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Monitoring Well Installation Report—Former Unocal Service Station 90187, Stockton,CA . August 2,2000 The wells were developed and sampled on June 7, 2000 Depth-to-water was measured in all on-site g roundwater monitoring wells on May 30 and 31, 2000 during the scheduled second quarter 2000 groundwater monitoring and sampling event (Appendix D) A groundwater potentiometric map was generated from this data (Figure 4) The wells were checked for the presence of separate phase hydrocarbons (SPHs) No SPHs were observed in the wells The wells did not dewater during development Following development, a groundwater sample was collected from each well Purge water generated during development and sampling procedures was transported by GR to the Tosco Refinery for disposal Well development procedures are included in Appendix A Copies of the development forms are included in Appendix D Monitoring data for wells U-10 through U-13 are summarized in Table 2 Wellhead Survev Following installation of the wells, elevations were surveyed by Virgil Chavez Land Surveying (California licensed land surveyor 96323) The top of casing and vault boa elevations were measured relative to MSL, and the horizontal location of the wells were measured The surveyor's report is included in Appendix E Well elevations are summarized in Table 2 RESULTS OF THE SUBSURFACE INVESTIGATION Soil encountered during this investigation consisted of interbedded silts, sandy silts, silty sands, and sands to the total depth explored with minor amounts of clay within the first 13 feet bgs This is similar to conditions encountered during previous investigations at the site Detailed descriptions of the soil encountered during drilling are presented on the boring log for well U-12 in Appendix C Groundwater was first encountered in well boring U-12 at approximately 28 feet bgs and stabilized at depths between 24 and 26 feet bgs in all well borings Based on the groundwater monitoring data er beneath the site is flowing to the east-northeast at a collected an May 30 and 31, 2000, groundwat gradient of 0 005 ft/ft, which is consistent with historical data CHEMICAL ANALYTICAL RESULTS A total of eleven soil samples from the well borings, one composite soil sample from the stockpiled drill cuttings, and four groundwater samples were submitted under chain-of-custody for chemical analysis Analyses were performed by Sequoia Analytical (ELAP -41271 and 91624) Copies of the laboratory re included in Appendix F Soil and ground"ater chemical reports and chain-of-custody forms a analytical data are summarized in Tables 1 and 2 respectively Chemical Analvtical Procedures All soil and groundwater samples from the well borings were analyzed for TPHg, benzene, toluene, ethylbenzene, and xylenes (BTEX), and MtBE by DHS LUFT Method The groundwater samples were also analyzed for tert-butyl alcohol (TBA), MtBE, ethyl tert-butyl ether (ETBE), di-isopropyl ether (DIPE), and tert-amyl methyl ether (TAME) by EPA Method 8260A As required by the disposal facility, the stockpiled drill cuttings sample was analyzed for TPHg, BTEX, and MtBE by DHS LUFT Method and total lead by EPA 6000/7000 Series Methods 24004205-1 5