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present at higher elevations in the area of the site. Permanent bodies of surface water are not located within Yz-mile of the site. Grazing of livestock (cattle) occurs north and east of the site. The full history of the SWMU has been presented in earlier reports. 2.1 Site Lithology, Stratigraphy and Hydrogeology The geological map (modified from Dibblee, 1980; and Dugan and Matelek, 1990) shows the site surface to consist of Quaternary landslides underlain by the Neroly and Clerbo formations. The map shows that the Callahan fault which trends NNW on and near the property is, at the closest, over 1000 feet southeast of the site. However, the Callahan fault separates the known logged geology of the southeastern portion of Site 300 with thqat of SWMU 21, especially in regard to absolute elevations of the formations. A large portion of the area, around the tank, was excavated to a depth of up to 15 feet and imported soils, consisting of gravelly silty sands were emplaced. However the original soils, as shown by the MW-3, MW-5 and MW-7 borings also consisted of silty sands with varying amounts of clays and gravels. Underlying the fill is a loam; a clayey silty sand with varying amounts of clay. In places the clay predominates and may be the majority constituent of the soils. These soils continue until 30 to 40 feet bgs. This clay-bearing soil acts as a semi-permeable aquitard. This appears to be the Middle Claystone (Tnsct) of the lower Neroly Formation, which is the upper formation of the San Pablo Group. Underlying the loam is a conglomerate, consisting of greywacke, chert, quartz and greenstone. In some places the conglomerate is weakly cemented or not cemented at all and consists of loose gravel. In the eastern side of the site MW-4f and MW-2, the cementing is particularly strong. The conglomerate is consistent with the published makeup of the Lower Blue Sandstone (Tnbst) of the lower Neroly Formation, and can be assumed to be the top strata of the Tnbst. Under the conglomerate, the silty sands contain gravels consisting or containing arkose, greywacke, basalt, chert and greenstone. Again, this is consistent with the Lower Blue Sandstone, but the gravels more typically found in the Franciscan formation. The thickness of the Lower Blue Sandstone (Tnbst) of the lower Neroly Formation in the adjacent southeastern portion of Site 300, is greater than 200 ft, with the "Claystone Marker Bed" up to 100 ft below the top of the Tnbst. If the conglomerate logged onsite, at an average of 30 bgs, is the top of the Tnbst, then the aquifer is entirely within the upper Tnbst, above the "Claystone Marker Bed". At MW-3 the loose uncemented gravels underlying the conglomerate extends about 7 ft, to about 45 ft bgs. There the gravels are again cemented into a conglomerate of about 3 ft thick. Underlying that second conglomerate is again uncemented gravels. CE Project No.99R-4041 Additional Investigation Work Plan 2