SITE INFORMATION AND CORRESPONDENCE

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C. Dean Hubbard October 13, 2006 Page 3 the Tidewater Associated Oil Company(TAOC)pipeline. It was used from approximately 1900s to the mid- 1960s. The historic features include office, pump and boiler buildings, aboveground storage tanks (ASTs), and pipelines. The site is currently undeveloped and surrounded by fencing. Residential developments lie to the south and to the northwest, a vacant 3-acre property lies directly to the west followed by a larger residential development. A UPRR right-of-way lies immediately north of the site. The area to the east seems undeveloped. The soil consists of a complex sequence of interbedded clay, silt, sand, and gravel deposits underlying the site. Groundwater was found at depths of approximately 7 to 15 feet below ground surface (bgs), and the regional flow direction varies from north to northwest. The risk assessment is based on the assumption that the soil already collected in piles will be distributed and graded on site, i.e. that no soil will be moved off the site. Site Characterization 1. The site soil contamination seems to extend vertically below 10 ft bgs. However, this risk assessment follows typical practice by considering soil contamination up to 10 feet bgs. 2. Geomatrix used silica gel clean up of groundwater samples before analysis to eliminate biodegradation products. OEHHA is of the opinion that risk assessment based on analytical data from pre-treated samples may underestimate risk. Site Conceptual Model Groundwater Pathways 3. This risk assessment does not include groundwater-related pathways (neither direct consumption nor as a source of volatiles for vapor intrusion). While it is understood that the site groundwater will not be used as a source of drinking water(Letter from a local Department of Health), the locations of the nearest public wells are not provided nor discussion about the potential for public wells contamination due to this site groundwater is provided. Page 7, par. 2 states "Groundwater samples from the two on-site wells (REW-2 and REW-3) were not analyzed because of ongoing product removal activities. Thus there are no current COPCs in groundwater;groundwater was not considered further in this HHRA. " However, a RWQCB letter entitled "Former TA OC Pum, Station, 880 Beechnut, Tracy, San Joaquin Co. " and dated 24 February, 2004 states: "Three of the onsite wells sampled in 1985, contained concentrations of petroleum hydrocarbons (<200µg/L, 4,300µg/L, and 135,000µg/L), PAHs and BTEX compounds."(p. 2, Groundwater,par. 1). Considering that "groundwater occurs at depth of approximately 7 to 15 feet below ground surface (bgs)... "(p. 2, 2.2 Geology and Hydrogeology)the future constriction worker might be exposed to chemicals in ground water