2.7. Description of Remedial Alternatives

  1. No-Action Alternative
  2. Ground Water Remedial Alternatives
    1. Ground Water Remedial Alternative No. 1 (The Selected Alternative)
    2. Ground Water Remedial Alternative No. 2
    3. Ground Water Remedial Alternative No. 3-Deferred Action
    4. Comparison of Ground Water Treatment Option Costs
  3. Unsaturated Zone Alternatives
    1. Unsaturated Zone Remedial Alternative No. 1-Vacuum-Induced Venting (the Selected Alternative)
    2. Unsaturated Zone Remedial Alternative No. 2-Deferred Action
    3. Comparison of Unsaturated Zone Treatment Option Costs
In the FS, three remedial alternatives were assembled for ground water for the LLNL site:

  1. Ground water extraction throughout the contaminated area, including source areas, thereby preventing further contaminant migration and enabling the most rapid cleanup. Ground water would be treated at the surface using UV/oxidation or air stripping-based technology with GAC to prevent any measureable air emissions. The treated water would be recharged or used at the LLNL site.
  2. Ground water extraction at the downgradient edges of contamination to prevent further contaminant migration. Ground water would be treated at the surface, as for Alternative No. 1, and recharged or used at the LLNL site.

  3. em>Ground water monitoring and treatment at the point of use, if drinking water supply wells should ever contain contaminants from LLNL in concentrations above drinking water standards. Ground water would be treated at the surface as described in No. 1 above.
The remedial alternatives for contaminants in the unsaturated sediment were:

  1. Vacuum-induced venting with surface treatment of vapors using GAC, thermal oxidation, or catalytic oxidation.
  2. Deferring action to see if contaminants migrate to the ground water, and, if they do, extracting and treating the ground water as described for the ground water remedial alternatives.
A third alternative, excavation and treatment and/or disposal, was also considered for unsaturated sediment. However, this alternative would be applicable only if (1) contaminant concentrations are found in the unsaturated zone that are high enough to cause concentrations above MCLs in the ground water, and (2) they occur at relatively shallow, accessible depths. Currently, no known locations meet these criteria, and this alternative was not considered further. However, excavation, treatment, and/or disposal could be employed in the future if high concentrations of contaminants, treatable perhaps by bioremediation or aeration, are discovered at excavatable depths.

The volume of ground water that contains contaminants above MCLs is much greater than the volume of unsaturated sediment containing contaminants that may impact the ground water in concentrations above MCLs.

The ground water and unsaturated sediment alternatives were developed by considering the nine evaluation criteria prescribed by EPA, as discussed in the FS. The FS discusses the various technologies for treating extracted ground water and vapor and assembles them into treatment options. The preferred treatment options vary from place to place because different parts of the site contain somewhat different combinations of contaminants in ground water and unsaturated sediment.

All the remedial alternatives considered for the LLNL site would include long-term ground water monitoring and reporting, in compliance with CERCLA requirements, until demonstrated achievement of the remedial action objectives. The costs of these activities, which are common to all alternatives for their respective estimated times of operation, were not explicitly addressed in the FS, but were presented in the PRAP to reflect the additional costs of maintaining a remediation program into the distant future. Monitoring activities will be conducted and reviewed periodically to gauge the effectiveness of the remedies. For all alternatives, the costs and implementation times were estimated using the assumptions discussed in the FS. The program operations costs, which were not described in the FS, are summarized in Appendix A of the PRAP (Dresen et al., 1991).

All the treatment options for ground water will reduce the effluent concentration of VOCs, FHCs, chromium, and lead below Applicable or Relevant and Appropriate Requirements (ARARs) (Isherwood et al., 1990). Tables 3-1 and 3-2 in the FS, and Table 1 and Appendix B of this ROD summarize the ARARs for the LLNL site.

As discussed in Section 2.8, Ground Water Alternative No. 1 and Unsaturated Zone Alternative No. 1 meet all ARARs. Ground Water Alternatives 2 and 3 and Unsaturated Zone Alternative 2 do not fully comply with the California non-degradation ARAR.

For treatment options that include disposal of treated ground water or air emissions, the effluent concentrations will be in compliance with RWQCB Waste Discharge Requirements, National Pollutant Discharge Elimination System (NPDES), and BAAQMD standards. Treated ground water will be recharged at the LLNL recharge basin south of East Avenue, in local drainage ditches and arroyos, or in infiltration trenches or recharge wells. Treated water will also be used for onsite landscape irrigation and in LLNL's cooling towers.

The approach for tritium is to keep it in the subsurface as much as possible where it will decay naturally (i.e., self-remediate) and to minimize its migration. Extraction systems will be designed and operated to prevent tritium from entering a treatment system in concentrations above its MCL. This will be accomplished by monitoring the influent water to the treatment system, both in pipelines and in the well(s). If water containing tritium above the MCL enters a treatment system, the facility will be shut down, and the water containing tritium will be treated by evaporation under existing National Environmental Standards for Hazardous Air Pollutants requirements, or released within allowable limits under the existing permit to the sanitary sewer system. No treated ground water will be recharged back to the subsurface if the tritium level exceeds the MCL.

Treatment options utilizing air stripping will be designed with GAC on the effluent air stream, so there are no measurable VOC air emissions. For those options employing GAC to treat water or air streams, the GAC will be shipped offsite where it will be commercially regenerated to destroy or recycle, if possible, the adsorbed contaminants. Options employing ion exchange for treatment of metals will require offsite recycling or disposal of the ion-exchange resin as a hazardous waste. The expected risk reduction after cleanup is complete is described in Section 2.9.1 of this ROD.

2.7.1. No-Action Alternative

A No-Action Alternative was considered in the FS for the LLNL site to establish a baseline for comparison. Under this alternative, LLNL would cease all characterization and remedial activities. Limited ground water monitoring would continue to track changes in ground water chemistry. The No-Action Alternative is not the same as the Deferred-Action Alternatives discussed in the FS and the PRAP, in that remedial actions may be taken in the future under the Deferred-Action Alternatives. The No-Action Alternatives for ground water and unsaturated sediment do not meet Federal and State standards to protect human health and were not considered viable in the FS and the PRAP.

2.7.2. Ground Water Remedial Alternatives

Two ground water extraction plans that use different arrays of extraction wells form the basis for immediate-action alternatives to remediate ground water. Each extraction plan is discussed subsequently with its remedial alternative.

Costs for the ground water remedial alternatives are summarized in Table 5. In the FS, costs were analyzed using a present worth calculation procedure, as prescribed by EPA. This is the standard procedure for comparing alternatives with costs and revenues beginning, ending, or extending over different periods of time.

  1. Ground Water Remedial Alternative No. 1 (The Selected Alternative)
  2. Ground Water Remedial Alternative No. 2
  3. Ground Water Remedial Alternative No. 3--Deferred Action
  4. Comparison of Ground Water Treatment Option Costs

2.7.3. Unsaturated Zone Alternatives

Costs of remedial alternatives for the unsaturated zone are summarized in Table 6. The remedial alternatives and treatment options are described below.

2.7.3.1. Unsaturated Zone Remedial Alternative No. 1--Vacuum-Induced Venting (the Selected Alternative)

Current data indicate that only FHCs in the Gasoline Spill Area, VOCs in the Building 518 Area in the southeastern part of the LLNL site, and possibly VOCs in the vicinity of the Trailer 5475/East Taxi Strip Area in eastern LLNL will need unsaturated zone remediation (Isherwood et al., 1990). FHCs and/or VOCs would be removed from the subsurface by vacuum-induced venting using extraction wells. Treatment options for the extracted vapor are described in the following section. If vapor extraction were ever considered for any of the localized areas at LLNL where elevated levels of tritium occur in the unsaturated zone, the water portion of the vapor could be (1) released to the atmosphere or (2) separated from the vapor by condensation. For possible tritium air releases from treatment systems, the AIRDOS-EPA computer model would be used to evaluate the potential annual dose to a hypothetical maximally exposed individual. LLNL will shut down any treatment system that emits tritium to the atmosphere at a rate predicted to contribute to an exposure of greater than 10 millirem/year (the Federal standard for clean air).

We estimate that it would take about 10 years to remediate the unsaturated zone under this alternative and that remediation would be underway by late 1992.

Treatment Options for Unsaturated Zone Remedial Alternative No. 1

Treatment Option 1. GAC Treatment.
Vapors from vent wells would pass through a chamber containing GAC to remove VOCs or FHCs. The treated vapor would be discharged to the atmosphere.
Treatment Option 2. Thermal Oxidation.
Vapors from vent wells would pass through a thermal oxidation chamber where the FHC and VOC vapors would be oxidized with the assistance of a heat source such as propane. The VOCs and FHCs would be destroyed and treated air would be discharged to the atmosphere.
Treatment Option 3. Catalytic Oxidation.
Vapors from vent wells would be heated and passed through a catalyst, where organic compounds would be converted to harmless oxidation products, such as carbon dioxide and water. The treated air would be discharged to the atmosphere. A catalyst suitable for both VOCs and FHCs has recently been found. The rationale for preferring catalytic oxidation over thermal oxidation for treatment of vapors is presented in Appendix B of the PRAP. If use of catalytic oxidation results in emission of vapors with compounds above regulatory standards, secondary treatment or alternative technologies, such as GAC, will be evaluated and implemented to comply with regulatory standards.

2.7.3.2. Unsaturated Zone Remedial Alternative No. 2--Deferred Action

Under this alternative, all contaminants in the unsaturated zone would be left in place and allowed to degrade, volatilize, or migrate to ground water under natural conditions. Ground water would continue to be monitored according to the requirements of CERCLA. If any contamination of ground water above MCLs occurs, it would either be remediated by ongoing ground water extraction and treatment, or by additional ground water extraction and treatment systems, if necessary.

2.7.3.3. Comparison of Unsaturated Zone Treatment Option Costs

The relative present worth costs for the three vadose zone treatment options are discussed in Section 4 of the FS. In summary, the present value of GAC is about 50% greater than for thermal oxidation, and catalytic oxidation is about 20% less than thermal oxidation.

2.8. Summary of the Comparative Analysis of Alternatives
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