Construction workers digging a trench for a gas pipeline in a Queens front yard made a grisly discovery Tuesday — human bones, police said.

Investigators later recovered five fragments ranging from 6 to 8 inches in length from the property across from PS 90 on 108th Street. They included two femurs, sources said.

The workers from a private construction company had been digging a trench for a natural-gas line for National Grid around 11:10 a.m. when they saw the white skeletal fragments about 3 feet beneath the surface, sources said.

They called 911, and a forensic anthropologist from the city Medical Examiner’s Office responded with police.

The anthropologist said it appears that the remains have been there for an “extended period of time,” a source said.

“We think they’ve been there more than a few decades,” one source close to the investigation said.

Police are waiting for the ME to determine a cause of death and test the evidence for DNA and identification.

The family who lives in the home has been there for 22 years and told police they knew nothing about how the remains wound up in their yard, sources said.

A woman who answered the phone at the home told The Post, “I don’t want to comment on anything like that. If you need to talk to somebody, the cops are across the street. Thank you very much.”