By Bill Rankin for The Atlanta Journal-Constitution

As far as legal arguments go, the stakes don’t get much higher: water supply for more than 3 million people in metro Atlanta.

On Wednesday, the state of Georgia will ask the federal appeals court in Atlanta to overturn a judge’s ruling that found it illegal for the Army Corps of Engineers to draw water from Lake Lanier to meet most of the metro area’s needs.

In that shock-and-awe ruling in 2009, Senior U.S. District Judge Paul Magnuson set a doomsday clock ticking. If Georgia, Alabama and Florida cannot arrive at a water-sharing agreement that is approved by Congress by July 17, 2012, metro Atlanta can only take the same amount of water it received in the mid-1970s.

At that time, the metro population was about 1.5 million people, less than a third of what it is today. Even Magnuson recognized it would be “a draconian result.”

A three-judge panel of the 11th U.S. Circuit Court of Appeals will hear Georgia’s appeal, which is joined by Atlanta, Gwinnett County, the Atlanta Regional Commission and other local interests.

“This is the most important case for Georgia’s future in decades,” state Attorney General Sam Olens said. “The potential impact to metro Atlanta alone, if Judge Magnuson’s order goes into effect, is estimated at between $25 billion and $40 billion per year.”

Gwinnett County, which draws all its drinking water directly from Lake Lanier, may have the most to lose.

Frank Stephens, the county’s water resources program manager, said the court must know the consequences of Magnuson’s ruling because water is so elemental to the public’s welfare. He ticked off the basics — drinking water, fire protection, sanitation — and noted water is needed to sustain hospitals, schools, industry and local businesses.

“When you think about the effect this ruling would have on several hundred thousand jobs here, I don’t think it takes any extrapolation to consider its ramifications on the national economy,” Stephens said.

Fred Smith, president of Accurate Fence in Snellville and a lifelong Gwinnett resident, predicted an exodus from the county if Magnuson’s ruling stands.

“It would be devastating — for everybody,” he said. “Just look how much Gwinnett has grown since the 1970s. There wouldn’t be nearly enough water to go around.”

Georgia has retained one of the top lawyers in the country, former U.S. Solicitor General Seth Waxman, to argue on its behalf. Waxman has delivered more than 50 arguments before the U.S. Supreme Court, winning landmark rulings that banned the death penalty for juvenile offenders and upheld habeas corpus rights for detainees at Guantanamo Bay. According to published reports, Waxman was on President Barack Obama’s short list two years ago as a possible Supreme Court nominee.

Waxman is sure to attack the 97-page ruling issued by Magnuson and drawn from an 85,000-page administrative record. Magnuson, from St. Paul, Minn., was chosen in 2007 to decide the decades-old dispute because of his experience overseeing litigation involving water rights to the Missouri River.

In recently filed legal briefs, Georgia sharply criticized Magnuson’s handling of the case. The state accused the judge of overstepping his authority, misinterpreting the intent of Congress and making critical miscalculations regarding how much water in Lake Lanier’s conservation pool is being diverted for water supply.

The parties also denounced Magnuson for setting the July 2012 deadline without allowing the state to offer a full account of its potentially devastating impact. The order imposes massive harm on Georgia’s residents while providing Alabama and Florida minimal benefit, the appeal says.

In response, Alabama and Florida called Magnuson’s order “detailed and carefully reasoned.”

The three judges who will hear the case are 11th Circuit Judge Stanley Marcus of Miami; R. Lanier Anderson III of Macon, a senior judge on the court; and visiting Judge Richard Mills from Springfield, Ill.

Anderson, a distant relative of poet Sidney Lanier, Lake Lanier’s namesake, is known for his independent streak and unassuming manner. Mills, who graduated from Mercer University’s law school in 1957, is a retired Army colonel who has served for more than four decades as a state and federal judge.

Marcus is perhaps the most notable judge assigned to the case. A former prosecutor who fought organized crime, Marcus often engages lawyers during oral arguments, pressing them to get to the heart of the issue and not stray from the point.

Marcus also was part of an earlier 11th Circuit decision that could prove influential. In a related tri-state water lawsuit, a three-judge panel of the court found in 2005 that Congress explicitly authorized Lake Lanier for three primary purposes: hydropower generation, flood control and navigation. Water supply was an incidental benefit of the Buford Dam project, the court said at the time.

These passages alarmed Georgia’s lawyers, who said the conclusions could be mistakenly interpreted as findings in future tri-state water litigation. Shortly after the ruling was published, the lawyers asked the court to take that language out and rewrite the decision to say that water supply is one of the reasons the corps operates Lake Lanier, although the extent to which Congress authorized it is disputed.

But the 11th Circuit stood by its 2005 opinion, sticking to its determinations that Lake Lanier was authorized for three primary purposes only and that water supply was incidental. In his 2009 order, Magnuson made almost identical findings. In their joint legal brief, Alabama and Florida reminded the court about that 2005 decision.

On Wednesday, Waxman is expected to tell the judges that the court got it wrong six years ago. There is plenty of evidence in the congressional record to show that the 1946 law that authorized construction of Buford Dam empowered the corps to accommodate downstream water-supply needs, the state’s appeal says. “Not only were releases to provide water supply for the metropolitan area authorized, but it was expressly contemplated that water-supply releases would be increased over time as the Atlanta area developed.”

Magnuson also determined that the corps has been reallocating 21.5 percent of Lake Lanier’s conservation pool to supply most of the metro area’s water needs. Such a large diversion constitutes a major operational change in the lake’s purpose and, absent Congress’ approval, the corps is violating the Water Supply Act of 1958, he found.

Georgia contends Magnuson had no factual or legal basis for arriving at the 21.5 percent figure. The corps, not the court, should make such a complicated determination, the state said.

Throughout the litigation, the Georgia parties have maintained a united front, even though they have somewhat differing interests. Atlanta and Cobb, DeKalb and Fulton counties get their water from pumping stations along the Chattahoochee River after the water passes through the hydropower turbines at Buford Dam. Forsyth and Gwinnett counties and the cities of Buford, Cumming and Gainesville get their water out of the lake.

If the 11th Circuit agrees that water supply for downstream users was a congressionally authorized purpose of the Buford Dam project, it will strengthen claims for the entire region. If the court does not go that way, there could be much less water for all metro interests — except for Buford and Gainesville, which were granted the right to tap into the lake when its construction destroyed their water intake systems.

After Magnuson’s ruling, Georgia enacted comprehensive water conservation legislation and the three states began private negotiations. Last week, Gov. Nathan Deal said the state is continuing to pursue a settlement and for now is focused primarily on resolving disputes with Alabama over the Apalachicola-Chattahoochee-Flint river basin.

“We feel we’re getting very close to some kind of agreement,” Deal said. “If we can reach an agreement with Alabama, it certainly facilitates reaching an agreement with Florida.”

During the current session of the General Assembly, legislation has been introduced to allow for the construction of new reservoirs through public-private partnerships. On Wednesday, the Senate approved the bill by a 49-1 vote, and passage in the House is expected. But reservoirs are a long-term strategy and will not provide immediate relief should Magnuson’s order take effect next year.

Gil Rogers, a senior attorney with the Southern Environmental Law Center in Atlanta who has closely followed the case, said “it’s anybody’s guess” as to how the 11th Circuit will rule. The court is not expected to decide the case for at least a few months, perhaps longer.

“All the while, the clock continues to tick,” Rogers said. “Some agreement needs to be reached. Otherwise, we’re going to be hard-pressed to find good, cost-effective solutions to a water crisis if Judge Magnuson’s ruling takes effect little more than 18 months from now.”

Staff writer Aaron Gould Sheinin contributed to this article.