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1 <br /> i <br /> I <br />' Mr Bill Little <br /> Advanced Geo Environmental (North) <br />' GUERDINO and CRAWFORD <br /> May 5, 1997 <br /> I Page 2 <br /> COMMENT <br /> The results from these analyses indicate that there is considerable environmental heterogeneity <br /> between sources for the samples analyzed, which is unrelated to evaluated physicochemistry <br /> Evidence for this conclusion is derived from comparative microbial enumerations which <br /> indicate biological suppression associated with Sample P7-10 Although the pH for both <br /> samples is relatively alkaline, this alone cannot account for differences in microbial viability <br /> • noted for the samples since there appears to be no suppression associated for Sample P5-15 <br /> Furthermore, all other physicochemical parameteres appear to be within acceptable ranges for <br /> microbial growth and metabolic activity <br /> There is a high proportion of selective microbial biodegraders noted for P5-15,suggesting both <br /> a relatively long degree of localized miocrobial exposure to the contaminant, and a well- <br /> established and adapted microbial population capable of biodegrading gasoline Together with <br /> the noted physicochemical data, such information is consistent with natural bioattenuation <br /> protocol (although periodic monitoring will be required to ascertain the degree of <br /> bioattenuation which is occurring over time) Conversely, both general (heterotrophic) and <br /> selective (contaminant-specific) microbial subpopulations are well below normal for Sample <br /> P7-10, suggesting the presence of biotoxicity possibly due to undefined chemicals, metals, <br /> or other factors which may preclude active microbial growth and metabolism Presently <br /> therefore, these soils would not be considered undergoing active bioattenuation Per our <br /> discussion, you may wish to evaluate subsurface waters to determine whether and to what <br /> degree natural attenuation may be occurring, since localized physicochemical and <br /> ' microbiological conditions will likely be dissimilar to those encountered for the associated soils <br /> ' Should you have any questions concerning this information, please do not hesitate to contact <br /> me <br /> I <br /> AKK ch <br />