 Enhanced Surface Water Treatment Rule Toolbox Guidance Manual," EPA Office of Water (4606), EPA 815-R-09-016, April 2010.
3. Sampling lines shall be designed to minimize the reaction time (typically less than 10 seconds conveyance time).
F. Alarms shall be provided for ozone process control safety. Automatic shutdown features shall be considered.
Statutory Authority
§§ 32.1-12 and 32.1-170 of the Code of Virginia.
Historical Notes
Derived from Virginia Register Volume 37, Issue 20, eff. June 23, 2021.
12VAC5-590-1005. Ultraviolet light (UV) disinfection.
A. All UV reactors shall conform to NSF/ANSI/CAN standards.
B. Each reactor train shall be equipped with an individual flow meter or a single flow meter in conjunction with differential pressure sensors in each treatment train. Reactors shall be sized to treat the design flow.
C. Hydraulic design shall ensure that lamps are submerged and that the entrance of air, negative pressure, or pressure surges in the reactors is prevented. Open channel flow reactors are prohibited.
D. A pressure gauge shall be provided upstream of each reactor. The design shall ensure that the reactor's maximum rated pressure cannot be exceeded.
E. Water quality parameters that may affect UV disinfection system performance shall be evaluated, including calcium, iron, manganese, hardness, and alkalinity. Pretreatment shall be considered for water quality parameters that may result in lamp sleeve fouling.
F. A building to enclose and protect all UV equipment shall be provided. Adequate space between control panels, power supply, and the reactor equipment shall be provided to allow for routine operation and maintenance, including removing lamp and wiper assemblies and for off-line chemical cleaning of reactor lamps.
G. An operation and maintenance manual shall be provided for all UV reactors.
H. UV systems may be used for primary disinfection and shall be granted log inactivation credit for Giardia lamblia, Cryptosporidium, and viruses in accordance with Table 401.7, provided that they meet the requirements of 12VAC5-590-401 E 7 c and this subsection.
1. Only UV reactors that have undergone independent, third-party oversight of the validation testing on a fully assembled system to determine the operating conditions under which the reactors deliver the required UV dose shall be considered for log inactivation credit.
2. The dose-monitoring strategy shall be either the UV intensity set point approach or the calculated dose approach as described in the "Ultraviolet Disinfection Guidance Manual For The Final Long Term 2 Enhanced Surface Water Treatment Rule," Office of Water (4601), EPA 815-R-06-007, November 2006. The dose-monitoring strategy shall be demonstrated through the UV reactor validation testing.
3. At least two reactors shall be provided. Reactors shall be sized to treat the design flow with the largest reactor out of service.
4. Continuous monitoring sensors shall be provided to measure UV intensity. A continuous sensor shall also be provided to measure ultraviolet transmittance (UVT) if the calculated dose approach is utilized.
a. The number of sensors provided shall be the same as that used in validation testing of the reactor.
b. Output from a continuous UVT analyzer shall be capable of being input directly into a control loop for each UV reactor, a SCADA system, or both. A bench-top spectrophotometer may be provided instead of a continuous UVT analyzer.
c. All signals from the sensors shall be displayed for operator response and for recordation.
d. At least one reference sensor for calibration of online UV intensity sensors shall be provided. Reference sensors shall be capable of calibration against a traceable standard.
e. Continuous recording equipment shall be provided with the monitoring sensors to store in memory or print one data point at least every four hours.
5. A means of flow distribution and control among multiple reactors shall be provided. The hydraulic flow profiles and piping configuration shall be identical to or more protective than that tested during equipment validation.
a. For onsite validation, the inlet and outlet piping configuration for the UV facility shall be designed according to manufacturer recommendations and to accommodate any site-specific constraints.
b. To avoid jetting flow and swirling flow, consideration shall be given to exclude expansions for at least 10 pipe diameters upstream of the reactor and to exclude out-of-plane 90-degree bends in series.
c. Each UV reactor shall be capable of being isolated and removed from service. Isolation valves upstream and downstream of each reactor, a drain, and sample taps for each reactor treatment train shall be provided. If the isolation valves are also used for flow control, then the flow control valve shall be located downstream of the UV reactor to limit the disturbance of the flow entering the UV reactor. Bypass piping shall not be allowed.
d. The lateral piping for each UV reactor train shall be sized and configured to provide approximately equal head loss through each UV reactor train over the validated range of flow rates.
6. The control system shall be capable of meeting the monitoring and reporting requirements in 12VAC5-590-401 and 12VAC5-590-570.
7. Automatic shutdown capability under critical alarm conditions shall be provided, including lamp or ballast failure, low liquid level, and high temperature. Alarms shall be provided for low UV validated dose, low UV intensity, low UV transmittance, high flow rate, and mechanical wiper failure.
8. Ground-fault circuit interrupters shall be provided for all lamps. Backup power shall be considered.
9. The owner shall develop a start-up plan and submit the plan to the department for approval. The plan shall include functional testing, determination of validated operating conditions and control settings, performance testing, development of an operation and maintenance manual, and inspection schedules.
I. UV systems not intended for primary disinfection may be used provided that they meet the requirements of this subsection.
1. Continuous sensors to measure UV intensity shall be considered.
2. Each UV reactor shall be capable of being isolated, removed from service, and be provided with bypass piping.
3. Automatic shutdown capabilities shall be provided in the event of lamp or ballast failure.
Statutory Authority
§§ 32.1-12 and 32.1-170 of the Code of Virginia.
Historical Notes
Derived from Virginia Register Volume 37, Issue 20, eff. June 23, 2021.