Let’s say that there’s a field in which a grave was lost and a house was built with an upper level over it. If the entrance to that upper level was directly above the entrance to the house, then the upper level remains ritually clean; if this is not the case, then the upper level is rendered unclean. Rabbi Eliezer says that pieces of soil from a beis hapras and pieces of soil from a foreign land that came in with vegetables combine to convey impurity in the size of a packing-bag seal; the Sages, however, say that there must be one piece of soil the size of a packing-bag seal. Rabbi Yehuda related an incident in which mail arrived from overseas for the sons of the Kohanim Gedolim and they had on them a seah or two seah worth of soil seals but the Sages remained unconcerned about any issues of ritual impurity.
Grapes are harvested in a beis hapras as follows: They sprinkle the harvesters and the utensils once, and then a second time, after which they may harvest the grapes and remove them from the beis hapras. Others receive the grapes from them and bring the grapes to the winepress. Beis Hillel say that if the two groups of people touched one another, they are rendered ritually unclean. Beis Shammai say that the gatherer must hold the sickle with rope or harvest the grapes using a flint, letting them fall into a basket, at which point he takes them to the winepress. Rabbi Yosi said that these rules only apply in the case of a vineyard that became a beis hapras; if a person plants in a beis hapras, the grapes are sold in the market.