Where an individual domestic well has a depth of sixty-five (65) feet or less, only the bottom one-fourth of the casing shall be perforated; provided, that the building official, after submission to him of sufficient evidence that the well will not be thereby polluted or contaminated, may permit perforations above the bottom one-fourth of the casing. Wherever possible, the perforations shall be kept below an impervious stratum. (Prior code § 7798)