CHARLOTTE, N.C. -- Charlotte officials say something containing dangerous PCBs and other organic chemicals has been found in the city sewer system.

The chemical dumping does not affect the drinking water system, City manager Ron Carlee said Friday.

Charlotte-Mecklenburg Utilities Director Barry Gullet says the substance was found Thursday in a wastewater treatment plant when workers noticed an oily sheen. The wastewater was routed to a storage area for investigation.

Officials think the water flowing into the treatment plant Friday is safer than earlier this week.

But Carlee said people are asked to avoid human or animal contact with Mallard Creek and the Rocky River in Cabarrus County until more testing can be done.

Gullet says PCBs, polychlorinated biphenyls, have been banned since the 1970s but can still be found today.

Officials think the material entered the sewer system in northeast Charlotte.

Carlee called it a deliberate and illegal discharge.

Charlotte-Mecklenburg police are investigating it as a criminal case. They say the person responsible could face state and federal charges.