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Ms. Penny Fottrell GEOMATRIX Chevron Environmental Management Company September 12, 2002 Page 4 I y' Borings will be advanced using a hollow stem auger rig. Borings M113-1 and M113-2 will be advanced to the bottom of visually affected soil to assess the vertical extent of petroleum hydro- carbons in the vicinity of borings GP 96 and GP 120,respectively. The remaining borings (MH3-3 through MH3-7)will be advanced to depths up to 30 feet bgs to assess the lateral extent of affected soil and groundwater quality. Additional step-out borings may be advanced if petroleum-stained soil is observed in borings M113-3 through - . Typica y, step-out borings will be—s—pa-c—eT_ approximately 50 to 100 feet from borings that contain visually-affected soil. A continuous core of n� the soil will be collected and examined from each location and the lithology will be logged by a Geomatrix field geologist. In addition, organic vapor meter(OVM)readings will be taken an recorded at various depths. Soil samples will be collected in butyrate sleeves or brass tubes sealed with Teflon sheets, end caps, and tape. Sample depths will be as follows: • To assess potential risk posed by petroleum hydrocarbons, soil samples will be collected from 2 feet bgs and from the most affected soil shallower than 10 feet bgs at all boring locations. If no affected soil is observed above 10 feet bgs, soils samples will be collected �_. from depths of 2 and 6 feet bgs. • In boring M113-1 and MH3-2 a soil sample also will be collected from a depth immedi- ately beneath observed staining to confirm the vertical extent of affected soil. To assess lateral extent soil samples will be collected in borings MH3-3 through M113-7 from the most visibly affected portion of the soil core, regardless of depth. If no petro- leum hydrocarbon affected soil is observed a soil sample will be collected from the inter- val in which petroleum hydrocarbon affected soil was encountered in the closest previous 1, onngs. z. Grab groundwater samples will be collected from borings M113-1 (anticipated to be within affected soil)and from upgradient and downgradient borings where stained soil is not observed. To minimize the amount of affected sediment entrained in the sample from MH3-1, a pre-packed well will be placed in the borehole and the sample will be collected using a pump set at a low flow rate. For the remaining grab groundwater samples, a temporary slotted polyvinyl chloride (PVC) ' well casing will be placed in the borehole and grab groundwater samples will be collected using a disposable bailer. After collection of the samples, the PVC casing will be removed and the bore- holes will be grouted to ground surface. Soil and groundwater samples will be labeled and stored in an ice-cooled chest until transfer to a California-certified laboratory under Geomatrix chain-of-custody procedures. All borings will be grouted to ground surface upon completion. Soil samples will be analyzed for total petroleum hydrocarbons (TPH)quantified as crude oil (TPHc) using EPA Method 8015M; BTEX using EPA Method 8021; and PAHs using EPA Method 8270 with a selective ion monitoring system (SIMS). Grab groundwater samples will be analyzed for TPHg and TPHd using EPA Method 8015M;BTEX using EPA Method 8021; and