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Groundwater Monitoring Well,CPT,and Ozone Microsparge System Installation Report Tosco(76) Service Station No 11192, Stockton,California May 9 2003 Prior to well development and groundwater sample collection on January 3, 2003, GR personnel measured the depth to groundwater in wells MW-1 and MW-3 through MW-13 at depths ranging between 13 79 and 18 81 feet below top of casing (TOC) SPHs were not observed in any of the wells These data were used to construct a Potentiometric Map (Figure 4) Based on these data, shallow groundwater beneath the subject site generally flows northeast at a calculated hydraulic gradient of 0 001 to 0 0003 feet/feet, which is generally consistent with historical data 5-7,Laboratory Analysis The soil samples collected from the two well borings and the groundwater samples from the two CPT borings were analyzed by Sequoia Analytical in Sacramento, California (FLAP No 1624) The groundwater samples collected from the monitoring wells were analyzed by STL in Pleasanton, California (ELAP No 2496) The soil and CPT groundwater samples were analyzed for TPHg by EPA Method 8015 modified, BTEX and MtBE by EPA Method 8021, the fuel oxygenates TBA, ETBE, TAME, DIPS, MtBE, ethanol, and lead scavengers 1,2-DCA and 1,2- dibromoethane (EDB) by EPA Method 8260B, and methanol by 8015B modified The groundwater samples from the monitoring wells were analyzed for TPHg, BTEX, and fuel oxygenates by EPA Method 8260B Copies of the laboratory analytical reports and chain-of- custody records are included in Appendix F 5.3 Groundwater Ana ayheal Results TPHg and BTEX constituents were not detected above laboratory detection limits in the groundwater samples analyzed from the two new wells MW-12 and MW-13 MtBE and TBA were the only fuel oxygenates detected in the groundwater samples from wells MW-12 and MW-13 at concentrations of 220 and 1,700 ppb, and 13,000 and 20,000 ppb, respectively Groundwater chemical data are summarized in Table 1 TPHg and BTEX constituents were not detected above laboratory detection limits in the groundwater samples analyzed from select depths in the CPT borings CPT-2 and CPT-3 Of the fuel oxygenates, MtBE and methanol were detected in the groundwater sample CPT-2 75 at concentrations of 2 0 and 2,700 ppb, respectively MtBE was detected in CPT-3 100 at a concentration of 6 8 ppb MtBE and TBA were detected in CPT-3 125 at concentrations of 290 and 88, respectively Grab groundwater chemical data are summarized in Table 2 and presented on Figure 5 5-4 So*1 Anal3lical Result MtBE was detected in soil boring MW-12 (6 5') at a concentration of 0 0067 ppm TPHg, MtBE, TBA, and TAME were detected in soil boring MW-12 (11 5') at a concentration of 0 68, 1 1, 0 25, • 140245 8 9