Whether the six-year statute of limitations for 'remedial' work is triggered, as the court of appeals held below, only when the construction of a permanent solution for environmental contamination meets a threshold level of comprehensiveness

QUESTION PRESENTED The Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA), contains two different statutes of limitations for suits to recover environmental clean-up costs: (1) a three-year limitations period for suits to recover “removal” costs; and (2) a six-year period for suits to recover “remedial” costs. See 42 U.S.C. § 9613(g)(2)(A), (B). The three-year period to seek removal costs starts when the removal work is completed; the six-year period to seek remedial costs starts when physical on-site remedial construction begins. The terms “removal” and “remedial” are defined terms under CERCLA. See 42 U.S.C. § 9601(23), (24). “Removal” activity generally consists of clean-up measures taken in response to immediate threats to public health and safety; “remedial” activity means “actions consistent with [a] permanent remedy.” 42 U.S.C. § 9601(24). The question presented is: Whether the six-year statute of limitations for “remedial” work is triggered, as the court of appeals held below, only when the construction of a permanent solution for environmental contamination meets a threshold level of comprehensiveness. (i)