7 
of only a single positive tube in the presumptive tests. The 
results of the second grid were a little more variable than the 
first, but here also, over 60% of the counts were concentrated 
within a narrow range. 
There is no evidence of any significant loss of coliforms 
from the sewage field in the time elapsed between the two grid 
samplings near Hyperion. Actually the average MPN for the second 
grid, 11,500, was somewhat higher than the average for the first 
grid, 7,100; more significantly, the median values were 2,300 
for the first and ),300 for the second, and the geometric averages 
were 3,100 and 3,300 respectively. However, there was a considerable 
reduction in count between the samples taken in the boil and those 
from the grid 1.6 hours later. 
A comparison of the data from the two grids with that of 
the earlier dye patch experiment shows that similar couts were 
obtained at O and 2 hours, but that the counts continued to 
decrease in the dye patch whereas the grids showed no further 
decrease over the next two hours. Of the 50 four-hour grid 
samples run, five (10%) had MPN lower than the dye patch sample 
at corresponding time and 11 (22%) had just slightly higher MPN. 
Thus, the data from the dye patch experiment, although not neces- 
sarily reflecting the average behavior of the sewage field, was 
certainly typical of part of the sewage field. 
Subsurface Distribution of Coliforms 
Approximately 30 vertical stations were occupied during four 
trips to the Orange County area; 30 stations on two days at Whites 
Point and 20 on two days at Hyperion. Typical results are shown 
