For any provision of this subchapter where treatment of Indian Tribes as identical to States is inappropriate, administratively infeasible or otherwise inconsistent with the purposes of this subchapter, the Administrator may include in the regulations promulgated under this section, other means for administering such provision in a manner that will achieve the purpose of the provision. Nothing in this section shall be construed to allow Indian Tribes to assume or maintain primary enforcement responsibility for public water systems or for underground injection control in a manner less protective of the health of persons than such responsibility may be assumed or maintained by a State. An Indian tribe  shall not be required to exercise criminal enforcement jurisdiction for purposes of complying with the preceding sentence.
42 U.S. Code § 300j–11 - Indian Tribes
(a) In generalSubject to the provisions of subsection (b), the Administrator—
(b) EPA regulations
(1) Specific provisionsThe Administrator shall, within 18 months after June 19, 1986, promulgate final regulations specifying those provisions of this subchapter for which it is appropriate to treat Indian Tribes as States. Such treatment shall be authorized only if:
(2) Provisions where treatment as State inappropriate