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STANDARD BIOLOGICAL APPROACHES As a prerequisite to determining which, if any, bioremediai approach will be effective at a given site, it is important to understand and evaluate all the parameters at work, particularly the environmental (micro- biological/physicochemical) and physical (geotechnical) parameters which can influence overall bioreme- dial efficacy. Before selecting a method, the practitioner should first determine what the desired objectives are, and what the data collected throughout the project duration will be used to accomplish. The first and most significant step in determining which biological approach(including mechanical oxygen- enhancement techniques) is appropriate for a given site is the evaluation of certain fundamental site-specific parameters, particularly the presence and viability of existing localized microbial populations. To exem- plify the importance of performing analyses that characterize site-specific microbial parameters before making bioremedial decisions, consider the following questions derived from actual project experiences. How could a passive or biostimulatory (nutrient, peroxide additions, bioventing, biosparging) approach logistically be proposed to effect site cleanup when little or no organisms capable of degrading the contaminant (selective microbes) were recovered from a site? Conversely, how could the expense associated with an exogenous bioaugmentation approach be justified when there are high levels of organisms present which could be enhanced to effect contaminant degradation? Whether in situ or ex situ applications of bioremediation are considered, there are two general approaches to bioremedial site cleanup: Passive/Intrinsic -just let sit and monitor with little or no physical interaction - primarily reliant on reduced conditions and anaerobic processes. Active- includes biostimulation - stimulatelenhance activity of indigenous (existing) bacterial populations via supplementation with nutrients, oxygen, moisture, etc.; method includes mechanical technologies - stimulation of microbial activity via mechanical introduction of oxygen (eg., bioventing, biosparging, etc); inherently reliant on microbial activity and nutrient availability/utilization parameters; bioaugmentation -introduction of exogenous com- mercial bacteria and/or the cultivation and reintroduction of indigenous microorganisms. Environmental practitioners should be careful not to confuse passiv&'tntrinsic bioremediation with "Natural Attenuation"(NA) or "Risk Based Corrective Action" (RSCA). While passive/intrinsic biore- mediation is perhaps quite often the most important and integral component of NA & RBCA approaches, the investigation, implementation and effectiveness of these methodologies also take into consideration parameters such as dilution, sorption, and migratory activity(fate&transport) of potential sensitive recep- tors. As such, caution must be taken in making biological interpretations in consideration of these factors. SITE SAMPLING CONSIDERATIONS There are several general factors that Biologic routinely takes into consideration when identifying sampling locations including, but not limited to: site lithology, depth, saturated vs. unsaturated zones (soil), aerobic/anaerobic cores, substrate types/concentrations (diffusion thereof), ground water velocity/fluctua- tions, soil vs. aqueous matrixes, and appropriate sampling techniques. Any of these environmental influences, alone or in combination, can dictate not only the appropriate sampling areas/zones, and the quantity and number of samples to be collected, but can directly impact the validity of data interpretation from site characterizations and evaluations. 3