As bad as tanker oil spills are, they are only about $12 \%$ the 3.5 million tons of oil that enters the oceans each year. The rest comes from routine tanker operations, sewage treatment plants' runoff, natural sources, and offshore oil rigs. One month's maintenance and routine operation of a single supertanker produces up to $17,000$ gallons of oil sludge that gets into the ocean! If a cylindrical barrel is about 1.6 feet in diameter and 2.8 feet tall, how many barrels are needed to hold $17,000$ gallons of oil sludge? Recall that a cubic foot water is about 7.5 gallons.