The state has made a rare binding pledge to offset whatever pollution it may cause by depositing the muck it dredges from Baltimore harbor in a cove south of downtown.
Bowing to concerns raised by environmentalists, the state Department of the Environment is requiring the Maryland Port Administration to limit or make up for the nitrogen and phosphorus expected to drain back into the Patapsco River from the dredged material to be placed in Masonville Cove.
The port administration has spent $153 million to clean up trash and debris in the cove area and build an environmental education center there. In return, residents of the adjacent Brooklyn and Curtis Bay neighborhoods have supported the port's plan to target the cove for much of the 1.5 million cubic yards of sediment dredged annually to keep the harbor's shipping lanes clear. The first loads of sediment were expected to go there this month.
State regulators had planned to issue a permit to the port setting no limits on the nutrients allowed to drain off the dredged material back into the harbor. Port officials had argued that the nitrogen and phosphorus already are in the river's sediments, so no new pollution is being added.
"We're not putting anything into the system that isn't already there," said Frank L. Hamons, deputy director of the Maryland Port Administration.
But environmentalists argued that although nutrients buried in the bottom pose minimal pollution risk, they could get into the harbor if sediments are dredged up and mixed with water that is subsequently drained off.
The harbor, like the rest of the Chesapeake Bay, is impaired by nutrient pollution, which causes algae blooms and even fish kills in spring and summer. The state and federal governments are working on a baywide pollution "diet" designed to reduce the amounts of nitrogen and phosphorus allowed to get into the water.
Most nutrients come from municipal wastewater discharges, and from lawn fertilizer and pet waste washing off city and suburban streams. But environmentalists pointed to estimates that depositing dredged sediments at Masonville Cove has the potential to put more than 200,000 pounds of nitrogen back into the water annually.
In the discharge permit issued recently, the Department of the Environment ordered the port to "fully offset" the nitrogen and phosphorus released by the dredge disposal, beginning 4 1/2 years from now. In the meantime, the state set "interim" limits of 231,000 pounds of nitrogen and 3,620 pounds of phosphorus from the site.
The delay in requiring offsets is meant to give the port time to monitor how much of the nutrients are escaping back into the harbor from the dredged material.
Beth McGee, senior scientist with the Chesapeake Bay Foundation, called the offset requirement a "victory" for water quality since state regulators originally planned to impose no conditions on nutrient releases. McGee said she understood the need to delay the requirement so the port could determine how much it needed to do.
"We had hoped it would be sooner," she said of the restriction. The O'Malley administration has vowed to reduce nutrient pollution enough to restore water quality in Maryland's portion of the bay by 2020.
Port officials aren't sure how they'll comply with the pollution offset requirement when it takes effect, Hamons said. It may be possible to adjust the deposits of dredged material at Masonville to minimize or even eliminate the discharge of nutrient-enriched water from the site, he suggested.
If that's not feasible, he said, the port may opt to offset harbor pollution by paying farmers outside Baltimore to plant "cover crops" in winter, soaking up nitrogen that might otherwise wash off the farm fields and wind up in the harbor. Or the agency could build a plant to treat the discharge water, he said.
For now, Hamons concluded, "we're going to have to monitor the release water very carefully."