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2.3 Investigations Undertaken. + In accordance with the approved workplan dated March 19, 1999, a total of eight soil borings were advanced at the site. Two of the borings, SBI and SB2, were advanced to a depth of approximately 16 feet bgs in the area proposed for installation of new UST's to determine the suitability of the material for backfilling(it is anticipated that the material generated by installation of the new UST's will be used to backfill the excavation currently open as a result of UST removal). These borings were located west of the office building on the property(Figure 2): The remaining six soil borings, SB3 through SBS, were advanced to investigate the lateral and vertical extent of residual soil contamination, as well as the potentialimpact to groundwater. Borings SB3 through SB8 were located around the perimeter of the UST excavation and in the area of the former lines and dispensers(Figure 2). I 3.0 ]NVESTIGATIVE PROCEDURES On April 19, 1999, Sean Garvey of Ground Zero arrived at the site to supervise the subsurface investigation in the vicinity of the former UST's. Mr. Michael Infurna of San Joaquin County Public Health Services, Environmental Health Division conducted the site °inspection and- observed field activities. _ Fisch advanced the borings under the supervision of field geologist Sean Garvey, and project manager Greg Stahl, a California Registered Geologist. Fisch utilized a truck mounted Geoprobe 5400 direct push rig to advance the borings and collect soil samples. Soil samples were collected at 5-foot intervals using a 1-inch diameter by 24-inch long core sampler. The sampler was lined with clear acetate sleeves, affording soil identification and subjective evaluation for contamination. 'A flame ionization detector (FID) was used to } monitor the presence of volatile organic compounds in the soil. Soil samples from the borings were sealed, labeled, and immediately placed in an iced cooler for transport to Argon, a state- certified analytical laboratory. Soil samples were selected based on observations and field screening results. "Grab" groundwater samples were also collected from boring SB3 and SB4. The samples were collected by driving the core sampler to the desired depth and exposing the screen to the bed within the formation. A 0.17 diameter PTFE tube equipped with a stainless steel check valve was then inserted into the rods to the bottom of the sampler. Water was extracted -from the boring by creating a positive displacement effect within the tubing, forcing the water sample towards the surface where it was collected directly into sample containers. Borings SB l and SB2 were advanced to depths of 16 feet. Boring SB3 was advanced to a depth of approximately 3 LS feet bgs where refusal was encountered: SB4 was advanced to a depth of 31 I feet. Due to the lack of drilling rods, as well as time constraints, it was decided to abandon tliis boring and twin it the next day. Boring SB4A was advanced approximately 1 foot west of SB4 to continue the investigation. Samples collected from.this boring ranged from 34 to 51 feet bgs: Borings SB5-SB8 were advanced to depths of approximately 16 feet below ground surface(bgs)to investigate the lateral extent of contamination: Waalscychonar+npdrellsummwy.aoc 3 I