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That slimy green and white growth in an
unnamed tributary of Honeycutt Creek in
north Raleigh is a combination of an
algae, the green, and a sulfur-digesting
bacteria, the white.
Neither is toxic, Susan
Massengale, the spokesman for the state
Division of Water Quality, said in an
e-mail Tuesday. She also attached the
complete state reports.
State biologists with DWQ
have been testing the growth since early
this month after residents in the
Sheffield Manor subdivision complained.
The creek, which flows into
Falls Lake upstream of the water intake
for the majority of Wake County
residents, receives treated wastewater
from Raleigh’s E.M. Johnson Water
Treatment Plant on Falls of the Neuse
Road.
The green algae, which was
also present in the stream above the
water plant’s outfall, is common and is
sometimes very abundant in polluted
rivers. If large mats of it form and
then die, it will release an unpleasant
odor and reduce the oxygen supply in the
stream or lake. It is a good source of
food and homes for fish and other
aquatic creatures. It has a filament
form.
The white bacteria also have
a filament form. Staff members at the
plant identified it in the stream. The
bacteria use sulfur as its source of
energy. A reference says the bacteria
“are generally found in areas where one
body of water with adequate oxygen
content converges with another which
supplies the sulfur.”
There may be algae and
bacteria, Massengale wrote, but “Test
results from water samples taken last
week indicate that the nutrient levels
in the creek are not very high and none
of the metals tested exceeded water
quality standards.” The state tested for
manganese, among others.
Earlier tests by the city
showed the white substance to be
calcium. A form of calcium, calcium
thiosulfate, is used in treating the
wastewater before it is released to the
stream.
“Calcium, a metal does not
have a water quality standard, but the
level there was not high either,”
Massengale wrote.
She said the state is doing
further testing for sulfate.
Massengale also included the
2005 study of the life in the creek as
sampled from Raven Ridge Road. The
stream had been sampled in 2002, when
almost no organisms were found. “It
surely is still an urban stream,”
Massengale wrote, “but the tests do
indicate some improvements in the number
and variety of organisms since 2002.”
The city will have its final
test results in two weeks, Public
Utilities Director Dale Crisp is
reported to have told the city council
this week. He said they are checking the
creek weekly and his department has
hired a consultant to evaluate what
happened.
The city may consider
returning the wastewater, about 4
million gallons a day, to the treatment
process rather than putting it into the
stream.
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