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t The report did not include a calculation for estimated risk due to the escape of $oil and/or <br /> groundwater vapor during excavations. 'Ibis risk is minimal due to the low concentrations of VOCs <br /> remaining. The total risk is within the U.S. EPA recommended risk management levels for Site <br /> cleanup despite the maximum reasonable exposure scenario considered. <br /> 19. The remaining risk{s} can be managed by implementing deed restrictions, a long-term monitoring <br /> program, and a contingency plan if monitoring indicates that additional remediation is necessary <br /> i <br /> MASS BALANCE CALCULATIONS <br /> 20. Varian made VOC mass balance calculations and determined that about 0 01 gallons of TCA remain <br /> in the aquifer, and estimated that this mass of VOCs will be attenuated onsite through dispersion, <br /> sorption onto soil, and natural degradation before dissolved VOCs greater than the appropriate <br /> MCLS would reach the Site's downgradient property boundary. <br /> I <br /> 21. A regular monitoring program is needed to determine if off-site VOC migration will occur <br /> FINAL REMEDIATION PLAN <br /> i <br /> 22. Varian submitted a Remedial Investigation/Feasibility Study in 1993 providing a summary of costs <br /> associated with four groundwater remediation alternatives- <br /> a. Alternative No. 1: No Action <br /> This alternative consists of leaving the site "as is" and performing no additional <br /> ( remedial actions Interim remedial measures would be terminated and the <br /> existing groundwater extraction and treatment systems would be removed <br /> Remedial action objectives would be achieved through natural processes such as <br /> biodegradation, volatilization, adsorption, and dilution The period of time to <br /> achieve VOC reduction would be more than 10 years, based on observed trends. <br /> Total present worth is estimated at $295,000. <br /> b Alternative No 2- Institutional Controls <br /> Institutional controls would reduce the possibility of exposure to groundwater <br /> contaminated VOCs through the following actions <br /> I continue use of city supplied water <br /> ii establish deed restrictions preventing the installation of groundwater <br /> water-supply wells or use of shallow aquifer groundwater <br /> iii establish building permit or land-use restrictions <br /> Remedial action objectives would be achieved through natural processes such as <br /> biode.gregation, volatilization, adsorption, and dilution The period of time to <br /> achieve VOC reduction would be more than 10 years, based on observed trends <br /> Total present worth is estimated at $315,000 <br /> 4 <br />