2.4. Scope and Role of Response Actions

The remedial alternatives described in the FS (Isherwood et al., 1990) and the PRAP (Dresen et al., 1991) are summarized in this ROD and address VOCs, FHCs, chromium, and lead in ground water, and FHCs and VOCs in sediment above the water table (the unsaturated zone). In addition, tritium has been detected locally in the soil and ground water, but as described in Section 4.2.1 of the PRAP, tritium at LLNL is self-remediating via natural decay and does not require cleanup. There is no significant way for people to be exposed to the contaminants in the unsaturated zone at LLNL except by migration of the contaminants to the ground water.

This ROD addresses all known ground water and unsaturated zone contamination and any resultant human health and environmental risks, and incorporates the results of LLNL pilot studies. Amendments to this ROD may be made in the future to address significant new or additional contaminants and/or source areas or other unforseen conditions.

The cleanup objectives for all contaminants originating at LLNL are to:

  1. Prevent future human exposure to contaminated ground water and soil.
  2. Prevent further migration of contaminants in ground water.
  3. Reduce contaminant concentrations in ground water to levels below MCLs, and reduce the contaminant concentrations in treated ground water to levels below State discharge limits (Table 1).
  4. Prevent migration in the unsaturated zone of those contaminants that would result in concentrations in ground water above an MCL.
  5. Meet all discharge standards of existing permits for treated water, and to treat vapor so that there are no measurable atmospheric releases from treatment systems.
The selected remedial alternatives will achieve these cleanup objectives and address all of the principal concerns at the site by removing the hazardous compounds from the ground water and subsurface soil, when warranted, and treating them at the surface at about seven onsite facilities. Ground water extraction will contain contaminant plumes, stop further migration of contaminants in ground water, and prevent any human exposure to them via water wells. The ground water treatment facilities will use different remediation technologies appropriate for the different influent contaminants and will be designed to reduce contaminant concentrations in the treated ground water to levels below established State discharge standards.

Ground water extraction and treatment will continue until the Federal and State agencies agree that the remediation standards have been met. The target objective is to reduce the concentrations in the ground water after cleanup to levels below MCLs (Table 1).

The ground water remediation standards in Table 1 are the lower of the Federal or State MCLs, and apply to the concentrations remaining in the ground water after remediation is complete. Ground water cleanup is complete when samples taken anywhere in the plume demonstrate that the remediation standards have been achieved. The discharge limits in Table 1 apply to the effluent water from treatment systems that may be discharged to ditches or arroyos. Although some discharge limits are lower than MCLs, remediation will continue until the remediation standards are met.

Volatile contaminants in the unsaturated zone will be removed by extracting them in vapor, which will be treated onsite. Atmospheric emissions from treatment systems will comply with Bay Area Quality Management District (BAAQMD) standards. Contaminants in the unsaturated zone will be remediated only if it is predicted that they would result in concentrations above an MCL if allowed to migrate into the ground water. Unsaturated zone remediation will be complete when modeling shows that contaminants will no longer migrate to ground water and create concentrations in the ground water above an MCL.

As part of the additional source investigations that are in progress, evaluations of the transport of VOCs and non-VOCs from the unsaturated zone to the ground water will be conducted. These investigations may identify areas where additional soil and ground water remediation is necessary. Results of these investigations will be summarized in Monthly Progress Reports for review by the regulatory agencies and the public.

Treated ground water will be recharged via wells, the LLNL recharge basin, and local arroyos, and/or used for LLNL landscape irrigation or in LLNL cooling towers, to conserve water resources.

2.5. Site Characteristics
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October 1, 2007
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