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Work Plan for Additional Subsurface Assessment and Feasibility Study—Former Unocal Station#0187 September 14,2000 Task 5. Laboratory Analyses Selected soil and groundwater samples will be submitted for chemical analysis at Sequoia Analytical, a California state-certified Hazardous Material Testing Laboratory (FLAP #1210, #1271, and #1624) Soil and groundwater samples will be analyzed for TPHg by EPA Method 8015 (modified), and benzene, toluene, ethylbenzene and xylenes (BTEX) and MtBE by EPA Method 8020 In addition, the groundwater samples will also be analyzed for the five oxygenate compounds by EPA Method 8260 Task 6. Report Preparation Following receipt and analysis of all data, a report will be prepared which summarizes the procedures and findings associated with this investigation This report will be submitted to Unocal for its use and distribution FEASIBILITY STUDY Based on data collected to date,three hydrocarbon-impacted zones have been identified in the subsurface A shallow zone extends from the current top of groundwater at approximately 24 feet bgs to approximately 50 feet bgs An intermediate zone corresponds to a sand horizon at approximately 65 to 75 feet bgs A deep zone corresponds to a sand horizon starting at approximately 112 feet bgs and extending beyond 121 feet bgs (total depth explored) The highest concentrations of petroleum hydrocarbons detected in the soil are in the shallow zone The highest concentrations detected in the groundwater are in the intermediate zone Since monitoring of the site began in 1994 the groundwater level has risen by more than 20 feet Petroleum impacted soils that were previously above the groundwater are now submerged Based on the assessment work completed to date, petroleum hydrocarbons in soil and groundwater have been delineated in the shallow zone, but not in the intermediate and deep zones At present, questions also exist as to whether petroleum hydrocarbons detected in the deep zone are an accurate measure of the conditions in that zone, or if the hydrocarbons detected at that depth migrated along preferential pathways created by the well borings Site assessment work is continuing on the site GR has evaluated the available information and reviewed various remedial options that are available for the subject site The following is a brief description and comparison of those options reviewed OPTION#1 -NO REMEDIAL ACTIONILONG TERM MONITORING Over time petroleum compounds have been found to degrade through natural processes Under this option petroleum levels in the groundwater would continue to be monitored but no active remediation steps would be taken COST Low TIME FRAME Long term i 240042 08 6