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1'f•LME IROGEOLOGICAMSE SSMEN: 1410 Lower Sacramento Road,Stockton,California Delta Project V V} 147 Paso 6 Soo, 3,0 RESULTS 3.1 Site WIN and Geoloy A total of six soil borings were drilled durlrg Aoqust 1989 in order to characterize the subsurface geology and to evaluate the presence of petroleun. .�,%rttltuents In soils beneath the site. f in order to evaluate the extent of petroleum constituents detected during tank removal in December 1986, soli and monitoring well borings were advanced in the vicinity of soil sampling locations where TPH had _ previously been detected. Soil boring SB-1 w4s advanced near pump island sampling location T-3. Soil boring SB-2 was located near pump island sample T-1. Soil boring SB-3 was advanced through the former tank excavation backfill, in the vicinity of tank samples T-5 and T-7. Monitoring well borings MW--1, MW-2, and N.W 3 were located around the perimeter of the former tank excavation, to the southwest, M northeast,and northwest,respectively. Locations of the soil borings and monitoring wells arc shown In Figura 7- Soil borings SB-1,SB-2,and SB-3 were advanced to depths mrtging from 41S to 565 fact below ground surface. The monitoring well borings were advanced to 68 feet below grade. The borings were advanced using 9-Inch-diameter hollow-stem augers for soil borings,and 10-inch-diameter hollow-stem augers for monitoring well borings. Monitoring wells MW-1,MW-2,and MW-3 were drilled and installed on August 11 and 13, I.M. Feld soil boring Iogs are presented in Appendix A. Two cross-sections were generated to illustrate the subsurface geology. Figure 3 shows the surface trace of gross-sections A-A' and B-B' which are presented in Figures 4 and 5. Silty clays to clayey sats 1 pi'edomiaate beneath the sit& A 173-foot-thick silty sand layer was encountered from 13.5 to 30 feet y.. below grade in soil boring SB-1 (Figure 4). A silty sand layer of equivalent thickness was encountered i.� from 33 to 51 feet below grade in soil boring SB-3(Figure 4 Minor layers of sandy silt,silty sand,and � sand are Interbedded with the silty clay and clayey silt layers beneath the site. pay,silty clay,and clayey silt surround the backfill of the former tank excavation. t j qw Sora samp=ns were collected at 5-foot depth intervals and scr6ened with a portable photoionization detector t (PID) for total organic vapors. Samples selected (based on PID readings) for chemical analysis were ' submitted to a California-certified laboratory for analysis of TPH,BTEX,and total kad. The results of t these analyses sus presented in Table 4. The certified laboratory reports for soil boring samples are presented In Appendix B. «i r s t.,