Space could be tight inside the Vicksburg Convention Center when the Environmental Protection Agency veto hearing on the Yazoo Backwater pump station convenes Thursday amid flood stages on the Mississippi River and major tributaries.

Officials at the Mulberry Street facility expect about 500 people to fill the bottom-floor exhibit hall reserved for the hearing, which is shaping up as a make-or-break moment in the six-decade history of the federal flood control project.

The EPA has anounced its intent to veto the pumps and is taking public comments as a step in that process. It would be the 12th veto by EPA since the Clean Water Act was passed in 1980.

“If I were a betting man, I’d say it would be on the higher end of that,” VCC director Larry Gawronski said of the turnout.

In addition to EPA officials and Army Corps of Engineers pump project managers, elected officials from some of the 11 counties that passed resolutions in support of the pumps are likely to be in attendance. Other non-public groups with an interest for or against the Corps plan have promised to bring large contingents. Staff of the Tulane Environmental Law Clinic has arranged for bus trips to the hearing for agencies opposing the pumps, such as National Wildlife Federation and Lower Mississippi Riverkeeper.

Comments and questions about the pumps proposed along Mississippi 465 in Issaquena County just west of the Steele Bayou Control Structure will be fielded by EPA officials and sent to the agency’s regional office in Atlanta for review. Public comments can be submitted by mail or online until May 5.

A recommended determination by Region 4 Administrator J.I. Palmer Jr. is expected by May 20. The decision also faces review by water management and administrative offices at EPA headquarters in Washington D.C.

Authorized by Congress in 1941, the project has undergone multiple revisions. Following completion of the Yazoo Backwater Levee in 1978, plans to build the pump station ran into changes to its overall capacity and funding formula. Its latest version calls for a facility with per-second pumping capacity at 14,000 cubic feet to remove some of the water that becomes trapped inside levees during flood years. Pumps would not be turned on until the water reaches 87 feet above sea level inside the levees. About 55,000 acres would be reforested as part of the Corps’ plan, touted the current version of the pumps’ specifications as a balance between flood protection and habitat conservation.

EPA announced in March it would begin the formal veto process on the pumps on grounds it still threatened wetlands and aquatic wildlife in the South Delta. EPA’s letter was among a torrent of more than 22,000 e-mails and letters commenting on the Corps’ Recommended Plan.

Other opposition has been voiced by Sierra Club, National Wildlife Federation, American Rivers and the National Audubon Society. Objection has also appeared on the editorial pages of The Clarion Ledger, The New York Times and Time magazine.

Most notable among supporters are U.S. Rep. Bennie Thompson, D-Miss., U.S. Sen. Thad Cochran, R-Miss and Gov. Haley Barbour.

If you goThe Environmental Protection Agency public hearing on the Yazoo Backwater Project will be at 7 p.m. Thursday at the Vicksburg Convention Center

To submit commentsThe EPA Docket ID for the Yazoo Backwater Project is EPA-R04-OW-2008-0179-Yazoo Pumps. Comments may be submitted by mail or online at ow-docket@epamail.epa.gov with the Docket ID in the subject line. The mailing address is Wetlands, Coastal and Nonpoint Source Branch, Water Management Division; U.S. Environmental Protection Agency, Region 4, 61 Forsyth St. SW; Atlanta, GA 30303-8960. Also, comments can be submitted at the Federal eRulemaking Portal at www.regulations.gov. Instructions are available on the Web site.