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%TC I.► ASS O C I ATE S I N C . �.. Laboratory analysis of a soil sample collected from beneath the former diesel UST locations indicated the presence of detectable concentrations total petroleum hydrocarbons as diesel (TPHd) at a concentration of 6,150 parts per million(ppm). Of the seventeen soil samples collected from the pipeline trench, only one sample, located near r the fill end, contained TPHd above the laboratory reporting limits at a concentration of 1,550 `- ppm. Because the original backfill material removed from the trench contained TPHd at concentrations less than the 100-ppm threshold for acceptable backfill material, the soil removed from the pipeline trench was used to backfill the trench. Gasoline Tanks In January 1997, two gasoline USTs were removed from the northwest portion of the property and soil samples were subsequently collected from the open excavation (see Figure 2). Only one �. sample was reported to have contained TPH as gasoline (TPHg) above laboratory detection limits. Composite samples of the stockpiled excavated soil were collected and analyzed for TPHg, benzene, toluene, ethylbenzene, xylenes (BTEX), and methyl tert-butyl ether (MTBE). Because laboratory results did not detect any of the analytes above the laboratory detection limit, the stockpiled soil along with clean pea gravel and Class A/B subbase was used to backfill the F excavation. Helmick and Lerner Inc. subsequently submitted a work plan titled Work Plan for Soil Investigation, Transportation Center/Corporation Yard- Stockton Unified School District dated February 6, 1998. The work plan purposed methods and procedures to evaluate the vertical extent to which petroleum hydrocarbons have migrated into native soil. This work plan was approved by PHS/EHD, in correspondence dated March 25, 1998. Figures showing the location of soil samples collected and tabulated laboratory analytical data, as presented in Helmick and Lerner's work plan, are presented as Appendix A in this report. 2.0 METHODS AND PROCEDURES 4. To evaluate the presence of petroleum hydrocarbons in soil, a total of nine soil borings were advanced at the site. Of these soil borings, two were placed at the end of the remote fill trench, 4 three were in the vicinity of the former diesel USTs, and four were in the vicinity of the former �- gasoline USTs. All field activities were performed in accordance with Helmick and Lerner's Work Plan for Soil investigation, Transportation Center/Corporation Yard - Stockton Unified School District dated February 6, 1998 and ATC's Site Safety Plan and Quality Assurance/Quality Control Plan (QA/QC Plan) submitted to PHS/EHD on February 1, 1999. w:1172921rcportslsumwe1.doc 2 �.r