By David Russell, reporter at OptionMonsterNEW YORK -- Option traders are coming back to Covanta ( CVA) after hitting a home run in the waste-management stock earlier this year. OptionMonster's tracking programs detected the purchase of almost 22,000 March 22.50 calls for 75 cents. Volume was more than 450 times open interest at the strike, indicating that new positions were initiated. These calls lock in the price where shares can be purchased, letting investors cheaply position for a rally. They also have the potential to generate significant leverage from even a small move in the stock. That's exactly what happened after our scanners detected bullish option activity on May 23: With CVA at $20.22, the July 22.50 calls were bought for 10 cents. The stock traded up to $21.29 the next day, a gain of just 5%, and those contracts more than tripled to 35 cents. Covanta was green when the calls hit Tuesday, but it ended the session down 0.74% to $21.35. Its last earnings report on July 17 beat expectations on the top and bottom lines, and the shares are currently near their highest level since the broader market crashed in early 2009. Total option volume in the name was 160 times greater than average in the session, with calls accounting for a bullish 97%. Russell has no positions in CVA.