SITE INFORMATION AND CORRESPONDENCE

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Y Former TAOC Pump Station - 3 - 24 February 2004 880 Beechnut Tracy, San Joaquin Co. compounds at the respective detection limits. In October 2001, the analytical results for wells REW-1,E, and F were ND for all BTEX and PAH constituents; TPH-d for REW-1 was ND and 660 p g/L and 310 pg/L, respectively. In 1989, a human health risk assessment (HHRA) was conducted as part of a Preliminary Endangerment Assessment (PEA) for the site. The study, assessing surface soils only, concluded that potential exposure to chemicals detected were unlikely to pose a health risk to current or future receptors. However, the report also concluded that potential exposure to chemicals in groundwater may be of concern if the shallow groundwater was used for drinking water (subsequently, the City of Tracy has enacted municipal code(s) that prohibits the use of the shallow groundwater for domestic purposes). Consequently, in December 1990, the Department of Health Services (DHS) approved the PEA provided the oil-stained soil (stockpiles and surface) was removed from the "habitable" areas of the site. CURRENT INVESTIGATION In September 2003, Geomatrix conducted a soil and groundwater investigation, advanced borings to collect soil and groundwater samples for analysis, and conducted a quarterly groundwater monitoring event. According to the 16 December 2003 Soil Investigation and Groundwater Monitoring Report, the purpose of the investigation was to: a) assess the vertical extent of TPH in soil; b) confirm PAH data near REW-2; c) collect data for use in assessing human health risks associated with chemicals at the site, and d) commence quarterly groundwater monitoring and removal of product from two on-site wells. Consistent with previous investigations, depth to groundwater at the site remains approximately 12 to 14- feet and the gradient generally north-northwest. Soil Soil boring depths ranging from 12 to 49 feet (maximum exploration depth) were advanced at seven different locations. Unfortunately, sample recovery was poor, with several samples lost between 15 and 49 feet in the three deepest borings. Elevated concentrations of TPH-c ranging from ND to a high of 20,000 mg/kg (@ 5 feet in GMX-7) were reported in the 17 samples obtained from the seven borings. Based on review of the boring logs and analytical results, it appears that the soil encountered in the deep borings is impacted from near surface to greater than 20 feet in GMX-1, to approximately 20 feet in GMX-2, and to 48 feet in GMX-3. However, due to the high TPH-c concentrations reported in some of the samples, the minimum BTEX detection limits were higher for a portion of the samples reported as ND. Elevated PAHs were reported for soil samples from one of the new borings (GMX 7), confirming previous PAH concentrations in soil at 5 feet in boring REW-2. Other samples reported ND to low PAH concentrations. Sample recovery was poor, but according to the analytical results, PID readings, and visual observation of core samples, the vertical extent of impacted soil attenuates with depth, decreasing to 110 mg/kg in GMX-3 at 48 feet, and terminating by 48 feet in GMX-2. Consistent with previous investigations, soil samples from the two borings advanced in the southeast portion of the site were ND for TPH-c, PAHs, and BTEX constituents.