Evolving science from the Chesapeake Bay Program has stalled an attempt to tighten phosphorus limits for stormwater runoff in Virginia's portion of the Bay watershed.

New stormwater regulations, passed in December by the Virginia Board of Soil and Water Conservation, require enhanced management practices to hold and absorb stormwater on newly developed land, but they will not reduce the phosphorus standard as anticipated.

Instead, the statewide standard for annual phosphorus discharge will remain at .45 pounds per acre, while the Department of Conservation and Recreation works with the EPA to identify the appropriate phosphorus limit based on the latest estimates from the Bay Program's computer models, which help to guide cleanup efforts.

"We want to continue to base these regulations on the best science available, and the latest EPA numbers suggest that the phosphorus standard should be revised," said DCR Director Joseph Maroon. "Because we don't yet know the level of the adjustment, the board opted to go with the current phosphorus standard along with the regulation's other enhancements, and work to develop a new standard for the Bay watershed once the latest science is available."

The soil and water conservation board passed an earlier version of the regulations in October and then immediately suspended them for additional public comment.

During the comment period, the Bay Program released data that raised questions about the proposed phosphorus reduction.

The regulations called for reducing the annual phosphorus discharge limit in Virginia's portion of the Bay watershed from .45 to .28 pounds per acre. The limit was based on state tributary strategies written to meet nitrogen and phosphorus goals established in 2003, and has served as a regional guide for reducing pollution in the Bay's rivers.

But Bay Program models now suggest that the allowable phosphorus limit for Virginia's rivers might be higher than outlined in the tributary strategies.

The Bay Program is using a newly calibrated watershed model to identify the levels of nitrogen, phosphorus and sediment allowed to enter Bay waterways on an annual basis. The findings will lead to pollution limits, or total maximum daily loads, for the region's rivers.