If ĥametz is buried under less than three tefaĥim (24 cm) of stones, dirt, and the like, it is not considered to have been disposed of, and it must be uncovered and disposed of before Pesaĥ. This is because it is possible for a dog to smell it and dig it up.
However, if the ĥametz is covered by more than three tefaĥim, it is considered to have been disposed of and does not cause one to transgress bal yera’eh and bal yimatzei. Therefore, it need not be dug up and disposed of. Bitul ĥametz is nonetheless required, because it is possible that some of the stones will be moved during Pesaĥ, and the ĥametz will no longer be covered by three tefaĥim, causing the person to violate bal yera’eh and bal yimatzei. Likewise, in a case where ĥametz falls into a pit in one’s yard, if it is the sort of pit one does not generally enter, one may nullify the ĥametz without extracting and disposing it.
Accordingly, if ĥametz is stuck behind a wall cabinet and impossible to remove without first taking the cabinet apart or emptying it out and moving it, one need not remove the ĥametz. In this case, one may rely upon its bitul (SAH 333:19). If ĥametz is located where it can only be removed with some difficulty, one may pour bleach or soapy water on it until it is no longer fit for consumption, and hence no longer considered food (not even for an animal). Once this has been done, it need not be removed.
A storage room where one keeps articles not in use or merchandise that he does not intend to use until after Pesaĥ need not be searched for ĥametz. It is sufficient to nullify any ĥametz that might be there. However, if one wishes to fill the storage room during the thirty days prior to Pesaĥ, he must search it first, because the obligation to prepare for Pesaĥ has already taken effect. If one did not search it beforehand, it must be thoroughly searched for ĥametz on the night of the fourteenth (SA 336:1). If it is difficult to move all of the storeroom’s contents in order to carry out the search, one may sell or rent it to a gentile and thus exempt oneself from the obligation to perform bedikat ĥametz there.
. I have written in accordance with the opinion of Rashi, Ran, and the majority of poskim that if the ĥametz is covered by more than three tefaĥim it is considered destroyed, and one would not violate bal yimatzei with this ĥametz. However, the opinion of Sefer Mitzvot Katan is that if it is covered by something that is generally moved, the ĥametz would indeed be considered in the owner’s possession and he would violate bal yimatzei. In such a case, he would only be exempt from destroying the ĥametz if he nullified it verbally.
In a case where the ĥametz is covered by less than three tefaĥim, one would be required to remove the ĥametz, as I have written, but only if one is certain that there is ĥametz under this particular covering. Even if there is a danger of snakes and scorpions, he still must take a shovel and remove the covering to expose and destroy the ĥametz. However, if one merely suspects that there is ĥametz under the covering but is not certain, he is not required to check for the ĥametz if there is a danger of snakes and scorpions, and is only required to nullify the ĥametz verbally. If there is no danger, though, he is required to check (SA 433:8, MB ad loc. 35). In any situation where one is required to check, he can exempt himself from checking by selling the item to a gentile.