The Zoning Board of Appeals may authorize a variance for a particular use of a parcel of land or to an existing building thereon from the terms of this bylaw where, owing to circumstances relating to the soil conditions, shape, or topography of such land or structures and especially affecting such parcel or such building but not affecting generally the district in which it is located, a literal enforcement of the provisions of this bylaw would involve substantial hardship, financial or otherwise, to the applicant, and where desirable relief may be granted without substantial detriment to the public good and without nullifying or substantially derogating from the intent or purpose of this bylaw. The Board may impose conditions, safeguards and limitations both of time and of use, including the continued existence of any particular structures, but excluding any condition, safeguards or limitations based upon the continued ownership of the land or structures to which the variance pertains by the applicant, petitioner or any owner. If the rights authorized by a variance are not exercised within one year of the date of the grant of such variance, they shall lapse, and may be reestablished only after notice and a new hearing pursuant to this section.