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<br /> A S S O C I A T E S I N C
<br /> 2.5 Groundwater Sampling and Analysis
<br />' On February 22, 2001, groundwater samples were collected from wells MW1, MW2, MW3,
<br /> MW4, and MW5. The samples were collected after purging a minimum of three well volumes
<br /> and stabilization of electric conductivity, pH, and temperature. Field development/purge logs are
<br /> presented in Appendix C. Subsequent to purging, groundwater was sampled and transferred to
<br /> appropriate sample containers, using a clean, dedicated disposable bailer with a bottom-emptying
<br /> device to reduce volatilization. Sample containers were then labeled with sample identification,
<br /> 1 placed on ice, and shipped under chain-of-custody to Argon Laboratories.
<br /> The groundwater samples from wells MW1, MW2, MW3, MW4, and MW5 were analyzed by
<br /> ' Argon Laboratories for total petroleum hydrocarbons as gasoline (TPHg), benzene, toluene,
<br /> ethylbenzene, xylenes, and oxygenate fuel additives. Groundwater analytical results are
<br /> summarized in Table 2, and laboratory data sheets are presented in Appendix D.
<br /> 3.0 SUBSURFACE CONDITIONS
<br /> ' 3_1 Geology
<br /> Soils in borings MW2through MW5 consisted primarily of lean clay, silty clay, elastic silt and/or
<br /> clayey silt from the ground surface a depth of 30 feet, the maximum depth advanced. Boring logs
<br /> with soil descriptions and well construction details are included in Appendix A.
<br /> ' 3.2 Hydrosteology
<br /> ' Water level measurements were collected from wells MW 1, MW2, MW3, MW4, and MW5 on
<br /> February 22, 2001. The groundwater levels ranged in elevation from a high of-4.81 feet at MW4
<br /> to a low of-4.97 at MW5.
<br /> The site's underlying groundwater direction of flow was observed to be to the northeast.
<br /> Regional groundwater flow is estimated to be in an easterly direction, based on San Joaquin
<br /> ' County Flood Control and Water Conservation District data (Lines of Equal Elevation of
<br /> Groundwater, Fall 1997). The groundwater gradient was calculated to be approximately 0.0016
<br /> feet per foot or 8.45 foot per mile.
<br /> 4.0 ANALYTICAL RESULTS
<br /> ' 4_1 Soil Analytical Results
<br /> Soil samples collected from borings MW2, MW3, MW4, and MW5 showed TPHg, benzene,
<br /> toluene, ethylbenzene, total xylenes, and oxygenate fuel additives were not detected above their
<br /> . respective laboratory method detection limits. Lead was detected at MW2-10.5', MW3-10',
<br /> ' MW4-15', and MW5-10' at 14 parts per million (ppm), 15 ppm, 13 ppm, and 13 ppm,
<br /> respectively. These levels appear to be representative of background concentrations.
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