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i Mr. Harlin Knoll October 19, 1999 Page 2 of 6 i F All investigative work was performed under the supervision of Mr. John Lane, CA Registered Geologist 6795,and Mr.Greg Stahl,CA RG 5023,CA Certified Hydrogeologist 264. 2.0 BACKGROUND INFORMATION 21 Initial Investigation and UST Removal The site formerly operated as a convenience store and retail gasoline station. A limited subsurface assessment was conducted by Ground Zero in Decemb r 1996. Results of the assessment provided evidence that petroleum hydrocarbon impact to the soil and groundwater had occurred. Soil boring locations are shown on Figure 2. Analytical results are summarized in Table 1. One 10,000-gallon UST for storage of diesel fuel and two 10,000 gallon USTs for the storage of gasoline and associated piping were removed under permit from PHS/EHD on January 21, 1999. Analytical results of sidewall soil samples and groundwater grab sample collected from beneath the USTs indicated that elevated levels of petroleum hydrocarbons were p�esent in the soil and groundwater. Sample locations are shown on Figure 2. Analytical results are summarized in Table 2. 2.2 Investigations Undertaken In accordance with the approved workplan dated June 29, 1999,five direct push soil borings were advanced along the perimeter of the former UST location to investigate the vertical and lateral extent of soil and groundwater contamination, and four hand augered soil borings were advanced to investigate the lateral extent of shallow soil contamination. Soil boring locations Ie shown on Figure 2. 3.0 INVESTIGATIVE PROCEDURES On-site activities were conducted on July 28 and July 30, 1999. Sean Garvey of Ground Zero supervised the drilling of borings SBI through SB5 with a Geoprobe 400 direct push drilling rig operated by Fisch.!M Mr. Harlan Knoll of San Joaquin County Public PHS/El-1D conducted site inspections on July 28 and' July 30, 1999 to observe drilling activities. Borings SB2 and SB4 were advanced to a depth of g p appro � ly i6 feet below the ground surface (bgs) ins accordance with the workplan. Boring SB 1 was advanced o a depth of approximately 12 feet (bgs) before. rod refusal was encountered. Borings SB3/3A and SB5 were advanced to depths of approximately 25 feet bgs and 20 feet bgs, respectively, at the request of Mr. Knoll. No boring was placed in the center of they former excavation pit because the excavation has not yet leen backfilled. However, boring SB3/3A was: placed as close as possible to the eastern boundary of the excavation. SB3 was advanced to a depth of 18;1 feet where refusal was encountered. Boring SB3A was adv ced approximately 1 '/Z feet south of SB3 as a; twinned boring to determine the vertical extent of soil contamination in the vicinity of the former USTs. ` Samples were collected from boring SB3A at depths of approximately 20 and 25 feet bgs. Soil samples were collected from borings SBI through SB5 at 5-foot intervals using a 1.5-inch diameter by;, 24-inch long core sampler. The sampler was lined with clear acetate sleeves, affording soil identification'f and subjective evaluation for evidence of contamination. �k flame ionization detector (FID) was used to monitor the presence of volatile organic compounds in the 61. Two soil samples each from borings SB 1,;:I nmserZsummary.doc i ;r