155 



Radioactive isotopes were used on the cruise on May 22, 

 1956, to trace the dispersion of sewage in the immediate 

 vicinity of the Hyperion outfall. Previous to this, direct 

 information on dilution factors around the outfall with which 

 to compare the nutrient salts had not been available. Twenty 

 curies of scandium 46 were injected in the sewage and on its 

 appearance in the boil, the radioactive count was picked up 

 by a scintillator probe over the stern of the VELERO IV and 

 followed for the next 24 hours. At the time vertical profiles 

 of the radioactivity were made, phosphate and ammonia deter- 

 minations were also made. The limit of measurable dilution 

 of the scandium 46 in the sewage field was 1 to 10,000. Sur- 

 face samples of the station occupied in the boil on the first 

 appearance of radioactivity gave the highest values yet found, 

 in the area of 11.6 ng^-^L for phosphate-phosphorus and 112 

 iig-i^L for ammonia-nitrogen o The ammonia-nitrogen concentration 

 is the highest recorded at any of the outfalls. The approxi- 

 mate dilution of the scandium at this time was 40, At a depth 

 of 45 feet, the dilution was not measurable and the phosphate 

 and ammonia had decreased rapidly to 0,8 ug-^/L and 4 ug-a/L, 

 respectively. 



In tracking the radioactive field, the concentrations of 

 ammonia and phosphate did not decrease in the proportions 

 indicated by dilutions derived from the radioactivity. This 

 can be partly explained on the basis that the radioactive field 

 was being mixed with water from the surrounding area, which it- 

 self contained variable and unknown quantities of nutrients. 



Therefore, the time rate of change in ammonia and phosphate could 

 not be determined from the radioactive experiment. 



