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Ms. Penny Fottrell GEOMATRIX Chevron Environmental Management Company February 11, 2003 Page 3 Caltrans's right-of-way. The borings will be advanced and using a sonic rig, and the soil and grab groundwater samples will be collected by continuous coring and discrete-depth sampling, respectively. SOIL BORING AND SAMPLING ACTIVITIES It is anticipated that each boring will be advanced to 90 feet bgs, the depth at which previous on-site borings were drilled to obtain soil samples without petroleum constituent detections. Geomatrix proposes to collect grab groundwater samples from each of the two borings, GMX-10 and GMX-11, at sample intervals between 36 and 40 feet bgs and 76 to 80 feet bgs, where petroleum constituent affected soil was identified on-site. Groundwater samples will be collected by advancing a hydropunch tool through the center of the sonic drill casing ahead of the drilling apparatus, exposing a four foot screen, then using a disposable bailer to collect a sample. The sample will be decanted into 1-liter amber bottles and 40 milliliter acidified volatile organic analysis vials provided by the laboratory. Samples will be labeled, stored in ice-filled coolers, and delivered to a state-certified analytical laboratory under Geomatrix chain-of-custody procedures. A soil sample will be collected for laboratory analyses from each boring from impacted soil within the vadose zone, if observed. If no petroleum-impacted soil is observed in the vadose zone, then a soil sample will be collected from directly above the water table. Another soil sample will be collected from the terminus of each boring for laboratory analyses to confirm the vertical extent of affected soil (i.e., the sample will be collected from a depth where field observations/measurements do not indicate the presence of petroleum constituents). Soil samples will be collected by pressing brass sleeves (labeled and sealed with Teflon sheets, end caps, and tape) into the continuous soil core, stored in ice-filled coolers, and delivered to a state-certified analytical laboratory under Geomatrix chain-of-custody procedures. Soil bor- ings will be logged using the Unified Soil Classification System (USCS) as presented in the American Society of Testing and Materials(ASTM) Standard D2488-90. Following sample collection, the borings will be backfilled with grout in accordance with the San Joaquin County requirements. ANALYTICAL METHODS Groundwater samples will be submitted for analysis of TPHg2 using Environmental Protection Agency(EPA) Method 8015 Modified, benzene, toluene, ethylbenzene, and xylenes (BTEX) using EPA Method 8021, polynuclear aromatic hydrocarbons (PAHs) using EPA Method 8270 SIM, and TPHd using EPA Method 8015 Modified. The laboratory will perform the Z The revised CTA recommends sampling for TPHg in groundwater only if site history indicates the presence of gasoline range hydrocarbons. The high concentration of TPHg relative to TPHd in the previously collected sample from MW-1 indicates that gasoline range hydrocarbons may be present.