TM 5-814-9
CHAPTER 7
OTHER DESIGN CONSIDERATIONS
7-1. Water source
supplies of water throughout the entire washing
season.
All treatment systems will require a reliable source for charging
the CVWF initially and for make-up, regardless of the form of
7-2. Piping
secondary treatment. The volume of water required will depend
on the type of wash facility constructed, type and configuration
Wastewater should be conveyed by gravity whenever possible
of the treatment system, frequency of use, losses, and the local
for economy. Pumping should be avoided because residual oils
climate. If a recycle system is provided, the designer must
may become emulsified and difficult to remove, solids cause
determine the most feasible and economical method of filling
wear on pumps and pumps add significant capital and operating
the system initially, and then maintaining the water level in the
costs to the facility. Conveyances, whether gravity sewers or
system by adding makeup water from the water source. Makeup
open channels, must be constructed to grades which will
water will be required to restore the system to a working level
provide adequate scouring velocity to prevent solids deposition.
as water is carried off by the vehicles or lost to evaporation and
All pipes must be designed for peak hydraulic and solids
overspray. All original source and makeup water should be
loadings, including that contribution from stormwater runoff
added at the water supply basin, if provided. This water should
from hardstands. Because of the external and internal abuse and
be uncontaminated, reasonably clean, and should not require
because of inaccessibility, piping systems must be durable.
treatment before being introduced into the system. All sources
Leakage or infiltration allowances normally associated with
of water available at the installation should be considered for
gravity piping should not be used; gravity lines should be water
use, singly or in combination, as sources of water at a CVWF
tight. Other factors such as soil corrosion and freeze protection
including dedicated wells, surface water, tapping into the
need to be addressed also. Open-channel flow should be used
existing potable water supply or captured rainwater.
whenever possible for ease of maintenance. If siting problems
or severe slopes make open-channel flow impractical, the
a.
Type of facility. A wash facility that has a prewash
designer should use large-diameter pipes. Locate manholes at
will require more makeup water than a facility with
each change in slope or direction and at each pipe intersection.
only wash stations because of increased water lost
Design long, straight sections of conduit to minimize the
by vehicle carry-off, overspray and evaporation.
number of manholes required. All frequently operated, buried
Water losses from carry-off can be as high as 160
valves should be accessible through pits or manholes.
gallons per vehicle. Losses due to overspray and
7-3. Hoses, water cannons, and nozzles
evaporation can be as high as 10 percent from water
cannons and 5 percent from hoses at wash stations.
Hoses must be of a size and weight which a person can handle,
but yet be durable enough to withstand the abuse of repetitive
b.
Type and configuration of treatment system. The
use, vehicular traffic, and internal abrasion from fines in the
type and configuration of the treatment system is
water. Nozzles and water cannons undergo similar treatment.
another factor to consider when estimating the
The industry is lacking for equipment that can stand up under
volume of makeup water required. A discharge
the continuous use given at a CVWF; therefore the designer
system will require that the total water demand
must be very selective when selecting hoses, water cannons and
including makeup be taken from the developed
nozzles.
water source. In a recycle system, only the water
lost to overspray, evaporation and vehicle carry-off
7-4. Control systems
will need to be replaced from the water source.
The process controls for a CVWF can be very complex to a
Treatment systems with basins that have large
Contractor who has never seen a wash facility. Material
surface areas may have greater water losses due to
specifications for controls are standard. The logic of the control
evaporation than basins with smaller surface areas.
system is special to the design. It is very important that the
This loss will increase the volume of makeup water
designer clearly describe within the plans and specifications
required, as discussed below.
how the components are to function.
c.
Climate. The evaporation rate at the installation
7-5. Systems operating manual
must be considered when calculating the volume of
Complete manuals should be prepared by the designer de-
make-up water needed to maintain the total demand.
scribing the various components of the CWF and how they were
The volume of rainfall at the installation as well as
designed to be used. The manual should establish standard
the amount lost to evaporation should be calculated
operating procedures including staffing, scheduling, safety,
to determine the volume of water needed from the
records keeping, and other operational responsibilities. All the
water source. Water balance computations should
control systems should be illustrated and step-by-step
be performed by the designer to assure adequate
7-1
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