Lake Michigan environmental survey : final report / [edited] by John C. Ayers.

PROVISIONAL FORECAST FOR LAKE MICHIGAN IN 1975

Natural Radioactivity
The most significant natural contributors to radioactivity in water are
H-3 (5.6xl09 uCi/ml), K-40 (l.lxlO9 uCi/ml), and C-14 (0.2xlO 9 uCi/ml).
These concentrations should change very little over the next five years. The
radium, thorium, and potassium content of lake sediments should also remain
constant through 1975.
Fallout
If there are no further atmospheric detonations, the fallout contribution to total radioactivity in Lake Michigan will not be significantly different in 1975 than it is in 1970. In the interim five years there will be
additional fallout into the lake,(29) but this activity will be offset by
radioactive decay and run out from the lake of that activity presently there.
It is estimated earlier in this paper (Table A-3) that the total Sr-90 in
Lake Michigan in 1975 will be approximately 7 percent less than at present.
Most of this activity will probably be in the water medium as it was in 1965
(see pages A-5 - A-13).
The amount of Cs-137 in the lake environment in 1975 will be approximately the same as it is now (Table A-5). However, most of this activity
is thought to be in the sediment and not in water. In 1970, it is estimated
with the following assumptions that there are 4000 Ci of Cs-137 in the sediment environment of Lake Michigan. This is two-thirds of the 6000 Ci of Cs-137
which are thought to be in the lake at this time.
2
1. The bottom area is twice that of the surface, or 44,800 mi.
2. Most of the Cs-137 is in the upper 1.5 cm of sediment (approximately
the depth of sampling).
3. The density of sediment is 1.6 g/cc.
4. The average concentration of Cs-137 in sediment is 1.4x10 Ci/g
(see page A-21.).
Reactor Effluents
Currently, nine power reactors are scheduled to be generating electric
power before 1975 (Table A-ll) but of these units only Big Rock Nuclear Power
Station is presently operating. The eight remaining units are expected to

A-25