SITE INFORMATION AND CORRESPONDENCE

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- 2 - 21 November 2007 Scott Mansholt • TAOC Tracy Pump Station* Soil Investigations between 1985 and 2006 confirmed the presence of residual weathered petroleum hydrocarbons in soil and groundwater. According to the investigations, concentrations of total petroleum hydrocarbons, semi-volatile organics (SVOCs, including polynuclear hydrocarbons [PAHs]) in soil generally extends from near the surface to approximately 16-feet. Except for xylenes detected in one sample at 780 milligrams per kilogram (mg/kg), BTEX (benzene, toluene, ethylbenzene, and xylene) constituents were non detect in other samples above the method detection limits (MDLs) used at that time. Samples submitted for metals analysis did not report elevated concentrations present and the results were consistent with background conditions. Historically, investigations were conducted using test pits to obtain samples and make visual observations of shallow soil conditions. However, small stockpiles of soil were eventually spread and re-graded which has re-distributed portions of soil across the irregular surface of the site. Consequently, the majority of subsurface soil sample locations reporting TPH concentrations are located in the northwest portion of the site. In September 2003, a soil borings investigation was conducted to obtain samples for analysis using MDLs consistent with current health risk assessment evaluation requirements and to confirm prior PAH analytical data. According to the data, BTEX compounds were not detected above the laboratory MDLs. Similar to prior investigative findings, low concentrations of TPH and PAH compounds, commonly found in crude oil were present in affected soil to approximately 16-feet. The vertical extent of affected soil extends to between approximately 38 and 48-feet based on visual and lithologic descriptions for the investigative borings. Consequently, according to the soil and groundwater investigation reports, the extent of impacted soil has been adequately defined. Groundwater There are five monitoring wells associated with the site: two are onsite, one is offsite upgradient to the south, and two are offsite, downgradient to the north. The approximate groundwater depth is between 10 and 15 feet and flows generally north-northwest. Groundwater lab data for samples collected from borings and monitoring wells between 1985 and 2006 shows the presence of TPH as diesel (TPHd) from non-detect in the upgradient well to approximate concentrations from 200-pg/L to 900-pg/L in the two downgradient, offsite wells since 2001 . In 2003, ND analytical results for TPH constituents in groundwater grab samples obtained from the 2003 offsite borings delineated the lateral extent of TPH affected groundwater downgradient of the site. The two onsite wells contain a petroleum sheen and are not sampled; approximately 80-gallons of crude oil and water have been removed from these monitoring wells since 1996. Based on review of the site maps and analytical results summarized in December 2003 and the June 2005 HHRA Geomatrix reports, it was concluded that the extent of impacted groundwater is limited, has been delineated, and concentrations are attenuating.