Document ID: EPA-HQ-OW-2008-0667-0030
Agency: epa
Document Type: Supporting & Related Material
Title: 
Posted Date: 2010-11-08T05:00Z

Site Visit Report

	Nebraska City Station
	7264 L Road
	Nebraska City, NE 68410
      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.  Nebraska City was selected for a site visit due to its location on a large freshwater river.

2.0 Facility Description

      Nebraska City began operations in May 1979 on a 1600-acre site about 8 miles southeast of Nebraska City, Nebraska.  The facility withdraws cooling water from the Missouri River (at river mile 556.2) and is regulated by NPDES permit NE0111635, which was renewed on July 1, 2008.  Nebraska City is owned by the Omaha Public Power District (OPPD) and employs approximately 158 people.

3.0 Electricity Generation and Transmission
      
      Nebraska City is a 650 MW coal-fired power plant with 1 generating unit.  The facility's capacity utilization rate (CUR) is approximately 77%.
      
      The transmission system is owned by OPPD but is operated by a different business unit of the company.

4.0 Cooling Water System and Intake Structure

      Once-through cooling water is withdrawn through a shoreline CWIS with 6 intake bays; each intake bay houses one coarse mesh (3/8") traveling screen and each pair of bays feeds one circulating pump with a capacity of 244.8 million gallons per day (mgd or 170,000 gallons per minute [gpm]) each.  Typically, two pumps are used during generation; facility representatives noted that they prefer to use the northernmost pumps, as these are less prone to debris and sediment fouling.
      
      The traveling screens are typically rotated continuously (at 2.5 feet per minute) to best handle debris loading.  The original screen design included intermittent screen rotation, but the sedimentation in the intake bays prompted more frequent screen rotation.
      
      In total, the facility has a design intake flow (DIF) of 670 mgd and an average actual intake flow (AIF) of 450 mgd.  The average design intake velocity of the CWIS is 1.36 feet per second (fps).

5.0 Impingement and Entrainment Information

      EPA did not collect any information about biological studies at this site.
      
6.0 Cooling Tower Feasibility

      Nebraska City is adding a second unit (see Section 8.0 below) that will utilize closed-cycle cooling.  The 18-cell mechanical draft tower was built at a cost of $40-60 million and will withdraw makeup water from an existing intake pipe.  The towers include drift eliminators, but no plume or noise abatement technologies were installed.  The towers are aligned in two back-to-back rows.
      
      Facility representatives have not considered closed-cycle cooling for Unit 1.

7.0 Debris Handling

      Nebraska City has historically had greater problems with sedimentation than other OPPD facilities (such as North Omaha).  The facility is located downstream of the confluence with the Platte River, which adds a significant volume of suspended sediment, as well as debris.  Every 6 months, the traveling screens become silted in and sediment must be pumped out.  A water sparging system is used; a 3" screen wash header removes debris from the screen face, a 4" water line sparges the screen boot whenever the screen is in service, an 8" water line expels sand from each screenwell and two 20" lines sparge sediment at the entrance to the CWIS as needed.  Additionally, fine grain sand erodes screen parts and water pumps.
      
      In winter, the facility deploys an ice barge.  Facility representatives noted that the Army Corps of Engineers regulates the water levels, leading to additional difficulties in the winter as water levels are lower, making ice a greater danger to the operation of the CWIS.  The facility is also able to recirculate warm water and use a cold water agitator at the water's surface to address icing.  The agitator can also be used to expel floating debris.

8.0 Repowering/Future Uses
      
      Construction of Unit 2 is nearly complete.  It will also be a 650 MW coal-fired unit.

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

      Bottom ash is handled wet; some is sold for beneficial uses, but most is stored in an onsite landfill.
      
      Fly ash is stored dry and sold for beneficial uses.

13.0 Air Emissions Controls

      Nebraska City Station uses a cold-side electrostatic precipitator for control of particulate matter, SO3 Injection to reduce opacity, and over-fire air for reduction of NOx.

14.0 Additional Information
      
      Facility representatives noted that there are no additional design considerations for being located in a tornado-prone region.
      
      Facility representatives considered variable speed pumps for the CWIS, but cannot justify the capital cost for replacing the equipment.
      
      Facility representatives stated that they are concerned about the use of fine mesh screens, as the river conditions (especially during spring due to increased runoff and in winter due to icing) could jeopardize operations.  Specifically, the concern is that the differential across the screens would increase significantly due to debris plugging, possibly jeopardizing generation activities.  See Section 7.0 below.

Attachments

Attachment A		List of Attendees
Attachment B		Aerial Photos
Attachment C	Nebraska City Facility Description
Attachment D	Engineering Diagrams
Attachment E	Information on Debris 
Attachment F		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
Kirk Miller, OPPD
Ray Lynn, OPPD
Tim Yager, OPPD
Mike Krumland, Nebraska Public Power District (NPPD)
Joe Citta, NPPD
Justin Reimers, NPPD

Attachment B -- Nebraska City Aerial Photo

Please see DCN 10-6520A accompanying this document

Attachment C -- Nebraska City Facility Description

Please see DCN 10-6520B accompanying this document

Attachment D -- Engineering Diagrams

Please see DCN 10-6520C accompanying this document

Attachment E -- Information on Debris

Please see DCN 10-6520D accompanying this document

Attachment F -- Site Visit Photos

Please see DCN 10-6520E through G accompanying this document