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Michael P. Kenny, Executive Officer -4- September 3, 1998 summer are approximately 5 - 10 µg/m3. Normal wintertime concentrations are as high as 80 µg/m3. On August 9, 1998, the Springfield Flying Service of Columbia (ARB contractor) reported descriptions of the tire fire smoke as well as the routine air temperature profiles for "burn day" predictions. They reported the base of the plume in the morning was 2500 feet, with a layer about 2000 feet thick fanning out about 10 miles south of Tracy. A higher layer 6000-7500 feet thicker was observed to the east and north. This layer extended over the foothills to the east and north. In the afternoon the base of the smoke was at about 2000 feet and the tops about 5000-5500 feet, with higher layer merging with that to the south. The higher layer had a base at about 7000 feet and tops at about 8500 feet. The smoke plume was reported to be fanning out to the north and south, covering much of the San Joaquin Valley. The layers merged about 50-60 miles south of the burn. The worst visibility was estimated to be about seven miles. Late in the afternoon of August 11, 1998, Dr. Karen Furst, Director of the San Joaquin County Health Department, contacted Bob Leonard of the CD and requested that the monitoring be renewed. On August 12, 1998, the Compliance Division Emergency Response Team continued monitoring for CO, toluene Ti and THC in the affected area, while re Fire Plume with Inversion Layer-8/11/98 the MLD team monitored for Total Carbon (TC) as a surrogate for smoke. Staff continued the gaseous monitoring effort until August 14, 1998 when the Public Health Officer determined that there was no point in monitoring further. Air Monitoring Results Table 1 summarizes the results of the gaseous ambient air monitoring conducted by Compliance Division staff at various locations near the Tracy tire fire. Monitoring sites were changed throughout the night and day due to the changes in the plume direction and in order to monitor the plume at locations between the fire and any possibly affected residents. Background CO levels ranged from 1 ppm to <1 ppm; background THC levels ranged from 8 ppm to <1 ppm, and background toluene levels ranged from 4 ppm to <1 ppm. (Note: Detection limit of the instrument is about 1 ppm; these readings are at the extreme bottom of the instrument range and as such constitute primarily background concentrations and instrument noise.) In-plume