Before we discuss the law regarding one who finds Chametz on Pesach, let us first address two points:
The first is that if one renounced one’s Chametz before Pesach by reciting the customary “Kol Chamira” text either after the search for or burning of Chametz (or both), although the Chametz may still be in one’s physical possession during Pesach, according to Torah law, the Chametz is null and void and one does not transgress the prohibition of owning Chametz on Pesach. This is because the mechanism of renunciation of Chametz turns any Chametz in one’s possession into dust and ash. Nevertheless, our Sages enacted that one may not leave any Chametz in one’s possession on Pesach (even after renouncing it), for they were concerned one might come to eat it and transgress a Karet prohibition.
The second point is that the prohibition to “see” Chametz applies only when it is one’s possession. However, if one bumps into Chametz that happens to be lying in a public domain on Pesach, there is no prohibition whatsoever to see or look at it. Thus, those who live among non-Jews who sell Chametz during Pesach need not close their eyes as they walk down the street on Pesach, since there is no prohibition to see such Chametz since it does not belong to the individual.
Let us now discuss the law regarding one who finds Chametz on Pesach, both during Yom Tov and Chol Ha’Moed.
The Gemara (Pesachim 6a) states: “Rav Yehuda said in the name of Rav, one who finds Chametz on Yom Tov must cover it with a vessel.” This means that if one finds Chametz during Yom Tov of Pesach, since it is Muktzeh like sticks and stones, one may not move it. Rather, one must cover it with a pot or any other vessel so that it is out of eye-shot. Immediately after Yom Tov at the onset of Chol Ha’Moed, one must burn it, flush it down the toilet, or subject to any other form of elimination.
The Poskim disagree whether this prohibition to move the Chametz on Yom Tov applies only to one who renounced one’s Chametz before Pesach, since, in this case, the possession of Chametz in one’s home is merely a rabbinic prohibition, or perhaps, even if one did not renounce one’s Chametz before Pesach, it will nevertheless remain forbidden to move the Chametz, although every second the Chametz remains in one’s possession, one transgresses a negative Torah commandment of owning Chametz on Pesach.
Maran Ha’Shulchan Aruch (Chapter 446) does not differentiate between the two above scenarios. Therefore, several Acharonim, among them the great Peri Chadash, rule that even one who did not renounce one’s Chametz before Pesach may not move it in order to remove it from one’s possession. Thank G-d, nowadays, almost everyone renounces their Chametz before Pesach, such that this scenario is obsolete.
Thus, halachically speaking, if one finds Chametz in one’s home on Yom Tov, one should cover it with a vessel. If one finds it on Chol Ha’Moed, one should immediately destroy it by burning it or flushing it down the toilet, as we have explained above.
The Rivash (Rabbeinu Yitzchak ben Sheshat) writes that if one sees Chametz in a public domain on Pesach, one may not pick it up, for the moment one does so, one will acquire it and transgress the prohibition of owning Chametz on Pesach. The Be’ur Halacha (Chapter 446) rules likewise. If one wishes, one may certainly burn it in its current place.