The probability of a spill during the extended
Identification of
season was quite low in all cases. Generally the
probable spill materials
The frequency and amount of substances
probability was an order of magnitude less than
shipped through the St. Lawrence Seaway De-
the probability of a spill in the normal season, in
velopment Corporation (SLSDC) locks in 1977
part due to the lower frequency of shipping. How-
(Nicholson and Dixon 1979) and the St. Clair
ever, it was found that there was an increased
Detroit River System (SCDRS) for the period 1974
risk of a spill per transit during the extended season
1979 (Shulze and Horne 1982) have been tabu-
period of 1.53 times the normal season. In Lake
lated.
St. Clair it was found to be five times the normal
By far the largest amount of potential spill ma-
risk. This increased risk was largely due to oper-
terial is oil and petroleum products. The major-
ating in ice.
ity of this is residual fuel oil (also called number
The likely spill size in the extended season was
6 and Bunker C) on all the systems studied. Also,
determined by summing the products of the av-
refined fuels, mostly gasoline and fuel oil, are
erage spill size resulting from an accident and
extensively transported. Residual fuel oil is not
the probability of a spill from each accident type.
thought likely to spill in winter because of its high
It was found that the likely additional discharge
viscosity. At low ambient air temperatures, re-
of oil during the extended season is small and,
sidual fuel is nearly solid (Shulze and Horne 1982),
for the St Marys River, generally less than an
with the consistency of toothpaste (USCG 1973).
operational spill during the normal season. Be-
The potentially hazardous substances shipped
cause of the limitation of data that are available,
are approximately 10% of the volume of petro-
it was not possible to compute an expected value
leum products on the Detroit River and 32% of
of spill size for the SCDRS.
the volume of petroleum products on the St. Clair
River. Approximately 85% of the potentially haz-
Identification of spill impacts
ardous substances on the St. Clair and 70% on
To date, the potential impacts of an oil or haz-
the Detroit River are basic chemicals and chemi-
ardous substance spill associated with extending
cal products (Shulze and Horne 1982). In many
the navigation season have been discussed
cases these are a bulk cargo and are not likely to
(USACE 1979a, Baca et al. 1986). Actual data de-
spill, and many are not necessarily hazardous if
scribing impacts of spills in the Great Lakes are
they are released in the water. Potentially toxic
scarce, reflecting the relatively minor nature of
chemicals such as insecticides and disinfectants
spills in the Great Lakes.
make up only 0.4% of the chemicals shipped.
The general effects of a spill on an aquatic en-
vironment could vary by impact and degree. These
include:
Determination of
Direct kill of organisms through coating and
spill probabilities
The probability of a spill on the St. Marys River
asphyxiation;
and the SCDRS has been calculated for various
Direct kill through contact poisoning of or-
options of the Extended Season Navigation Pro-
ganisms;
gram (Schulze and Horne 1982, Schulze et al. 1982).
Direct kill through exposure to water-soluble
The probability of a spill is determined by sum-
toxic components of oil at some distance in
ming the product of the probability of an acci-
space and time from the accident;
dent and the probability of a spill, given that an
Destruction of the generally more sensitive
accident has occurred, for all the possible acci-
species;
dents. The accidents assumed to be possible were
Destruction of the generally more sensitive
grounding, collision, collision with ice and, for
juvenile forms of organisms;
the SCDRS, grounding in ice. For each river sys-
Incorporation of sublethal amounts of oil and
tem the probability for each type of accident was
oil products into organisms, resulting in re-
determined by compiling the accident record and
duced resistance to infection and other
the number of vessel transits. The probability of
stresses (the principle cause of death in birds
a spill given an accident was determined by ex-
surviving the immediate exposure to oil);
amining the records from tank ships for all of the
Destruction of food values through the in-
Great Lakes. It was felt that tank ships represented
corporation of oil and oil products into fish-
the principal threat for a spill.
eries resources; and
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