SITE INFORMATION AND CORRESPONDENCE

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Former Union Oil Bulk Plant, Tro -2- • 2 August 201 { ground surface (bgs) in the sample from U-1. Table 1 presents the historical soil analytical data and Figure 1 shows the soil sample locations. In May 1991, ConocoPhillips installed three additional monitoring wells (U-4 through U-6). Soil samples showed detections of TPHg, TPHd, benzene, toluene, ethylbenzene, and xylenes (collectively BTEX) in U-5 and U-6 only. Boring U-5 (6.5 feet bgs sample) had the maximum concentrations. In addition, ConocoPhillips drilled three soil borings near the AGTs and former semi-buried tank. Maximum petroleum hydrocarbon concentrations were detected at 6.5 feet bgs in all three borings. In March 1992, ConocoPhillips installed four additional monitoring wells (U-7 through U-10). No petroleum hydrocarbons were detected in soil samples collected from these wells, except minor TPHd detections at 6.5 feet bgs in the sample from U-7. In September 1994, ConocoPhillips investigated 13 test pits to further evaluate soil contamination. Soil samples were collected from 5 to 15 feet bgs. Petroleum hydrocarbons were detected in the vadose and saturated zones near the former AGTs, near the underground piping between the former loading rack and loaders, and near the former semi- buried transmission fluid tank. In 2008, ConocoPhillips installed six confirmation soil borings adjacent to the locations of the historical maximum soil concentrations. Maximum soil concentrations of TPHg and TPHd were 1,300 mg/kg and 290 mg/kg, respectively. Table 2 presents the soil data in relation to the historical locations. In 2009, ConocoPhillips excavated contaminated soil around CB-2, CB-3, and CB-5 to between 8.5 and 10 feet bgs. Remaining soil concentrations were below the California Regional Water Quality Control Board — Bay Area Region Environmental Screening Levels (ESLs) for gross contamination. Table 3 presents the 2009 soil data. In November 2010, ConocoPhillips excavated contaminated soil in the area of the highest soil vapor concentrations. Sidewall and floor samples from the excavation did not contain petroleum hydrocarbons above the laboratory reporting limit. Table 4 presents the 2010 soil data. GROUNDWATER INVESTIGATIONS ConocoPhillips conducted quarterly groundwater monitoring from 1991 to 1994 and semi- annual monitoring from 1995 to 1999. Groundwater monitoring ceased from 2000 to 2003, and then was conducted once in 2004 and once in 2005. ConocoPhillips restarted quarterly monitoring during the first quarter of 2006. Groundwater flow is to the northwest and depth to water varies from about seven to nine feet bgs. Wells U-1 through U-6 and U-10 have not contained petroleum hydrocarbons above water quality objectives (WQOs) since 1999. Wells U-7 through U-9 contained TPHd in 2006. In October 2006, TPHd was at the highest concentration ever detected in wells U-8 and U-9 at 280 micrograms per liter (Ng/L) and 630 pg/L, respectively. The laboratory flagged these results indicating that the laboratory control sample surrogate recovery for TPHd was not within the laboratory established control limits. U-8 and U-9 did not contain petroleum hydrocarbons in January 2007. In March 2009, ConocoPhillips properly abandoned all Site monitoring wells and subsequently removed several during the various excavation projects.