Virginia’s State Water Control Board has endorsed a far-reaching proposal to help clean up the Chesapeake by setting nutrient discharge limits for wastewater treatment plants in the watershed.

The board is expected to give its final approval to rules that would officially implement the new policy, which is expected to cost about $1.1 billion, by the end of next year.

“It’s a very, very ambitious initiative,” said Virginia Secretary of Natural Resources Tayloe Murphy. He added that restoring the Bay’s water quality is “critically important” to the state’s economy.

Controlling wastewater discharges are a major part of the state’s tributary strategies, which are aimed at meeting nutrient and sediment goals agreed upon by all states in the Bay watershed last year. Wastewater discharges account for about a third of of the nitrogen entering the Bay from Virginia, and a quarter of the phosphorus.

The proposal reviewed by the board in August would require more than 100 of the largest wastewater treatment plants to install technologies by the end of 2010 that would reduce nitrogen concentrations in discharges to 8 milligrams per liter of water. Those limits would be phased in over a longer period for smaller plants.

Discharges at plants without nutrient control technology can have concentrations of around 20 mg/l.

In addition, the proposal would set annual limits on the total amount of nitrogen and phosphorus that can be discharged from all major facilities.

That cap is determined by multiplying the total design flow of a plant times an average effluent concentration of 4 mg/l for nitrogen, and 0.3 mg/l of phosphorus. For plants in tidal areas of the Potomac basin, which have the greatest impact of the Bay, the caps were determined using average effluent concentrations of 3 mg/l of nitrogen, and 0.3 mg/l for phosphorus.

The formula is essentially the same method Maryland used to assign maximum cap loads to wastewater treatment plants and allows plants to use their full capacity, rather than capping discharges at expected 2010 levels. Plants that are near their design capacity will need to upgrade soon to stay within their total annual nutrient discharge cap, while those with a lot of excess capacity can postpone upgrades.

Murphy said that would allow some plants to engage in nutrient trading or to explore other cost-effective means of achieving and maintaining their nutrient cap loads.

Over time, though, all facilities will have to ratchet down on nutrient discharges to offset added effluent from a growing population while remaining within their assigned cap.

The caps assigned to facilities in the York and James river basins are considered interim until the state adopts new water quality standards, which is not likely to happen until the end of next year.

That’s because nutrient reductions in other rivers are linked to new dissolved oxygen criteria for the Chesapeake agreed upon last year by all Bay Program participants. The York and James rivers do not significantly contribute to the Bay’s dissolved oxygen problems, although they do contribute to problems with water clarity and chlorophyll a (a measure of algae) within each river.

Once the state adopts new standards for chlorophyll a and water clarity, final allocations will be made to treatment plants in the York and James basins based on the level of nutrient reductions needed to meet those standards, Murphy said.

“While we acknowledge that the allocations for the York and James may need to be recalculated, it is also clear that significant nutrient reductions are necessary for the health of these rivers,” he said. “Therefore, we will continue working to reduce nutrients and sediments in the York and James rivers even before final allocation numbers for each basin are established.”

Some environmentalists praised the proposal. “We’ve been arguing for bringing sewage-treatment plants into the 20th century for quite a while,” said Roy Hoagland, Virginia director of the Chesapeake Bay Foundation. “This is a dramatic step in that direction, and the [Gov. Mark R. Warner] administration deserves praise for it.”

Sewer bills of many Virginians would probably have to increase to pay for the plant improvements, said Christopher Pomeroy, a Richmond lawyer representing sewage systems in 50 localities.

Putting an annual total on how much nitrogen a plant can release could hinder a locality’s ability to take new sewer customers, sending them to other localities and fueling sprawl, Pomeroy said.

“I don’t know if it will slow growth. It will certainly shape it. It could shape it with negative environmental consequences” he said. “That’s my real fear.”

Al Pollock, the state Department of Environmental Quality's water-quality director, said low-interest state loans, and possibly grants, would be available to localities for sewage-plant improvements.

Improving the sewage plants is expected to help the state achieve a third of its nutrient reductions.

The Associated Press contributed to this report.