261 



the intrusion of cold water from deeper levels caused by the 

 passage of tidal currents over a shallow bottom of complicated 

 submarine topography. 



The sewage field determined from temperature distribution 

 is embodied in a large unit of slightly diluted sea water 

 varying in thickness from 5 to 20 feet and covering ein area of 

 from 10 to 20 square miles. However, it should be remarked 

 that the field thus determined by refined methods is con- 

 siderably larger than that detectable by visual observation 

 or by other qualitative standards. 



Temperature and the Rising Effluent 



The effective heat contributed to the bay from man-made 

 sources is now 3.9% of the total amotint in stimmer and 10.7% 

 in winter. These figures will rise to 10.7% and 18.7%, res- 

 pectively, when installations that are now being planned are 

 placed in operation. 



Most of the sea water for initial mixing with effluent 

 from the existing outfall is derived from layers at or near 

 the bottom. Thus,, considering the annual range of bottom 

 temperatures and the spread between the bottom and the sur- 

 face waters, both sludge and effluent will rise to the surface 

 as visible boils when normal winter temperature conditions 

 exist. In summer, due to the greater temperature differential 

 between bottom and surface, they may sometimes be at least 

 partly suppressed. 



