of the RFA were reasonably ascertainable at the time of the public comment period, but Sandoz did not raise the issue in its comments on the draft permit. See Letter dated November 19, 1990 from Keith E. Lynott to Laura J. Livingston (Exhibit E of Appendix to Sandoz' Petition). The issue has not been preserved for review, and review is therefore denied.5 B. Areas of Concern AOCs 4, 5, 6, 8, and 9 consist of areas where seven underground storage tanks (USTs) were once situated. (AOC 9 contained three separate underground fuel and gasoline tanks.) Sandoz asserts, and the Region does not dispute, that the seven USTs were used to store raw material or fuel and never contained solid or hazardous waste. Sandoz states that four of the fuel oil tanks were leaking when they were removed from the ground, but it represents that: (1) releases from the leaking tanks (with one exception) have not caused contamination at concentrations exceeding NJDEP action levels; (2) Sandoz has appropriately remediated all releases in accordance with its NJPDES Permit and with the oversight of the NJDEP; and (3) any contamination not remediated by Sandoz is encapsulated in a dense glacial till which, according to Sandoz, serves as a protective barrier against migration of any release into the aquifer. Sandoz argues that, for two reasons, the sites of the removed USTs are not SWMUS and therefore do not fall within the ambit of the Agency's corrective action authority under RCRA § 3004(u), which is limited to releases from SWMUS.6 First, Sandoz contends concerns raised by the permit, thereby promoting the Agency's longstanding policy that most permit issues be resolved at the Regional level."); In re Texaco Refining and Marketing, Inc. (Anacortes, Washington), RCRA Appeal No. 89-12, at 3 (Nov. 6, 1990) (same). 5 Our determination that Sandoz failed to preserve the RFA issue extends only to the alleged formal defects in the RFA (e.g., the Region's alleged failure to prepare a separate written report, or to conduct sampling). Sandoz' challenge to the Region's use of the RFA to justify corrective action for potential (as opposed to confirmed) releases is addressed in Section D below. 6 RCRA § 3004(u) provides: Standards promulgated under this section shall require, and a that the USTs contained fuel or raw materials, not solid or hazardous waste. Second, Sandoz argues that, notwithstanding the passive leaks from the tanks, there were never any routine and systematic releases from the tanks that would render the sites SWMUS. Sandoz is correct that the term "solid waste" as defined in RCRA generally does not extend to stored raw materials or fuel.7 The investigation requirements at issue here, however, are directed to potential releases or spills of the stored materials, not to the materials in their original condition of storage. A spill or release of stored materials into the surrounding area would generally constitute "solid waste" under RCRA. See In re Amerada Hess Corporation, Port Reading Refinery, RCRA Appeal No. 88-10, at 2 (August 15, 1989). Even though a release from a tank to the surrounding area is "solid waste," to invoke RCRA §3004(u) it is still necessary to determine that the area is a "solid waste management unit." The term "solid waste management unit" includes areas contaminated by routine and systematic releases, but not by a one-time, accidental spill or a passive leak. See 55 Fed. Reg. 30809 (July 27, 1990). Sandoz argues that there is no evidence of any routine or systematic releases from the USTs. The Region, however, does not argue that the UST sites are SWMUS, but instead cites the statutory and regulatory omnibus provisions as legal authority for imposing corrective action requirements on non-SWMUS.8 It is well established that RCRA §3005(c)(3) provides authority to require corrective action for certain non-SWMUS. See In re Morton International, Inc. (Moss Point, Mississippi), RCRA Appeal No. 907, at 13-14 (February 28, 1992); In re American Cyanamid Co., RCRA the permit) and assurances of financial responsibility for complet ing such corrective action. 42 U.S.C. § 6924(u) (emphasis added). 7 The term "solid waste" is defined as: any garbage, refuse, sludge from a waste treatment plant, water RCRA § 1004(27), 42 U.S.C. 6903(27). 8 The statutory omnibus provision reads as follows: Each permit issued under this section shall contain such terms RCRA §3005(c)(3), 42 U.S.C. §6925(c)(3). The regulatory omnibus provision essentially tracks the language of the statute. See 40 CFR § 270.32(b)(2). Appeal No. 89-8, at 13 (August 5, 1991); In re LCP ChemicalsNorth Carolina, Inc., RCRA Appeal No. 90-4, at 3-4 (February 14, 1991). This authority, however, is not unlimited; by its own terms, § 3005(c)(3) authorizes only those permit conditions necessary to protect human health or the environment. Accordingly, the Region may not invoke its omnibus authority unless the record contains a properly supported finding that an exercise of that authority is necessary to protect human health or the environment. The Region has arguably made a finding that the basis for invoking Section 3005(c)(3) exists with respect to the UST sites simply by designating them as “Areas of Concern." In the Region's Response to Comments, the Region explains that the term "Area of Concern" is defined in the permit as an area that the Region is regulating under its omnibus authority because of suspected but unconfirmed releases of hazardous waste: Pursuant to the authority granted by Sec. 3005(c)(3) 9 In the Subpart S proposal, the Agency notes that it has interpreted the "routine and systematic" criterion as not including areas where a one-time spill or "passive" leakage has occurred. The Agency then observes that its interpretation has the effect of removing some environmental problems at RCRA facilities from the reach of §3004(u). The Agency notes, however, that it intends to exercise its authority, as necessary, under the RCRA 55 Fed. Reg. 30809 (July 27, 1990). Sandoz cites National-Standard Company v. Adamkus, 685 F. Supp. 1040 (N.D. Ill. 1988), for the proposition that the Agency's corrective action authority does not extend to non-SWMUS. Adamkus does contain dicta to the effect that Section 3004(u) does not extend to non-SWMUs. Id. at 1050. Because the Region is not relying on §3004(u) as authority for requiring investigations of the UST sites, however, Adamkus is inapposite. (Region's Response to Comments, at 1-2, Exhibit B in Appendix supporting Petition for Review.) In view of the Region's reference to the omnibus provision, the designation of the UST sites as “Areas of Concern" could arguably be viewed as the Region's shorthand method of indicating that at least a preliminary investigation of those areas is necessary to protect human health and the environment. It is not enough, however, for the Region to simply make a finding that a corrective action measure is necessary to protect human health and the environment. To justify an exercise of its omnibus authority, the finding must have a sufficient factual basis in the record. In this regard, we find the Region's response to comments to be inconsistent with the permit. Sandoz has described the steps it has taken under State supervision to remedy releases from the USTS at issue here, and the Region has not disputed Sandoz' account. When Sandoz raised those State-supervised remediation efforts during the comment period, the Region, in its response to comments, stated that such efforts "will be accepted." (Region's Response to Comments, at 2 and 7, Exhibit B of Appendix supporting Petition for Review.) The federal portion of the permit nonetheless requires Sandoz to investigate these units as part of the RFI. To correct this inconsistency, we are remanding this issue to the Region so that the Region may supplement its response to comments on the draft permit. On remand, the Region should provide a properly supported finding that the required UST site investigations are necessary to protect human health and the environment, and specifically address why the remedial steps already taken by Sandoz are insufficient. Alternatively, the Region may determine that Sandoz' past remedial efforts are adequate to protect human health and the environment for some or all of the units at issue and adjust the permit accordingly. C. Action Levels Under the permit, action levels will be used to trigger a Corrective Measures Study (CMS), but these levels will not be incorporated into the final permit until after Sandoz completes the RFI. Sandoz believes that the action levels should be set in the final permit before it is required to perform the RFI. Sandoz argues that the absence of specific, numerical action levels in the final permit impedes performance of the RFI. In response, the Region states that the RFI only requires the comparison of actual contamination levels to background levels, and that the absence of action levels in the permit does not hamper Sandoz' ability to make this comparison. The Region argues that it is appropriate to require a permittee to identify contamination based on background levels, leaving it to the Region to then specify the releases that require remediation. On July 27, 1990, the Agency proposed a comprehensive set of regulations for the implementation of RCRA § 3004(u), the Subpart S proposal. See 55 Fed. Reg. 30798 (July 27, 1990). The Subpart S proposal constitutes the Agency's most recent, comprehensive statement of its views regarding corrective action under RCRA § 3004(u). The preamble to the Subpart S proposal makes clear that action levels should be specified when the permit is first issued. For example, at one point in the preamble, the Agency states: Action levels will, whenever possible, be incorporated 55 Fed. Reg. at 30814. In another passage, the preamble contains the following statement: Requirements for the remedial investigation would Id. at 30810. It is certainly conceivable that, in certain cases for site-specific reasons, a Region will be justified in deviating from this approach, but Region II has not offered any site-specific reasons for such a |