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(CNN) -- New documents released by a congressional subcommittee indicate that Coast Guard officials allowed BP to use excessive amounts of chemical dispersants in the Gulf of Mexico.

BP used the chemicals to break up oil after the April 20 Deepwater Horizon rig explosion sent millions of gallons of crude gushing into the Gulf.

Despite a federal directive restricting their use, the Coast Guard routinely granted exemptions, said Rep. Edward J. Markey, chairman of the House Energy and Environment Subcommittee.

In May, the Environmental Protection Agency, along with the Coast Guard, ordered the oil giant to stop surface application of the chemicals during the oil spill except in rare occasions, according to a House subcommittee on energy and environment.

In rare cases, exemptions had to be requested, documents show.

"BP carpet bombed the ocean with these chemicals, and the Coast Guard allowed them to do it," Markey said in a statement Saturday. "After we discovered how toxic these chemicals really are, they had no business being spread across the Gulf in this manner."

The exemptions granted "were in no way rare," Markey said in a letter to retired Adm. Thad Allen, the former commandant of the Coast Guard who is now overseeing the federal response to the oil spill.

The Coast Guard approved more than 74 exemptions in 48 days, Markey said. In one instance, Coast Guard officials allowed the oil giant to use a larger volume of dispersants than it had applied for, he said.

Dispersants are "a toxic stew of chemicals, oil and gas, with impacts that are not well understood," Markey, a Democrat from Massachusetts, said in the letter to Allen.

Markey said the findings are based on an analysis by the Energy and Environment Subcommittee.

Calls to a BP press office and the Joint Information Center were not immediately returned.

"The use of dispersant is always a difficult decision, with environmental trade-offs that must be taken seriously into consideration," EPA spokesman Brendan Gilfillan said Sunday. "As a result, its use in response to the BP spill was subject to numerous strict conditions once it quickly became apparent that BP wanted to use it in unprecedented quantities and in novel ways."

BP's use of disperants peaked at 70,000 gallons on May 24, the EPA said. It was after that the EPA ordered the halt on its use, except for rare occasions. From the time that directive was issued, dispersant use dropped 72 percent, Gilfillan said.

Initially, the EPA was not involved in the day-to-day decisions about which exceptions were granted, but that changed in late June.

"While EPA may not have concurred with every individual waiver granted by the federal on-scene coordinator, the agency believes dispersant use has been an essential tool in mitigating this spill's impact, preventing millions of gallons of oil from doing even more damage to sensitive marshes, wetlands and beaches and the economy of the Gulf coast," Gilfillan said.

Markey said the subcommittee also found contradictions on how much chemical dispersant was being used. On other occasions, BP used more than the amount approved by the Coast Guard, Markey said in his letter.

The report brings into question the total amount of dispersants used in the Gulf. BP says it has used 1.8 million gallons to break up oil flowing from the Deepwater Horizon's ruptured well.

"The validity of those numbers are now in question," Markey said.