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| Resource Library > Technology Transfer > Programs and Initiatives > Source Zone Treatment > Background > TI Waiver |
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Technical Impracticability Waivers
The properties of NAPL chemicals and the characteristics of NAPL (in particular, DNAPL) migration and persistence in the subsurface environment suggest that in many circumstances, total restoration of groundwater to drinking-water standards may not be technically or economically feasible. There are provisions in federal and state regulations for exceptions to the application of drinking-water standards as cleanup goals, with establishment of risk-based or other alternative cleanup levels. In particular, it may be possible to demonstrate non-attainability of drinking-water standards in groundwater under USEPA's technical impracticability (TI) waiver protocol. Applicable and relevant or appropriate requirements (ARARs) that might otherwise be used to establish cleanup goals may be waived by USEPA for any of six reasons specified in CERCLA 121[d][4], including technical impracticability from an engineering perspective.
The TI evaluation must include the following components based on site-specific information and analyses (USEPA, 1993):
- A proposal of specific ARARs or media cleanup standards for which TI determinations are sought;
- Designation of the spatial area over which the TI waiver will apply;
- A current conceptual site model that describes contaminant sources, site geology and hydrology, and chemical migration and fate processes.
- An evaluation of the restoration potential of the site, including data and analyses that support assertions that attainment of ARARs or media cleanup standards is technically impractical from an engineering perspective. At a minimum, this generally should include:
- A demonstration that the sources have been identified and have been or will be removed and contained to the greatest extent possible;
- An analysis of performance of any ongoing or completed remedial action;
- Predictive analysis of the time frames to attain required cleanup levels using available technologies; and
- A demonstration that no other remedial technologies (conventional or innovative) could reliably, logically, or feasibly attain the cleanup levels at the site within a reasonable time frame.
- Estimate of cost of the existing or proposed remedy options, including construction and O&M costs.
- Any additional information or analyses that USEPA deems necessary for the TI evaluation.
The process of applying for a TI waiver, and providing the necessary documentation, is expensive and time consuming. Nevertheless, the relative costs and benefits involved in seeking a TI waiver often compare favorably with the relative costs and benefits associated with installing and maintaining a large remediation system. As a consequence of the significant difficulties in remediating DNAPL below the water table, this category of DNAPL site should be regarded as a potential candidate for a TI waiver. In fact, the presence of DNAPL at a site is cited in the USEPA (1993) TI guidance and in other USEPA guidance as a mitigating factor favoring adoption of alternate cleanup goals and/or a TI waiver. Adoption of a TI waiver generally will require implementation of land-use controls and other institutional measures, to ensure that groundwater is not used as a potable water supply within the area designated in the TI waiver. Effective, long-term land-use planning and zoning are needed to ensure that future remedial actions are compatible with future uses of the land. Institutional controls are considered to be an important complement to other treatment technologies, and in most cases are critical to the successful implementation of a remedial action. Risks from exposure to contaminants in groundwater can be reduced or eliminated by controlling the migration of the dissolved-phase plume.
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