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2 Chevron Products Company Aril 5 2002 Chevron Service Station 20&118 3355E imer Lane Stockton CA January 10, 2002. Groundwater samples were collected in laboratory supplied sample vials,placed on ice, and submitted for chemical analysis with chain-of-custody documentation. The field and laboratory procedures used during this assessment are summarized in Attachment A. Field data *4W sheets from well development and sampling activities are included in Attachment B. • Subsurface Conditions. Review of the boring logs suggests sand mixtures with silt and/or clay mixtures with silty sand comprising the stratigraphy to an approximate depth of 72 feet bgs at each boring location. Groundwater was generally encountered at approximately 60 feet bgs at each boring location. Boring logs and well construction details are included in Attachment C. • Soil Analytical Result. Soil samples were collected from the three borings and submitted for chemical analysis for total petroleum hydrocarbons as quantified gasoline (TPHg), benzene, toluene, ethylbenzene, xylenes (BTEX) and methyl-tertiary-butyl-ether(MtBE). The laboratory analytical report and chain-of-custody documentation are presented in Attachment D. TPHg, BTEX, and MtBE were not detected in any of the soil samples submitted for chemical analysis. • Groundwater Analytical Results. Groundwater samples were collected from each well during the two monitoring events and submitted for chemical analysis for TPHg, BTEX and MtBE. A copy of the laboratory analytical report and chain-of-custody documentation are presented in Attachment D. Low concentrations of toluene, ethylbenzene, and/or xylenes were detected in the samples collected from the three wells during both events. TPHg, benzene, and MtBE were not detected in any of the samples collected during either event. Groundwater analytical results are summarized in Table 1. • Well Surveying and Groundwater Gradient Interpretation. A state-licensed surveyor surveyed the newly installed wells to known vertical and horizontal datum. Depth to groundwater measurements were collected prior to sampling activities during each monitoring event and utilized for interpretation of groundwater flow and gradient beneath the site. The interpreted groundwater flow direction was to the east/southeast at a gradient of 0.005 foot per foot (ft/ft) during the first monitoring event(Figure 3), and to the southeast at a gradient of 0.0005 ft/ft during the second monitoring event(Figure 4). • Slug Test. On January 16, 2002, slug tests were performed in wells MW-1, MW-2, and MW-3. Slug insertion and removal tests were conducted in the wells by creating a near instantaneous change in water level by inserting or removing a PVC "slug" in the well. The hydraulic response was recorded using an automated pressure transducer, containing an internal data logger(MiniTroll'-') until the water equilibrated to its pre-test level or until sufficient data was obtained for analysis. The hydraulic conductivity ranged from 3.4 x 10-3 to 1.3 x 10"2 centimeters per second (cm/sec) with a calculated geometric mean of 7.9 x 10-3 cm/sec (22 feet/day). These values of hydraulic conductivity are consistent with those for poorly-graded sands with fines present at the site as described in the boring logs for the tested wells. The transmissivity was I:1Chevron12081 I81Reports1208118 site assessment 2001.doe