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F �P- Passive Bioremediation Assays -%, Passive bioremediation is generally based on the microbiological degradation of contaminants under reduced (anaerobic) conditions. Passive bioremedial considerations require detailed site characterizations encompassing historical data review and process modeling, typically generated .. from geologic, hydraulic, biological, geochemical, analytical (contaminant) and distribution data } (presumably reflects decreasing concentrations over time). The general premise behind passive modeling is to correlate various parameter measurements (i.e., contaminant, biological, and al- ternate electron acceptor/donors, etc.) obtained from the impacted interior of the plume with measurements from the unimpacted exterior area of the plume. Based on observed increases or decreases in levels of these parameters, comparative interpretations can be made as to 1) whether and to what degree microbial degradation of the contaminant is occurring; 2) the existence of background parameter concentrations; and 3) the potential to continuously replen- ish the "nutrients" utilized via biodegradation processes. Once the efficacy of passive biore- mediation is scientifically established, a Long Term Monitoring Plan (LTM) is implemented to ensure that what is expected is actually occurring. Site characterizations performed to assess the potential for passive bioremediation are often incomplete, and, at the minimum, typically require one hydrogeological cycle (four quarters) of monitoring data to evaluate site conditions. In addition to possessing the capabilities to perform complete required biotechnical site assess- ment and modeling, BioLogic offers the following specific tests routinely performed for both initial site assessment or long term monitoring. Routine Testing for Passive Bioremediation 0 General and Selective Enumerations 8 Total Organic Carbon (TOCK 0 Physicochemistry (inclusive of nitrate) 0 Alkalinity 0 Sulfate 0 Iron II(Fe 2-1) -- Ll Chloride 0 Manganese In addition to conducting biotechnical laboratory analyses, BioLogic recommends that field personnel conduct on-site analyses consisting of temperature, dissolved oxygen (DO), Redox potential, and conductivity measurements when collecting samples (please inquire with Bio- Logic for procedures and appropriate sampling techniques). Environmental evaluations should consist of contaminant concentration analysis and perhaps, more importantly, analyses of methane, ethane and ethene levels with additional considerations (and precautions) given to the accumulation of ammonium and hydrogen sulfide both of which are metabolic byproducts of anaerobic processes which could threaten environmental health and safety and preclude the use of a passive bioremediation approach. Environmental practitioners should be careful not to confuse passive intrinsic bioremediation with "Natural Attenuation" (NA) or "Risk Based Corrective Action" (RBCA). While pas- sive/intrinsic bioremediation is perhaps quite often the most important and integral component of NA & RBCA approaches, the investigation, implementation and effectiveness of these method- ologies also take into consideration parameters such as dilution, sorption, and migratory activity (fate & transport) of potential sensitive receptors. As such, caution must be taken in making biological interpretations in consideration of these factors. 8