40 CFR §264.95

1. (a)The Regional Administrator will specify in the facility permit the point of compliance at which the ground-water protection standard of § 264.92 applies and at which monitoring must be conducted. The point of compliance is a vertical surface located at the hydraulically downgradient limit of the waste management area that extends down into the uppermost aquifer underlying the regulated units.
2. (b)The waste management area is the limit projected in the horizontal plane of the area on which waste will be placed during the active life of a regulated unit.
   1. (1)The waste management area includes horizontal space taken up by any liner, dike, or other barrier designed to contain waste in a regulated unit.
   2. (2)If the facility contains more than one regulated unit, the waste management area is described by an imaginary line circumscribing the several regulated units.