Fluctuating E.coli levels and a Composite Samples for beachmonitoring

["Shannon Briggs" <BRIGGSSL@michigan.gov>]

Please see article below for more information:

http://www.journaltimes.com/articles/2004/05/29/local/iq_2905191.prt

City changing beach guidelines for summer

By David Steinkraus
RACINE - Swimmers may find Racine's beaches open more often this summer
and the city of Racine is likely to save some money, because of a new
method for monitoring water quality in Lake Michigan.

Every day during the week, a city Health Department worker collects
water samples from seven points about 600 feet apart on North and Zoo
beaches. Drops of water are placed in a dish and incubated to stimulate
the growth of bacteria. After 18 hours later, a laboratory worker counts
the number of bacteria colonies that have grown, and if they exceed
certain limits, the city advises swimmers not to use the beaches. City
workers don't lift the advisory until two consecutive water samples are
below the bacteria limit. That's been the drill.

But a study completed by city health laboratory people and colleagues
at the U.S. Environmental Protection Agency found reason to change that
practice. The results of the sample study were presented last weekend in
New Orleans at the annual meeting of the American Society for
Microbiology.

"The concentration of bacteria along the coast can vary dramatically
from hour to hour, and maybe even from minute to minute," said Julie
Kinzelman, the city's microbiologist.

In studying the results of water tests from a whole summer, scientists
found that the water was almost always safe for swimming the day after a
high count. There were only a few times when bacteria concentrations
remained high after heavy rains, and in those cases concentrations
exceeded limits for several days.

So this summer, Kinzelman said, the city will lift beach advisories
after one good test.

The study also showed how the city's water analyses could be simplified
to cost less. Until this summer, each water sample was incubated
independently, and that drives up the cost. But the study showed that
there was little difference in the results between separately incubated
samples and a combined sample. So several samples will now be combined,
Kinzelman said.

There is the potential for a composite sample to conceal a very high
bacteria concentration at one point, but the counter argument is that
one sample at one point doesn't necessarily represent the whole beach.
For example, Kinzelman said, there may have been a flock of seagulls
sitting nearby on the sand. Seagulls carry very large amounts of E.
coli, the bacteria that health workers test for.

Analyzing one water sample for bacteria costs the city $5.06, she said.
Using two composite samples - one for North Beach and another for Zoo
Beach - will save the city about $2,150 over the course of the season.

Given the results found in Racine, Kinzelman said, EPA scientists said
they'll ask officials in Washington to review the sample method. It may
be, she said, that other communities could find similar benefits and
savings in the method.

On the Net:

Visit http://infotrek.er.usgs.gov and follow the links to "Southeastern
Wisconsin Beach Health Task Force" to check the conditions of
Wisconsin's swimming beaches.

 


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