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UCRL-MI-127711 | Privacy & Legal Notice |
October 1, 2007 |
7000 East Avenue • Livermore, CA 94550
The selected remedies for this site protect human health and the environment, comply with Federal, State, and local requirements (ARARs), are implementable, and permanently and significantly reduce the toxicity, mobility, and volume of the contaminants.
The goal of this remedial action is to remediate ground water to the ARARs specified in the PRAP and this ROD. Based on information obtained during the RI and on a careful analysis of all remedial alternatives, DOE, LLNL, EPA, DTSC, and the RWQCB believe that the selected remedy will achieve this goal. The approach to be taken to the remediation will involve close monitoring of ground water quality in monitor wells, extracted water quality in extraction wells, and water level elevations near the extraction centers. The extraction well field will be operated dynamically to optimize the cleanup. That is, based on the results from the monitoring plan, individual wells may operate continuously, may be turned off, or may be pumped intermittently. During the course of the remediation, new wells will be installed at appropriate locations and will be operated in the same manner.
To ensure that cleanup levels continue to be maintained, the ground water will be monitored until DOE and the regulatory agencies agree that cleanup is complete.
The selected ground water remedy involves immediately pumping water at approximately 18 initial locations within the ground water plume (Fig. 7). The total rate of ground water removal for this extraction plan is estimated to be about 350 gpm. Water will be pumped from one or more wells at each of these locations using existing monitor and extraction wells, along with new extraction wells. The well locations will be chosen to prevent any VOCs from escaping from the area in concentrations above their MCLs. To enable more rapid remediation, wells will also be placed in all areas where VOC or FHC concentrations in ground water exceed 100 ppb. Additional extraction locations may be added to ensure complete hydraulic capture of the plume, and/or to expedite cleanup, if field data indicate additional wells are necessary.
Seven onsite facilities (A to G) will be constructed initially to treat the extracted ground water (Fig. 7). Each treatment facility will be designed to treat a somewhat different combination of compounds. Treatment Facilities A, B, E, and F will use UV/oxidation as the primary treatment technology. Treatment Facilities C, D, and G will use air-stripping as the primary treatment technology. All facilities will use GAC to remove VOCs and FHCs from air streams, and Treatment Facility F will use GAC to remove lead from ground water. Treatment Facility D will use ion exchange to remove chromium from ground water.
The maximum additional cancer risk after remediation is complete is calculated at seven in one hundred million (7 x 10-8) using the best estimate assumptions. This is over 100 times lower than the one in ten thousand to one in ten million (1 x 10-4 to 1 x 10-7) acceptable level of risk specified in the NCP (U.S. EPA, 1990). The HI for this scenario is far less than 1.0, indicating that no adverse health effects from noncarcinogens would occur following the planned remediation. Using health-conservative assumptions that EPA prescribes for assessing site risks, the risk of cancer after remediation, based on a potential monitor well drilled 250 feet west of LLNL, is 4 x 10-5, and 3 x 10-5 for potential receptor wells in downtown Livermore. Both of these values are within the EPA acceptable risk range. The hazard indices for both health-conservative scenarios are far less than 1 (2.7 x 10-2 and 3.1 x 10-2, respectively), indicating no adverse health affects from noncarinogens after the planned remediation.
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 East Taxi Strip in eastern LLNL will need unsaturated zone remediation (Isherwood et al., 1990). FHCs and/or VOCs will be removed from the subsurface by vacuum-induced venting using extraction wells.
The selected treatment option for the extracted vapors is catalytic oxidation. In this process, vapors from vent wells will be heated and passed through a catalyst, where organic compounds are converted to harmless oxidation products, including carbon dioxide and water. If use of catalytic oxidation should result 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.
The decision regarding whether an area requires vadose zone cleanup will be based on unsaturated zone modeling and ground water monitoring. If modeling indicates that hazardous materials will impact ground water in concentrations above an MCL, remediation will be implemented. Remediation will continue until in situ concentrations, as verified by soil sampling, are below those predicted to impact ground water above MCLs. In addition, the ground water near the potential source will be monitored for impacts on ground water quality. Details of the modeling and monitoring will be presented in the Remedial Design.
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Lawrence Livermore National
Laboratory 7000 East Avenue • Livermore, CA 94550 |
Operated by Lawrence Livermore National Security, LLC, for the Department of Energy's National Nuclear Security Administration | ||