FIELD DOCUMENTS - Laserfiche WebLink

Home Browse Search

Chevron Products Company 2 Chevron Service Station 20-0764.4747 West Lane Stockton California • April 5 2002 during a second monitoring event on 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. Field and laboratory procedures followed during the assessment activities are summarized in Attachment A. Field data sheets from well development and sampling activities are presented in Attachment B. • Subsurface Conditions. Review of the boring logs indicates 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 58 feet bgs. Boring logs (for the monitoring wells) and well construction details are included in Attachment C. • Soil Analytical Results. Soil samples were collected from the three borings and submitted for analysis for total petroleum hydrocarbons quantified as gasoline(TPHg), benzene, toluene, ethylbenzene, xylenes (BTEX) and methyl tertiary butyl ether(MtBE). A copy of 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 two monitoring and sampling events and submitted for chemical analysis for TPHg, BTEX and MtBE. A copy of the laboratory analytical report and chain-of-custody • documentation for the monitoring well install are presented in Attachment D. Low concentrations of toluene, ethylbenzene, and xylenes were detected in sample collected from wells MW-1 and MW-3 during one or both sampling events. None of the analytes were detected in samples from MW-2 on either sampling event. 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 at a gradient of 0.006 foot per foot(ft/ft) during the first monitoring event (Figure 3), and to the northeast at a gradient of 0.0003 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"slug" in the well. The hydraulic response was recorded using an automated pressure transducer, containing an internal data logger(MiniTroll') until the water elevation equilibrated its pre-test level or until sufficient data was obtained for analysis. •