This is a link to a set of fascinating USGS maps related to our sole source aquifer. A free plugin is required to view the document but it is readily installed (at least on PC’s) in less than a minute.

http://pubs.er.usgs.gov/publication/ofr82114

If the [EPA] Administrator determines, on his own initiative or upon petition, that an area has an aquifer which is the sole or principal drinking water source for the area and which, if contaminated, would create significant hazard to public health, he shall publish notice of that determination in the Federal Register.

That quote was taken from this US EPA page documenting that the determination that the Ramapo Aquifer meets these criteria.