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A)r <br /> 0 V(: <br /> A S S O C I A T E S I N C <br /> 3.0 SUBSURFACE CONDITIONS <br /> 331 Geology <br />' Soils in boring MW7 consisted of sandy clay from the surface to approximately 10 feet bgs with <br /> a Unified Soil Classification System USCS designation of SC At 10 feet, organic clays were <br /> encountered with a USCS designation of OH At 15 feet, a layer of peat with abundant plant <br />' material was encountered At 20 feet bgs, soils encountered were organic clays with USCS <br /> designation of OH From 25 feet bgs, poorly graded fine sands were encountered with a USCS <br /> designation of SP, to a depth of 31 5 the maximum depth advanced <br />' 3.2 Hydrogeologv <br />' Water level measurements were collected from monitoring wells MWI, MW2, MW3, MW4R, <br /> MW5, MW6, and MW7 on April 6, 2001 The groundwater level elevations ranged from a high <br /> of-6 21 feet above mean sea level at MW7 to -19 25 feet above mean sea level at MW1 <br />' The site's groundwater flow direction was observed to be to the northeast, away from the slough <br /> g Y g <br /> Regionally, groundwater typically flows away from the levees towards the lower lying areas and <br /> is also influenced by tidal fluctuations A primary use of surface water in the Delta region 1s <br /> irrigation of agricultural land, and is controlled by irrigation ditches found throughout the region <br />' The groundwater gradient was measured to be 0 08 feet per foot or 420 feet per mile <br /> 4.0 ANALYTICAL RESULTS <br />' 4_1 Soil Analytical Results <br />' The soil sample collected at a depth of 5 feet bgs from boring MW7 contained detectable <br /> concentrations of TPHg, benzene, ethylbenzene, xylenes, and MTBE Concentrations of <br /> petroleum hydrocarbons attenuated rapidly with depth The soil sample collected at a depth of <br />' 10 feet bgs from boring MW7 only contained detectable concentrations of benzene and MTBE <br /> Soil samples collected at depths of 30 feet bgs from boring MW7 did not contain detectable <br /> concentrations of benzene and MTBE Soil samples collected at depths of 30 feet bgs, from <br />' boring MW7 did not contain detectable levels of any petroleum hydrocarbons Analytical results <br /> of soil samples are contained in Table 1 Laboratory data sheets and chain-of-custody <br /> documentation for soil samples are presented in Appendix B <br /> 1 <br /> 1 W 1625141reportslsup_sub_inv doc 5 <br />