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The sample under the diesel tank (Tank No . 1) found no significant detectable residues of the contents of the tank . The sample from under the two gasoline tanks found detectable amounts of total petroleum hydrocarbons and lead . 1 of the findings, the lead level was the most significant . Lead under Tank 2 was reported as 17 mg/kg. Tank 3 soils were reported to contain 20 mg/kg of lead . 2 . 5 Estimates of liquid quantity and composition leaked: No estimate of liquid can be made with existing information . The constituents detected in the soil samples are typically derived from gasoline . Although existing soil information is limited, soil contamination appears to be primarily ; concentrated near the gasoline tanks fill openings, therefore, we believe overspillage is the most likely L source . 2 . 6 Topography, geology, hydrology: The site is situated on level terrain. The soils at the Chevron property have been mapped by the U. S .D .A. Soil Conservation Service as Stockton clay (adobe) . Stockton clay is a fine-textured, dark gray to black clay, deposited by quiescent or slow moving water . The parent material was of mixed origin, but primarily igneous rock . According to the survey some in-place development of this soil has occurred also. The development is a tight clay subsoil and is the result of transport and re-deposition of very fine particles from the top of the soil profile to the subsoil, resulting in a high colloidal clay content and impervious structure in the subsoil . The impermeability causes temporary perched water tables and rapid development of surface ponding during normal precipitation events. The importance of the above soil properties is that when they exist at depth they significantly contribute to a site ' s ability to attenuate the impacts of any past releases of petroleum fuels . Any lead released to these soils from gasoline would most likely be rapidly adsorbed onto the clay particles, and the high moisture holding capacity of these soils would likely cause soil voids to be continuously filled with water such that vapor transmission of the solvent portions of the gasoline would likely be impeded . It appears this site may have soils of this type below the lowest portion of the removed tanks . Deeper lithology and site geology is related to the surface soils . The site is mapped by the U. S . Geological Survey : as "basin deposits . " Basin deposits have lithologic profiles dominated by fine-textured materials . However, C intercalating layers of coarser textured materials are common and usually capable of freely releasing water . Municipal water wells drilled in the general area penetrate 3