Cook Plant preoperational studies 1970 / John C. Ayers ... [et al.].

improvements in methods. They also produced some preliminary results which
are given below and discussed.
Following the generalized instructions of the Millipore bacterial method,
the sampling gear were well rinsed in the water to be sampled and 100 ml of
water put through the nutrient pad culture dish for each of total bacteria and
coliforms. Inocculated with the specified nutrient media, the culture dishes
were incubated at 35~C for 18-24 hours and the resultant bacterial colonies
counted under a binocular microscope at about 7X magnification. It is now
evident that 100 ml subsamples are too large to be used in the inshore waters
of southern Lake Michigan. After 18 hours of incubation the filter pads for
total bacteria were so overgrown that colonies merged and counting was impossible. This was not true for the coliform pads, though the numbers of colonies
to be counted were excessive. It appears that 25 ml will be a sufficient subsample in the inshore waters of Lake Michigan. Several culture dishes were
discarded after it was discovered that a loose fitting on the syringe-pump
of the Millipore gear was passing air bubbles whose air-borne bacteria would
be deposited on the filter. The usable results are given in the following
table. No conclusions are drawn from these results, other than that the method
is usable.
Sample Coliforms/ml Total bacteria/ml
IA-2-C-100 460 -----
IA-2-T-100 --- Too overgrown to count
OA-2-C-100 291 -----
OA-2-T-100 --- Too overgrown to count
OP-2-C-100 0. —
OP-2-T-100 --- Too overgrown to count
The Hach-kit dissolved oxygen method is adjudged to be too insensitive
for the needs of this type of experiment. In all the samples the dissolved
oxygen measured 9 mg/l, or 9 ppm. It will be necessary to return to a fullfledged Winkler oxygen determination to ascertain, whether passage through a

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