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within the trench These samples will be analyzed for concentrations of dissolved oxygen and other electron acceptors In addition, periodic vapor samples will be collected from the vapor extraction piping during the one-two month air sparging test and will be analyzed for concentrations of TPH-G, BTEX and CO2 A five-day vapor extraction pilot test, using the horizontal piping as the extraction point, will then be conducted at the end of the one-two months of air sparging The use of an air sparging/vapor extraction system assumes that the groundwater velocity at the site will be sufficient for the treatment system to impact the contaminant plume beyond the immediate environment of the trench If the pump test and direct experience from the excavation of the trench show high rates of groundwater transport, the air sparging/vapor extraction trench may be useful in treating submerged soil and groundwater contaminants from a larger area of the site If the groundwater velocities are lower than expected, it may be possible to pump groundwater from the trench and expose more vadose zone to vapor extraction within the evacuated trench TASK I: INSTALLATION OF DOWNGRADIENT GROUNDWATER MONITORING WELLS AND GROUNDWATER RECOVERY WELL. LATERAL EXTENT OF GROUNDWATER CONTAMINATION Monitor well MW1 is located hydraulically downgradient (northwest) from the source of the contamination at the site, see Figure 3 The groundwater samples from this well have consistently shown significant concentrations of TPH-G and BTEX constituents Additional monitoring wells, located downgradient from MWI and MW3, are necessary to further delineate the lateral extent of the groundwater contamination plume in the hydraulically downgradient direction from its source The groundwater flow direction at the site during the most recent quarterly monitoring round was to the west This is consistent with previous quarterly monitoring rounds, which show the groundwater flow direction at the site ranging from west to northwest On October 25, 1995 seven Strata probe test holes were drilled to the west and north of the site in order to establish the lateral limits of the soil and groundwater contamination Groundwater samples from 20-22 feet bgs in Strataprobe test holes P2 and P3, located on the southern edge of Country Club Blvd West of Mission Road both showed concentrations of TPH-G and BTEX constituents with a maximum of 326 ug/l TPH-G at P3 Groundwater samples from test holes P4, P5, P6, and P7, located northwest of the site on the north edge of Country Club Blvd did not show TPH-G or BTEX concentrations above the laboratory detection limits (see Figure 4) 3