If this condition were happening to me the first thing I would be concern with is the pump. Sand will do great damage to it. My suggestion would be to contact a well rep. and see if the pump is to low in the well as sand does not usually come through the water vains but from the bottom of the well as it settles to that point. As I stated above that this is only a suggestion as by know means am I a proffesional well person.
Good luck
