53. The intrinsic vulnerability of groundwater must be assessed by a professional for each category 1 water withdrawal protection zone delimited pursuant to this Division in accordance with the DRASTIC method of the National Water Well Association, as established in Aller, L., Bennet, T., Lehr, J.H. et al. (1987), DRASTIC: A Standardized System for Evaluating Ground Water Pollution Potential Using Hydrogeologic Settings, report no. EPA 600/2 87-035, the results of which must be used to rate vulnerability using the following vulnerability ratings:
(1) “Low”: a rating equal to or less than 100 for the entire protection zone;
(2) “Medium”: a rating less than 180 for the entire protection zone, except if a “low” rating has been assigned;
(3) “High”: a rating equal to or greater than 180 in any part of the protection zone.
The intrinsic vulnerability of groundwater within a category 2 or 3 water withdrawal protection zone is deemed to be high, unless a professional assesses it otherwise in accordance with the method referred to in the first paragraph.