13 
younger effluent. Unfortunately, the data do not permit an 
estimate of how much younger effluent could have been present 
in the samples analyzed. 
In a steady state condition, with constant discharge of 
unchlorinated effluent instead of only two hours discharge sub- 
sequent to the introduction of the tag as was the situation, the 
coliform counts could have been higher than those observed and 
thus a slower disappearance rate would have been measured. Since 
the coliform count on the beach depends on the disappearance 
rate and the time of travel to the beach, a slower disappearance 
rate with a longer time of travel would have the same effect on 
the beach count as a more rapid rate of disappearance with a 
shorter time of travel. 
The problem of the reinforcement of the coliform population 
of a particular volume of effluent by younger effluent can be 
examined in another way. Let us assume that a volume of effluent 
"Aw. discharged six hours before a second volume "B", has a path 
of travel that causes it to intersect volume "B” when the latter 
is two hours from the outfail. The danger of pollution on the 
beach would, of course, be from volume “B"™ and not from volume 
"A" in this situation. The total time of travel of "A" to 'B™ 
is 8 hours, and during this period the coliform population would 
be reduced by about 90% from dilution alone (Fig. 1). Volume 
"B", having traveled only two hours, has its coliform population 
reduced about 20% due to dilution alone. The contribution of 
coliforms from "Bt to “At is significant, but the contribution 
of coliforms from *A*®" to *"B* is not, and calculated numbers of 
coliforms reaching the beach from “B™ based on normal disappearance 
