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| Resource Library > Technology Transfer > Programs and Initiatives > Source Zone Treatment > Regulatory Issues |
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Source Zones: Regulatory Issues (Federal)
The overall goals for protection of human health and the environment, established in the Resource Conservation and Recovery Act (RCRA) and the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) are to:
- prevent exposure to contaminants at levels that could pose an unacceptable risk to potential receptors (whether human or ecological);
- minimize the continued contribution of contaminants from source zones to the environment;
- minimize the continued migration of contaminants in the environment; and
- to the extent practicable, restore affected environmental media to cleanup levels appropriate for current or future beneficial uses.
The RCRA and CERCLA regulatory paradigms each contain a statutory preference for treatment of contaminants, as opposed to control of potential exposure pathways.
In keeping with the statutory requirements of RCRA and CERCLA, USEPA has expressed a strong preference for source control measures for at least a decade -- a preference that continues to be expressed in recently issued guidance. USEPA defines "sources" to be contaminated material that acts as a reservoir supporting the continued migration of contaminants to surrounding environmental media (i.e., soil, groundwater, surface water, sediment, or air), or provides a direct threat to a receptor. Sources are not always stationary, but can migrate from a location, such as a landfill or surface impoundment, where the contamination was originally released. For example, DNAPLs may be present as a "mobile" phase that continues to migrate deeper into the subsurface, migrate along a subsurface feature, or accumulate in a subsurface feature, such as a depression in a layer of clay.
To the regulatory community, "source control" refers to a range of possible actions (e.g., removal, treatment-in-place, containment, etc.) designed to protect human health and the environment from sources of contamination. USEPA generally expects facilities to control or eliminate surface and subsurface sources of groundwater contamination, and requires that facilities implement source controls as necessary to achieve short-term protectiveness goals. For example, placing a temporary cover over highly contaminated soils may be appropriate to prevent leaching of the contaminants to underlying groundwater in the short-term while a facility pursues long-term remedies. USEPA also considers source control to be an important element in final remedies - the continuing emphasis on source control reflects the Agency's strong preference for remedies that are protective in the long term. As such, USEPA questions whether final remedies that fail to include source control would meet the overall RCRA statutory mandate to protect human health and the environment. Controlling contaminant source zones also is consistent with USEPA's longstanding policies dealing with pollution prevention, as the Agency recognizes that it generally is easier to deal with contaminants at the source than to address contaminants after they have become more wides-spread in the environment.
USEPA considers sources or "source materials" including NAPLs to be "principal threat wastes", which are regarded as highly toxic or highly mobile if they cannot be reliably contained or would present a significant risk to human health or the environment should exposure occur. USEPA prefers approaches that use treatment to address wastes and contaminated media that are considered "principal threats". However, program experience has shown that removal and/or in-situ treatment of NAPLs may not be practicable. Hence, USEPA generally expects that the quantity of free-phase NAPL (i.e., "free product") should be reduced to the extent practicable and that an appropriately designed engineering controls, such as containment, may be for developed for NAPLs and other wastes and contaminated media that cannot be removed from the subsurface, but which can be reliably contained and pose relatively low long-term threats, with the exact balance among treating, removing, and containing source zones determined on a case-by-case basis during remedy evaluation and selection. USEPA applies this policy to both DNAPLs and LNAPLs.
On the other hand, USEPA acknowledges that at many sites, restoration of groundwater to cleanup levels defined by applicable or relevant and appropriate requirements (ARARs) or risk-based levels may not be possible throughout a contaminated area, using currently-available technologies. Numerous studies by USEPA and others (USEPA, 1989, 1992a, 1992b; and the National Research Council [NRC], 1994) have concluded that complex site conditions associated with hydrogeologic factors and contaminant-related factors can greatly reduce the likelihood that groundwater quality can be restored, and that these factors are more common at hazardous waste sites than originally anticipated. Under such conditions, the most realistic approach may be to seek a waiver of ARARs as a consequence of technical impracticability of groundwater restoration ("TI waiver"). Source control generally is an important part of an acceptable alternative remedial strategy developed in the event that a TI waiver is proposed, and is one of the three recommended threshold criteria for final remedies. In such cases, ongoing reviews of the remedy are mandated under CERCLA to occur at five-year periods, to verify continued protectiveness of the remedy, and to determine whether new technologies exist that can achieve numerical cleanup goals in source zones.
Source Zones: Regulatory Issues (states)
Although many US States have not established policies regarding source-zone treatement, those that have generally follow applicable Federal standards. However, standards established by most US States for remediation of fuel hydrocarbon compounds in soil and groundwater, as reported by the Association for the Environmental Health of Soils in the 2001 Survey of States' Soil and Groundwater Cleanup Standards, make clear that a responsible party must address potential LNAPL source zones in conjunction with any response action for releases of petroleum fuels. In general, State regulatory agencies are highly supportive of efforts to remove, treat, or control NAPL source zones.
Source Zones: Maturity and Acceptance
The concept of Source Zones or removal is widely accepted by the regulated community, by regulatory agencies, and by the general public, to the extent that many or most remedial approaches developed to address contaminants in soil or groundwater incorporate some element of source identification, with concomitant removal, treatment, or control. In fact, source removal or control to the extent practicable even is a requirement for sites proposed for waiver of ARARs on the basis of technical impracticability.
Source removal (excavation of source zones) has been practiced almost since environmental restoration efforts began in the 1980s, and can be an effective, though costly, technology for addressing NAPL source zones. However, numerous innovative technologies for dealing with source zones have been introduced (here, here, and here) at a rapid pace since the early 1990s. These innovative technologies historically have had life cycles encompassing initial development in the laboratory through completion and evaluation of large-scale field trials, extending through periods of 5 to 10 years. The objective of all of these innovative technologies typically has been "restoration" of the source zone, a condition in which very large fractions of the contaminant mass would be removed, and environmental media within, and surrounding the source zone would be restored to near-pristine conditions. In reality, the best achievable performance of most innovative technologies appears to be "renovation", a condition in which the NAPL source is stabilized, some fraction of the contaminant mass is removed, thereby reducing the longevity of the source to some degree, and the flux of contaminant mass from the source is reduced. In fact, to date, few large NAPL sources have been completely eliminated using innovative technologies, which consequently are regarded as experimental.
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