A well cap used on a well that has a pitless adapter or pitless unit must have a screened vent hole, pointing downward, with not less than 24-mesh noncorrosive screen, and that is at least 1/2 inch in diameter. Vent openings shall terminate at least 12 inches above finished ground surface. Venting is required on all wells except Class 3 wells or flowing water wells.
Iowa Admin. Code r. 567-49.17