[In the case of] barrels that are outdoors, standing upright or lying on their sides, which touch one another by a square handbreadth, [if there is] tumah underneath one [barrel], tumah penetrates directly up and directly down. In what case does this apply? When [the barrels] are tahor. However, if they are tamei, or a handbreadth above the ground, and there is tumah under one of them, [the area] beneath all of them becomes tamei.