RESTRICTED 



19 



Table 8. Reduction of surface contamination by- 

 vertical diffusion in test Able (fo of 

 concentration 3 minutes after blast] 



water by the covmter current is iraportant in maintaining a high 

 and relatively uniforiii rate of reduction of concentration in 

 the sxu-face laj'^er, a reduction that is estimated to continue 

 at a rate of about 257;, to 30^ per hour after the first four 

 hours. 



In test Baker it is assumed that the contamination is 

 initially distributed in a cylinder of 400 m, radius extending 

 from the sxorface to the bottom. The part of the cylinder in 

 the surface current, namely the upper one-fourth, will move in 

 a WSl/V direction at a speed of 0,3 imot. The lower three-fo\arths 

 will move ENE with the bottom current at 0.1 knot. 



As the patch of contaminated surface water moves away from 

 the target area, vertical mixing with uncontaminated water 

 underneath will reduce the sxirface concentration about 25% per 

 hour. The material lost from the surface layer will be carried 

 back toward the target area by the counter current. Reduction 

 of concentration will also occ\ur in the patch of contaminated 

 bottom water moving eastward from the target area, but the rate 

 of reduction will be only about one-third as high, or 8% per 

 ho\ir, because of the greater thickness of the bottom layer. 

 From this figure, the amount of contaminant moving into the 

 surface layer at any time is readily determined. 



Since a part of the radioactive material diffuses out of 

 the patches of contaminated water and into the opposite current 

 moving back past the target area, the net result of the current 

 system and vertical diffusion v/ill be to produce a long, narrow 

 strip of contaminated water passing through the target area 

 along a WSWT-ENE axis. The strip will be gradually broadened by 

 horizontal diff\ision, but this effect is of relatively minor 

 importance. Table 9 shows the estimated reduction in concentra- 

 tion of contaminant by horizontal and vertical diffusion. 



At the end of the first day the eastern end of the strip of 

 contaminated water is expected to reach Bikini Island. The 



