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. i .. .-. ._.. _ - :: Harlen Knoll 44 March 17, 1991 Page 2 Laboratory Analysis All samples were delivered within 24 hours to a California Certified analytical laboratory. Samples collected during this fourth round of sampling were analyzed for both purgeable halocarbons(EPA Method 601)and volatile aromatic hydrocarbons(EPA Method 602)per our discussion in February, 1991. Along with normal laboratory quality control measures, at least 10 percent spike and 10 percent duplicate samples will be run with each analysis set for quality assurance and quality control. A sample blank obtained by passing deionized water through a cleaned bailer was also analyzed to verify on-site decontamination procedures. The most significant analytical results are summarized below in Table 1, detailed analytical reports and field logs are provided in Appendix 1. Conclusions and Recommendations The absence of volatile aromatic compounds and the presence of only very low concentrations of purgeable halogenated hydrocarbons indicates that there is little or no health risk associated with the uppermost groundwater, even if it were being used far public consumption. For example, 1,1,1 trichloroethane has been found consistently in the groundwater collected from MW-1 at levels ranging from 4.2 to S ug/L. The Primary Maximum Contaminant F.evel and EPAs goal for this constituent is 200 u 25 times the concentration actually found in the groundwater. As a result, Murray & Associates recommends that Mr. Lambert Barnum be allowed to discontinue the groundwater monitoring program at the Stan Mori Ford Dealership in Tracy, and that a Site Closure be granted. If you have any questions concerning this data,or would like additional information, please 4 call me at your earliest convenience. Si rely, ent S. Murray, Ph.D. President KSM:ca1- -- - --- -- Attachment cc: Mr. Lambert C. Barnum to -