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The substance leaked during construction of a natural gas pipeline.

A company drilling a natural gas pipeline route under Tampa Bay this summer spilled a chemical that has killed about 2 acres of seagrass, according to the state Department of Environmental Protection.

"We are investigating the seagrass die-off," DEP spokeswoman Pamala Vazquez said Monday.

The spill by Gulfstream Pipeline killed seagrass beds about 1,500 feet due east of the Progress Energy power plant on Weedon Island, she said. Investigators have snorkeled through that area of the bay several times, including last week, trying to chart the extent of the die-off and figure out how to make up for it.

Earlier this month, the company finished removing the chemical that leaked, said Gulfstream spokesman Christopher Stockton. The company's experts say the seagrass die-off may not be as extensive as the DEP fears.

Six years ago, Gulfstream built a $1.6-billion pipeline that stretched for more than 400 miles under the Gulf of Mexico to carry natural gas from Mississippi and Alabama to Port Manatee, just south of the Sunshine Skyway bridge. The company then ran about 300 miles of pipeline overland to connect to power plants throughout Central Florida.

Then Progress Energy announced plans to modify its Pinellas County plant to double its generating capacity and switch it from burning fuel oil to cleaner-burning natural gas. In January Gulfstream began digging a 17-mile branch from the Manatee County end of its pipeline to connect to the refurbished plant. Work on the new 20-inch diameter pipeline wrapped up this week, Stockton said.

To avoid damaging environmentally sensitive areas in the bay, Gulfstream used a technique called horizontal direct drilling, cutting its hole for the pipeline a minimum of three feet down from the bay's bottom. To lubricate the drill, the company uses a chemical called bentonite, which is made from volcanic ash.

On June 25, the bentonite broke out of the hole being drilled, Vazquez said, an incident known in the drilling industry as a "frac-out." The company notified the DEP within 30 minutes, but the damage was done.

The bentonite that leaked into the bay did not poison the seagrass, she said, but slowly smothered it by blocking off sunlight that it needs to live. It is possible the frac-out also wiped out some of the smaller creatures that live on the bottom of the bay.

Once the DEP knows how extensive the damage is, she said, "there will have to be corrective action taken by Gulfstream." That could include planting new seagrass to replace what was killed, she said.

However, Stockton said an in e-mail, "early reports" from the section of the bay where the bentonite leaked are "indicating much of the area has not been killed and will recover."


About seagrass

Purpose: Seagrass covers about 28,300 acres of Tampa Bay, providing habitat and food for fish, manatees and other creatures of the state's largest estuary.

Losses: From 1950-1984, more than 40 percent of the bay's seagrasses were wiped out by sewage dumping and coastal development.