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V11. CLOSURE PLAN A. SYSTEM SHUTDOWN DETERMINATION As discussed in previous sections, data from the long-term monitoring of the system will be routinely evaluated When the groundwater concentrations are trending below the applicable MCLS, the measurements will be monitored closely If measurements remain stable for three consecutive months, the system will be shutdown The SJVAPCD and CA DoH will be notified promptly of the action Standard groundwater monitoring events will continue monthly after the system shutdown The system will be restarted if dissolved-phase hydrocarbon concentrations rebound in any wells during the next three consecutive events However, if concentrations continue to remain below risk- based levels during these events, quarterly monitoring will be conducted for three additional quarters to statistically verify stability prior to submittal for a closure request The operating parameters and performance of the SVE system will be considered separately in the determination of system shutdown The SVE performance parameters will primarily involve hydrocarbon concentrations being recovered from the wells These concentrations will primarily affect the switching or removal of vapor abatement equipment and will not be the sole determining • factor for the continuation of SVE operations SVE operations will continue beyond the point of elevated hydrocarbon vapor concentrations in order to enhance AS operations (i e hydrocarbons volatilized by the AS System) B. CONFIRMATION SAMPLING Following the system shutdown and documented stability of groundwater concentrations, confirmation soil samples will be collected to determine compliance with target PRGs Data obtained will be used for evaluation for closure under the Plan B nsk assessment criteria established in accordance with the EPA Region 9 PRG standards Soil Sampling When the aforementioned cntena are reached, a work plan detailing a soil sampling plan will be submitted Soil borings will be advanced with a standard drilling ng equipped with solid-flight augers The boring will be advance to a depth of 60 feet bgs Soil cores for the drilling ng will be taken continuously at 4-foot intervals to the termination depth An organic vapor meter (OVM) calibrated to an appropriate standard will be utilized to screen the soil samples at the ground surface Collection, handling, storage and transportation of the soil samples will be in accordance with CDH • guidelines A work plan for confirmation sampling will be submitted upon shut down of the remediation equipment The selected soil samples will be analyzed for concentrations of BTEX, TPH, and the various gasoline oxygenates VII-1