Document ID: EPA-HQ-OW-2008-0667-0019
Agency: epa
Document Type: Supporting & Related Material
Title: 
Posted Date: 2010-11-04T04:00Z

Site Visit Report

	Walter Scott, Jr. Energy Center
	7215 Navajo Road
	Council Bluffs, IA 51501
      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 (CWIS) 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 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.  Walter Scott, Jr. Energy Center (WSEC) was selected for a site visit due to its location on a large freshwater river.

2.0 Facility Description
      
      WSEC is located approximately four miles south of downtown Council Bluffs, Iowa.  The facility began operations in 1954.  Units 1, 2, and 3 withdraw once-through cooling water from the Missouri River, and Unit 4 withdraws closed-cycle cooling tower make-up water from four lateral alluvial wells.  WSEC is regulated by NPDES permit IA0004308 (which expired February 26, 2008) and is owned by MidAmerican Energy Company.  The facility employs approximately 220 people.  The facility and surrounding land encompasses approximately 1,195 acres.

3.0 Electricity Generation and Transmission
      
      WSEC consists of four coal-fueled generating units with a total generating capacity of 1623 MW.   The facility's low sulfur coal comes via rail from the Powder River Basin in Wyoming; 128 car trains arrive approximately every 18 hours and the facility uses about seven million tons of coal per year.  The facility's capacity utilization rate (CUR) is approximately 80%; all four generating units operate as baseload units. 
      
      The transmission system is owned by MidAmerican Energy Company but is operated by a different business unit.

4.0 Cooling Water System and Intake Structure

      WSEC has two CWISs that withdraw cooling water from the shoreline of the Missouri River.  Units 1 and 2 share one CWIS; it has four traveling screens and four circulating water pumps.  Unit 3's CWIS has four screens and four circulating water pumps.  The design intake flow (DIF) for the facility is 662 million gallons per day (mgd) and the average actual intake flow (AIF) for 2009 was 470 mgd.  Units 1-3 utilize once-through cooling and Unit 4 uses a closed-cycle cooling system (see Section 6.0 below).
      
      Units 1-3 employ coarse mesh traveling screens.  Units 1 and 2 have standard debris return troughs that return fish and debris to the river; Unit 3 has a separate fish spray wash and trough that combines with the debris return before being discharged to the river.  The screens automatically rotate every 15-20 minutes and are cleaned with a high pressure spray wash; during high debris loading periods, the screens often operate continuously.  The design through-screen velocity ranges from 1.7 to 1.9 feet per second (fps) at Units 1-2 and approximately three fps at Unit 3.
      
      Scheduled four to six week major maintenance outages are taken on each unit as needed (typically once every 4 years).  For Units 1-3, one traveling screen and circulating pump are refurbished each year.  Maintenance can be scheduled during the winter, when all of the screens and pumps are not required for normal operations. 

5.0 Impingement and Entrainment Information

      WSEC is currently working to finalize a 2007 impingement study; this study will also include an evaluation of intake technologies and compliance approaches.

6.0 Cooling Tower Feasibility

      Facility representatives stated that close-cycle cooling was not reasonably feasible for WSEC Units 1-3.  They noted a number of potential problems: space constraints, a loss of generating efficiency, high costs, and icing on the transmission lines.
      
      The cooling tower for Unit 4 (a 22-cell mechanical draft tower with two back-to-back rows of 11 cells) was not designed with plume abatement and typically cycles water 6-8 times before blowdown.  The towers use a standard mix of biocides -- 12.5% sodium hypochlorite and bisulfate at the basin discharge.  The system loses approximately two percent of the circulating flow to evaporation.

7.0 Debris Handling

      WSEC has historically had issues with debris in the spring, when leaves, sticks, and eroded low-grade coal (found in the surrounding soil) are swept up in the rising waters.  Because a major outage occurred on Unit 3 as a result of debris, the facility installed a 5mm Tapproge debris filter on Unit 3.  
      
      According to facility representatives, ice is not a significant problem at WSEC.  The facility is capable of recirculating warm water to the CWIS to address the issue.  However, at the time of the site visit, Unit 1 had been taken offline due to ice blocking the intake and causing condenser vacuum problems.
      
      The condenser also experiences some scaling and calcium deposits, but this issue is manageable; a firm is hired once per year to remove these deposits.

8.0 Repowering/Future Uses
      
      WSEC's Unit 4 began operations in 2007.  There are no plans for additional units at the facility at this time.
      
      The facility also provides steam to a neighboring ethanol manufacturing plant that recently began operations.  WSEC provides approximately 475,000 pounds of steam per hour from Unit 3, which represents approximately 10% of the main steam flow.
      
9.0 Cooling Ponds
	
      There are no cooling ponds on site.

10.0 Ownership
      
      The WSEC facility is operated by MidAmerican Energy, an investor-owned utility. Units 1 and 2 are 100% owned by MidAmerican Energy Company, whereas Units 3 and 4 are jointly-owned units.

11.0 316(a)

      Facility representatives stated that, under the current NPDES permit, WSEC is not subject to any 316(a) limitations. They expect to complete a thermal plume mixing zone study later this year.

12.0 Ash Handling

      Fly ash from Units 1-3 is typically sold for beneficial uses, but is occasionally stored in a lined monofill when market conditions are unfavorable.  Bottom ash from Units 1-3 is wet sluiced to two onsite impoundments; facility representatives noted that they are researching potential markets for the sale of the bottom ash.
      
      Fly ash and bottom ash from Unit 4 is stored in an onsite lined monofill.
      
      The Army Corps of Engineers conducts inspections of the levees surrounding the surface impoundments and performs any necessary maintenance.

13.0 Air Emissions Controls

      WSEC uses low NOx burners on all of its generating units, and overfire air is installed on Units 2-4.  Dry scrubber and baghouse systems are installed on Units 3 and 4; and a selective catalytic reduction system and activated carbon injection system is installed on Unit 4.  Materials provided by the facility also note that Unit 4 uses a supercritical boiler, increasing efficiency and reducing carbon dioxide emissions by approximately 15%.  There are no firm plans for any additional air emission control equipment at this time.

Attachments

Attachment A		List of Attendees
Attachment B		Aerial Photo
Attachment C		Walter Scott Energy Center Fact Sheet
Attachment D		Walter Scott Energy Center CWIS Information
Attachment E		Engineering and Flow Diagrams
Attachment F		Site Photos
Attachment G		Proposal for Information Collection

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
Matt Finnegan, MidAmerican
John Lusan, MidAmerican
Spencer Moore, MidAmerican
David O'Dell, MidAmerican
Mark Podany, MidAmerican
Jeff Walters, MidAmerican

Attachment B - Aerial Photo

Please see DCN 10-6518A accompanying this document

Attachment C--Walter Scott Energy Center Fact Sheet

Please see DCN 10-6518B accompanying this document

Attachment D--Walter Scott Energy Center CWIS Information

Please see DCN 10-6518C accompanying this document

Attachment E	--Engineering and Flow Diagrams

Please see DCN 10-6518D accompanying this document

Attachment F	--Site Photos

Please see DCN 10-6518E accompanying this document

Attachment G--Proposal for Information Collection

Please see DCN 10-6518F accompanying this document