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. Subsurface Investigation Report - - - CHP Facility, 385 West Grantline Road, Tracy April 20 1999 constitute the major aquifer of the Central Valley and yield large quantities of water to wells Lithologically, these deposits are heterogeneous mixtures of poorly sorted clay, silt, sand, and gravel, and in places some beds of claystone, siltstone, sandstone, and conglomerate The maximum duckness reported for these formations is 3,000 feet (USGS 1986) Continental deposits of Quaternary age outcrop primarily along the major rivers and streams of the valley, as well as along other low-lying areas, the deposits include river and flood-basin deposits, and sand dunes River deposits, including channel and flood-plam deposits, are considered to be the most permeable deposits in the valley, however, they are generally not tapped by wells Flood- basin deposits consist largely of fine-grained beds that restrict the vertical movement of water Saturated soils are generally encountered at depths between 10 and 11 fbg (USGS 1986) 3.0 SITE ASSESSMENT ACTIVITIES On March 25, 1999, four borings(SB-1 through SB-4) were advanced onsite to approximately 25 fbg at the locations shown on Figure 2 using direct-push methods Soil samples were collected at 5-foot intervals in each boring using a large bore sampler Groundwater was encountered at 5 to 7 fbg Groundwater samples were collected at the request of San Joaquin County Public Health Services iFollowing completion of the sampling activities, each boring was sealed from total depth to the surface grade using neat cement The boring logs and general field procedures are provided in Appendix A Select soil and groundwater samples collected from each boring were submitted to a state-certified laboratory and analyzed for total petroleum hydrocarbons as gasoline (TPH-G) by EPA Method 8015 modified, benzene, toluene, ethylbenzene, and total xylenes (BTEX) by EPA Method 8020, and oxygenates by EPA Method 8260 The results of the laboratory analyses are listed in Tables 1 and 2 The analytical results are displayed relative to their collection location on Figures 3 and 4 Refer to Appendix B for a description of the analytical methods used and copies of the official laboratory reports, quality assurance/quality control(QA/QC)reports, and chain of custody records 4.0 FINDINGS Soil types encountered during drilling generally consisted of silts with trace amounts of clay and sand from surface to the total explored depth of 25 fbg Groundwater was detected at 5-7 fbg in each boring No hydrocarbon concentrations were detected in soil and groundwater except for MTBE Concentrations of MTBE in soil samples SB-1 through SB-4 at 24 5-25 fbg are 7 parts per billion (ppb), 4 ppb, 16 ppb, and 93 ppb, respectively Refer to Table 1 and Figure 3 for a summary of soil • sample analysis results