temperature for human pathogens), total coliforms, fe-
zen storage on these bacteria by McCarron (1965),
cal coliforms, and fecal streptococci. The tests for
Mackay (1984), and Kraft (1992).
coliform bacteria and fecal streptococci are typically
Snow column studies
used to demonstrate contamination by feces, i.e., the
presence of sewage bacteria. All the procedures used
First indoor study
are given by the American Public Health Association
(APHA), American Water Works Association (AWWA),
Figure 1 shows the color change in the first meltwa-
ter fractions. Table 3 gives information on the odor and
and Water Environment Federation (WEF) (1992). The
total Heterotrophic Plate Count (HPC) was prepared
color of the various meltwater fractions. Clearly, the
by using a Pour Plate Method with R2A agar. The mem-
first few bottles had the deepest yellow color and stron-
brane filter method was used for both the total coliform
gest odor. Figure 2 and Table 3 also show that there
and fecal coliform tests. For the total coliform tests,
was another increase in color and odor on May 8. On
May 19, there was a similar but less dramatic increase
M-Endo agar was used with verification of 10% of the
in odor and color (Table 3). Generally, later meltwater
colonies in Lauryl Tryptose broth followed by confir-
appears to be cleaner (Table 3). Thus, the contaminants
mation in Brilliant Green Lactose broth. The fecal
responsible for color and odor are concentrated in the
coliform procedure used M-FC medium with agar
early runoff. The concentration phenomenon occurs
added. Fecal streptococci were determined using the
several times during the course of this study; each time
Multiple Tube Fermentation Technique with Azide
it is a little less pronounced than the previous event,
Dextrose broth. All turbid tubes were streaked onto
and this concentration phenomenon appears to be associ-
Pfizer Selective Enterococcus agar for confirmation.
ated with freezing followed by prolonged warming.
Table 3 also gives the mean total number of het-
RESULTS AND DISCUSSION
erotrophic bacteria and mean number of fecal strepto-
cocci found in the snow and meltwater fractions. Al-
Snowmaking study
though not shown in this table, we did not detect any
total coliform or fecal coliform bacteria in any of these
We were unable to detect either total coliform or
samples. When compared with the manufactured snow
fecal coliform bacteria after snowmaking. This was
samples, the total number of bacteria was reduced in
equivalent to more than a 3-log reduction in the total
the initial meltwater samples but was approximately
coliform counts and more than a 2-log reduction in the
three orders of magnitude greater in the final meltwa-
fecal coliform counts. The snowmaking process may
ter samples (Table 3). The total number of bacteria in
be able to yield even larger log reductions but we were
the last meltwater fraction (alone) was greater than the
limited in our ability to detect any greater effect by the
total number of bacteria in the whole snow column
initial number of these bacteria present in the waste-
(Table 4). Therefore, we believe that the microbial
water. The fecal streptococci were not nearly as ad-
growth occurred during the warming periods and was
versely affected, with less than a 1-log reduction, or
most pronounced when the "nighttime" or storage tem-
72% loss (Table 2). The decrease in the total number of
perature was above 0C. Some bacteria are able to grow
heterotrophic bacteria was almost 2 logs, from 2.0
105 CFU/mL to 2.2 103 CFU/mL (Table 2). Appar-
at temperatures around 0C. It is possible that a biofilm
ently, the gram-positive fecal streptococci survived this
layer, rich in nutrients, formed at the bottom of the col-
process better than the gram-negative coliforms. This
umn and that this allowed growth of some species of
agrees with findings on the effects of freezing and fro-
bacteria. Because this environment would be rich in
Table 2. Effect of snowmaking on bacterial counts.
Mean total
Mean total
Mean fecal
Mean fecal
Sample
count (CFU*) coliform (CFU) coliform (CFU)
streptococci (CFU)
2 105/mL
3.2 103/mL
2.2 104/100-mL
Wastewater
390/mL
(or 220/mL)
2.2 103/mL
4.8 103/100-mL
Fresh snow
<1/10-mL (or
<1/10-mL
<0.1/mL)
(or <0.1/mL)
(or 48/mL)
*Colony Forming Unit
6
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