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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 sitespecific 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.1

3.0 Electricity Generation and Transmission

North Omaha consists of 5 coal-fired2generating units that typically operate as 

load-following3units. 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 

 

1 Another 70 OPPD maintenance staff are also based at North Omaha.

2 North Omaha’s coal comes via rail from the Powder River Basin in Wyoming; 125-car trains arrive every 

2 days.

3 Load following plants typically operate near capacity during the day and early evening when demand for 

power is highest; these facilities then reduce generation at night when demand is lower.
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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 pump4and 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.

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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).6 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 timeconsuming. 

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 

 

4 The pumps for Units 1-2 each have a capacity of 43.2 million gallons per day (mgd) (30,000 gallons per 

minute [gpm]). The pumps for Units 3-4 have an average capacity of 53.3 mgd (37,000 gpm).

5 This CWIS was built with the expectation that Unit 6 would eventually be constructed and has a total of 

12 intake bays. Unit 6 would use the other 6 intake bays.

6 At normal river elevation; at low water, the range of through-screen velocity changes to 3.64 to 5.67 fps.
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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.”

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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.

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 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 River9 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 closedcycle recirculating system (CCRS): limited land availability and proximity to an 

airport.

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See elsewhere in the record for the proposed rule.

8 Three sampling events were for one hour and the fourth was a 24-hour collection.

9 Test species included bluegill, channel catfish, and fathead minnows. Approximately 2400 fish were 

introduced in front of the screen.

10 The airport is 2 miles from North Omaha.
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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.
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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.
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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
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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
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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