- water
- groundwater
A sole source aquifer is an aquifer that the EPA has designated as the principal drinking-water source for its service area — one supplying at least half the area's drinking water with no economically feasible alternative if it were contaminated. The designation does not create a cleanup program, but it triggers EPA review of federally funded projects that could contaminate the aquifer.
The label raises the stakes of any subsurface contamination in the designated area: a release that would be a local matter over a redundant aquifer becomes a threat to the region's only water supply. Where a sole-source aquifer underlies a facility already inside a federal cleanup — a CERCLA site — the two designations compound, and the groundwater pathway becomes the controlling exposure route in the record.