Upgrading treatment
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Major upgrades of treatment at Metro mean improved water quality in Onondaga Lake.
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The Metropolitan Syracuse Wastewater Treatment Plant (Metro) provides high quality treatment for
270,000 people and many industrial and commercial
customers in the City of Syracuse and some areas
outside the city in Onondaga County.
Metro treats an average of 84 million gallons per day.
Full secondary and tertiary treatment can be provided
for up to 126 million gallons per day. Metro has a total
hydraulic capacity of 240 million gallons per day
during wet-weather events such as rainstorms.
Project superlatives.
Construction photos
This $125 million state-of-the-art facility is
providing advanced treatment at Metro and reducing
levels of ammonia and phosphorus in the plant's
effluent to Onondaga Lake.
What do the latest data show?
Onondaga Lake water quality continues to improve in
response to reduction in nutrient loading from the
wastewater treatment plant. However, the 2006 Lake
conditions demonstrate the effect of a wet year on
nutrient loading. Nonpoint source phosphorus input to
the Lake increased in 2006 as a consequence of the
above-normal precipitation and runoff. In response,
Lake phosphorus and algal abundance showed a slight
increase over 2005 conditions.
Dissolved oxygen content of the Lake has increased to
the point where water quality standards are now
routinely met during fall mixing. Algal blooms are
diminishing and cyanobacteria (blue-greens) represent
a minor component of the algal community. Improvements
in the Lake have allowed the beds of aquatic plants to
greatly expand; this has increased the amount of
nesting and nursery habitat for the warmwater fish
community.
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Average ammonia-N concentrations in Metro Outfall 001, seasonal basis, 1995-2006
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Improvements to the county's
wastewater collection and
treatment system at the Syracuse Metropolitan
Wastewater Treatment Plant (Metro) are primarily
responsible for the improved water quality conditions
in the Lake. Significant investment in wastewater
treatment technology has achieved far lower discharges
of wastewater-related pollutants, particularly ammonia and phosphorus.
Onondaga Lake had exhibited high ammonia
concentrations for decades. Monitoring results from
1970 to 2002 documented that ammonia levels in the
Lake waters were above New York State's ambient water
quality standards designed to protect aquatic life.
Effluent from Metro was the largest source of ammonia
to the Lake, averaging about 90% of the total annual
input. Recent improvements to Metro were designed to
reduce ammonia levels in the treated effluent and
bring the Lake's water quality into compliance with
state standards.
The final stage of the Metro improvements for ammonia
treatment came on-line in early 2004. The biological aerated filter (BAF) system has
resulted in year-round nitrification (conversion of
ammonia to nitrate) in wastewater. Prior to this final
stage, various improvements to the treatment system
had resulted in substantial reductions, particularly
in the summer ammonia levels.
| Average annual Metro ammonia load, Outfall 001 |
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Years
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Metric tons
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1990-1997
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1210
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1998-2003
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521
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2004-2006
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85
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Average daily phosphorus discharge from Metro, 1990-2006
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Enhanced phosphorus removal from wastewater is another
objective of the Metro improvements currently
underway. A high-rate flocculated settling (HRFS)
physical-chemical treatment system (known as
Actiflo) came on-line in 2005 to reduce effluent total
phosphorus (TP) concentration.
This stage of
phosphorus treatment is designed to meet a 12-month
rolling average TP limit of 0.12 mg/L. Evaluation of
compliance with this limit began in April 2006,
following 12 months of operation. In 2006, Metro
effluent TP concentration met the 0.12 mg/L limit.
| Average annual Metro TP load, Outfall 001 |
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Years
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Metric tons
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1990-1997
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53
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1998-2004
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34
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2005
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19
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2006
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11
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In 2006 Metro contributed about 29% of the total
external phosphorus load to Onondaga Lake through
outfall 001 (26%) and outfall 002 (2.7%). The
remainder of the phosphorus load came from nonpoint
sources throughout the 285 square mile watershed.
Bacteria
concentrations were monitored at a network of
nearshore stations as well as at South Deep (the
primary water quality monitoring site). In 2006,
bacteria concentrations within the Class B portion of
Onondaga Lake met the New York State ambient water
quality standard for fecal coliform bacteria, which is
meant to assess suitability for water contact
recreation. However, concentrations in the Class C
portion of the Lake, near the major southern
tributaries and Metro discharge, were elevated
following storms during the rainy summer of 2006. This
result highlights the need for continued progress with
CSOs, as well as the need for improved storm water
management to reduce nonpoint source pollution from
urban areas.
Dissolved oxygen (DO)
levels continued to show improvement in response to
reduced productivity in the Lake. The DO
concentrations in surface water during the fall mixing
period, a historically critical period in Onondaga
Lake, were in compliance with regulatory standards.
Phosphorus
concentrations in the Lake are declining as loading
reductions are achieved at the wastewater treatment
plant. In 2006, the summer average total P
concentration was approximately 39 µg/L in the Lake's
upper waters.
Chlorophyll-a concentration
averaged 16.5 µg/L during the summer of 2006; the
annual peak of 35 µg/L was measured at the end of
March. Spring algal blooms are typical in Onondaga
Lake. Moderate and variable algal levels were measured
through much of the summer recreational period;
slightly more than half exceeded 15 µg/L, the
state-designated threshold of impaired suitability for
recreational use. In 2006, cyanobacteria comprised
about 2% of the total algal biomass. Nuisance algal
blooms have been steadily diminishing, presumably in
response to reductions in nutrient loads.
Water clarity
of the Lake is variable both within and between years.
A spring clear-water phase was evident from the
mid-1990s through 2000 but is no longer typical. The
loss of the clear water phase is attributed to
biological factors, cascading from the proliferation
of the alewife, as discussed below.
Zooplankton
grazing is a significant factor affecting water
clarity. Throughout the 1980s and 1990s, a spring
clear-water phase was attributed to a seasonal peak in
the abundance of larger zooplankton. However, larger
zooplankton are now essentially absent from the Lake,
and the spring clearing events have disappeared as
well. Larger zooplankton, which are efficient grazers
of phytoplankton, are the preferred food source of the
fish species alewife. The reduction in population of
the larger zooplankton taxa was evident in late summer
2002 when young-of-the-year alewives first became
abundant. Alewives are now prolific in the Lake, and
their effects are seen throughout the food web.
Destruction of larger zooplankton by alewives caused a
decline in total zooplankton biomass from 2003 to 2005
and a diminution in their average size. The average
size of zooplankton is gradually improving from the
minimum values measured in 2003.
Fish
are one of the most visible components of the
ecosystem. Results of the 2006 fish program indicate
that the community continues to be dominated by
warmwater species. Popular gamefish such as largemouth
and smallmouth bass are common and tend to be more
abundant in the northern basin. This spatial pattern
is consistent with the distribution of aquatic plants
and macroinvertebrates, demonstrating that the
northern basin provides better habitat quality. Other
gamefish, such as walleye and northern pike, are
present but are far less common than bass. Panfish,
such as yellow perch, pumpkinseed, and bluegill, are
abundant in nearshore areas.
Of the twenty-nine fish species captured in Onondaga
Lake in 2006, thirteen (45%) showed evidence of
successful reproduction. The young-of-the-year
community was dominated by largemouth bass, which
represented 49% of the catch. Overall abundance of
young fish was notably lower in 2006 compared with
2000-2005 results.
Alewife abundance was evaluated using hydroacoustics,
gill nets, and electrofishing. Length frequency
analysis indicated that a strong year class of alewife
was produced in 2005 and is augmenting the strong 2002
year class. Abundance of alewives is high compared
with regional lakes.
The New York State Department of Health (NYSDOH)
produces an annual report detailing advisories for the
consumption of fish and game in New York. The May 2007
report, "2007-2008 Health Advisories: Chemicals in
Sportfish and Game," included a significant revision.
The NYSDOH now advises that largemouth and smallmouth
bass greater than 15 inches in length from Onondaga
Lake should not be consumed because of elevated
mercury concentrations.
Macrophytes
(rooted aquatic plants and algae) have changed
profoundly in recent years. The number of species has
increased from five in 1991 to seventeen in 2005,
although the community is still dominated by a few
species. Percent cover of macrophytes increased about
three-fold between 2000 and 2005. Year-to-year
variability is evident from the annual aerial
photographs; this variability is typical of other
regional lakes. Much of the littoral zone has plant
coverage within the ideal range for largemouth bass
propagation. A notable feature of the 2006 macrophyte
abundance was a collapse in July, most likely due to
extreme rainfall and associated runoff.
Tributary macroinvertebrates
were monitored in 2006. The combination of habitat
degradation, nonpoint source pollution, and CSO
discharges affects the streams' macroinvertebrate
communities. In 2006 the macroinvertebrate communities
of Onondaga Creek, Ley Creek, and Harbor Brook showed
varying levels of impact. Sites in Ley Creek tended to
be the most severely affected followed closely by
Harbor Brook. Sites in Onondaga Creek tended to be the
least affected. Only minor changes to the
macroinvertebrate community have occurred since
completion of baseline surveys in 1999-2000.
Onondaga County completed a focused water quality
monitoring effort at selected stations along the
Seneca-Oneida-Oswego river system in 2006. The wet
summer of 2006 kept stream flow high in the Seneca
River through most of the summer and prevented
violations of ambient water quality standards for
ammonia-N and nitrite-N. Frequent measurements using
sondes detected brief periods where DO concentrations
dropped below the standards. The river's water quality
conditions continue to be strongly influenced by zebra
mussels.
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Advanced phosphorus removal
Susan Miller, Project Deputy Director
Onondaga County Dept of Water Environment Protection