RESTRICTED 



21 



The nature of the difrusion process is such that the rates 

 will decline rapidly after the first two aays except insofar 

 as random variations in current direction carry patches of con- 

 taiainated water into uncontaminated areas, leading to rapid 

 dilution. If the radioactive material were spread uniformly 

 through the southern half of the lagoon, the concentration 

 would be reduced to 0,1% of the initial value, but it seems \m- 

 likely that this could occur in less than one to two weeks. It 

 is clear that the natural processes of current flow and vertical 

 diffusion act together to maintain a gradient in concentration 

 with the greatest amount in or iiear the target area, and the 

 gradient will be destroyed only very slowly by horizontal dif- 

 fusion and random variations in currents. 



After the first few weeks, further dilution will take place 

 only by tidal Interchange, Since the major path of contajxLnated 

 water lies south of the area of most complete stagnation, it is 

 expected that the radioactive materials will be removed at least 

 as rapidly as the average lagoon flushing rate of about 3% per 

 day. This will require tv/o and a half months to reduce the con- 

 centration by a factor of 10, 



AXi unpredictable but probably small quantity of radioactive 

 material will become attached to bottom sediments and sinking 

 organic matter, from which it will be liberated gradually over 

 a long period of time and will be a minor source of contamina- 

 tion, particularly in the eastern part of the lagoon where up- 

 welling of bottom water is most pronounced. It is not expected 

 to be of any practical significance at the surface but might be 

 hazardous to diving operations. 



^ 



