| (a) A wastewater treatment facility must use a coarse
screen, unless all flow entering a wastewater treatment facility is
processed through a grinder pump or grinding device.
(b) A coarse screen must include an emergency overflow
sized to handle the peak flow of the wastewater treatment facility.
(c) A coarse screen must include a way to divert flow
to the emergency overflow.
(d) If the primary channel uses a mechanically cleaned
coarse screen, the emergency overflow must also have a coarse screen.
(e) Coarse Screen Design.
(1) For a manually cleaned coarse screen, the clear
openings between the bars must be at least 0.5 inch but not more than
1.0 inch.
(2) For a mechanically cleaned coarse screen, the clear
openings between the bars must be at least 0.25 inch but not more
than 1.0 inch.
(3) A manually cleaned coarse screen must use a bar
rack sloped at least 30 degrees but not more than 60 degrees from
horizontal.
(4) A manually cleaned coarse screen must be attached
to a horizontal platform that allows draining and temporary screenings
storage to prevent unauthorized discharge between cleanings.
(5) A mechanically cleaned coarse screen must be designed
with equipment that automatically collects and disposes of screenings.
(f) Coarse Screen Hydraulics.
(1) The velocity of wastewater through a coarse screen
must be at least 1.0 foot per second, but not more than 3.0 feet per
second at design flow.
(2) The inlet channel for a coarse screen must be designed
to minimize the deposition of solids.
(3) The flow line of the inlet channel must not exceed
6.0 inches below the invert elevation of the influent.
(g) Corrosion Resistance. A coarse screen and related
structures must be designed to resist the effects of a corrosive environment,
including long-term exposure to hydrogen sulfide.
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