Document ID: EPA-HQ-OW-2008-0667-0107
Agency: epa
Document Type: Supporting & Related Material
Title: 
Posted Date: 2011-02-28T05:00Z

Site Visit Report

	Possum Point Power Station

	19000 Possum Point Road

	Dumfries, VA 22026

March 10, 2009

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.  Possum Point Power
Station was selected for a site visit due to its proximity to EPA
Headquarters, its use of combined cycle, and its use of partial
closed-cycle cooling.

Facility Description

Possum Point is located on a 640 acre site in Dumfries, Virginia.  Most
of the developed area of the site is on a peninsula at the confluence of
the Potomac River (a tidal river) and Quantico Creek.  The facility
began operations in 1948 and employs roughly 110 people.

Possum Point is owned and operated by Dominion Virginia Power
(Dominion).  The facility’s NPDES permit (VA0002071) is due to expire
May 31, 2009.

Electricity Generation and Transmission

Possum Point consists of four active generating units with a total
generating capacity of 1740 MW (gross summer capacity).  Units 3 and 4
(100 MW and 225 MW, respectively) are 1950s-era units that were
converted from coal to natural gas in 2003.  Unit 5 (840 MW) was added
in 1972 and uses #6 fuel oil.  Unit 6 (575 MW) was built in 2003 and is
a combined cycle gas combustion turbine with a heat recovery steam
generator (HRSG).  Six small oil-fired (#2) combustion turbines provide
additional peak generating capacity at 72 MW (gross summer capacity).

Units 3, 4 and 5 operate as peaking units, with a capacity utilization
rate (CUR) of 15-20%.  Unit 6 is approaching becoming a baseload unit,
with a CUR of 75-80%; in the past, it typically cycled off at night, but
has been running continuously in recent months.  Facility
representatives also noted that Possum Point is an important part of
grid reliability and voltage support in the area.

Natural gas (mostly from the Cove Point liquefied natural gas [LNG]
facility in Maryland) is provided via new 14-mile pipeline constructed
to supply the new Unit 6.  There is no natural gas storage onsite.  Fuel
oil arrives via boat at an onsite dock and is stored in tanks.

The transmission system is owned by Dominion but is operated by a
different business unit.

Cooling Water System and Intake Structure

Possum Point has two CWISs on the Potomac River; one for Units 3 and 4
and a second for Unit 6.  Units 3 and 4 employ once-through cooling and
have a design intake flow (DIF) of 224 million gallons per day (mgd) and
an actual intake flow (AIF) of 207 mgd.  Units 5 and 6 were each
constructed with mechanical draft cooling towers.  Unit 5 withdraws
makeup water from the discharge for Unit 3 and has an AIF of 12-28 mgd. 
Unit 6 withdraws makeup water from the former CWIS for Units 1 and 2,
with an AIF of 6-14 mgd; raw water is sent through a treatment process
before being fed to the tower.

Each CWIS is a shoreline intake structure with a bar rack and standard
(i.e., 3/8” coarse mesh) traveling screens, as well as a floating boom
to divert debris.  A debris trough returns debris and impinged organisms
to the river just downstream of the screens.  The CWIS serving Unit 6
has two 8-foot traveling screens and one dual flow traveling screen. 
The CWIS for Units 3 and 4 has two 10-foot screens.  Both CWISs have two
circulating pumps per unit (one operating and one backup), for a total
of 8 pumps.  The traveling screens are rotated automatically on a timer
or based on a head differential across the screen.  The design
through-screen velocity at each CWIS is 1.3 feet per second (fps).

Facility representatives noted that they will be replacing the traveling
screen on the former Unit 2 soon.  Screen maintenance is performed on an
as-needed basis, with maintenance typically occurring every few years. 
Inspections by divers are conducted approximately every two years.

Possum Point is capable of recirculating hot water to its CWISs to
address icing, but has not needed to do so in several years.  The CWIS
also has an air aspiration device that can create turbulence at the
CWIS; in recent years, continuously operating the aspirator has been
sufficient to control icing.

Impingement and Entrainment Information

The Potomac River is approximately 1.5 miles wide at the facility and up
to 60 feet deep.  The river is tidal, but has fairly small changes in
depth.  As a result of the brackish waters, a mix of marine and
freshwater species are present.  The facility is also home to many rare
birds that reside in the tidal marshes and surrounding areas.

Possum Point collected impingement samples in 1976 and again in
2005/2006.  In order to facilitate comparison of the data, Possum Point
used the same procedure and methodology during both sampling periods. 
During the sampling periods, Possum Point conducted impingement sampling
two times a month for a year for a total of 24 sampling events.  During
each 24-hour sampling event, the facility ran the screens continuously
and collected impingement samples from each screen wash for 10 minutes
each hour.  The facility did not conduct entrainment sampling during the
2005/2006 study.

The table below shows results from the two impingement studies.  The
facility collected 18 common species during the two sampling periods. 
In both studies, more fish were collected at night.  The total fish
counts are raw numbers; they do not reflect an annual estimate of
impinged organisms.

	Sampling Period

	1976	2005/2006

Number of species collected	24	24 + 2 shellfish1

Primary species	White perch

Gizzard shad

	White perch

Bluegill

Pumpkinseed

Total number of fish collected	4550	703

1 The facility did not sample for shellfish during the 1977 sampling
period.

During the 2005/2006 sampling period, Possum Point also conducted
ambient studies, in which the facility collected 925 fish from 13
species.

Cooling Tower Feasibility

The two largest units at Possum Point already employ closed-cycle
cooling (see Section 4.0).  Facility representatives stated that there
are no plans to study retrofitting the remaining units to closed-cycle
cooling.  They added that, due to the facility’s location on the
peninsula, available space is virtually non-existent.  Space may be
available further inland, but would require an expansion of the
facility’s fenced perimeter.

Debris Handling

Possum Point does not have significant problems with debris loading. 
Facility representatives did note that there are occasional problems
with hydrilla or logs, but these events do not significantly affect
operations.  

Repowering/Future Uses

Possum Point has no current plans for re-powering or upgrades.

Cooling Ponds

	

There are no cooling ponds on site.

Ownership

Possum Point is owned by Virginia Electric and Power Company d/b/a
Dominion Virginia Power, a subsidiary of Dominion Resources, Inc., an
investor-owned company.

316(a)

Possum Point has a BTU heat rejection limit with no 316 (a) variance. 

Ash Handling

Possum Point no longer burns coal, but still maintains two ash ponds
onsite.  Pond D (or Delta) was constructed in the 1980s and is clay
lined.  Pond E (Echo) is an unlined pond that was built in the 1960s. 
Pond E was the primary pond for handling wet fly and bottom ash that was
sluiced from the facility.  Pond E would overflow into another pond
(referred to as the beaver pond) and eventually into Quantico Creek. 
Ash was hydraulically dredged into Pond D for long-term storage, which
had a projected lifespan of approximately 25 years when Possum Point
converted to natural gas.  Discharges from Pond D, although very rare,
were controlled and flowed into Pond E.

Both ash ponds are regulated by the Virginia Department of Environmental
Quality (DEQ) and are subject to licensing (five year terms) and annual
state inspections.  Dominion also conducts quarterly inspections.

Air Emissions Controls

Possum Point no longer burns coal and has no air emissions control
equipment.

Additional Information

With regard to the 2004 316(b) Phase II rule, Possum Point completed its
biological studies including impingement.  The facility did not complete
technology feasibility evaluations nor did they come to conclusions as
to how they would have complied with the 2004 rule.  However, facility
representatives indicated they would have considered pursuing reduction
credits that were achieved by improving generating efficiency and
cooling water intake flows.  They thought it was imperative that the new
rule offer multiple compliance options to allow each facility to
accommodate site specific issues.  Specifically, Dominion Power
representatives would like to see rule options that consider waterbody
type, as man-made reservoirs likely do not merit entrainment protection.

The former coal pile was located at the southern end of the peninsula;
coal handling equipment remains intact to preserve the facility’s
ability to switch fuels again if necessary.  Remaining coal left after
the fuel conversion was stored in the ash ponds.  This coal is now being
re-processed for use at the Chesterfield Power Station.

Attachments

Attachment A		List of Attendees

Attachment B		Aerial Photos

Attachment C	Aerial View of Possum Point Power Station

Attachment D	Possum Point Station Water Flow Diagram

Attachment A--List of Attendees

Paul Shriner, EPA

Jan Matuszko, EPA

Josh Hall, EPA

Erik Helm, EPA

Julie Hewitt, EPA

Richard Witt, EPA OGC

Shari Goodwin, Tetra Tech

Kelly Meadows, Tetra Tech

Peter Sherman, Tetra Tech

Christine Wong, Tetra Tech

John Sunda, SAIC

Bill Bolin, Dominion 

Cathy Taylor, Dominion 

Bill Clancy, Dominion 

Jeff Marcell, Dominion 

Attachment B--Aerial Photos



Attachment C—Aerial View of Possum Point Power Station

Please see the attached materials.

Attachment D--Possum Point Station Water Flow Diagram

Please see the attached materials.

 Prior to a recent court ruling, Maryland also claimed jurisdiction to
regulate discharges to the Potomac River and NPDES permits were jointly
issued.  The ruling gave sole authority to the state of Virginia; going
forward, Possum Point’s permit will be issued by only Virginia.

 Units 1 and 2 are retired in place. 

 Unit 6 also has the capability to use #2 fuel oil, but rarely uses it;
since startup, Unit 6 has used oil for only approximately 250 hours,
including startup and testing activities.

 Unit 5 and 6 cooling towers employ drift eliminators, but do not use
plume or noise abatement.  Unit 5 has two- eleven (11) cell cooling
towers of an older less efficient splash bar tower fill design.  The
tower fill was replaced in with Marley’s Optibar (more efficient
design of polypropylene material) and partial replacement of broken or
missing drift eliminators.  The Unit 5 towers operate at 2 or less
cycles of concentration when Unit 5 is generating power and do not
currently employ chemical treatment.  Biocides for maintaining condenser
and equipment cooler cleanliness may need to be added in the future. 
Unit 6 has one-ten (10) cell cooling tower of a modern design that uses
high efficiency honeycomb type fill.  The fill is more prone to fouling
or plugging so cleaner makeup water is provided and chemical treatment
is employed consisting of an acid sulfuric acid for scale control and a
biocide sodium hypochlorite (bleach) for organics control.  The Unit 6
tower operates at 4 or less cycles of concentration.

 The circulating pumps for Unit 5 operate continuously, even if the unit
is not generating; during these periods, circulating water is not pumped
to the top of the towers and is bypassed directly to the basin and
returned to the condenser.

 The treatment process is clarification for suspended solid removal. 
The Unit 6 intake also supplies high purity demineralized water for
boiler makeup at the facility through further processing by sand
filtration, carbon filtration, reverse osmosis, and electrodeionization
(EDI).  As such, not all of the water withdrawn is for cooling purposes.

 In the 2005/2006 study, the study plan assumed that the facility would
not meet the 15% CUR threshold and would therefore not be subject to
entrainment requirements.

 Pond E also receives other discharges, such as boiler blowdown and
industrial wastewater.

 Unit 6 is a combined cycle generating unit—it is more efficient that
other generating units.  Up to 2/3 less cooling water is used since
approximately 2/3 of the power generated is from the combustion turbines
which provide waste heat to generate steam in the HRSGs and do not
require the same cooling water quantity as a steam turbine.

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