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PANOCHE BURN SITE REMEDIATION The ash was dry and hydrophobic, and moisture-conditioning was difficult. To prevent fugitive dust and hazardous air emission from the lead and zinc, two 4,000-gallon water trucks were used. 3.2.4 Stained Material On the north slope below the rock outcrop and two areas along the south slope, black staining was observed 4 to 5 feet below the ash layer. Black staining was along the side slopes in the natural clay soils. The stained soil did not have an odor, was more pronounced toward the bottom, occurred in random elevations, and did not contain ash residue or elevated levels of zinc. After reviewing the laboratory results (See Section 3.4.4) and site conditions, the CIWMB engineer concluded the black stained soil was probably due to the pyrolysis of the oil in the soil column. As the tire fire burned, large quantities of pyrolytic oil were released and saturated the soil column below. With the extreme temperatures from the fire from below the canyon rim and above, the pyrolytic oil on the side slopes presumably chemically decomposed, leaving only carbon black (i.e., tire filler). 3.2.5 Pyrolytic Oil Contamination Initially, all or most of the pyrolytic oil was assumed to have been consumed during the tire fire. However, the CIWMB investigation showed the oil was 30 to 40 feet below the original surface, 50 to 100 feet long, and 25 to 30 feet wide. After examining the removed soil at the bottom of the retention basin, the CIWMB engineer determined the pyrolytic oil from the tire fire permeated through a gravel lens in the upper part of the canyon and traveled downward toward the creek. The lens acted as a conduit allowing the pyrolytic oil to advance and bypass the above clay layers. Because the oil stain migrated along a gravel lens down the canyon, the CIWMB engineer directed Sukut to perform exploratory trenching to locate the extent and depth of the contamination. To define the area of concern, the old check dam was removed. Figure 5 shows the excavated area of pyrolytic oil. The cut slope along the northern embankment showed the gravel lens containing the oil. See the photo log in Appendix G for further details. Trenching indicated the oil migrated under the majority of the old check dam and ended at a natural clay barrier in front of the new retention dam. The natural barrier prevented the oil from contaminating Little Panoche Creek. Figure 6 shows the general path of the pyrolytic oil. To reduce the possibility of the oil contaminating the surface water within the basin, the CIWMB engineer elected to remove as much of the stained soil as feasible. When the excavation was stopped, pyrolytic oil was observed in a gravel lens located at the bottom of both slopes and at the toe of the fill. The excavated material was placed in the upper region of the fill on top of the ash and then capped with soil. Based on actual scraper counts, a total of 5,600 cubic yards of oil-contaminated soil was placed on top of the fill area under the foundation layer. Unfortunately, not all of the pyrolytic oil material could be safely removed. Removing all the contaminated gravel would have required a massive construction effort. First, the entire CIWMB 17