SITE INFORMATION AND CORRESPONDENCE

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-6- Oily Soil Oil in the shallow soils has been a nuisance in the yards and gardens of the home owners . In some cases, citizens can recognize oily soil by its dark color . To give some practical perspective, we did some simple laboratory tests . Oil sampled from observation wells was mixed with soil from Tracy at various concentrations, then the odor and visual appearance of the mixtures was compared. We detected an oily odor near 0 .1% oil concentration and began to detect oil visually (darker color ) above 1% . The soil becomes saturated (dripping) with oil at about 15% . The hard asphalt "rocks" found at the surface .in some home owners yards are over 10% oil, but are solid due to weathering and biodegradation in the shallow soils where they were found. We also observed soil with water levels at 7% looked similar to oily soil , which may confuse any visual observers into concluding wet soil was oily. The extent of the oily soil has been well defined by the 131 locations where soil was sampled at 2-, 4-, and 8-ft depths . The site assessment report includes all of the analytical results on these. Maps showing concentration contours around Alden Park are included. Our decision not to excavate oily soil in the shallow surface is based on toxicity testing of the soil and groundwater . These tests demonstrated that the oily soil and the groundwater below it passed regulatory requirements for toxicity and are not hazar- dous. We used this result and other data presented in the site assessment report (Reference 1) to determine the soil should be treated in place. The public will not be eager to see additional soil excavated for these reasons: First, excavating the soil creates a disposal problem. Second, the excavation of soil from yards will cause disruption to the neighborhood. Since oily soil can be found along the fences , excavating it would require removing fences. Ornamental plants and landscaping would also be destroyed.