Ohalos 16:4-5

Ohalos 16:4

A person searching for graves must search a cubit by a cubit, skipping a cubit, until he reaches rock or virgin soil. A kohein who removes dirt from a ritually-unclean place may eat his trumah but one who clears away a mound may not eat his trumah.

Ohalos 16:5

If one who was searching for graves reached a brook, a channel or a public road, he can stop. When it comes to a field in which people were killed, one may gather the bones one by one and everything is considered ritually clean. If one was removing a grave from his field, he may gather the bones one by one and everything is considered ritually clean. When it comes to a pit into which fetuses or murdered people were thrown, one may gather the bones one by one and everything is considered ritually clean. Rabbi Shimon says that if the place had been designated as a grave in the first place, then the rule of blood-soaked ground applies.