I agree with PeterHursey. You locate the stress line of the aquifer and place the cure upstream where it enters your property across the aquifer. Usually they are not that large, but it is possible that you are able to sense the aquifer from several metres away. I have read an article in German about the connection between these so-called "announcing aquifer stress lines" and the depth of the actual acquifer.
The easiest way is to recheck after placing your cure across the middle of the aquifer. If you are still able to locate the stress then maybe one or two more cures in a line covering the width of the aquifer will help.
You are absolutely correct. Aquifers are covered in the section of the course that deals with Geopathic Stress. They are described on page 11 of the Diamond Dowsing Manual and you follow the guidelines for curing Geopathic Stressors.