The EPA gave states revised nutrient reduction targets this summer, but said it will not require any additional actions or nutrient reductions at this time beyond those already set forth in strategies the states wrote last fall.

But it's not clear that the new targets, if achieved, will result in water quality that meets standards - an issue that the EPA will revisit in 2017 at the latest.

The agency had warned last fall when it issued its "pollution diet" for the Bay - formally known as a "total maximum daily load" - that the nutrient goals it established would likely change this year based on updated computer modeling.

That's because two issues had remained unresolved, including the amount of impervious cover in the watershed, and how some aspects of nutrients from agricultural activities were handled in the watershed model. The model predicts the amount of nitrogen, phosphorus and sediment that reaches the Bay from different land uses.

When the model was updated this spring, it estimated that more nutrient and sediment runoff was coming from developed lands and many agricultural areas than previously thought. That meant that many of the nutrient and sediment reduction strategies written by the states last fall, known as Phase I watershed implementation plans, no longer achieved nutrient goals set in the TMDL. On average, the difference was 2-3 percent for most basins.

Rather than asking for new strategies that would close that gap, EPA officials decided states should stick with the "level of effort' - that is, the same amount of nutrient and sediment reductions - outlined in the Phase I WIPs. The level of nutrient reductions that would be achieved by implementing those plans will be used as "planning targets" to guide nutrient reduction efforts.

The TMDL issued in late December, established nitrogen and phosphorus allocations which represent the maximum amount of those nutrients the Bay can get and still meet water quality standards. The nitrogen allocation was 185.93 million pounds a year, while phosphorus was set at 12.54 million pounds. The planning targets are 191.57 million pounds of nitrogen, and 14.56 million pounds of phosphorus.

"The numbers represent the same level of effort that was encapsulated in the TMDL, and that is what we want the states to focus working on," said Katherine Antos, water quality team leader with the EPA's Bay Program Office in Annapolis. "The Chesapeake Bay TMDL, based largely on the jurisdictions' WIPs, is a solid road map for cleaning up the rivers and streams that flow into the Bay. As a partnership, we should focus our efforts on turning this road map into a reality with the help of our local partners."

The TMDL calls for re-evaluating the nutrient and sediment goals in 2017, using new models and updated information. At that point, the EPA will also determine whether efforts are on track to meet the 2025 deadline of implementing all actions needed to clean up the Bay.

"If the latest science in 2017 indicates that the planning targets do not quite meet all water quality standards, then at that point we will ask states to fill any remaining gaps," Antos said.

For now, Antos said the EPA prefers that the states spend their energy implementing their Phase I plans and writing new Phase II WIP which involve local communities and set nutrient reduction targets at county or small watershed scale.

The EPA has required states to achieve 60 percent of the TMDL goal by 2017. The planning target figures will be used as the basis for measuring whether that goal is met.

Because the planning targets were not finalized until Aug. 1, the EPA extended the deadline for draft Phase II WIPs from Dec. 1 to Dec. 15. The deadline for final Phase II WIPs remains March 30.

Excessive amounts of nutrients and sediment have degraded Bay water quality for decades, triggering algae blooms, vast stretches of oxygen-starved water, and silt-covered bottom havitats.

The goal of the TMDL is to reduce sediment and nutrient pollution enough to restore healthy water quality conditions throughout the Bay.

The EPA uses a suite of complex computer models to estimate the amount of nutrient and sediment controls needed to clean up the Bay. Updating those models is always a two-edged sword. Refinements - like those just made - are intended to provide more realistic estimates. But they also result in different nutrient reduction numbers being assigned to states and rivers - something that has caused many complaints about changing cleanup effort goalposts.

As a result, EPA officials have said that after this latest revision, the models will be "locked down," with no further changes until 2017.