1 Site Visit Report Nebraska City

Station 7264 LRoad 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 th e cooling water intake structure (CWI S) technologies in use at facilities, including the site

specific characteristics of each facility and how these affect the selection and performance of CWI S technologies. EPA is also visiting facilities to better unde rstand 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 1 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 J uly 1 , 20 08 . Nebraska City is ow ned by

the Omaha Public Power District (OPPD) and emplo ys approximately 158 people. 3.0 Electricity Generation and Transmission Nebraska City

is a 650 MW coal

- fired 2 power plant with 1 generating unit. The facility ’s capacit y utilization rate (CUR) is approximately 77 %. The transmission sy stem 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- through cooling w ater is withdrawn through a shoreline CWI S with 6 intake bay s; each intake bay houses one coarse mesh (3/8”) traveling screen and each pair of bay s feeds one circulating pump with a capacity of 244.8 million gallons per day (mgd or 170 ,000 gallons per minute [gpm]) each
. Ty picall y, two pumps

1 Over 1200 acres are leased as farmland. 2 The facility’s coal comes via rail from the Pow der River Basin in Wyoming; 135

- car trains arrive every 20 hours.2 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 ty picall y rotated continuous ly (at 2.5 feet per minute) to best handle debris loading. 3 The original screen design included intermittent screen rotation, but the sedimentation in the intake bay s prompted more frequent screen rotation. In total, the facility

has a design intake flow (D IF) of 670 mgd and an average actual intake flow (AIF) of 450 mgd. The average design intake velocit y of the CWI S is 1.36 feet per second (fps). 4 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

- cy cle cooling. 5 The 18
- cell mechanical draft tower was bu ilt at a cost of $40

- 60 million and will withdraw makeup water from an existing intake pipe
. 6 The towers include drift eliminators, but no plume or noise abatement technologies were installed. The towers are aligned in two back

- to - back rows. Facilit y representatives have not considered closed

- cy cle cooling for Unit 1. 7.0 Deb ris 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 spar g ing s ys tem is used; a 3” screen wash header removes debris from the screen face , a 4” water line sparge s the screen boot wh enever 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 CWI S as needed
. Additionally , fine grain sand erodes screen parts and water pumps.

3 The screens can be rotated on a fast speed (10 feet per minute) for heavy debris loads. 4 At low water, the through

- screen velocity is 1.8 fps; at high water, 1.1 fps. 5 The planning for the design of Unit 2 began before the Phase I and Phase II rules w er e published; at the time, OPPD assumed that the new unit would likely be required to install closed

- cycle cooling. 6 Nebraska City has been able to use much of the existing infrastructure in regards to its cooling tow er installation3 In winter, the facility

deploy s 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. 7 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 nearl y 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 b y the state of Nebraska. The entire state is supplied by

public power. 11.0 316(a) The permits for all OPPD facilities have therm al discharge limits; facility representatives noted that the most troublesome time of y ear 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 qual ity 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 c old

- s ide electrostatic precipitator for control of particulate matter , SO 3 In jection to reduce opacit y , and o ver - fire air for reduction of NO x .

7 Facility representati ves cited a recent alert from the Corps about an ice bridge upstream that could affect water levels at Nebraska City by as much as 2 feet.4

14.0 Additional Information Facilit y representatives noted that there are no additional design considerations for being located in a tornado

- prone region. Facilit y representatives considered variable speed pumps for the CWI S, but cannot justify the capital cost for replacing the equipment. Facilit y 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 p lugging, possibly

jeopardizing generation activities. See Section 7.0 below.
Attachments Attachm ent A List of A ttendees Attachment B Aerial Photo s Attachment C Nebraska City Facility Description Attachment D Engineering Diagrams Attachment E In formation on Debris Attachment F Site Visit Photos5

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, Nebr aska Department of Environmental Quality Kelly Meadows, Tetra Tech Russ Baker, OPPD Kirk Miller , OPPD Ray Lyn n , OPPD Tim Yager , OPPD Mike Krumland, Nebraska Public Power District (NPPD) Joe Citta, NPPD Justin Reimers, NPPD6

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 accompany ing this document Attachment D

— Engineering Diagrams Please see DCN 10

- 6520C accompany ing 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 accompan yi ng this document