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rl � ZP �� Quarterly Momlormg Report,Site Code 1243 • Stockton Regional Wastewater Treatment Fac3hty 2500 W Navy Drive,Stockton,CA August 6, 1992 Page 4 ADDITIONAL SUBSURFACE SOIL CHARACTERIZATION Soil Boring Installation In accordance with a written request by PHS/EHD, on May 28, 1992, RESNA advanced three hand augered borings on June 24 and 24, 1992,in the vicinity of soil boring SBI to further characterize subsurface soil conditions at the site The borings were advanced to depths of approximately 9 feet below grade Two soil borings were placed near SB1 and one near the former tank (Figure 2), where soils were previously found to contain residual diesel hydrocarbons Soil Sampling Soil samples were collected from each boring at approximately 5 and 8 5 to 9 0 feet below grade utilizing a drive sampler with a six-inch brass sleeve insert Groundwater exists at approximately 9 5 to 11 feet below grade Samples were field screened (odor, discoloration) for the presence of diesel hydrocarbon contamination Collected samples were sealed at each end with teflon sheets and taped end caps, and placed on ice in preparation for transport to RESNA Environmental Laboratories located in Fremont, California The deepest soil sample from each boring (capillary fringe) was submitted to the laboratory and analyzed for BTEX and TPHD using EPA methods 8020 and modified 8015, respectively Results are summarized in Table 3 Chain-of-custody documentation and laboratory reports are included as Attachment 3 Soil Characterization Summary Soils encountered beneath the site consisted predominately of silts (ML) and clays (CL) No hydrocarbon impacted soils were obvious during field activities Groundwater was not encountered in the hand-augered borings Benzene was not detected in any soil samples collected at the site, and toluene, ethylbenzene, and xylene were detected at levels below the respective State Maximum Contaminant Levels (MCLs) TPHD was detected only in boring SB4 (near the former tank) at 1 9 ppm Based upon these results, residual hydrocarbons in soils beneath the site exist at very low levels and are limited to a very small area within the capillary fringe Based upon the limited areal extent, the level of impaction, and the absence of contaminants in groundwater, residual hydrocarbons in the soil do not appear to pose a threat to public health or the waters of the state LR080392]PL