CHICAGO (AP) _ A sixth Chicago alderman has been convicted of bribery charges as federal prosecutors neared the end of their seven-year Operation Silver Shovel investigation of political corruption.

Percy Z. Giles, 47, whose West Side ward was the site of a notorious mountain of dust and debris left by illegal dumpers, was found guilty Tuesday of racketeering, extortion, official misconduct, bribery and fraud.

Some of the charges in the 13-count indictment carry sentences as stiff as 20 years. Prosecutors said a sentence of just over three years would be realistic. Sentencing was set for Feb. 11.

U.S. Attorney Scott Lassar said after the verdict that the marathon Silver Shovel investigation, based heavily on undercover tapes made for the FBI by corrupt contractor John Christopher, was finally nearing an end.

In all, 19 individuals have been indicted and 15, including six aldermen, convicted in the investigation, in which the undercover phase began in 1992. It surfaced publicly in 1996. One alderman was acquitted.

On tapes made secretly by Christopher, jurors heard Giles accepting two bundles of hundred-dollar bills totaling $5,000 each while the corrupt contractor told how he was hoping to land city contracts.

Christopher became an undercover mole for the FBI in hopes of softening his own sentence on charges of bankruptcy fraud and tax fraud. He awaits sentencing.

Giles, the son of an Arkansas sharecropper, had claimed to think that the bundles of cash represented legitimate campaign contributions. As for the other charges, his attorneys declared that federal prosecutors were out to get Giles and put everything he did in the worst possible light.

For example, the $80,000 from the dumpers went to a Giles-controlled fund that helped Little Leaguers and hungry families. But it also paid for voter literature that trumpeted the alderman's accomplishments.