includes data from four types of measurements. The closed circles 
represent the minimum dilutions (maximum radioactivity and there- 
fore maximum effluent concentration) detected on the various 
underway traverses, and the upper line is the approximate best 
fit through these points. The squares represent the dilutions 
calculated from the radioactivity of the samples collected in 
the two dye patches, and the lower line is the approximate best 
fit line through these points. The triangles and open circles 
are dilutions calculated from radioactivity measurements on the 
surface samples collected underway and from the surface samples 
collected at the profile stations, respectively. 
The main point to be emphasized, besides the marked dilution 
of the radioactivity with time shown by all four types of measure- 
ments, is that there is no great Hatt erenre between the minimum 
dilution found by traversing the sewage field and that measured 
by following a dye patch. The dilution curves from the two 
types of measurements do diverge somewhat; however, the difference 
between the two lines at six hours (the usual length of most dye 
patch experiments) is only about two fold. Considering the 
variations that occur in the properties of the effluent being 
discharged, this difference would not introduce any significant 
error in measurements of coliform disappearance rates. It can 
be concluded that the dye patches represent a typical part of 
the sewage field and that confidence can be placed in data 
obtained by the dye patch technique. 
