The casing of domestic water wells shall not be perforated within fifty (50) feet of the ground surface if the depth of the well is greater than fifty (50) feet. When possible, the uppermost perforations shall be below an impervious stratum in an aquifer of good quality water. If a domestic water well with perforations fifty (50) feet or less from the ground surface is deepened, the perforations fifty (50) feet or less in depth shall be sealed off to prevent commingling of water from that level with deeper water. (Prior code § 7797)