14 
rates would not differ appreciably from the actual numbers. 
The extra disappearance of coliforms due to factors other 
than dilution is clearly seen from Figure 4. The data are 
strikingly similar to those obtained in the vicinity of the 
Orange County outfall (May 1 report, Fig. 4), except that in 
the latter area the calculated MPN‘'s based on chlorinity show 
a slow but significant decrease with time that is not seen in 
the Hyperion data. The probable reason for this is that the 
effluent field around the Orange County outfall covers a smaller 
area and in most of the experiments performed the dye patches 
moved fairly consistently towards the perimeter of the field. 
Subsurface Radioactivity Measurements 
The subsurface radioactivity measurements taken at the 
profile stations indicate that mixing of the discharged effluent, 
most of which reaches the surface, eventually distributed it 
throughout the entire column of water in the part of the bay 
sampled. A qualitative inspection of the chlorinity data show 
that most of the subsurface water below 15-30 feet in the 
vicinity of the outfall is of essentially normal chlorinity, 
whereas the surface water for a considerable distance around 
the outfall contains well over 1% of the fresh water effluent 
(see Final Oceanographic Report). This means that all of the 
water in the bay is not equally effective in the dilution of 
the sewage and that surface currents and surface (horizontal) 
diffusion and mixing play the most important roles in effluent 
disappearance. 
