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Work Plan for Additional Subsurface Assessment and Feasibility Study—Former Unocal Station#0187 September 14,2000 RECOMMENDATION GR recommends that ozone microsparging be initiated on the site on a pilot test basis More traditional remediation technologies which were investigated have significant limitations when applied to this site Based on the distribution of hydrocarbons at the subject site, four infection points each would be required in the intermediate zone and four in the deep zone Three of the points would be installed near the eastern property boundary The fourth would be installed further west, near the former UST location If initial results indicate that the technology is feasible, use of the technology for off-site contamination will be evaluated In addition, as requested by SJCPHS,a VET will also be performed Currently, unsaturated soil impact is limited to the former UST pit located in the southeast corner of the site Unsaturated soil is impacted beneath and adjacent(southwest and west)to the UST pit from approximately 13 feet bgs to groundwater at approximately 24 feet bgs Vapor-extraction well U-P/UV-1 installed within the former UST pit is screened from approximately 15 to 45 feet bgs Two additional vapor-extraction wells will be installed southwest and southeast of the former UST pit(Figure 2) PILOT TEST SYSTEMS Task 1. Sparge Point and Vapor-Extraction Well Installation The sparge point and vapor-extraction well installation will be completed in conjunction with the monitoring well installation Eight KVA sparge points and two vapor-extraction wells will be installed Locations are shown on Figure 2 Drilling and sparge point/well installation will be performed by a California licensed driller The sparge points will be installed in four borings with two points per boring Each sparge boring will be drilled to a depth of approximately 115 to 120 feet The first sparge point will be installed at the bottom of the boring, or at the bottom of the sand horizon The second point will be installed at or near the bottom of the sand horizon in the intermediate zone in the same boring Sparge borings will be logged at a minimum of every 10 feet Because these sparge bonngs are being drilled for a remediation system,no soil or grab groundwater samples will be collected from these well borings for chemical analysis The sparge point's construction includes a check valve to prevent groundwater from entering the well casing, and therefore prevents the collection of groundwater samples frbm the wells Sparge point construction details are presented on Figure 6 Each vapor-extraction boring will be drilled to approximately 25 feet bgs A GR geologist will monitor the drilling activities and prepare a log of the each boring Soil samples collected at 5 feet intervals, and samples collected at 15, 20 and 25 feet bgs will be submitted for chemical analysis The samples will be analyzed for TPHg/BTEX/MtBE by EPA Method 8015/8020 modified The vapor extraction wells will be constructed with 4-inch diameter Schedule 40 polyvinyl chloride (PVC) well casing and 0 02-inch machine slotted well screen The wells will be screened from approximately 15 to 25 feet bgs Proposed well construction details are presented on Figure 7 • 240042 08 9