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It is permitted on Chol ha'Mo'ed to repair a well by clearing it of rocks but it is forbidden to dig a well unless it is needed by the public for drinking water.
It is permitted on Chol ha'Mo'ed to clear out the rocks from a well that is needed by an individual, but if it is not needed by the individual it is only permitted to fill it with water but not to clear out the rocks.
It is permitted on Chol ha'Mo'ed to remove thorns from the streets and to repair the roads and measure the Mikva’os and add water to them if necessary. (1)
Our sages learn from a Pasuk that it is a Mitzvah to mark the graves and it is permitted to do so even on Chol ha'Mo'ed.
Only graves that convey Tum'as Ohel (ritual impurity that is spread through an indoor facility) should be marked. (2)
Only uncertain impurities are marked, such as trees branches that overhang a corpse, stones that jut out from a wall and overhang a corpse, and a Beis ha'Pras. (3)
There are three types of Beis ha'Pras: a field that contains a grave that was plowed over, a field that contains a misplaced grave, and a field that the deceased is placed in where the people that accompanied the bier from one town to another take their leave.
In a field that contains a misplaced grave, if there are trees in the field we can be sure that it has been plowed and no longer needs to be marked.
A BIT MORE
1. If the Beis Din does not go out to repair the roads and remove the thorns and someone gets killed as a result it is regarded as if they killed him as the Pasuk says, “And the blood will be on you”.
2. A grave that contains flesh from a corpse that is exactly the size of an olive should not be marked even though it conveys Tum'as Ohel because it will soon diminish to less than the size of an olive and will no longer convey Tum'ah.
3. The only type of Beis ha'Pras that conveys Tum'as Ohel and must be marked is a field that contains a misplaced grave.
The Gemara learns out from a Pasuk in Yechezkel that we should mark graves. The Gemara asks that until Yechezkel came along how did we know this Halachah? The Ramban explains that the question of the Gemara is based on the concept that a Navi may not institute his own Halachah and thus it is impossible that this Halachah does not have a source prior to Yechezkel. The Gemara answers that its source is a Halachah l’Moshe mi'Sinai and Yechezkel merely supported it with a Pasuk. (Sefer ha'Mitzvos)
It is permitted on Chol ha'Mo'ed to do work that is needed by the public, such as repairing roads, removing obstructions, marking graves so that the Kohanim will be aware of them, and repairing Mikva’os. Only work that is needed physically by the public is permitted but other public necessities such as building a Beis Keneses is forbidden. Additionally any work that is needed for a Mitzvah can’t be done professionally on Chol ha'Mo'ed. (Shulchan Aruch OC 544:1)
Work that is needed by the public is permitted on Chol ha'Mo'ed because work for the public is only accomplished at a time that the public is off from work and can get together to do the work. (Mishnah Berurah)
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