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__.._.. _ _ Oscrept.bac Page 22 information pertaining to prior tire dump operations . V. Difficulties Encountered Some problems encountered during the removal action included extinguishing the tire fires, pyrolytic oil production and migration and use of the infrared camera to detect underground fires . The burning tires that had been buried under tons of earth during construction of the access ramp/fire break eventually re-ignited necessitating a second response action. Burying the burning tires within the access corridor was the only option. The ramp had to be constucted to provide access and a working platform for the excavator at the bottom of the canyon. It was assumed that the burning tires would be smothered by the soils . Furthermore, the barrier trench and water flood was expected to prevent the spread of surface fires into the landfill . Although the burning tires were entombed in tons of dirt, they were not completely smothered. In fact, the continuing combustion of the buried tires created sufficient heat to ignite the tires in the landfill . The lesson learned is that the act of burying a tire fire does not necessarily smother them. In situations where continuing combustion is unacceptable, the tires should be excavated and extinguished as soon as possible. Although the possibility of a pyrolytic oil problem was considered, the extent of the problem was not identified until later in the remediation phase . During the early stages of the fire, pyrolytic oil that flowed from the piles of burning tires pooled in the retention basin. The basin fires generated extreme temperatures which quickly consumed the oils . Surface soils collected beneath the ash residue were clean. Based on these tests and observations it was assumed that the oils had undergone complete combustion. During excavation activities to enlarge the retention basin, significant pyrolyic oil contamination was encountered. A large volume of pyrolytic oil had seeped into the soils and infiltrated into a gravel layer several feet below ground surface . The oil had migrated along this subsurface pathway down the canyon to the check dam. The oil did not resurface. Fortunately, the gravel layer did not extend beyond the check dam. If it had, the oil may have migrated undetected to Little Panoche Creek. The lesson learned is that deeper core samples should be collected to assess subsurface conditions, especially within drainage channels . There are some limitations in the use of infrared cameras for detecting underground fires . The infrared camera survey failed to detect the burning tires beneath the fire break embankment . An infrared camera measures the temperatures of surface surroundings, but cannot penetrate into the subsurface . The survey team speculated that if underground tires were smoldering, the heat generated by this process would be measured