FRESNO, Calif. (AP) — For the second time in four months, federal investigators have found problems at a central California landfill that local residents blame for birth defects, and ordered the West's largest toxic waste dump to clean up soil tainted with a cancer-causing chemical.

The U.S. Environmental Protection Agency sent a notice of violation on Thursday to the Chemical Waste Management landfill near rural Kettleman City, citing federal laws on the disposal of PCBs, or polychlorinated biphenyls, a now-banned transformer fluid.

The agency said the company needs to fix problems found outside a storage facility for large electrical equipment where the company's independent tests detected three samples that tested positive for PCBs last week.

"This is clearly a release of PCBs in an area where we shouldn't be finding them in the soil," said Michael Hingerty, deputy branch chief in the EPA's Office of Regional Counsel in San Francisco. "PCB-bearing stuff is subject to pretty strict regulation, and when those things are taken out of service they need to be disposed of."

In April, the EPA told the landfill it could lose the ability to receive hazardous Superfund waste if it did not clean up the first area where PCBs were found. Last week, the agency allowed the landfill to keep accepting that waste. But Thursday's action means the facility is again on notice to clean up its problems in 60 days or lose the ability to dispose Superfund wastes.

Residents of Kettleman City, an impoverished Central Valley farming community, have blamed the toxic waste dump for at least 11 birth defects, including cleft palates and heart problems seen in newborns, since 2007. But state waste management officials have said there is no evidence linking the landfill to the deformities.

Company officials also have said there's no evidence linking the dump to the birth defects. They did not immediately return calls Thursday seeking comment.

State environmental authorities are taking samples of the air, water and soil and going door to door to talk with families to assess community exposure and determine the source of the birth abnormalities.

The 1,600-acre Kettleman Hills Facility is about three miles from the largely Spanish-speaking community of 1,500 along Interstate 5, the busy artery linking Northern and Southern California.

The town is crisscrossed by high-tension power lines; pesticides and chemical fertilizers are routinely sprayed on nearby fields, and some local drinking water sources are contaminated.