Site Visit Report

	Oswego Harbor Power

	261 Washington Boulevard

	Oswego, NY 13126

April 2, 2008

Background and Objectives

The Environmental Protection Agency (EPA) is in the process of
developing 316(b) cooling water intake structure requirements that
reflect the best technology available (BTA) for minimizing adverse
environmental impact for all existing power plants and manufacturing
facilities. As part of this process, EPA staff is visiting electric
generators and manufacturers to better understand the cooling water
intake structure (CWIS) technologies in use at facilities, including the
site-specific characteristics of each facility and how these affect the
selection and performance of CWIS technologies.  EPA is also visiting
facilities to better understand cooling water use and specific issues or
technologies that can affect 316(b) compliance.  Oswego Harbor Power
(Oswego) was selected for a site visit due to its use of an offshore
intake location and its large intake flows.

Facility Description

The Oswego facility, owned and operated by NRG Oswego Harbor Power, LLC,
is a fossil-fueled steam electric generating facility located in Oswego,
NY. The facility occupies a large industrially-zoned site approximately
90 acres in size on the southern shore of Lake Ontario near the Oswego
River. Residential and municipal use areas border the facility to the
south, east and west. 

Cooling water withdrawals from and discharges to Lake Ontario for Units
5 and 6 are permitted under SPDES Permit No. NY0002186, which has been
administratively extended pending adoption of a new permit. An
additional discharge to Oswego Harbor is covered under the same permit
for Units 1-4 but is currently inactive. The facility discharges from
Units 5 and 6 offshore into Lake Ontario beyond the intake structures.

Electricity Generation and Transmission

Oswego Harbor originally began operating with four coal-fired units
(Units 1-4) first constructed in 1939 with a total nameplate rating of
400 MW. These units were converted to burn fuel oil (#6) in the early
1970s. While not all Units 1-4 have been formally retired from service,
market conditions and environmental restrictions, combined with their
age and relative inefficiency, make their future use highly unlikely. 

Units 5 and 6, constructed in the mid 1970s and early 1980s, are each
rated at 817 MW and use fuel oil (#6) as their main fuel source.  Unit 6
is capable of burning natural gas up to a 170 MW capacity and both units
require approximately 16 hours to be brought online. Unit 5’s
condenser tubes were originally composed of admiralty brass and were
changed to stainless steel, the same as Unit 6.

Oswego Harbor is now a peaking facility that provides electricity to the
grid infrequently and only during periods of high demand or when
baseload facilities such as nearby nuclear plants are taken offline for
refueling, emergencies, or maintenance.  Most recently, on an annual
basis, Oswego Harbor has a capacity utilization rate of 1-2 percent. The
facility representative indicated that the facility will typically
operate Units 5 and 6 for no more than a two week continuous period in
the summer and/or during a cold winter. At peak operation, the plant can
provide 1700 MW. The plant also operates briefly once a month for
station service. 

There are no immediate plans to repower or replace the existing units.

Oswego Units 5 and 6 typically have a spring and fall outage for
maintenance, but have a great deal of flexibility in determining the
outage period due to their minimal operation.

  

Cooling Water Intake Structure

The facility maintains 3 distinct cooling water intake structures:  one
serving Units 1-4 and one each serving Units 5 and 6. 

The Unit 1-4 intake extends approximately 500 feet offshore into Lake
Ontario and withdraws water through a submerged wooden anti-vortex
octagonal structure supported by steel pedestals bolted to the concrete
intake tunnel. The Unit 5 intake extends approximately 850 feet offshore
where the lakebed depth is approximately 22 feet deep at the intake
structure. The lakebed is primarily a rocky substrate at this depth and
distance from shore. The Unit 1-4 intake does not use technologies
specifically designed to reduce impingement and/or entrainment, although
an offshore location may result in reduced or different impacts compared
with an onshore location. Unit 5 is fitted with a velocity cap but does
not have a fish diversion and return system like Unit 6. 

The Unit 6 structure is also located offshore at a distance of 950 feet
at a depth of approximately 22 feet (see Attachment A).  The intake
conduit is submerged beneath the lakebed with the terminal end rising 10
feet from the bottom, the same as Unit 5. On average, the top of the
structure is approximately 12 feet below the lake surface. The intake is
fitted the same as Unit 5, with a 2 foot thick, hexagonal velocity cap,
each side 21.2 feet wide by 5 feet high. Each aperture is equipped with
heated bar racks to prevent the formation of frazil ice.  The bars are
spaced at 12 inch centers to keep large debris from entering the system.
 The intake is designed so the horizontal approach velocity is 1.0 feet
per second (fps) when the generating unit is operated at maximum (two
pump operation) output.  There is negligible vertical approach velocity.
 A 3 foot sill at the bottom of the structure prevents silting of the
intake.

The onshore portion of the Unit 6 intake structure consists of two
parallel trains.  Each train has a trash rack, two angled traveling
screens, and one circulating water pump (two pumps total).  A fish
bypass and collection system, and fish return pipe starts at the
convergence of the traveling screens. The trash rack is installed on a 5
on 1 slope and consists of 3 inch by 3/8 inch parallel steel bars spaced
at 3½ inch centers. The angled traveling screen assemblies consisting
of 10 foot wide panels with 3/8 inch mesh are mirror images of each
other divided by a concrete barrier wall and offset at a 25º angle. At
their nearest point the screen assemblies are 5 feet apart (see
Attachment B). A secondary diversion screen well exists for extremely
high debris loads, but it has not been necessary to use the secondary
system.

The fish diversion system consists of a diversion duct, fish pump and
return conduit. The diversion duct directs fish through the narrow point
between the angled screen assemblies and into a secondary screenwell. 
This contains a secondary traveling screen identical in design to the
main screens and moves the fish into a 6 inch wide bypass slot that
converges to the secondary jet pump.  This pump discharges into a 30
inch diameter discharge pipe embedded in the roof of the intake tunnel
for approximately 925 feet offshore where it rises vertically and
terminates as a horizontal discharge approximately 6 feet off of the
bottom and 270 feet from the offshore intake structure.  Fish impinged
on the angled screens are collected in a dumpster and removed to a
landfill.

Intake pumps are single speed rated at 162,500 gallons per minute (gpm),
or 234 million gallons per day (mgd), for a unit total intake capacity
of 468 mgd. When operating the facility at higher loads, greater than
400 MW, both intake pumps will run at their maximum capacity.  The pumps
on Units 5 and 6 have slightly different pumping capability.

The facility does not chlorinate intake water to control biofouling but
does conduct periodic heat treatments that raise circulating water
temperatures to 90-95º F. Thermal treatments are used  as necessary to
control zebra mussel buildup in the intake system.   

Facility representatives noted the intake structure and associated
components require little maintenance and that debris build-up is not an
issue because of long-shore currents and wave activity.  Facility
representatives stated that Oswego had originally planned to comply with
the Phase 2 rule with a combination of variable speed drives, reduced
flow, fine mesh, and the location of the intake offshore.

Impingement and Entrainment Information

Oswego Harbor has conducted impingement and entrainment sampling as part
of its reapplication process at the direction of NYSDEC. 

The entrainment analysis has consisted of weekly sampling in the onshore
portion of the intake structure (the forebay) as well as in the vicinity
of the velocity cap at the offshore location. Oswego also collected
nearshore samples to establish a baseline to evaluate the effectiveness
of the offshore placement.  In conducting its entrainment sampling at
each location, Oswego collected a 24-hour composite sample from multiple
depths (surface, bottom, and middle) from April to September, 2007 via a
pump and then filtered the samples through plankton nets.   The
entrainment samples were invalid, however, due to an influx of
cladophora (seaweed) which plugged the plankton nets.  Oswego believes
it has resolved this issue and is repeating its entrainment study in
2008.

The facility has conducted more extensive sampling to evaluate
impingement impacts and the effectiveness of the Unit 6 velocity cap and
fish diversion/return system by comparing impingement rates at Unit 5
with Unit 6. Impingement sampling consists of weekly 24-hour gill net
samples collected in the vicinity of the intake structure as well as in
nearshore areas to establish a baseline for comparison over a one year
period.   The gill net data showed a 2-3 fold increase in the numbers of
fish caught near shore in comparison to the number of fish caught near
the velocity cap.

Alewife, spottail and emerald shiner are typically the most abundant
species subject to impingement. A 1991 study conducted by LMS showed a
high 96-hour survival rate for fish returned through the diversion
system. 

The facility has not evaluated other technologies to reduce impingement
and entrainment. 

Cooling Tower Feasibility

The facility representative stated that siting wet cooling towers on the
existing location would be difficult due to the proximity of residential
and municipal use areas as well as the limited space at the site. 

Additional Information

Oswego noted the ecology of the Lake has changed significantly over the
past four years.  Phosphate control and invasive zebra mussels have
greatly increased the clarity of the lake which has significantly
altered light penetration.  Forage fish are rarely observed at the
intakes anymore.

The facility also houses approximately 7 fuel oil tanks on land it owns
approximately 4 miles south of the site.  Fuel delivered to this South
Oswego Terminal is typically delivered via rail and is either stored
on-site or piped to Oswego Harbor Power, as needed.  Oswego Harbor Power
typically receives fuel oil by barge/ship.

Attachments

Attachment A		List of Attendees

Attachment B		Aerial Photo

Attachment C		CWIS Line Drawings

Attachment D		Unit 6 Onshore Intake Structure Schematic

Attachment E		Site Photo

Attachment A--List of Attendees

Paul Shriner, EPA

Jan Matuszko, EPA

Tim Havey, Tetra Tech

Tom Coats, NRG

Gary Smythe, Shaw Environmental

Attachment B—Aerial Photo

Please see DCN 10-6511A accompanying this document.

Attachment E—Site Photo

Please see DCN 10-6511B accompanying this document.

Attachment C--CWIS Line Drawing

 



Attachment D--Unit 6 Onshore Intake Structure Schematic

 

 Oswego runs once per month for station service.

 This reflects the typical entrainment season for this location.

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