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o ` 8 Soil Boring Report,—Former Unocal Station No 0123,Tracy,California March 10 2000 v A Phase I Environmental Site Assessment report dated December 16, 1994, was prepared by Enviros Inc for Unocal , The study identified twelve sites in the vicinity of the subject site that had impacted soil and f groundwater None of the sites were located in the immediate upgradient direction from the subject site Two of the sites identified were former service stations that were located across from and downgradient of the subject site a former Shell Oil service station at the northwest corner of 110' Street and Central Avenue (operating from arproximately 1949 to 1962), and a former service station (possibly Chevron) at the northeast corner of 11 and Central Avenue(operating from approximately 1913 to at least 1962) In May 1995, nine exploratory soil borings were drilled and three groundwater monitoring wells (U-1 through U-3) were installed by Pacific Environmental Group, Inc (PEG) at the subject site Exploratory test pits were dug and two abandoned USTs were encountered at the northern property boundary; beneath the l l'i' Street sidewalk In November 1996, the two abandoned 550-gallon USTs were removed A third UST that was encountered during the removal activities was abandoned in place by grout injection One groundwater monitoring well (U-4) was installed in December 1996 in the location of the removed USTs to evaluate soil and groundwater conditions On October 7, 1998, PEG drilled and installed two groundwater monitoring wells (U-5 and U-6) and one soil boring (B-4) Soil samples collected from the borings had detectable concentrations of Total Petroleum Hydrocarbons as gasoline(TPHg) (220 parts per million(ppm)at 11 feet bgs in U-6) and Total Petroleum Hydrocarbons as diesel (TPHd) (2I 5 ppm at 10 feet bgs in B-4 and 12 3 ppm at 11 feet bgs in _ U-6) Benzene, methyl tert-butyl ether (MtBE), lead, or volatile organic compounds (VOCs) were not detected in the soil samples Grab groundwater samples had concentrations of TPHg (968 parts per billion (ppb) in U-6) and TPHd (115 ppb in B-4 and 312 ppb in U-6) Benzene, MtBE, or lead were not detected in the groundwater samples Groundwater monitoring and sampling has been conducted quarterly since June 2, 1995, in wells U-1, U-2, and U-3, since March 3, 1997, in well U-4, and since October 22, 1998, in well U-5 and U-6 In the latest event on June 14, 1999,concentrations of TPHg(I 10 ppb in U-1 and 1,400 ppb in U-4), TPHd (720 ppb in U-4), benzene (1 3 ppb in U-1 and 5 5 ppb in U-4), and MtBE(2 9 ppb in U-1, 5 6 ppb in U-2, and 2 5 ppb in U-6) were present Also, the halogenated volatile organic compounds (HVOCs) cis-1,2- dichloroethene (0 67-1 9 ppb), tetrechloroethene (2 1-6 2 ppb), and trichloroethene (0 55-2 5 ppb) were detected Depth to water during this monitoring event ranged from 9 33 to 10 45 feet bgs and groundwater flow direction was to the north-northwest,which is consistent with available historical data FIELD ACTIVITIES To further evaluate the distribution of residual petroleum hydrocarbons in soil and groundwater downgradient of the subject site, GR advanced one soil boring (B-5) to 16 feet bgs by Geoprobe at the location shown on Figure 3 This work was performed under SJCEHD permit#021095 and City of Tracy encroachment permit #99372 Copies of the permits are included in Appendix A Field work was performed in accordance with GR's Site Safety Plan #240073 03, dated December 6, 1999 GR Field Methods and Procedures are included in Appendix B Underground Service Alert was notified prior to beginning site activities, and a private subsurface utility locating service was contracted to locate subsurface utilities at the boring location Geoprobe activities were performed by Vironex Inc (C57 #705427) 24007303-1 2