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S E C O R ARCO Service Station 595 May 6, 2004 Page 2 in Livermore, California. Results of this investigation are included in SECOR's report titled Soil Samples During Product Line and Dispenser Upgrade Activities, dated December 10, 1999. Historical soil analytical data is included in Table 1 and historical sampling locations are included in Attachment 2. In June 2000, four groundwater monitoring wells (MW-1 through MW-4) and three soil borings (B-1, B-2, and B-3) were completed at the site. The subsurface assessment confirmed that petroleum hydrocarbons had impacted the soil and groundwater beneath the site. Results of this investigation are included in SECOR's Site Assessment Report, dated October 2, 2000. Historical soil analytical data is included in Table 1. Well construction details are included in Table 2 and soil boring logs are included in Attachment 3. In July 2001, three additional groundwater monitoring wells (MW-5 through MW-7) and two deep soil borings (PSB-1 and PSB-2) were drilled to further delineate the lateral and vertical extent of petroleum hydrocarbons in soil and groundwater beneath and downgradient of the site, and in the vicinity of on-site domestic water supply well WSW. With the exception of minor concentrations of benzene, toluene, and xylenes in the 15-foot, 25-foot, and 55-foot samples from the boring for MW-5, petroleum hydrocarbons and fuel oxygenates were not detected in any soil samples collected during the assessment. With the exception of minor concentrations of benzene, toluene, ethylbenzene, and xylenes (BTEX) constituents in boring PSB-2 at 95 feet bgs, concentrations of TPHg and BTEX were not detected in discrete-depth groundwater samples and groundwater monitoring well samples. MtBE (EPA Method 826013) and 1,2-DCA were reported in discrete-depth groundwater samples from boring PSB-1 (75 feet and 90 feet bgs), discrete-depth groundwater samples collected from boring PSB-2 (64 feet and 90 feet bgs), and in wells MW-5 and MW-7 at concentrations up to 94 ppb (MW- 7, August 2001) and 23 ppb (MW-7, August 2001), respectively. Approximately 10 cubic yards of soil was generated during fieldwork activities, and disposed of at Forward Landfill in Manteca, California. Results of this investigation are documented in SECOR's Site Assessment Report, dated December 11, 2001. The historical groundwater gradient direction within the shallow zone at the site has generally been to the northwest at gradients ranging from 0.0004 to 0.01 feet per foot. The historical groundwater gradient direction within the deep zone at the site has ranged from the northeast to the southwest at gradients ranging from 0.0007 to 0.11 feet per foot. SCOPE OF WORK The scope of work for this site assessment includes the installation of seven groundwater monitoring wells to delineate the extent of petroleum hydrocarbons in soil and groundwater at the site. Groundwater monitoring well locations are provided on Figure 2. The specific scope of work is discussed below: Health and Safety Plan. As required by the Occupational Health and Safety Administration (OSHA) Standard "Hazardous Waste Operations and Emergency Response" guidelines (29 CFR 1910.120), and by California Occupational Health and Safety Administration (Cal-OSHA) "Hazardous Waste Operations and Emergency Response' guidelines (CCR Title 8, Section 5192), SECOR will prepare a site-specific Health and Safety Plan (HASP). Field staff and contractors will review the HASP before beginning field operations at the site.