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Tmadwell&Rolb <br /> 3.5 Soils • <br /> The study area is capped with fill varying from a few feet deep in the northern portions to greater <br /> than 10 feet deep in the southern portions near the Stockton Ship Channel. Near surface, shallow <br /> soils are typically silts and clays with intermittent zones of permeable sand. The silts and clays <br /> are underlain by low permeability marsh and deltaic mud deposits. <br /> 3.6 Hydrogeology <br /> The geology of the study area has been characterized by numerous soil and groundwater studies <br /> performed by the City of Stockton and by private property owners. Near surface, shallow soils <br /> are typically silts and clays with intermittent zones of permeable sand. There is also evidence of <br /> fill comprised of soil mixed with debris, such as wood, glass, and metal. Although not evident in <br /> soil boring logs, historical reference to the use of dredge spoils as fill appears in some reports. <br /> Groundwater is typically encountered at 15 to 25 feet bgs. No groundwater in the study area is <br /> pumped for industrial use or consumption. The local groundwater gradient is away from the • <br /> Channel, generally to the northeast. <br /> During the April 2000 investigation 8 groundwater monitoring wells at Area 10 and 2 and Area <br /> 20 were surveyed by Siegfried Engineering. The well locations and elevation at the top of the <br /> well casings at Area 10 and 20 were surveyed and used to help determine the groundwater flow <br /> direction and gradient(Figure 8). Table 8 presents a summary of the groundwater elevations and <br /> elevations at the top of the well casings. The flow direction varies from northwesterly at Area 10 <br /> to northerly at Area 11 to northeasterly at Area 20. The groundwater flow direction appears to <br /> have localized variations, but generally tends to flow away from Stockton Channel. The <br /> quarterly groundwater monitoring conducted at areas 15, 16, and 21 include calculations of <br /> groundwater flow directions. Several years of groundwater elevation data at these sites has <br /> shown a fairly consistent flow direction to the north northeast. <br /> 24 • <br /> 25970309.DGD 24 August 2000 <br />