TM 5-814-9
6-19. Sediment removal
water trapped in the sediment is aided by gravel
packed drains placed along the center wall or in the
Sediment basins are not equipped for continuous removal of
bottom of each cell. The pumping system shown in
solids and therefore, the basin should be sized to allow solids
the figure is an alternate since, at this point in the
accumulation over at least one year based on the estimated
treatment system, the main stream flow is by gravity
solids removed from the vehicles. To remove the accumulated
and drainage may occur below the hydraulic grade
solids, the basins are first drained of water to the maximum
line. The immediate return of the water drained
extent possible with slow drains, sediment dewatering drains,
from the sediment basin to the treatment process is
and/or pumps as described in the previous section. The solids
desirable in order to facilitate the removal of any
are then removed using front-end loaders and dump trucks that
disturbed sediment and oil.
access the solids zone via the concrete ramp. The material is
hauled away for proper disposal in accordance with local, State,
c.
The valving depicted in figure 6-8 allows lowering
and Federal regulations.
the water level in the sediment basin to the expected
maximum sediment level and dewater the captured
6-20. Oil removal
sediment. Gravel packed drains or trenches are
Free floating oils and greases carried into the sediment basin as
located around the inside perimeter of the basin or
a product of vehicle washing are lighter than water and
in the floor and consist of a perforated pipe encased
therefore rise to the surface. The oils and greases are removed
in filter fabric and gravel. Valving and pumping
using motorized surface tube-type oil skimmers in each basin.
facilities may be placed at either end of the sediment
The skimmings are stored in an above-ground or underground
basin. Drains shall be located below the bottom of
waste oil storage tank located near the sediment basins.
the basin or otherwise protected so that, during
Skimmers are usually located at the downwind end of the
removal of sediment, they will not be disturbed or
basins. Floating or fixed baffles which extend below the effluent
damaged. The trench method can be used at either
weir elevation may be provided to direct oils toward the
the influent or effluent end of the sediment basin.
skimmer and to prevent the carryover of oils past the effluent
weir.
6-9
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