(a) Primary treatment must remove the settleable and
floatable solids in the influent prior to the wastewater entering
a stabilization lagoon.
(b) Odor Management.
(1) A stabilization lagoon must be located so that
odors from the stabilization lagoon will not cause a nuisance.
(2) If uncontaminated water is available, a stabilization
lagoon must be pre-filled with uncontaminated water to the 2.0 foot
level at start-up.
(3) A stabilization lagoon system must include a piping
arrangement that allows the recirculation of effluent from a final
lagoon to the influent side of an initial stabilization lagoon.
(4) A stabilization lagoon may return recirculation
water by surface spray to assist in maintaining aerobic conditions
at the lagoon surface and to reduce potential odor.
(c) Minimum Number of Wastewater Stabilization Lagoons.
At least two stabilization lagoons are required to comply with secondary
treatment limits. The stabilization lagoons must be operated in series,
following the primary treatment unit.
(d) Stabilization Lagoon Design.
(1) The minimum length-to-width ratio of a stabilization
lagoon is 3.0 to 1.0.
(2) Inlet and outlet structures must be adjustable
to assist in controlling vegetative growth. Inlet and outlet structures
must allow the water level to be raised and lowered by at least 6.0
inches.
(e) Pipe and Hydraulic Equipment.
(1) All structures and pipes in a stabilization lagoon
must be sized to transport at least 250% of the wastewater treatment
facility's design flow.
(2) The inlet and outlet structures must be sized
to convey the volume contained within the top 6.0 inches of a lagoon
within a 24-hour period, based on the normal water level at design
flow and the corresponding pressure head.
(3) The pipe and recirculation system must allow a
stabilization lagoon system to comply with the wastewater treatment
facility's permitted effluent limitations, even with any one lagoon
out of service.
(f) Maximum Surface Organic Loading Rate for Stabilization
Lagoons.
(1) The maximum surface organic loading rate on a
stabilization lagoon series is 35 pounds (lbs) of five-day biochemical
oxygen demand (BOD5 ) per acre per day.
(2) The maximum surface organic loading rate on the
first lagoon in a stabilization lagoon series is 75 lbs of BOD5 per acre per day.
(3) The surface organic loading rate applied to a
stabilization lagoon series is equal to the total influent organic
loading minus any reduction in organic load provided by the primary
treatment units.
(g) Inlet and Outlet Structures.
(1) A stabilization lagoon outlet must include removable
baffles to prevent floating material from being discharged, and must
be constructed to operate correctly as the level of the lagoon surface
varies under normal operating conditions.
(2) An outlet must be at least 18 inches but not more
than 24 inches below the water surface in a stabilization lagoon
to control the discharge of duckweed and floating algae.
(3) A multipurpose control structure may be used to
facilitate normal operational functions such as drawdown, flow distribution,
adjusting water depth, flow measurement, sampling, access for pump
for recirculation, chemical addition, and exclusion of floating materials.
A multipurpose control structure may also be used to minimize the
number of special purpose structures in a stabilization lagoon.
(4) A pipe embankment penetration must have a seep
water-stop collar.
(5) A stabilization lagoon must have a drainpipe that
allows the stabilization lagoon to be emptied for maintenance and
may use a pump as part of a drainage system. If a permanent drain
pipe will not be installed, a temporary pipe suction station must
be provided.
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