Variances. The Board of Appeals shall have the power to grant, upon appeal or upon petition, variances from the terms of this chapter, not including use variances, where the Board finds that, due to circumstances relating to soil conditions, topography or shape of land or structures and especially affecting such land or structures but not affecting generally the zoning district in which they are located, literal enforcement of this chapter would involve substantial hardship to the appellant or petitioner and that the desired relief may be granted without substantial detriment to the public good and without nullifying or substantially derogating from the intent or purpose of this chapter. The Board of Appeals may impose conditions, limitations and safeguards not based on the continued ownership by the applicant, petitioner or any owner. If the rights authorized by a variance are not exercised within one year from the date of grant thereof, they shall lapse, and a new petition, notice and hearing will be required for their reestablishment.