43 
many of them, are far below a reasonable value for a primary 
effluent. These low values show that coliforms disappear much 
faster than the liquid sewage phase and reinforce the conclusion 
from the dye patch experiments that factors other than dilution 
play a major role in coliform disappearance. 
The median count for the 23 samples is 73,000 per ml. If 
one accepts the maximum "100% counts" (1,000,000 per ml) as the 
average of the plant effluent, then one can conclude that about 
93% of the initial coliform population had disappeared for causes 
other than dilution in the time (or distance) of travel from the 
outfall to the area of the grid. On the other hand, one must 
also conclude that individual patches of sewage will show 
essentially no reduction in counts beyond dilution over the same 
path of travel. 
Two similar grids were run in the vicinity of the Hyperion 
outfall on March 8, 1956. The grids were located between two 
dye patches started almost simultaneously on opposite poles of 
the boil and were rectangular in shape, being about 1,000 by 
2,000 feet on the sides (Fig. 8}. The first was about 1.6 hours 
travel from the outfall, the second about ) hours (Fig. 9). Al- 
though the range of counts in these two grids was about as great as 
that observed at Whites Point (210/ml to 70,000/ml for grid one; 
62/m1 to greater than 70,000/ml for grid two), there was a much 
more uniform distribution of coliforms (Fig. 9). This is also 
shown in Figure 10 in which the per cent of the total samples 
giving a particular count is plotted against the log of the 
count. Almost 50% of the counts in the first grid were the 
same and a large share of the other values represent differences 
