25 Pa. Code § 250.403 – Use of groundwater.

(a) Groundwater will not be considered a current or potential source of drinking water where groundwater has a background total dissolved solids concentration greater than 2,500 milligrams per liter.
(b) Except as provided in subsection (a), current and probable future use of groundwater shall be determined on a site-specific basis.
(c) Drinking water use of groundwater shall be made suitable by at least meeting the primary and secondary MCLs at all points of exposure identified in § 250.404 (relating to pathway identification and elimination).
(d) Current drinking water or agricultural uses of groundwater, at the time contamination was discovered, shall be protected.