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Site Description Report

Sioux Power Plant

8501 North State Route 94

West Alton, MO 63386

March 4, 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. As part of its site visit to the Labadie Power Plant, EPA also 

collected information on Ameren’s Sioux Power Plant.

2.0 Facility Description

Sioux is located on the shoreline of the Mississippi River, approximately 25 miles 

north of St. Louis. The facility began operations in 1967 on a 994 acre site and 

operates under NPDES permit MO0000353; the permit is due to expire April 15, 

2009.

3.0 Electricity Generation and Transmission

Sioux is a 993 MW facility with two coal-fired generating units that typically

burns a coal blend from the Powder River Basin and Illinois. The capacity 

utilization rate (CUR) was approximately 66% in 2008.

Sioux schedules a major outage approximately every 3 years for maintenance and 

upgrades.

4.0 Cooling Water System and Intake Structure

Sioux withdraws water from the Mississippi River via a 1⁄4 mile intake canal just 

above the last set of locks and dams. The mouth of the intake canal is protected 

by a log boom. The CWIS has 4 intake bays (designated as 1A, 1B, 2A, and 2B), 

each with a bar screen, single circulating pump and coarse mesh (1/2” mesh) 

traveling screen. The screens rotate once per shift or when a pre-determined head 

differential is reached. The screens are washed with a high pressure spray that 
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discharges back to the river via a discharge trough.1 The design through-screen 

intake velocity is 1.4 feet per second (fps).

The design intake flow (DIF) is 749 million gallons per day (mgd) and the 

average actual intake flow (AIF) is 619 mgd.

The river elevation is controlled by the Army Corps of Engineers and is highest in 

the summer to allow for navigation. Water levels are reduced significantly during 

non-navigational periods. During low water periods, possible pump cavitation is 

a concern.

5.0 Impingement and Entrainment Information

Ameren conducted impingement studies at all of its Phase II facilities in 2005 and 

2006. During the sampling period, Sioux conducted 24 hour impingement 

sampling every other week for a year for a total of 26 sampling events. 

Approximately 98% of the fish collected at Sioux were shad and drum. Many of 

the fish were collected between November and February and many were 

moribund. The sampling estimated an annual impingement total of approximately

1.8 million fish.2The facility did not conduct any source waterbody 

characterization studies; there is ample publicly available research on the 

Mississippi.

6.0 Cooling Tower Feasibility

EPA did not collect any information about CCRS at this site.

7.0 Debris Handling

As with other facilities located on large rivers, Sioux experiences significant 

debris loading. In the past, traveling screens at Sioux have collapsed and debris 

has damaged the bar screens. Facility representatives stated that over the last 5 

years the facility has lost an average of one generating day per year to debris or 

icing.

Twice per year, the facility uses a crane barge to remove large debris from the 

trash racks. The traveling screens are inspected twice per year and the CWIS is 

inspected once per year by a diver. As needed, Sioux overhauls the screens 

during the plant’s regularly scheduled outages every three years. 

8.0 Repowering/Future Uses

 

1 During periods of high debris, the screens may be rotated continuously.

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Facility representatives noted that impingement rates may be higher than normal due to the intake canal; 

fish may enter the canal as a resting place from the fast-moving river.
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There are currently no plans to expand generating capacity or make other 

significant operational changes at Sioux.

9.0 Cooling Ponds

There are no cooling ponds onsite.

10.0 Ownership

Sioux is owned by Ameren, an investor-owned company.

11.0 316(a)

Sioux has a 316(a) BTU heat rejection requirement, but has had no problems 

meeting its limit. The facility has never had to change its operations or generation 

to meet thermal limits.

12.0 Ash Handling

Sioux has a clay-lined fly ash pond, as well as a bottom ash pond. Fly ash is 

handled wet and sluiced to the pond. All of the bottom ash that is currently 

generated is sold, but some residual bottom ash remains in the pond.

Ameren has an internal team that conducts inspections of all earthen dams and 

similar structures. Due to a dam failure at the Taum Sauk pumped storage facility

in 2005, Ameren instituted rigorous inspections at all facilities. Facility

representatives noted that Ameren’s inspections are more stringent than those 

conducted by state agencies.

13.0 Air Emissions Controls

EPA did not collect any information about existing air controls at this site. 

However, facility representatives indicated that scrubbers were currently being 

constructed at the site.

14.0 Additional Information

Facility representatives stated that they had begun to evaluate intake technologies 

for compliance with the 2004 Phase II rule.3 A number of technologies were 

evaluated:

 A bar rack with 1” spacing and an approach velocity of 0.4 fps at the 

entrance to the intake canal for an estimated capital cost of $34 million 

($2002) 

 Deployment of a 1⁄4” year-round barrier net at the canal entrance yielding 

an approach velocity of 0.2 fps for an estimated capital cost of $29 million

 

3 This evaluation did not include technologies to address entrainment.
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 Coarse mesh wedgewire screens on a bulkhead at the canal mouth 

(approximately eight 7’ diameter screens) for an estimated cost of $61.5 

million

 Ristroph screens with an approach velocity of 1.0 fps and fish return with 

scenarios for an expanded CWIS or existing CWIS and 21% flow 

reduction for an estimated cost of $63.4 million and $58 million, 

respectively

Facility representatives also stated that restoration was an attractive approach, 

especially from a cost-effectiveness standpoint.

Facility representatives noted that Sioux is located in an area with significant 

navigation traffic. Additionally, since the facility is located in a lock and dam 

region, the water level is controlled by the Army Corps of Engineers; it can vary

by as much as 7 feet.

Attachments

Attachment A Ameren PowerPoint Presentation (March 4, 2009)
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Attachment A—Ameren PowerPoint Presentation (March 4, 2009)

Please see the attached materials.