(1) The casing head or pitless unit of any water well shall extend not less than 18 inches above the finished ground surface or pump house floor, and not less than 18 inches above the local surface runoff level. No casing shall be cut off below land surface except during permanent abandonment of a well. The ground surface immediately surrounding the top of the well casing or pitless unit shall be graded so as to drain surface water away from the well. The casing of any water well shall extend not less than 18 inches above the established 100 year floodplain elevation or be capped with a watertight seal and vented above flood level.