6, 
Los Angeles Sanitation District Data 
The personnel of the Los Angeles Sanitation District have 
been conducting "viability" studies on coliforms discharged at 
periodic intervals in the unchlorinated secondary effluent of the 
Hyperion Plant. Their data are interpretated as showing a much 
slower rate of disappearance of coliforms than was observed in 
the dye patch experiments of the Hancock Foundation. Figure 17 
is based on a composite of the data of the LASD experiments and 
indicates that roughly a 6.5 hour period is required to give a 
90% reduction of the initial boil count and a 2); hour period to 
reduce the count to the 10 per ml level. As is described below, 
the field techniques they used in their experiments differ from 
those we employed. Since their rate of disappearance differs so 
markedly from ours, several questions arise. First, are the 
differences in methods employed responsible for the differences 
in results? If so, which method is superior for estimating dis- 
appearance rates and which, if any, should be the basis of pre- 
dicting the situation around the proposed outfall? These questions 
will be dealt with in turn. 
As already described, in our dye patch experiments a single 
point at the edge of the boil is marked with dye. Samples are 
periodically removed from the dyed area, and dye is renewed as 
required to follow the marked field. An effort is made to choose 
all samples from the most intensely dyed area of the patch and to 
renew the dye in this area. In the Hyperion experiments, the 
sewage field is marked with one or more dye patches as well as 
with current crosses. For each point on their disappearance 
