TM 5-814-9
Section III. PRIMARY TREATMENT
6-11. Function
c.
Dual-cell configuration with bath. A dual-cell
system for use with baths in large facilities is shown
All wastewater from the CVWF must undergo primary treat-
in figures 6-3 and 6-4. Before bath(s) are to be
ment. A concrete sediment basin with a oil skimmer device is
emptied into the sediment basin, the operator should
provided to separate and remove contaminants such as grease,
assure that the water level in one of the basin cells
oil, and sediment by gravity. Free oil shall be removed in this
in the sediment basin is at low level. The volume of
basin prior to pumping which could cause oils to emulsify.
bath water will be stored in this cell. The adjacent
Wheeled vehicle access shall be provided to this basin for
cell continues to provide primary treatment for
removing the large volumes of sediment that accumulate in this
wastewater from the washing facilities. This
basin. The bottom of the basin should be sloped approximately
configuration allows the entire surge volume of
one percent away from the entrance ramp to assist in dewatering
wastewater from the bath to be held for the proper
when the basin is emptied. Sediment basins are designed with
detention time and not become short circuited in the
oil recovery, inlet and outlet control structures, and drains.
sediment basin. The volume of each cell is designed
to hold the storage of sediment between scheduled
6-12. Number of basins
cleanouts plus the entire volume of a bath release
and clean-up water.
In a wash facility, with or without bath, a sediment basin with
only one cell may be provided, however, it must be designed to
d.
Single-cell configuration with bath. For small fa-
treat the entire volume of water and sediment expected.
cilities with bath, a single-cell configured similar to
Maintenance procedures must insure minimizing down time
that depicted in figure 6-3 may be provided if the
when the single basin is cleaned. A sediment basin with two
wash facility can be taken out of service during the
cells should be provided if the wash facility cannot be shut
cumulative period of time to drain the bath(s) and
down for scheduled cleaning and repairs. Providing a two-celled
draw down the sediment basin.
sediment basin allows one cell to be isolated for cleaning and
repairs while the other one remains in service for primary
6-13. Siting
treatment. The detention time of the waste water may be
Sediment basins are sited to receive gravity flow of wastewater
reduced in the basin if only one cell is operable due to closure
from the wash facility. The basin should be close to the washing
of the other, but the wash facility may still be utilized. During
operations to avoid long conveyance distances and severe
normal operations of a facility with a bath, one cell is used to
depths of conveyances being placed at the required grades.
treat the volume of waste wash generated from vehicle washing
Basins should be oriented along the axis of prevailing winds
water from the wash, while the adjacent cell is used to treat the
with the outlet end and oil skimmers located downwind so that
volume of water from the bath flush and clean-up activities. The
surface currents will carry free oils toward the removal
functions of the two cells should be alternated frequently, to
equipment. The basins must not be readily accessible to troops
distribute the sediment loads evenly between basins.
but should be visible from the control building and easily
accessed by the CVWF operators.
a.
Single-cell configuration without bath. At small
facilities without bath, a single-basin system as
6-14. Sizing
depicted in figures 6-l and 6-2 should be provided.
The size of each cell in the sediment basin will be based on the
A single sediment basin system should function
volume of water to be treated and the volume of sediment to be
hydraulically, such that the inflow volume is
stored in the basin between cleanings. The user must determine
equivalent to the overflow volume. If a large surge
how often the sediment will be removed from the basin. It is
of water is expected, then sufficient storage volume
recommended that each cell of the basin be cleaned at least once
must be allowed in the basin to ensure that a
per year; however, the exact number of basin cleanings will
minimum detention time of 2 hours is maintained.
depend on variations of soiling, user requirements, and other
The basin volume must account for the accumulated
considerations unique to the installation. In addition to the water
sediment storage volume between cleanouts. The
and sediment depths, from 1 to 2 feet (0.3 to 0.6 meter) of
outlet structure is a weir constructed across the
freeboard must be provided. Figure 6-4 shows typical water and
width of the access ramp. The location of overflow
sediment depths. Each cell should have a minimum length-to-
weir ensures a constant water level in the basin.
width ratio of 3 to 1 to allow for the proper settling time. The
turning radius of cleaning equipment, such as a front-end
loader, should be considered in determining the width of the
b.
Dual-cell configuration without bath. At larger
cells.
facilities, without bath, where washing down time
during basin cleaning may not be desired or practi-
a.
Velocity. A uniform horizontal flow-through ve-
cal, dual cells similar to figures 6-1 and 6-2 should
locity of from 0.5 to 2 feet per minute during
be provided. Cells would have a common wall and
washing operations is desirable. The lower range is
be provided with common inflow and outflow
preferred for predominantly silt and for clay-type
control structures.
6-4
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