enough leaves to cover 64,000 m2 (144 bags) would
considered a threat to the riverine aquatic life due
take 7.2 days. The rent for the leaf mulcher would
to the contaminants they contain. Before using the
then be for 8 days, since we could not rent the
leaves in a field trial we had the leaves chemically
mulcher for a fraction of a day.
analyzed using X-ray fluorescence (Hewitt 1994)
Based on the above discussion the cost per cov-
to check for the presence of heavy metals, as these
ered hectare (10,000 m2) is listed below.
could be harmful to the stream habitat if present
in high concentrations. For comparison we present
Estimated costs for covering one hectare using the
the chemical composition of the coal slag used on
hydroseeder cannon
the Platte River in Table 1.
Hydroseeder
7
The results of the X-ray fluorescence analysis
Leaf mulcher
62
of the leaf mulch shows that the leaves did not
Labor
450
contain any heavy metals. The only metal constitu-
Loader and operator
47
ent found in the leaves was iron, with a concen-
tration of 0.05 percent by weight. We note that the
Total
6/hectare
coal slag (Table 1) has an iron concentration over
100 times greater than the leaves. The coal slag
If we were to recalculate that based on the rate of
also contains other metals that the leaves do not,
application using the hose instead of the cannon,
namely aluminum, magnesium, titanium and so-
we would need to effectively double the amount
dium, all of which occur at high levels. From these
per hectare for the hydroseeder and loader. This
chemical analyses we conclude that the leaf mulch
would total about
||content||
,100/ha.
is more environmentally acceptable than the use
We compare these costs to the costs incurred
of coal slag. However, to avoid unnecessary intro-
for the dusting operations in Galena, Alaska, and
duction of contaminants to the riverine environ-
ment, we recommend that leaves collected for such
on the Platte River in Nebraska. The best estimate
a dusting operation should be taken from a "clean"
of costs for the dusting in Alaska come from the
area to avoid the inclusion of insecticides, lubri-
records of the Alaska Division of Emergency Ser-
vices, which has coordinated the dusting opera-
cants, etc., in the leaves.
tion for the last nine years. Here we present the
Aside from the introduction of contaminants,
costs for the most recent dusting operation at Ga-
small particles such as sand, coal dust and slag
lena which was done in 1993. In this application
can be a problem in many New England rivers,
92 m2 of sand were used. The application rate was
since they can clog the spaces between rocks where
about 0.27 kg/m2 and that sand weighs about 1300
the fish like to lay their eggs and thereby inhibit
kg/m3 (U.S. Army Corps of Engineers 1968). The
reproduction. Since leaves are biodegradable and
are naturally deposited in rivers, they are readily
total cost for the operation was ,000. The cost
absorbed into the river with only a fraction of their
estimate per covered hectare is about 4 (in 1993
total weight going to silting. Thus, in principle,
dollars).
using leaves should not adversely impact the fish
In the spring of 1994 the Omaha District initi-
ated a dusting operation on the Platte River. Here
it used 27,200 kg of coal slag. This operation cost
,000 to dust 8 ha with coal slag (U.S. Army
Table 1. Chemical analysis of coal slag (or bot-
Corps of Engineers 1994). This cost included ,500
tom slag) (U.S. Army Corps of Engineers 1979).
for use of a National Guard helicopter to docu-
ment the operation and the ice decay. The cost per
Ingredient
Amount (%)
hectare for this operation was ,470. If we remove
Silicon
23.3
the cost for the helicopter, the cost for the opera-
Aluminum
11.3
tion drops to
||content||
,938/ha. Even at this, the cost is
Calcium
5.4
more than double the cost of the operation at Ga-
Iron
5.2
lena, Alaska. We attribute the lower cost for the
Sulfur
3.1
operation at Galena to the 25 years of experience
Magnesium
1.4
Potassium
0.93
in dusting and the attendant cost optimization that
Titanium
0.64
can occur with such experience.
Undetermined
0.54
Sodium
0.20
Environmental considerations
Phosphorus
0.11
As previously mentioned coal dust and slag are
13
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