The 12-inch Silvertip pipeline ruptured July 1 near Billings, Mont., dumping about 1,000 barrels of oil into the Yellowstone River. Flooding along the river hampered cleanup operations but the EPA said it was getting access to more of the riverbank.
"Increased access means increased progress," Steve Merritt, regional coordinator for the EPA, said in a statement.
"The number of accessible sites for assessment and cleanup is going to increase as water levels continue to fall. We've seen a dramatic increase in the amount of shoreline our SCAT teams can access in the past 24 hours."
Exxon Mobil submitted a draft response plan to the EPA earlier this week. The agency returned the proposal because of concerns about the plan, giving the energy company another week to reconsider its response.
The EPA added that people near the area of the spill were complaining about strong odors, which the agency said were organic compounds like benzene, toluene, ethylbenzene and xylene, chemicals typically found in oil.
The agency said that while people could smell these compounds at levels lower than what is considered harmful, there may be some side effects.
"If you are sensitive to these chemicals, stay indoors," the agency said.