62 



with surface water and nearshore water within the sewage field 

 The sewage field is in steady state so that the loss of water 

 from it by diffusion and mixing at the edges is balanced by 

 the introduction of new effluent and of partly diluted shelf 

 water. A warm water field covers much of the inshore portions 

 of the bay in the summer and early fall, from the vicinity of 

 Venice south to Redondo, and seaward as far as three miles. 



It also appears, from an examination of the thermograms, 

 that the boundary between the field and the shelf water is a 

 rather sharp one in the winter. This is borne out by obser- 

 vations which indicate that the field is bounded by slicks 

 and marked color changes. Thermally it is larger than sali- 

 nity differences indicate. This implies that the recognizable 

 thermal character of the field is maintained beyond the range 

 of dilutions observable from salinity, or to dilutions greater 

 than 200 to 1. 

 Source of Mixing Sea Water 



Although evidence is limited, it is probable that the 

 initial mixing of the discharged effluent takes place partly 

 with the bottom water at the outfall terminus. This is 

 indicated by the fact that the average dilution does not 

 change appreciably during its rise to the surface, and also 

 by the action of a subsurface current cross which moved into 

 the boil area while a surface cross moved out with the field 

 during brief observations in May 1956. Therefore, the initial 

 dilutions of approximately 20 to 1 in the present discharge 

 boil represents initial mixing of the effluent with water at 

 the approximate depth of the pipe? the mixing water being 



