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w � � ti.. Fire Station No. 12 TL A68105.01 March 10, 1995 Page 4 screening of soils for petroleum hydrocarbons. It is anticipated that the borehole will extend a minimum of 10 feet below field detectable petroleum hydrocarbons or a maximum vertical depth of 45 feet BSG. The depth of the remaining three soil borings will be based on data generated from the initial soil boring. The remaining three soil borings will be located to the north, south, and east to assess the lateral boundaries of PPC-containing soils (Drawing 2). If PPCs are detected in soil samples through the field screening process, then additional soil borings would be necessary to fully assess the lateral extent of PPC migration. Additional soil borings would be proposed approximately 20 feet beyond the nearest soil boring containing PPCs detected through field screening. Actual soil boring locations will �— be determined based on field data. Soil samples will be collected at five-foot intervals beginning at five feet BSG. A Twining geologist will log the soils in accordance with the Unified Soil Classification System and will screen the samples for evidence of contaminants. The screening will consist of visual observation for staining or unusual fluids, unusual odors, and head space analysis with a photoionization detector (PID) for the presence of organic vapors. PID operation and procedures for the performance of head space analysis are described in our SOPs presented in Appendix A. Each soil boring will be backfilled with bentonite neat cement. Drill cuttings will be stored on and covered by plastic. Soil samples from each boring and the resulting soil stockpile will be preserved and retained for laboratory analysis. Soil disposal will be the responsibility of the client. Drilling activities will be supervised by a Twining geologist. The Twining geologist will be working under the direct supervision of a California registered geologist. 4.2 Analytical Procedures Soil samples collected during this investigation will be submitted to Twining's California certified (Certificate No. 1371) analytical laboratory in Fresno,California. Selected samples will be analyzed for TPH-D, TPH-G, and BTEX. Proposed preparation and analytical methods for the laboratory analyses are summarized in Table 1. A description of laboratory �6w quality assurance/quality control procedures proposed for the analyses are described in the SOPs presented in Appendix A. .y