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......._ _.... _ _._ scrept bac r _. _ Page 14 The State contractors discovered areas of oily saturated soil in the retention basin within the lower canyon and began removing the soil . The excavation encountered significant pyrolitic oil contamination at two feet below ground surface . The total amount of contaminated soil that would have to be removed was estimated to be 200 cubic yards . While this work continued, the contractors began placing the clay cap over the contaminated ash residue and soil that had been consolidated in the upper canyon. November 18 - November 23 , 1996 The contamination followed a gravel layer for about 150 feet up canyon (see figure 3) . The contamination was about 30 feet wide and up to 8 feet in depth. The contamination ended at the natural clay layer. The gravel layer did not extend beyond the dam, but did appear to continue into the fill area. The volume of pyrolitic oil contaminated soil greatly exceeded the original estimates . Approximately 3 , 000 cubic yards had to be removed. This material was placed in the upper region of the fill . The soil cap was then placed over this material . The State project engineer decided to place a clay plug below the fill . The wedged-shaped clay plug was 100 feet long and 40 feet at its maximum height (see appendix 2) . A 60 mil co-extruded HDPE geomembrane was placed on top of the clay fill and anchored into a grout cutoff wall that was keyed into natural clay. This was considered a sufficient barrier to prevent contaminated water from migrating through the fill and gravel layer and down the canyon. November 25 - November 30, 1996 Work continued throughout the week. Remedial activities consisted of constructing the fill foundation and clay cap. December 2 - December 7, 1996 The remedial contractors completed the placement of the geomembrane and clay cap. Drainage was directed to two V-ditches at the edge of the canyon. December 9 - December 14, 1996 The construction of a new retention dam began at the mouth of the canyon to minimize the runoff of sediments into Little Panoche Creek. Final grading of the last foot of cover was completed in preparation for hydroseeding. December 16 - December 27, 1996 The retention dam and erosion control devices were completed. The State began demobilization of personnel and