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# / Vol. 55, No. 61 / Thursday, March 29, 1990 / Rules and Regulations

system set forth in40 CFR 262.11 is effective, the Agency believes that imposing a testingrequirement does have some merit, in that it could increase the accuracy ofdeterminations, could clarify theresponsibilities of generators, and could facilitate compliance monitoring.

The Agency will continue to evaluate the comments on this issue as well as explore other options for a testing requirement. At present, however, the Agency is not yet ready to go forward with a testingrequirement based on any ofthe options ithas evaluated thus far. Should the Agency decide that an appropriate approach is available, it will propose and solicit comment upon the details of that approach in a separate
- rulemaking. In the meantime, the Agency believes that the existing determination requirement (as specified at40 CFR 262.11), as well as the liability for incorrect determinations, iseffective and practical.

H.Applicabilityto WastesManagedin SurfaceImpoundments

As discussed above, in response to theproposed TC,EPA received many comments questioning the validity of applying the TCto wastes, including wastewaters, likely tobe managed in surface impoundments. In response to commenters' concerns, on May 18.1987, EPA published a Supplemental Notice of Proposed Rulemaking in theFederal Register, which requested comments and data on several issues related to the regulation ofwastes managed in surface impoundments under the TCrule. The Agency also requested comment (assuming such an approach) on: (1)The criteria to be used to determine whether the surface impoundment scenario should apply to a particular waste, (2) thepoint at which concentration measurements should be made (e.g.,at thepoint ofgeneration or within the impoundment), and (3) how multiple surface impoundments should be handled under the TC rule.

Comments received in response to the notice concerning the surface impoundment management scenario are summarized and addressed in section II.A.2.c. Comments received in response to the notice, which addressed sampling point and multiple impoundment issues,

are discussed below.
1. Sampling Point

In the May 18, 1987notice, EPA requested comments on whether evaluations ofwastes managed in surface impoundments should be based

on measurements ofthe concentration in the impoundment or at the inlet to the impoundment. In response, some commenters supported sampling at the inlet to the impoundment and stated that sampling the waste within the impoundment is not only contrary to Congressional intent,but conflicts with EPA's own regulations that require the determination ofhazard tobe made at thepoint ofgeneration.

Other commenters, however, argued that wastes should be sampled within the impoundment or that the impoundment effluent should be sampled. Many ofthese commenters argued that measuring the concentrations in the impoundment

more accurately represents the concentrations ofhazardous constituents thatpose a threat to ground water. Some commenters argued that evaluation ofhazard should be based on impoundment effluent because concentrations ofthe wastewaters within the impoundment are approximately the same as the concentrations in the impoundment effluent.

Ifthe Agency were to allow persons to make their determinations on the
waste in the impoundment, it would raise questions that the Agency has not yet evaluated completely nor taken
comment on.For example, in this situation, shouldthe Agency actually require testing; ifso,how often and what should be tested? Would such a result allow persons to land dispose of
wastes that (but for thepoint ofhazard determination) would be hazardous, contrary to Congressional intent? Would such a result allow persons to treat wastes without a permit and thus be inconsistent with Congressional intent? EPA concedes that, forsome activities (e.g., closure), leachate quality may be

more appropriately assessed by measuring concentrations at multiple sites within the impoundment.

Thecurrent rules require that the determination ofwhether a waste Is hazardous bemade at the point of generation (i.e., when the waste becomes a solid waste). (A waste must be a solid waste before it can be classified as ahazardous waste under RCRA.) EPAbelieves thatdetermination ofthe regulatory status ofa waste at the point ofgeneration continues to be appropriate, especially since the Agency is not developing a separate mismanagement scenario or set of regulatory levels for wastewaters. To be consistent with otherhazardous waste regulations and until the Agency addresses the above questions, EPA is retaining the existing approach of requiring sampling at the point of generation. 2.Multiple Surface Impoundments

In theMay 18, 1987 notice, EPA requested comment on how multiple surface impoundments or "treatment trains" should be handled underthe TC rule.Some commenters favored regulating all surface impoundments in a treatment train as a single unit-ifthe first impoundment treats a hazardous waste, all impoundments would be required to comply with the RCRA regulations for hazardous waste treatment facilities. Other commenters, however, suggested that each impoundment should be regulated individually. Still other commenters stated that owners and operators should be required to determine whether the
most upstream surface impoundment is treating wastes that exhibit theTC, but they should onlybe required to evaluate downstream impoundments Ifan upstream impoundment exhibits theTC.

As discussed above, the Agency has decided not to develop a separate regulatory scheme for surface impoundments. Thus, the Agency will continue toregulate all surface impoundments as individual units and willnot pursue any ofthe other options discussed by commenters. Currently, under 40 CFRpart 261, each surface impoundment in a series ofmultiple surface impoundments is regulated separately. Ifa surface impoundment receives orgenerates a hazardous waste, the owner oroperator of the impoundment is required to comply with the RCRA regulations governing hazardous waste treatment, storage, and disposal facilities. On the otherhand, if

a downstream impoundment is not treating orgenerating a characteristically hazardous waste and upstream units have not managed, listed wastes, then the downstream unit isnot subject to RCRA subtitle C requirements.

I.Relationshipto OtherRCRA Regulations
1.Hazardous Waste Identification Regulations

a.HazardousWasteListings.Under the June 13. 198, proposal, the hazardous waste listings in subpart D of 40CFR part 261 would not be affected. All the listings would remain in effect, including those listings that were based

on the presence ofTCconstituents. It is EPA's intention that the hazardous
waste listings would continue to complement the revised TC as they had the EPTC.

A number of commenters, however, argued that the TCshould supersede certain hazardous waste listings.In

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