Total Maximum Daily Load is a “pollution budget” for a waterway, much like the Bay Program’s tributary strategies, which set specific limits on the amount of nitrogen and phosphorus entering the Chesapeake from different rivers.

In fact, EPA Administrator Carol Browner made that comparison when unveiling the new TMDL rules. “Addressing problems locally, on a watershed-by-watershed, river-by-river, bay-by-bay basis, is a proven, common-sense method for cost-effectively addressing our nation’s remaining water quality problems,” she said.

“This approach is not new. In fact, it has been used very successfully with regard to both the Great Lakes and the Chesapeake Bay. And it will work for citizens everywhere to improve the nation’s rivers and beaches.”

But there some key differences between the Bay cleanup and a TMDL.

TMDLs, under the new rules, have enforceable elements. The Bay Program nutrient reductions are largely voluntary. Proponents of the Bay Program approach say it is a more cost-effective and flexible way to control pollution.

Bay Program reductions to date, however, have been based on a mutually agreed upon goal — a 40 percent nutrient reduction set in 1987. The goal was to be met this year, but the Bay Program acknowledges it will fall short, at least for nitrogen. Even if it were met, the reduction would fall short of what was needed to meet water quality standards. Proponents of the TMDL approach, by contrast, like the fact that TMDLs have a specific goal — to meet water quality standards.

The Bay Program, in its Chesapeake 2000 Agreement, embarked on a new cleanup effort that merges the TMDL endpoint of attaining water quality standards with its present voluntary cleanup approach.

In this approach, the Bay Program will set new water quality standards that define what a “clean Bay” is, then determine new sediment and nutrient reductions that will be needed to achieve those standards by 2010.

If the Bay Program falls short, though, the TMDL process will kick in for the Chesapeake watershed in 2011.

In its new rules, the EPA makes clear — for the first time — that it has the authority to develop TMDLs for interstate and boundary waters. The EPA said it would do so when the states have failed to make “substantial progress” in establishing TMDLs and cleaning up waterways.