Article 5. Finished Water Storage Structures
12VAC5-590-1080. Basic finished water storage structure design criteria.
A. The materials and designs used for finished water storage structures, including associated pipe and valves, shall provide stability and durability as well as protect the quality of the stored water. Steel, concrete, composite, and plastic storage structures shall be designed, constructed, cleaned, disinfected, and tested in accordance with the following AWWA standards, where applicable: D100-11, D103-19, D107-16, D108-19, D110-13, D115-20, D120-19, D121-12, and C652-19.
B. Safety cages, rest platforms, roof-ladder handrails, and other safety devices shall be provided as required by VOSH laws and regulations.
C. Location of finished water storage structures.
1. The bottom of ground-level reservoirs, storage tanks, and standpipes should be placed above finished grade to ensure positive drainage away from the structure.
2. Where the bottom must be below normal ground surface, it shall be placed above the groundwater table. Sewers, drains, standing water, and similar sources of contamination shall be kept at least 50 feet from the finished water storage structure. Pipe conforming to water distribution pipe standards of 12VAC5-590-1110, pressure tested in place without leakage, shall be used for gravity sewers at lesser separations.
3. The top of all storage facilities shall not be less than two feet above the normal ground surface and shall be above the 100-year flood elevation. Any clearwell constructed under filters may be exempted from this requirement when the total design gives the same protection.
D. Pressure variation. The maximum variation between normal operational high and low water levels in finished water storage structures which float on a distribution system shall not exceed 30 feet.
E. Level controls.
1. Adequate controls shall be provided to enable sufficient tank turnover, water quality maintenance, avoidance of overflows, and efficient operations.
2. A telemetery system with recording capability shall be considered to transmit the operating levels in distribution system storage facilities to a location where qualified personnel may access the data at all times.
3. Altitude valves or equivalent controls shall be provided.
4. For tanks with a monitoring system, warnings or alarms indicating overflow, low level, and pump malfunction shall be provided.
Statutory Authority
§§ 32.1-12 and 32.1-170 of the Code of Virginia.
Historical Notes
Derived from VR355-18-011.01 § 3.45, eff. August 1, 1991; amended, Virginia Register Volume 37, Issue 20, eff. June 23, 2021.
12VAC5-590-1081. Atmospheric tank storage.
A. Protection.
1. All finished water storage structures shall have suitable watertight roofs or covers that exclude birds, animals, and insects.
2. All finished water storage structures shall be designed to prevent vandalism and entrance by animals or unauthorized persons.
B. Finished water storage structures shall be designed to facilitate turnover of water. Consideration shall be given to locating inlet and outlet pipes at different elevations and locations, tank mixers, and other acceptable means to avoid stagnation. Excessive storage capacity shall be avoided to prevent water quality deterioration. See 12VAC5-590-640 B 3.
C. Drains.
1. No drain on a finished water storage structure shall create a cross-connection hazard.
2. All finished water storage structures shall be equipped with separate drains discharging to the atmosphere. Drainage of finished water storage structures to the distribution system through inlet and outlet piping is prohibited.
D. Overflows.
1. Finished water storage structures shall be provided with a downward-discharging, screened overflow pipe. The discharge pipe shall be brought down near the ground surface and into a drainage inlet structure or a splash plate that will divert the overflow away from the storage structure. The overflow pipe discharge shall be high enough above normal or graded ground surface to prevent the entrance of surface water.
2. Overflow pipe screens shall be installed so as to withstand the force of overflows. Properly designed flapper valves or rubber flex-type valves may be used instead of screens if approved by the department.
E. Inlet and discharge pipes.
1. Elevated tanks with riser pipes over eight inches in diameter shall have protective bars over the riser opening inside the tank.
2. Inlet and outlet pipes from water storage facilities shall be located in a manner that will prevent the flow of sediment into the distribution system.
F. Finished water storage structures shall be designed with convenient access to the interior for cleaning and maintenance. Ladders, ladder guards, balcony railings, and safely located entrance hatches shall be provided where applicable. Hatches, manholes, or scuttles above the waterline shall be:
1. Framed at least four inches, preferably six inches, above the surface of the roof at the opening; on ground-level structures, manholes should be elevated 24 to 36 inches above finished grade;
2. Fitted with a solid watertight cover that overlaps the framed opening and extends vertically down around the frame at least two inches (shoebox type);
3. Hinged at one side; and
4. Fitted with a locking device.
G. Finished water storage structures shall be vented by separate vent structures. Open construction between the side wall and roof is prohibited.
1. Vents shall prevent the entrance of surface water.
2. Vents shall exclude birds, animals, and insects and be constructed of noncorrodible material. Screens shall be designed to be frost-free or capable of relieving pressure or vacuum in the event of frosting or clogging.
3. Vents on ground-level structures shall terminate in an inverted U construction, with the vent terminating 24 to 36 inches above roof or finished grade.
H. Penetrations. The roof and sidewalls of all structures shall be watertight with no openings except properly constructed vents, manholes, overflows, risers, drains, pump mountings, control ports, or piping for inflow and outflow.
1. All pipes running through the roof or sidewall of a finished water storage structure shall be welded or properly gasketed in metal tanks or should be connected to standard wall castings that were placed during the forming of a concrete structure; these wall castings shall have flanges imbedded in the concrete.
2. Valves and controls shall be located outside the finished water storage structure so that valve stems and similar projections will not pass through the roof or top of the structure.
3. Downspout pipes for roof drainage shall not enter or pass through the structure.
I. All finished water storage structures and their appurtenances, especially the riser pipes, overflows, and vents shall be designed to prevent freezing that will interfere with proper functioning.
J. Every catwalk over finished water in a storage structure shall have a solid floor with raised edges designed so that shoe scrapings and dirt will not fall into the water.
K. The area surrounding a ground-level structure shall be graded in a manner that will prevent surface water from standing within 50 feet of the structure.
L. Proper protection shall be given to metal surfaces by paints or other protective coatings, by cathodic protective devices, or both, in accordance with the NSF/ANSI/CAN Standard 61-2020, AWWA Standards D102-17, D104-17, and D106-20, or an approved equivalent, where applicable.
M. All finished water storage facilities shall be cleaned to remove all dirt and loose materials before disinfection of the structure. Only potable water shall be used to clean and rinse the water storage facilities. All equipment including brooms, brushes, spray equipment, and worker's boots shall be disinfected before they are used to clean the storage facilities.
N. Disinfection. All finished water storage facilities shall be satisfactorily disinfected in accordance with AWWA Standard C652-19 before being placed in operation. The disinfection of the storage facilities shall be repeated until it is determined, by bacteriological testing, that the water is free of coliform bacteria.
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.
12VAC5-590-1082. Pressure tank storage.
A. When hydropneumatic tanks are used, they shall comply with the requirements of state and local laws and regulations for the construction and installation of unfired pressure vessels.
B. Pressure tanks shall be located above the normal ground surface with the operating end of the tank containing the inlet pipe, the pressure gauge, and other appurtenances projecting into a building with climate controls to prevent freezing. Alternatively, it may be completely housed, if adequate access is provided for inspection, removal, and replacement.
C. Pressure tanks shall have bypass piping to permit operation of the system while the tank is being cleaned, repaired, or painted.
D. Pressure tanks shall have an access manway, a drain, and control equipment consisting of a pressure gauge, water sight glass, automatic or manual air blowoff, pressure and vacuum relief valves, and mechanical means for adding air. Pressure tanks smaller than than 120 gallons and bladder tanks are not required to have an access manway, sight glass, or vacuum relief valve.
E. Pressure tanks and pumps shall be designed to minimize pump cycling and to operate within manufacturer recommendations.
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.
12VAC5-590-1090. Plant storage.
A. Backwash water storage tanks shall be sized in conjunction with available pump units and finished water storage to provide the filter backwash water required. Consideration shall be given to the possibility of having to wash more than one filter at a time or several filters in succession.
B. Clearwell storage shall be sized, in conjunction with distribution system storage, to relieve the filters from having to follow fluctuations in water use or meet peak demands, including filter backwash water. When finished water storage is used to provide proper contact time for disinfection, special attention shall be given to size, drawdown, and baffling. Plant clearwells shall be equipped with a raised viewing port having a clear glass or plastic viewing window and a submerged, waterproofed electric light.
C. Finished water shall not be stored or conveyed in a compartment adjacent to nonpotable water when the two compartments are separated by a single wall.
D. Receiving basins and pump wet wells for finished water shall be designed as finished water storage structures.
Statutory Authority
§§ 32.1-12 and 32.1-170 of the Code of Virginia.
Historical Notes
Derived from VR355-18-011.02 § 3.46, eff. August 1, 1991; amended, Virginia Register Volume 37, Issue 20, eff. June 23, 2021.
12VAC5-590-1100. (Repealed.)
Historical Notes
Derived from VR355-18-011.03 § 3.47, eff. August 1, 1991; repealed, Virginia Register Volume 37, Issue 20, eff. June 23, 2021.