Probably straight down, but that will be determined by the well driller, whatever provides the easiest access and is less expensive. Ultimately, you will be paying by the foot so the shortest distance is best. Here is an article from the USGS, see Figure 5 on page 12. Go through the references and look a few of them up on Google to get a better description of your exact area. You might get lucky and find a study that was done in your backyard. Remember a 2-inch well can produce approximately 20 gpm, so you will most likely be looking at a 4-inch or possibly 6-inch well. Your contact in New York will help there. Good luck.
USGS
