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' 18' southeast of previously sampled boring S-27. S-30 will be sampled at depths of 15', 20' and 25' bgs and analyzed for TPH-d and TPH O&G. The second boring S-31 is ' planned for 20' southeast of previously sampled S-26. S-31 will be sampled at: 15', 20', 25', 30', 35', 40' and every five feet until in a fine grained material is encountered or a depth of approximately 50'. An additional boring will be drilled adjacent to a storm drain ' outfall east and downslope of SWMU #21. In the boring next to the outfall, soil samples will be collected at depths of 1',3',5' and 10' bgs And analyzed for TPH-d and TPH O&G. ' At various sample depths, from all borings, total petroleum hydrocarbon will be characterized using the Dexsil PetroFlag® field testing kit (or equivalent). These field ' tests along with visual observations and soil logs will be used as additional information in the subsurface characterization. Logs of soil penetrated by the boring will be compiled from samples collected from the borings using the Unified Soil Classification System. Soil cuttings and equipment decontamination liquids that are generated during the drilling of the boring will be properly containerized pending disposal of the material by the client. The locations of the proposed borings are presented on the site map in Appendix A. A description of the methodology for the installation of the borings, collection of soil samples, and equipment decontamination are presented in Appendix B. ' 3.4 Groundwater Impact of TPH-d and TPH-O&G ' A monitoring well (MW) is proposed for construction next to boring BH-4 to an estimated depth of 85' after the boring, if possible, penetrates 5-ft below the top of the water- bearing zone. Two-inch diameter Schedule 40 polyvinyl chloride (PVC) plastic, with ' sufficient screen (0.010-inch slot) to span the groundwater-bearing zone will be installed in the boring. A filter pack (sand) will be installed from the total depth of the boring to 2- ft above the top of the well screen. Two feet of hydrated bentonite pellets will be ' installed above the filter pack. The installation of the MW will be in accord with applicable regulatory requirements, i.e. permits, inspections, etc. After completing construction of the MW, if possible, five (5) casing volumes of groundwater will be extracted (purged) from the MW prior to the collection of groundwater samples for analysis to maximize the possibility of collecting a water sample representative of the formation water. Should recharge of the well be slow, groundwater samples will be collected after sufficient groundwater accumulates in the well casing to provide the requisite volume for the requisite analysis. Groundwater ' samples will be collected using a new clean Teflon® bailer and transferred to the appropriate sample container and transported to a laboratory certified by the DTSC for analyzed for TPHd and O&G. The soil cuttings and equipment decontamination liquids generated during the drilling of the boring will be properly contained pending disposal of these materials by the client. CE Project No.99R-4041 Additional Investigation Work Plan 4