Document ID: EPA-HQ-OW-2008-0667-0004
Agency: epa
Document Type: Supporting & Related Material
Title: 
Posted Date: 2009-11-05T05:00Z

Site Visit Report

	Big Bend Station

	13031 Wyandette Rd

	Apollo Beach, FL 33572

March 27, 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.  Big Bend Station (Big
Bend) was selected for a site visit due to its use of fine mesh
traveling screens and its large intake flows.

Facility Description

Big Bend is located on the western coast of Florida and withdraws from
Tampa Bay.  The facility is owned by Tampa Electric Company (TECO) and
is situated on a 1492 acre site.  Big Bend began operations in 1970 and
employs approximately 350 people.  The facility discharges via a 4000
foot discharge canal along the southern side of the property.

The facility’s NPDES permit (FL0000817) expires in 2010.

Electricity Generation and Transmission

Big Bend has four coal-fired generating units with a total generating
capacity of 1800 MW.  Units 1-3 were built in 1970, 1973, and 1976,
respectively.  Unit 4 was initially designed with a cooling dilution
system that would add ambient water to cool the effluent, but the
permitting authority eventually decided on a 4000 acre mixing zone to
address the thermal discharge.  Facility representatives estimated that
Big Bend’s capacity utilization rate was approximately 80% in recent
years.  Normally the facility is a baseload plant, but the retrofit of
Selective Catalytic Reduction (SCR) air pollution control equipment on
all four units to reduce NOx emissions, boiler maintenance, and other
substantial maintenance has necessitated longer than normal outages. 
The facility estimates a 6 month total outage per unit to complete the
SCR retrofits.  Ideally, the facility would have a scheduled outage of
2-6 weeks every 2 years.  The facility’s highest peak demand is in
winter, but summer demand is sustained at a higher level on average.

TECO also owns the switchyard and transmission facilities.

Cooling Water Intake Structure

Big Bend withdraws from a 3000 foot long intake canal at a depth of 25
feet from Tampa Bay.  The facility has two cooling water intake
structure (CWISs); Units 1 and 2 share one CWIS and Units 3 and 4 share
the other.  Both CWISs use a trash rack to screen larger debris; there
is no cleaning system for this first layer of screening.

Both CWISs employ dual flow screens.  Units 1 and 2 have a standard
3/8” mesh traveling screen with no return system.  The screens are
rotated approximately once per shift and all materials on the screen are
collected and disposed of in a landfill.

Units 3 and 4 employ fine mesh traveling screens with a mesh size of 0.5
mm.  The fine mesh screens (installed as overlays to the existing coarse
mesh screen panels) are deployed seasonally, from March 15 to October
15.  The off-season is used to repair and clean the fine mesh screen
panels. Facility representatives estimated that the maintenance costs
(including personnel) for the fine mesh screen assembly is approximately
$500,000-$600,000 per year; this includes screen repair, oil changes,
preventative maintenance measures for wash pumps and return pumps, and
replacement of the chain every other year.  Cleaning and repair takes 5
to 6 contractors and 4 staff on a full-time basis for several weeks, and
3 staff work 7 days a week during downtime. By comparison, the facility
estimates that the coarse mesh screens on Units 1 and 2 have annual
maintenance costs of approximately $50,000.  The facility noted the
harsh salt environment (up to 30 ppt) in which the screens are operated
and that Asian/New Zealand mussels necessitate the 6 month repair and
maintenance cycle.

During operation, the screens are rotated continuously, but also have
multiple rotation speeds and use an automated head differential system
to trigger faster screen rotation speeds.  Units 3 and 4 share an
organism return system, which pumps organisms to Apollo Bay.  While
running, the system is monitored daily.

Units 1 and 2 have four screen assemblies and four pumps while Units 3
and 4 have 6 screen assemblies and four pumps.  Each screen assembly can
withdraw 120,000 gallons per minute and generally two screens are
required to operate a generating unit.  The total design intake flow
(DIF) for the facility is nearly 1.4 billion gallons per day.

Facility representatives estimate that the through-screen velocity at
Units 1 and 2 are 1-2 feet per second.  At Units 3 and 4, the
through-screen velocity is approximately 0.55 feet per second at normal
tide.  The tides vary by approximately 2.5 feet at the intake structure.

The facility periodically dredges the intake canal, as sedimentation
near the intake structures is a substantial problem.  Dredging
activities are generally in the area of the CWIS for Units 3 and 4, as
silt cascades into the screenwell when the screens are removed for
maintenance.  Additionally, dredging activities must avoid the manatee
season.

Big Bend does not use biocides, instead relying on mechanical cleaning
of its intake structure.

Impingement and Entrainment Information

The most frequently impinged organism at Big Bend is the horseshoe crab.
 During the site visit, substantial amounts of the crabs were visible in
the screenwash.

Facility representatives stated that they expected that the fine mesh
screens on Units 3 and 4 would have been compliant with the entrainment
requirements of the now-suspended Phase II rule.  The facility expected
to make improvements to Units 1 and 2, but had not considered any
specific options in great detail.  The facility indicated it would most
likely have needed to make improvements to comply with the now suspended
impingement requirements.  The facility does not know of any physical
limitations that would restrict further expansion of the intake
structures in the intake canal.

Cooling Tower Feasibility

Facility representatives stated that retrofitting cooling towers would
be problematic for several reasons.  First, there are water use
restrictions in the Tampa area and the evaporative losses from a tower
may be unacceptable (meaning that the towers would need to use salt
water).  Second, given the site configuration, towers would need to be
sited on the southern portion of the property, and would be much closer
to residential areas and wetlands.  It is likely that some wetlands
would be filled to provide enough space to construct cooling towers. 
Third, the facility assumed that plume abatement towers would be
required due to proximity to the town of Apollo Beach, necessitating a
straight line configuration for towers and further limiting the possible
locations.  Fourth, the high average wet bulb temperature would cause
technical challenges.  Lastly, Big Bend’s discharge canal is listed as
a federal manatee refuge and cooling towers would remove nearly all of
the thermal discharge and eliminate the cold-weather refuge for the
endangered species.

Additional Information

A municipal desalinization plant is co-located to the north of the
facility.  The plant withdraws approximately 50 mgd from Big Bend’s
discharge canal, creates 25 mgd of potable water, and returns the
remaining 25 mgd to the canal.  Big Bend’s circulating pumps stay on
during outages for the desalination plant’s continuous operation.

Attachments

Attachment A		List of Attendees

Attachment B		Aerial Photo

Attachment C		Email to Kevin Young, TECO re: Manatees and Power Plants

Attachment D	An Assessment of the Biological Effectiveness of 0.5 mm
Fine-Mesh Traveling Screens in Reducing Entrainment at the Big Bend
Power Station (DRAFT)

Attachment E	Letter to Paul Shriner, EPA re: Units 3&4 Fine Mesh Screens
Follow-up Information

Attachment F	Site Visit Photos

Attachment A--List of Attendees

Paul Shriner, EPA

Jan Matuszko, EPA

Kelly Meadows, Tetra Tech

Kevin Young, TECO

Karen Zwolak, TECO

Stanley Kroh, TECO

Attachment B—Big Bend Aerial Photo

Please see DCN 10-6502D accompanying this document.

Attachment C--Email to Kevin Young, TECO re: Manatees and Power Plants

Please see DCN 10-6502A accompanying this document.

Attachment D--An Assessment of the Biological Effectiveness of 0.5 mm
Fine-Mesh Traveling Screens in Reducing Entrainment at the Big Bend
Power Station (DRAFT)

Please see DCN 10-6502B accompanying this document.

Attachment E--Letter to Paul Shriner, EPA re: Units 3&4 Fine Mesh
Screens Follow-up Information

Please see DCN 10-6502C accompanying this document.

Attachment F--Site Visit Photos

Please see DCNs 10-6502E-J accompanying this document.

 Big Bend uses eastern bituminous coal from mines in Kentucky.

 The estuary is very shallow, leading to the warming of intake water
withdrawals; intake temperatures can exceed 90 degrees in the summer. 
The facility is designed for a delta T of 17 degrees.  The canal is
tidal and fluctuates approximately 2.5 feet.

 At the urging of EPA Region IV, a pilot study for fine mesh screens for
Unit 4 was conducted in 1985 and demonstrated a 50% reduction in
entrainment exclusion. In order to reach an approximate reduction of no
net loss, fine mesh screen were also added to Unit 3.  The screen
material is a polymer mesh.

 The organism return system screens some larger organisms for collection
and disposal.

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