32 
Effect of Dilution 
One of the factors responsible for the decrease in coliforms 
with time in the dye patch experiments is certainly the dilution 
of the sewage effluent with normal sea water. Since the chlorinity 
of the sewage is low as compared to that of sea water, and since 
the chlorinity determination is accurate to about four significant 
figures, it is possible to determine dilutions of sewage out to 
about one part in several hundred. Assuming that coliform bacteria 
act like a dissolved solute, one can calculate the expected coliform 
count from a knowledge of the chlorinity and coliform count of the 
sewage, the chlorinity of the sample, and the normal chlorinity of 
the sea water in the areas The latter value varies over a small 
range and this variation introduces uncertainties into the cal- 
culations, especially at the higher dilutions. The coliform content 
and chlorinity of the effluent vary widely. Consequently, the 
calculated dilutions are not precise. Nevertheless, they should 
indicate the magnitude of disappearance due to this factor. 
The calculated and observed coliforms in the zero time samples 
taken from the edge of the boil at Orange County are shown in Table 
7. The calculations are based on 25 samples of sewage collected 
on three separate days at the junction of the land and marine 
sections of the outfall, and on five dye patch experiments run 
on the corresponding days. There is a very close agreement between 
the average calculated MPN and the observed range of counts found 
in the zero time samples. This correspondence of results indicates 
that essentially all coliforms rise to the ocean surface at the 
point of discharge. 
