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. -�' IN iodward•elyde Consuflstnts M ituent regardless of depth. As shown,liaoih TPH and BTEX constituents hydrocarbon const occur in soil gas concentrically around the area of the lremhved underground storage or ks tanks. This pattern suggests that contaminants moved directly downward and ponded either on the groundwater or on a shallow soil horizon. Relatively high TPH, toluene and xylene concentrations ohserved at sampling point ,P13a, and high tolutrnt3 and xylenes concentrations observed at sgmpling point P11, suggest that the plume is moving generally west. 2,2 Soil Boring WCC subcontracted Datura Exploration and Drilling Company to advance 380 lineal feet of soil borings and Install monitoring wells MW-5 thIrough MW-9 in the boreholes at the locations shown on Figure 7. A permit to drill thes11 e boreholes was obtained from the San Joaquin Local Health District, a copy of which Is included in Appendix B. The T borehole locations were selected after reviewing the results�of the soil gas investigation . h with the intent of identifying the downgradient edge oflconta6nationand the direction of I groundwater flow. WCC originally intended to advance 5 bo ehole5 to a depth of 60 feet alid a sixth borehole to a depth of 8o feet with the understanding that groundwater ... occurred at a depth of about 40 feet (see WCC 1987). At the time of WOO April 1994 field work, however, the groundwater level occurred almost 15 feet lower than expected. The drilling program was modified by OSA so that WCC installed 5 wells (MW-5, .6. - 7Fwas.g and, -9) and 1 soil boring (S-5) instead of the origi dal B wells. Soli boring S-5 advanced at the northwest Corner of the site adjacent to an open excavation of a waste ank that had been recently removed from the site. The total depth of the borehole 2b fee the maximum depth of ex l4raticn for iii mlonitoring wells was 70 feet. -- All boreholes were advanced using a truck mounted I ff CME I75 drill rig equipped with 8- inch O.D. hollow-stem augers. Soil samples were coltected at 5-foot intervals and logged according to the Unified Soil Classification System visual-Manual Procedure ASTM D2488-84 by a WCC geologist. Logs of the materials encountered while drilling are presented in Appendix C. Soils penetrated by drilling) consisted primarily of clay, clayey 'I 'f silt and silty clay, with lesser arnOUnts of silt, sandy shit, sand and clayey sand to depths of 52 to 55 feet. From 55 feet to total depth, the soils consisted generally of poorly �l graded fine grained sand. Groundwater was enoount Bred between 55 and 56 feet below grade. The subsurface distribution of the lithoiogtes encountered is shown on Cross Section A-A', in Figure 8. , 0 SEP 0 :8 1992 5 ENVIRONMENTAL--HEALTH PERMIT/SERVICES Glp S3D I O63S E,J I I,,IQH OT-:I SGl:i t h,/S L;'F,o