| (a) Pump Controls.
(1) A lift station pump must operate automatically,
based on the water level in a wet well. Pump controls must be designed
to prevent surcharges in the collection system and must be designed
to prevent adverse effects on the operation of the wastewater treatment
facility.
(2) The location of a wet well water level mechanism
must ensure that the mechanism is unaffected by currents, rags, grease,
or other floating materials.
(3) A wet well water level mechanism must be accessible
without entering the wet well.
(4) Wet wells with a bubbler system require dual air
supplies and dual controls.
(5) Motor control centers must be mounted high enough
above grade, but in no case less than 4.0 inches above grade, to prevent
water intrusion and corrosion from standing water in the enclosure.
Motor control centers must also be protected from the entrance of
corrosive gases from wet wells or piping.
(6) Electrical equipment and electrical connections
in a wet well or a dry well must meet National Fire Protection Association
70 National Electrical Code® explosion prevention requirements,
unless continuous ventilation is provided.
(7) Electronic wet well level control systems must
also use a float switch or similar manual backup.
(8) Wet well control settings must be designed to discourage
septic conditions in a lift station.
(9) Wet well control settings must be designed to prevent
overloading of downstream pipes and treatment units.
(b) Wet Wells.
(1) A wet well must be enclosed by watertight and gas
tight walls.
(2) A penetration through a wall of a wet well must
be gas tight.
(3) A wet well must not contain equipment requiring
regular or routine inspection or maintenance, unless inspection and
maintenance can be done without a person entering the wet well.
(4) A gravity pipe discharging to a wet well must be
located so that the invert elevation is above the liquid level of
a pump's "on" setting.
(5) Gate valves and check valves are prohibited in
a wet well.
(6) Gate valves and check valves may be located in
a valve vault next to a wet well or in a dry well. Valve vaults shall
be ventilated according to subsection (d) of this section.
(7) A pump must run continuously during the pump cycle
time, which begins when the pump is activated by the pump controls.
Pump cycle time, based on peak flow, must equal or exceed those in
the following table:
Attached Graphic
(8) An evaluation of minimum wet well volume requires
the following formula:
Attached Graphic
(c) Dry well access.
(1) An underground dry well must be accessible for
maintenance and shall be ventilated according to subsection (d) of
this section.
(2) A stairway in a dry well must use non-slip steps
and conform to Occupational Safety and Health Administration regulations
with respect to rise and run.
(3) A ladder in a dry well must be made of non-conductive
material and be rated for the load necessary for staff and equipment
to descend and ascend.
(d) Lift Station Ventilation.
(1) Passive Ventilation for Wet Wells.
(A) Passive ventilation structures must include screening
to prevent the entry of birds and insects to a wet well. The screening
must be made of corrosion-resistant material.
(B) All mechanical and electrical equipment in a wet
well with passive ventilation must be constructed in compliance with
explosion requirements in the National Fire Protection Association
70 National Electrical Code®.
(C) A passive ventilation system must be sized to vent
at a rate equal to the maximum pumping rate of a lift station, but
not to exceed 600 feet per minute through a vent pipe.
(D) The minimum acceptable diameter for an air vent
is 4.0 inches.
(E) All vent outlets must be at least 1.0 foot above
a 100-year flood plain elevation.
(2) Mechanical Ventilation in Lift Stations.
(A) Dry Wells.
(i) A dry well must use mechanical ventilation.
(ii) Ventilation equipment under continuous operation
must have a minimum capacity of six complete air exchanges per hour.
(iii) Ventilation equipment under intermittent operations
must provide a minimum capacity of 30 complete air exchanges per hour
and be connected to the lift station's lighting system.
(B) Wet Wells.
(i) Mechanical ventilation systems for wet wells must
operate continuously.
(ii) The ventilation equipment must provide at least
12 complete air exchanges per hour and be constructed of corrosion-resistant
material.
(iii) An owner shall implement odor control measures
necessary to prevent a wet well from becoming a nuisance. An owner
shall consider the source of potential odor, turbulence, residence
time, and other factors that contribute odor at a lift station when
selecting odor control measures.
(iv) All mechanical and electrical equipment in a wet
well with mechanical ventilation must be constructed in compliance
with explosion requirements in National Fire Protection Association
70 National Electrical Code®.
(e) Wet Well Slopes.
(1) A wet well floor must have a smooth finish and
minimum slope of 10% to a pump intake.
(2) A wet well design must prevent deposition of solids,
grease, and debris under normal operating conditions.
(3) A lift station with greater than 5.0 million gallons
per day firm pumping capacity must have anti-vortex baffling.
(f) Hoisting Equipment. A lift station must have permanent
hoisting equipment or be accessible to portable hoisting equipment
for removal of pumps, motors, valves, pipes, and other similar equipment.
(g) Valve Vault Drains. A floor drain from a valve
vault to a wet well must prevent gas from entering a valve vault by
including flap valves, "P" traps, submerged outlets, or a combination
of these devices.
(h) Dry Well Sump Pumps.
(1) Pumps.
(A) A dry well must use dual sump pumps, each with
a minimum capacity of 1,000 gallons per hour and capable of handling
the volume of liquid necessary to prevent accumulation of water from
condensation and incidental leaks during peak pumping operations.
(B) A sump pump must have a submersible motor and watertight
wiring.
(C) A dry well floor must slope toward the sump. A
sump must include sump pumps sized to prevent accumulation of water
from condensation and incidental leaks.
(D) The minimum sump depth is 6.0 inches. The sump
must prevent standing water from accumulating on a dry well floor
under normal operation.
(E) A sump pump must operate automatically by use of
a float switch or another level-detecting device.
(2) Pipes.
(A) A sump pump must use independent piping that is
capable of discharging more than the maximum liquid level of an associated
wet well at a rate that will prevent overflow of the wet well.
(B) A sump pump outlet pipe must be at least 1.5 inches
in diameter and have at least two check valves in series.
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