Hello Francis. Do you mean the original 1987 work by Aller et al. with over 600 pages?

It is a method based on index. You can use GIS to implement it. Some examples are:

Article A GIS-based DRASTIC model for assessing intrinsic groundwate...

Article A GIS-based DRASTIC model for assessing aquifer vulnerabilit...

Article A GIS based DRASTIC model for assessing groundwater vulnerab...

If you search on google scholar "aller 1987 drastic vulnerability", you can find the pdf at page:

http://rdn.bc.ca/cms/wpattachments/wpID3175atID5999.pdf

Regards, Marco

Hello Francis, I do not know of any software created for the purpose to apply DRASTIC model (I am also not so updated). In most cases you have to prepare your layers within a GIS software (QGIS for example), it is particularly useful to use a 'model builder' tool within the GIS, however, you can also process layers yourself, reclassifying values of rasters according to the DRASTIC index. The document Marco Discenza sent you is quite useful. I will also send you privately a document explaining the use of DRASTIC in USA (627 pages!). I know you are interested in DRASTIC, but other simpler models can be applied as a first approach or if you do not have all data requirements of DRASTIC, specifically I remember GOD by Foster et al.

It is a parametric method based on index to determine the vulnerability of an aquifer to the pollution, and you need to use any GIS softwatre to establish your DRASTIC model in your study area.

thanks

Thank you all for your help!!