Storage - Public Water Systems - page 963

drains, pump mountings, control ports, or piping for inflow and outflow. The following
additional factors should be considered:

Any pipes running through the roof or side wall of a finished water storage
structure should be welded or properly gasketed in metal tanks, or connected to
standard wall castings that are poured in place during the forming of the concrete
structure. These wall castings should have flanges embedded in the concrete.

•

Openings in a storage structure roof or top designed to accommodate control
apparatus or pump columns should be curbed and sleeved with proper additional
shielding to prevent surface water access.

•

Valves and controls should be located outside the storage reservoir so that valve
stems and similar projections will not pass through the roof or top of the reservoir
and will not be subject to contamination by surface water.

•

Drainage for Roof or Cover The roof or cover of the storage structure should be
well drained with a minimum 2 percent slope. Downspout pipes should not enter or
pass through the reservoir. Parapets or similar features that would tend to hold water
and snow on the roof are not recommended. Floating covers should be designed with
perimeter systems to collect and drain or pump away rainwater.

Freezing All finished water storage structures and their appurtenances, especially the
riser pipes, overflows, and vents, should be designed to prevent freezing. Consideration
should be given to heating and / or insulation of exposed pipes and valves. 13

Internal Walkways Every walkway over finished water in a storage structure should
have a solid floor with raised edges so that shoe scrapings and dirt will not fall into
the water.

Grading The area surrounding a ground-level structure should be graded in a manner
that will prevent surface water from standing within 50 feet (15.2 m) of the structure.

Painting and Cathodic Protection The AWWA standards for painting exclude the
use of paints that might add toxic materials to the stored water through leaching or
other action. Proper protection should be given to metal surfaces by paints or other
protective coatings, by cathodic protective devices, or by both. Use paint systems that
are consistent with AWWA standards and are ANSI / NSF certified for potable water
contact. Cathodic protection devices must be regularly inspected and maintained for
satisfactory performance. Painting and maintenance of storage tanks are critical ele-
ments in ensuring public safety and ensuring a long tank service life. 14-22
Exterior and interior coating systems for welded steel tanks and recoating of as-
sembled bolted steel tanks are specified ANSI / AWWA Standard D102. The quality of
application of any field-applied coating system is of critical importance in the long-
term serviceability of the tank. Therefore, prior to selecting and specifying the coating
systems, the designer must consider or define acceptable ambient conditions expected
during coating application.
Factory-applied coating systems for bolted steel tanks should be in accordance with
ANSI / AWWA Standard D103. This standard covers glass-fused-to-steel, thermoset
liquid suspension, and thermoset powder coatings. Several manufacturers offer bolted