(a) General. Steel finished water storage structures shall be provided using the requirements of the AWWA D100 or AWWA D103. All tank design and foundation design shall be performed by a registered professional engineer and the plans or contractor-furnished information shall so designate the registered engineer providing the design. Materials other than steel may be used for water storage tanks. - (i) Sizing. Storage facilities shall have the capacity to meet domestic demands, and where required, fire protection storage.
- (A) Water systems serving less than 50,000 gallons (189 m3) on the design average daily demand shall provide clearwell and system storage capacity equal to the average daily demand.
- (B) Water systems serving from 50,000 to 500,000 gallons (189-1,892 m3) on the design average daily demand shall provide clearwell and system storage capacity equal to the average daily demand plus fire storage, based on recommendations established by the State Fire Marshall or local fire agency.
- (C) Water systems serving in excess of 500,000 gallons (1.892 m3) on the design average daily demand shall provide clearwell and system storage capacity equal to 25 percent of the design maximum daily demand, plus added fire storage based on recommendations established by the State Fire Marshall or local fire agency.
- (D) Storage need not be provided in a well supply system where a minimum of two wells are provided and the maximum hour demand or fire demand, whichever is greater, can be supplied with the largest well out of service.
- (ii) Location of ground level reservoirs.
- (A) The bottom of reservoirs and standpipes shall be above or protected from the 100year flood or highest flood of record, whichever is greater.
- (B) When the bottom is below normal ground surface, it shall be placed above the groundwater table. Sewers, drains, standing water, and similar sources of possible contamination must be kept at least 50 feet (15.2 m) from the reservoir. Watermain pipe, pressure tested in place to 50 psi (345 kPa) without leakage, may be used for gravity sewers at distances greater than 20 feet (6.1 m) and less than 50 feet (15.2 m).
- (C) The top of the reservoir walls shall not be less than 18 inches (0.46 m) above normal ground surface. Clearwells constructed under filters are exempted from this requirement when the total design gives the same protection.
- (iii) Protection. All finished water storage structures shall have suitable watertight roofs which exclude birds, animals, insects, and excessive dust.
- (iv) Protection from trespassers. Security-type fencing, locks on access manholes, and other precautions shall be provided to prevent trespassing, vandalism, and sabotage at above ground storage facilities. Below ground level storage facilities may be exempt from the fencing requirements.
- (v) Drains. No drain on a water storage structure may have a direct connection to a sewer or storm drain. Water storage structures drained to sewer or storm drains shall be drained through piping which allows an air gap such that the drain pipe is at least three pipe diameters above the ground level at the drain point to the sanitary or storm drain.
- (vi) Overflow. All water storage structures shall be provided with an overflow which is brought down to an elevation between 12 and 24 inches (0.3-0.61 m) above the ground surface, and discharges over a drainage inlet structure or a splash plate. No overflow may be connected directly to a sewer or a storm drain. All overflow pipes shall be located so that any discharge is visible.
- (A) When an internal overflow pipe is used on elevated tanks, it shall be located in the access tube. For vertical drops on other types of storage facilities, the overflow pipe shall be located on the outside of the structure.
- (B) The overflow of a ground level structure shall open downward and be screened with noncorrodible screen installed within the pipe at a location least susceptible to damage by vandalism.
- (C) The overflow pipe shall be of sufficient diameter to permit wasting of water in excess of the filling rate.
- (vii) Access. Finished water storage structures shall be designed with access to the interior for cleaning and maintenance. Manholes above the waterline shall be framed at least 4 inches (0.1 m) above the surface of the roof at the opening; on ground level structures, manholes should be elevated a minimum of 24 inches (0.61 m) above the top. The manholes shall be fitted with a solid watertight cover which overlaps the framed opening and extends down around the frame at least 2 inches (5 cm). The cover shall be hinged at 1 side and shall have a locking device. The man-hold shall have a minimum inside opening diameter of 24 inches.
- (viii) Vents. Finished water storage structures shall be vented. Overflows shall not be considered as vents. Open construction between the sidewall and roof is not permissible. Vents shall prevent the entrance of surface water and rainwater, and shall exclude birds and animals.
- (A) For elevated tanks and standpipes, 24 mesh noncorrodible screen may be used.
- (B) For ground level structures, the vents shall terminate in an inverted U construction with the opening a minimum of 24 inches (0.61 m) above the roof and covered with 24 mesh noncorrodible screen installed within the pipe at a location least susceptible to vandalism.
- (ix) Roof and sidewall. 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.
- (x) Painting and/or cathodic protection. Protection shall be given to metal surfaces by paints or other protective coatings, by cathodic protective devices, or by both. Materials and procedures shall conform to AWWA Standard D102. Paint systems, after proper curing, shall not transfer any substance to the water which will be toxic or cause tastes or odors. Paints containing lead or mercury shall not be used. All paints and other protective coatings shall be compatible.
- (xi) Disinfection. Finished water storage structures shall be specified to be disinfected in accordance with AWWA Standard D105. Sampling shall be specified.
(b) Plant storage. - (i) Washwater tanks. Washwater tanks shall be sized, in conjunction with available pump units and finished water storage, to provide the backwash water required by Section 10(i). The storage and pumping shall be sized so that a minimum of two filters may be backwashed in rapid succession.
- (ii) Clearwell. Clearwell storage shall be sized, in conjunction with distribution system storage, to relieve the filters from having to follow fluctuations in water use. Where water is pumped from clearwater storage to the system, an overflow shall be provided.
- (iii) Adjacent compartments. Finished water must be separated from unfinished water in adjacent compartments by double walls.
- (iv) Basins and wetwells. Receiving basins and pump wetwells for finished water shall be designed as finished water storage structures.
(c) Hydropneumatic tanks. Hydropneumatic (pressure) tanks may be used as the only storage facility when the system serves less than 50 homes. When servicing more than 50 homes, ground or elevated storage designed in accordance with Section 13(a) should be provided. Pressure tank storage is not to be considered for fire protection purposes. Pressure tanks shall meet ASME code requirements or local laws and regulations for the construction and installation of unfired pressure vessels. - (i) Location. The tank shall be located above normal ground surface and be completely housed.
- (ii) Sizing. The capacity of the wells and pumps in a hydropneumatic system shall be at least 10 times the average daily consumption rate. The gross volume of the hydropneumatic tank, in gallons, shall be at least 10 times the capacity of the largest pump, rated in gallons per minute. For example, a 250 gpm (1,364 m3/d) pump should have a 2,500 gallon (9.46 m3) pressure tank.
- (iii) Piping. The tank shall be plumbed with bypass piping.
- (iv) Appurtenances. Each tank shall have an access manhole, a drain, and control equipment consisting of pressure gauge, water tight glass, automatic or manual air blowoff, means for adding air, and pressure operated startstop controls for the pumps.
020-12 Wyo. Code R. § 12-13