EP 1110-1-19
30 Jun 01
Natural Resource Trustees are authorized by the Comprehensive
Natural Resource
Environmental Response, Compensation, and Liability Act of 1980
Trustees
(CERCLA) to assist EPA in characterizing the nature and extent of site-
related contamination and impacts. The Trustees also act on behalf of the
public to determine whether environmental restoration is needed in light
of the response actions at a given site.
The NCP defines an operable unit (OU) as a "discrete action that
Operable Unit
comprises an incremental step toward comprehensively addressing site
problems. This discrete portion of a remedial response manages
migration, or eliminates or mitigates a release, threat of a release, or
pathway of exposure" (NCP 300.5). Hence, an OU can be a certain
geographic portion of a site or can address an environmental medium at
the site (e.g., groundwater, soil). OUs may also be comprehensive but
temporary remedies (e.g., temporary caps across a site) that provide
interim protection of human health and the environment before final
remediation. The cleanup of a site can be divided into a number of OUs,
depending on the complexity of the problems associated with the site.
For many sites, the completion of RA also marks the completion of the
Operational and
operational and functional (O&F) period. O&F activities are conducted
Functional
after physical construction of the remedy is complete to ensure that it is
functioning properly and operating as designed. The NCP provides a
maximum timeframe of one year for performing O&F activities; however,
EPA may extend the one-year period, as appropriate. O&F activities may
be conducted for containment, groundwater restoration, and surface water
restoration remedies in order to ensure that the remedy functions properly
and operates as designed. Monitored natural attenuation remedies do not
go through an O&F determination. The O&F period is part of the RA and
occurs during the last year of the RA. Formal O&F determinations are
made primarily for Fund-financed projects, since O&F governs when
O&M or LTRA begins. O&F is considered complete on the date that the
designated Regional official approves the interim RA report (for sites
with groundwater or surface water restoration remedies) or final RA
report in writing.
Operation and maintenance (O&M) are the activities required to maintain
Operation and
the effectiveness or the integrity of the remedy. In the case of Fund-
Maintenance
financed measures, O&M activities are required to restore groundwater or
surface waters, and to continue the operation of such measures beyond the
LTRA period until the cleanup goals have been achieved. Except for
Fund-financed groundwater or surface water restoration actions covered
under NCP 300.435(f)(4), O&M measures are initiated after the remedy
has achieved the remediation objectives and/or cleanup goals listed in the
ROD, and the remedy has been determined to be O&F. O&M typically
starts on the date that the designated Regional official approves the final
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