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VA. 9 A S S O C I A T E S I N C water table elevation over the course of the investigations, the three screened intervals of the remaining vapor wells, VW-2d, VW-4, and VW-5d, are now below the water table and are unusable Three new ' shallow vapor wells are proposed to effectively remediate impacted soil and to capture off-gas from air sparging The number of wells was not based on a specific calculation but the radius of influence of each well needed to sufficiently cover the impacted area The wells will be constructed of 2-inch ' schedule 40 PVC and will be screened from approximately 15 to 30 feet bgs The VES will be operated under similar conditions as the VET to achieve a similar estimated radius of ' influence for each well A map showing the radius of influence is included on Figure 9 The VES will be operated using individual wells or sets of vapor wells in sequence, rather than operating all wells ' concurrently This approach should minimize the size and inherent operating costs of the vapor extraction equipment,while stilt allowing maximization of airflow from individual wells Based on the removal rates of petroleum hydrocarbons observed during the vapor extraction pilot tests (about one pound per day per one well), vapor phase granular activated carbon was selected as the method off-gas abatement The removal rate is expected to increase with the addition of the air ' sparging component Removal rates will be the greatest during the first several months of operating the system and will likely exceed the allowable emission limit without off-gas treatment The use of vapor phase granular activated carbon is a proven technology and will result in minimal down time of the system When extraction rates decrease to less than two pounds per day, elimination of the off-gas treatment will be proposed ' Subsurface piping will direct extracted vapor from the wells to a nearby remediation shed Components of the VES located in the remediation shed will include the following a vapor extraction blower that will extract vapor from the wells through the subgrade piping, a flow indicator that ' measures extracted airflow, a condensate separator to remove entrained droplets of moisture, two canisters connected in series containing vapor-phase granular activated carbon, associated piping, control valves, pressure gauges, flow meters, instrumentation and controls, and a contained remediation system to preclude public access Based on ATC's experience at similar sites and the results of the pilot tests, a Gast R6P155R 50 vacuum blower would be sufficient to operate the vapor extraction component of the system The vacuum blower would create a maximum vacuum of 85 ' inches of water and an airflow rate of 280 standard cubic feet per minute A process and instrumentation diagram for the VES is shown on Figure 10 a t5.2.2 Groundwater Air Sparging ' The proposed groundwater AS system will utilize three new air sparge wells and a compressor to address the hydrocarbon impacted groundwater The AS system will be operated under similar conditions as the pilot test although with the use of properly designed sparge wells, the pressure ' required to achieve similar air flows may be lower The AS system will be operated using individual wells in sequence with on-line vapor extraction wells to control migration of the groundwater plume The wells will be constructed of 2-inch schedule 40 PVC and will be screened from approximately 37 to 40 feet bgs A map showing the radius of influence is included on Figure 11 W 162574 Oi1CAP report doe 8