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i • Remedial Action Plan and Further Site Assessment 4 7-Eleven Store No 19975, 1399 N Main St,Manteca CA May 30 2000 30 INTERIM REMEDIATION AND GENERAL CLEANUP GOALS j Proposed remediation goats are to remove and/or biodegrade hydrocarbons and particularly MTBE,within the plume area to within levels acceptable for site closure by all applicable regulatory agencies The best available most cost-effective technology will be used to reduce hydrocarbons to minimum achievable levels Groundwater extraction will be employed as an interim remediation method and plume control ' mechanism, to prevent further downgradient migration Additional remediation methods are tentatively proposed in this document from a cost-effectiveness and feasibility screening perspective Further evaluation may indicate augmentation of groundwater extraction with one or more of the remediation ' measures discussed is advisable Addendums to this remedial action plan will consist of letters with supporting documentation as to the selection and evaluation of remedial system modifications After extraction, the groundwater will need to be treated to meet NPDES requirements for discharge to the storm drain Regulated substances include BTEX Discharge of MTBE to the storm drain is newly- regulated by NPDES, with a discharge limit of no more than the State maximum contaminant limit (currently 13 ug/L) Different Regional Water Quality Control Boards or local agencies may have other requirements Permitting requirements for groundwater discharge will be established through the SJCPHS or other agency as appropriate prior to initiation of interim remediation To reduce concentrations of MTBE in the extracted groundwater, air stripping or some other form of volatilization might be used to transfer hydrocarbon mass from the liquid phase to the vapor phase, where it could be more cost-effectively remediated Groundwater exiting the mass-transfer process can be discharged directly or may need additional carbon treatment, depending on the initial concentrations and ' the treatment system efficiency Vapors exiting the mass-transfer process also need to be treated prior to discharge by either vapor-phase carbon or one of the incineration processes (either catalytic oxidation or ' thermal oxidation) Groundwater recovered during extraction can also be treated by an above-ground bioreactor (in addition to or as a substitute for carbon adsorption) Bioremediation of extracted groundwater in an above-ground ' self-contained unit can reduce dissolved hydrocarbon concentrations by 95 - 99 percent, depending on the unit used The success of bioreactors to treat MTBE is still not well-documented