25 USC 3905 - Contract authority

(a) Authority of Director 
To the maximum extent feasible, the Director shall carry out duties under this chapter through contracts, compacts, or memoranda of agreement with Indian tribal governments or Alaska Native entities pursuant to the Indian Self-Determination and Education Assistance Act (25 U.S.C. 450 et seq.), section 2004a of title 42, or section 1632 of this title.
(b) Cooperative agreements 
The Director is authorized, for purposes of carrying out the duties of the Director under this chapter, to contract with or enter into such cooperative agreements with such other Federal agencies as is considered necessary to provide cost-sharing for closure and postclosure activities, to obtain necessary technical and financial assistance and expertise, and for such other purposes as the Director considers necessary.