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GEOMATRIX Mr. Robert Mihalovich Chevron Environmental Management Company April 3, 2002 Page 5 A fifth soil boring (SB-13) will be advanced downgradient of petroleum affected soil to approxi- mately 10 feet below the water table (estimated depth of 35 to 40 feet bgs) and a soil sample will be collected from the most visually affected soil within the soil column and the terminus of the boring. If visually affected soil is not observed in the soil column, a soil sample will be collected from the capillary fringe and the boring terminus instead. The soil samples will be analyzed for TPHc, BTEX, and PAHs. In addition, a grab groundwater sample will be collected to evaluate the downgradient extent of organic compounds quantified as TPHd in groundwater. The grab groundwater sample will be analyzed for TPHg, BTEX, and PAHs. Groundwater in wells MW-1 through MW-4 will be monitored and sampled to evaluate the con- sistency of groundwater quality data. It is anticipated that MW-1 will contain separate phase petroleum; therefore, if evidence of separate phase petroleum is present a groundwater sample will not be collected and product thickness will be measured, if possible. Field Procedures and Laboratory Methods Prior to drilling, Underground Service Alert(USA) will be notified, the soil boring locations will be cleared by a private underground utility locator, and appropriate permits will be obtained from the San Joaquin County Public Health Services Environmental Health Division (SJC-EHD). The borings will be advanced using a hollow stem auger(HSA) drill rig and soil samples collected using a drive sampler. A nearly continuous core of the soil will be collected, examined, and logged at each location. Soil samples will be collected in brass sleeves sealed with Teflon sheets, end caps, and teflon tape. Samples will be labeled and stored in ice-filled coolers and delivered to a state-certified analytical laboratory under Geomatrix chain-of-custody procedures. The grab groundwater sample will be collected from boring SB-13 through temporary PVC casing place through the HSAs within the borehole. Prior to collection, the HSAs will be raised to above the capillary fringe as to expose the screened section of the casing to the native materials. Fol- lowing soil and grab groundwater sampling activities, the borings will be backfilled with grout according to SJC-EHD standards. Prior to groundwater well sampling activities, groundwater elevations and/or the presence of sepa- rate phase petroleum will be measure to the 0.01 of a foot using a electronic sounder or interface probe and wells will be purged until groundwater quality parameters (e.g.,pH, temperature and specific conductance)have stabilized. Groundwater samples will be collected using a disposable bailer and will be decanted into 1-liter amber bottles and 40 milliliter(ml) acidified volatile or- ganic analysis (VOA) vials provided by the laboratory. Samples will be labeled and stored in ice-filled coolers and delivered to a state-certified analytical laboratory under Geomatrix chain-of- custody procedures. The soil samples will be analyzed using the following methods: TPHc (CK to C36 carbon range) using EPA Method 8015 Modified, BTEX using EPA Method 8021, and PAHs using EPA Method 8270 SIM. Groundwater samples will be analyzed using the following methods: TPHg using EPA Method 8015 Modified, BTEX using EPA Method 8021, PAHs using EPA Method 8270 SIM, and TPHd using EPA Method 8015 Modified. The laboratory will perform the TPHd