in waterways from non-point pollution sources in
Table 18. Constituents of 1979 dust-
ing material.
nonharmful levels. Another material that has re-
cently been tried is leaf mulch (Haynes et al. 1994).
Amount
Equipment. The dust was applied by means of
Ingredient
% by weight
crop-dusting airplanes in 1979. This was consid-
Silica
50.00
ered the only practical means of distributing the
Phosphorus pentoxide
0.25
material on the ice in a short time. Aircraft have
Ferric oxide
7.50
been the most commonly used method of appli-
Alumina
21.30
cation in other areas of the country and world as
Titania
1.07
well. Dusting in Alaska has been done with B-25
Lime
7.50
Magnesia
2.24
(USAED, Alaska 1968, 1969) and B-26 (Meyer 1976)
Sulfur trioxide
7.70
aircraft outfitted with gravity-flow hoppers. Heli-
Potassium oxide
1.70
copters have also been used, with the helicopter
Sodium
0.20
carrying a hopper-type spreader. The crop-dust-
Undetermined
0.54
ing airplanes used in 1979 were outfitted with
rectangular-shaped venturi-type funnels.
used again for dusting, it should be chemically
It is necessary to secure a means by which to
analyzed again, since plant operations or fuel
load the aircraft. In 1979 the material was put into
source have changed since 1979.
a plastic funnel-shaped bag with a 6-in. circular
Small-diameter particles are more desirable
bottom discharge port, which was hoisted above
because, for a given weight, the smaller particles
the airplane hopper with a crane. The report on
will cover a larger ice area than larger-diameter
the 1979 dusting recommended using augers to
particles. However, if particles are too small, they
load the material into the airplane; however, the
may be blown off the target area before penetrat-
material may be excessively abrasive on auger
ing the ice cover. If particles are too large, they
flights. Another option which may be less affect-
may clog the spreader on the airplane. Bolsenga
ed by abrasive material may be a portable eleva-
(1968) cited Williams and Gold (1963), who stated
tor flight.
that field experience had shown the practical range
The areas to be dusted must be marked for the
in particle size was 0.0041.0 inches. The material
pilots' benefit. In the 1979 dusting operation, flight
used in 1979 had fewer than 1% by weight out-
paths were delineated with neon orange road
side this size range. Bolsenga also cited Konov-
cones by using two cones to mark the beginning
alov and Miasnikov (1956), who recommended
and end of the path and individual cones at sev-
particle sizes of 0.0080.02 inches. However, it
eral intermediate points. The cones were placed
would probably be prohibitively expensive to
by helicopter.
screen bottom slag to this fine gradation (only
Timing of application. The 1979 Platte River dust-
15% of the material used in 1979 was this fine).
ing operations were performed from 28 February
The areal concentration in the past has varied from
to 2 March, which was about a week later than
0.01 to 0.08 lb/ft2 (Bolsenga 1968); for compari-
initially recommended based on experience. The
son, the application rate in 1979 was 0.02 lb/ft2.
date will vary from year to year, depending on
Generally the lighter application rates were asso-
weather conditions, such as snowfall or rainfall,
ciated with smaller-diameter and less-dense par-
amount of sun and temperature. The recommend-
ticles.
ed time of application in 1979 was for three weeks
Materials used in the past have included sand,
prior to breakup. The report concluded that dust-
soil, coal dust, soot, fly ash, bottom slag, foundry
ing should be done three to four weeks prior to
loam, phosphate fertilizer, potassium salt, calci-
breakup, with trouble spots dusted even earlier.
um chloride, ammonium nitrate or mixtures of
Cavan (1969) stated that dusting should gener-
the above (Bolsenga 1968). Some of these materi-
ally be carried out just before natural break-up
als may not be environmentally acceptable today.
starts and that dusting is most effective when the
air temperature is 32F or higher. Williams (1967),
Dyes and powders in the form of a spray could be
used in areas where the cost of transporting and
as cited by Bolsenga (1969), reported that dusting
applying dust is high, but these materials are not
much before breakup is usually not worthwhile
as effective. Recently various agricultural prod-
because periods of freezing weather following
ucts, such as grain, feed and fertilizer, have been
dusting freezes the meltwater produced. Howev-
approved in certain areas, as these items are found
er, others have noted that the particles create tun-
43
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