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• From 1200 hours, March 3, 1988 through 1200 hours, March 4, 1988 the average wind speed was 4 mph. The predominant wind direction was from the 90-degree quad- rant bounded by the southeast and southwest axes. The wind directional samplers were oriented so they would be activated by winds coming from the 90-degree quadrant bounded by the west- northwest and north-northeast axes. Review of the wind data over the periods mentioned above indicates that the wind came from this quad- rant nearly 30 percent of the time during the 72-hour sampling period. Benzene, methylene chloride, tetrachloroethylene, carbon tetrachlo- ride, 1,1, 1 trichloroethane, trichloroethylene, and chloroform were detected during the 3 days of ambient air monitoring. Benzene, carbon tetrachloride, and chloroform concentrations were below their respec- tive regulatory detection limits. Field blanks collected on the same days contained benzene, methylene chloride, 1 ,1, 1-trichloroethane, trichloroethylene, and chloroform (see Table 7) . Methylene chloride and 1,1, 1-trichloroethane concentrations were Y elevated in Sample AA-13 probably due to the very limited sample volume collected over the 24-hour period. The limited sample volume may have resulted from a pump malfunction. Central Coast has ex- plained that for very limited sample volumes, sample contamination may occur due to methylene chloride from laboratory air infiltrating into the sample bag during the long time (up to 20 minutes) that it takes to load the sample (see Appendix D) . The Tedlar bags may also be contaminated with small amounts of methylene chloride; the concentra- tions in the samples may be augmented due to the small sample volumes involved. Sample AA-3, a 24-hour downwind sample, was designated as invalid because a poor connection of the Tedlar bag in the sampler resulted in no sample. PJ9 9390304.00D 3-4 Rev. 0 09/20/88