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H3.5.3 Methodology - Wind Erosion
The second major source of particulate emissions from sand and salt piles is wind erosion of the
piles. A detailed methodology for calculating these emissions is given in Section 13.2.5 of
Volume I of Compilation of Air Pollutant Emission Factors. This methodology calculates the
amount of erosion particulate emissions from the pile by applying an “erosion potential function”
to each surface of the pile. The erosion potential function is affected by the following
parameters:
· Moisture content of stored material
· Silt content of stored material
· Number of loading/unloading events in given time period
· Percent of pile disturbed in each loading/unloading event
· Physical dimensions of pile
· Threshold friction velocity of the material (i.e. the wind velocity at which wind shear
stress is great enough to cause particles to be released from the material surface)
· Surface roughness height of material (a measure of the resistance to wind flow near the
surface of the material caused by unevenness or roughness of the material)
· Wind speed and direction
The methodology is too complex to be reduced to a single equation. Although it is possible to
perform these calculations by hand, the number of computations required for each pile is very
large. EPA has incorporated this methodology into a freely available computer program, named
WIND (Reference 91). The use of this program is strongly recommended.
H3.5.4 Data Sources - Wind Erosion
The EPA methodology for calculating particulate emissions due to wind erosion of storage piles
requires several pieces of information about each pile, as described in paragraphs 3.5.4.1 through
3.5.4.8. As some of these parameters are not commonly available for each storage pile, default
values are given in Sections 13.2.4 and 13.2.5 of Volume I of Compilation of Air Pollutant
Emission Factors.
H3.5.4.1 Moisture Content of Stored Material (%)
This information can be obtained by direct sampling of the piles, or from the maintenance or
base operations section. Section 13.2.4 of Volume I of Compilation of Air Pollutant Emission
Factors provides information on the moisture content of a sand pile located at a municipal
landfill: 7.4%. This value may be used as a default if moisture content of piles located on the site
is not available.
H-29
H3.5.4.2 Silt Content of Stored Material (%)
Silt content is a measure of the percentage of material that passes through a No. 200 sieve. This
can be obtained by direct sampling of the pile or from the maintenance or base operations
department if this information has been recorded. Section 13.2.4 of Volume I of Compilation of
Air Pollutant Emission Factors provides the silt content of a sand pile stored at a municipal
landfill: 2.6%. This value may be used as a default if silt content of piles located on the site is not
available.
H3.5.4.3 Frequency of Loading/Unloading Events
Wind erosion is a factor of the number of times the surface of the pile is disturbed through
loading or unloading events. Information on the frequency of loading and unloading events
should be obtained from the maintenance or base operations section.
H3.5.4.4 Percentage of Pile Surface Disturbed in Loading/Unloading Events
The methodology for calculating wind erosion assumes that erosion occurs in those surfaces of
the pile that have been disturbed by unloading and loading activity. An estimate of the
percentage of the pile surface disturbed in each event must therefore be calculated based on the
material throughput rate and pile size, or if possible, from information supplied by the operator.
Both Section 13.2.5 of Volume I of Compilation of Air Pollutant Emission Factors and the
WIND program and user’s manual describe the specific informational requirements needed for
these calculations.
H3.5.4.5 Physical Dimensions of the Pile
Required dimensions include overall pile shape description (either flat, conical, or oval flattopped),
as well as pile height and diameter, expressed in meters. This information is available
through direct observation or from the maintenance or base operations section.
H3.5.4.6 Threshold Friction Velocity of the Stored Material
The threshold friction velocity is the wind velocity at which wind shear stress is great enough to
cause particles to be released from the material surface. This information can be obtained by
sampling of the pile surface according to a method described in the Section 13.2.5 of Volume I of
Compilation of Air Pollutant Emission Factors. Default parameters based on material type are
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