Document ID: EPA-HQ-OW-2008-0667-0037
Agency: epa
Document Type: Supporting & Related Material
Title: 
Posted Date: 2010-11-08T05:00Z

Site Visit Report

	North Omaha Station
	7475 Pershing Drive
	Omaha, NE 68112
      March 2, 2009

1.0 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.  North Omaha was selected for a site visit due to its location on a large freshwater river and onsite pilot testing of Beaudrey screens.

2.0 Facility Description

      North Omaha began operations in 1954 on a 100-acre site in northern Omaha, Nebraska.  The facility withdraws cooling water from the Missouri River (at river mile 625.2) and is regulated by NPDES permit NE0000621, which was renewed October 1, 2008.  North Omaha is owned by the Omaha Public Power District (OPPD) and employs approximately 120 people.

3.0 Electricity Generation and Transmission
      
      North Omaha consists of 5 coal-fired generating units that typically operate as load-following units.  The facility's capacity utilization rate (CUR) is approximately 75%.  North Omaha typically operates at a heat rate of 10,800 Btu/Kwh and has a total generating capacity of 663 MW.
      
      The facility schedules a one week routine maintenance outage annually and a three week boiler outage every three years.  The condensers are cleaned during each outage to ensure efficient operation of the generating unit.  Facility representatives noted that, despite the heavy debris loads, the condenser tubes have never needed to be replaced.  A major turbine outage occurs every 8-10 years.
      
      The transmission system is owned by OPPD but is operated by a different unit.

4.0 Cooling Water System and Intake Structure

      North Omaha has three CWISs that withdraw once-through cooling water from the shoreline of the Missouri River.  Each CWIS is located in a separate screenhouse with a trash rack with 3" spacing.  The screenhouses for Units 1 and 2 and for Units 3 and 4 each have 5 intake bays, each with one pump  and one coarse mesh (3/8") traveling screen.  The screenhouse for Unit 5 has 6 intake bays, with three pumps (84.6 mgd or 58,750 gpm each) and two screens per bay.  The screens automatically rotate every 8 hours or when a pre-determined head differential is reached.  The design intake velocity of the CWISs is 1.4 to 2.03 feet per second (fps).  In total, the facility has a design intake flow (DIF) of 758 mgd and an average actual intake flow (AIF) of 730 mgd which represents approximately 4% of the average river flow.  Thermal effluent is returned to the river adjacent to the CWISs.
      
      In 2006, North Omaha tested a new type of intake screen on one intake bay on Unit 5: the Beaudrey Water Intake Protection (WIP) screen.  North Omaha replaced one of its standard coarse mesh traveling screens in Intake Structure No. 3 with an 8 foot diameter 6 mm mesh Beaudrey WIP screen.  The facility placed the test screen, which was designed to fit into the existing traveling screen well, at the screenwell bottom and sealed the remaining open area (formerly occupied by the traveling screen) with steel plates to force all incoming water to pass through the screen.  
      
      The main reason North Omaha became interested in the WIP screen was the potential to eliminate debris carryover.  (See Section 7.0 below.)  Due to the debris and sediment issues, the facility performs a screen overhaul during each maintenance shutdown, including rebuilding the screen, resetting chains and tensioners, and replacing worn parts and seals; the process is expensive and time-consuming.  
      
      The WIP screen is a wheel-shaped, round screen which is divided into pie-shaped chambers by plates on the inlet side of the screen.  A hydraulic pump and drive gear rotate the screen wheel twice per minute, where fish and debris impinged on one section of the wheel are vacuumed off as they rotate under a stationary scoop mounted over one section of the wheel.  Fish and debris are vacuumed off via a specially designed fish-friendly backwash pump where the impeller is designed to separate the water into pockets that provide a safe place for the fish to remain as the water is moved through the pump.  The backwash flow then discharges through a pipe to a collection tank that overflows back into the river.  The through-screen velocity as operated was calculated to be 2.5 feet per second.  As part of the screen evaluation at North Omaha, Beaudrey conducted an impingement survival study of this pilot screen.  The study and its results are described fully in a report provided by Beaudrey and EPRI titled "Beaudrey Water Intake Protection (WIP) Screen Pilot-Scale Impingement Survival Study."
      
      No biocides are used at North Omaha.

5.0 Impingement and Entrainment Information
      
      North Omaha has not collected impingement or entrainment information for its existing traveling screens.  However, as described above, Beaudrey collected two years of biological monitoring for the pilot WIP screen beginning in 2007.  During the first year, impinged fish were collected four times per month.  At the end of the year, facility representatives determined that there were not enough fish impinged to provide a statistically significant sample size to examine the impingement survival rates.  A second series of tests were developed, where fish common to the Missouri River were introduced directly in front of the screen and impingement survival rates were compared to a control group.  Biologists used seine nets to collect fish from the river and other fish were purchased from local hatcheries.
      
      The screen testing concluded that the WIP screen has no effect on fish impingement mortality; in other words, fish passing through the screen return exhibited the same survival rates as fish that remained in the control test.
      
      North Omaha has not conducted any entrainment or ambient sampling, but indicated that various other organizations have conducted ambient sampling of the Missouri River.

6.0 Cooling Tower Feasibility

      Facility representatives have not considered closed-cycle cooling for North Omaha.  They noted a number of problems associated with retrofitting a closed-cycle recirculating system (CCRS): limited land availability and proximity to an airport.
       
7.0 Debris Handling

      The facility has had significant problems with debris in the past.  Spring (with rising water levels carrying deposited materials) and fall (leaves and grasses) are the heaviest times of year.  Sticks, sand, gravel, and rocks eventually clog the condenser and require a shutdown for cleaning.  Facility representatives noted that fine sand is the most troublesome, as it wears parts and clogs screen spray nozzles.  The facility has a permit from the Army Corps of Engineers for sediment and debris removal.
      
      The facility typically overhauls the traveling screens every 3 to 4 years.  On the average, 4 screens are overhauled per year at an annual cost of $586,000.
      
      Average river flow at the facility is 28,850 cubic feet per second (18,646 mgd) with an average velocity of 7 fps.

8.0 Repowering/Future Uses
      
      As noted in Section 4.0 above, North Omaha has CWIS infrastructure in place to add a Unit 6, but currently has no plans for expansion.

9.0 Cooling Ponds
	
      There are no cooling ponds on site.

10.0 Ownership
      
      OPPD is a public utility that is owned by the state of Nebraska.  The entire state is supplied by public power.

11.0 316(a)

      The permits for all OPPD facilities have thermal discharge limits; facility representatives noted that the most troublesome time of year for meeting these limits was in the summer, when the ambient water temperatures are highest.  They added that they have not had any problems meeting state water quality standards, though.

12.0 Ash Handling

      A recently re-lined onsite ash pond is used for bottom ash.  Much of the bottom ash can be sold for beneficial uses, but this is not done on a consistent basis as of yet.  The pond is serviced every 10 years and was constructed as an in-ground pond (with no berms).  Most of the ash is collected in hydrobins.
      
      Fly ash is handled dry and stored at an onsite landfill.  A significant portion is also sold for use in concrete, as minimal material has been added to the landfill in recent months.

13.0 Air Emissions Controls

      North Omaha Station utilizes the following air emission controls:
      
                                   Boiler ID
                                     Type
                                  NOx control
                                  PM control
                                 Other control
                                      NO1
                               Tangential-fired
                                       
                     Cold-side electrostatic precipitator 
Ammonium Nitrate Injection [Opacity]
                                      NO2
                               Tangential-fired
                    (1) Low-NOx burners; (2) Over-fire air
                     Cold-side electrostatic precipitator
                     Ammonium Nitrate Injection [Opacity]
                                      NO3
                               Tangential-fired
                    (1) Low-NOx burners; (2) Over-fire air
                     Cold-side electrostatic precipitator
                     Ammonium Nitrate Injection [Opacity]
                                      NO4
                               Tangential-fired
                                       
                     Cold-side electrostatic precipitator
                     Ammonium Nitrate Injection [Opacity]
                                      NO5
                                  Wall-fired
                                Low-NOx burners
                     Cold-side electrostatic precipitator

      

14.0 Additional Information
      
      Facility representatives stated that, based on the results of the WIP screen testing, they likely would have pursued the installation of WIP screens at all intakes to comply with the 2004 Phase II rule.  They did note that the calculation baseline might have been problematic to calculate due to low impingement rates.  Facility representatives added that meeting entrainment requirements would be very difficult given the river conditions, as fine mesh screens would require a significant expansion of the CWIS and that they question the feasibility of fine mesh screens in a high debris river.  Additionally, the state permitting authority noted that the portion of entrained organisms is a small percentage of the total number of organisms in the river.
      
      Summer (March to October) is navigation season on this portion of the Missouri River.  The Army Corps of Engineers regulates the season and determines water releases from reservoirs upstream.
      
      Facility representatives stated that facilities in Nebraska that are not located on a major river (i.e., inland facilities) have been restricted by state regulations from any further surface water withdrawals that would result in consumptive uses (except for domestic use).
      
      Facility representatives stated that they have been experiencing some problems in meeting effluent limitations guidelines for metal cleaning wastes.  Service water is withdrawn from groundwater wells and treated by reverse osmosis before being used in the plant.  Due to high ambient levels of iron (which is not removed by the reverse osmosis), the ash pond effluent has shown elevated iron levels as well.
      
Attachments

Attachment A		List of Attendees
Attachment B		Aerial Photos
Attachment C	North Omaha Facility Description
Attachment D	Engineering Diagrams
Attachment E	Information on Debris
Attachment F	WIP Screen Presentation
Attachment G		Site Visit Photos
Attachment A--List of Attendees

Paul Shriner, EPA Headquarters
Jan Matuszko, EPA Headquarters
Jamie Hurley, EPA Headquarters
John Dunn, EPA Region VII
Glenn Curtis, EPA Region VII
John Bender, Nebraska Department of Environmental Quality
Kelly Meadows, Tetra Tech
Russ Baker, OPPD
Greg Krieser, OPPD
Ron Stohlmann, OPPD
Timothy Yager, OPPD
Mike Krumland, Nebraska Public Power District (NPPD)
Joe Citta, NPPD
Justin Reimers, NPPD
Brian Hittle, Beaudrey

Attachment B--Aerial Photos

Please see DCN 10-6521A accompanying this document

Attachment C -- North Omaha Facility Description

Please see DCN 10-6521B accompanying this document

Attachment D -- Engineering Diagrams

Please see DCN 10-6521C accompanying this document

Attachment E -- Information on Debris

Please see DCN 10-6521D accompanying this document

Attachment F -- WIP Screen Presentation

Please see DCN 10-6521E accompanying this document

Attachment G -- Site Visit Photos

Please see DCNs 10-6521F through Q accompanying this document