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Ms. Diane Hinson and Ms. Margaret Lagorio Page 2 August 27, 1995 Site-specific information on the occurrence and rate of naturally occurring biodegradation can be derived through groundwater monitoring, in which the concentrations of the reactants and products in these biodegradation processes are measured. This information, in turn, allows projections of future groundwater plume migration. The objective of the intrinsic bioremediation demonstration at the Disco Site is to conduct groundwater'monitoring that will 1) provide insight into the role of naturally occurring biodegradation in plume migration, and 2) support a projection of future plume migration at the site. This information will be considered in selecting the final remedy for the site. Demonstration Monitorin2 Parameters The proposed protocol and parameters for the demonstration are detailed in the PAR/FRP. Attached to this letter is CH2M HILL's Standard Operation Procedure, Groundwater Sampling for Intrinsic Bioremediation Characterizations (SOP). The monitoring parameters recommended by CH2M HILL are consistent with the monitoring parameters recommended by the American Petroleum Institute and the Air Force Center for Environmental Excellence. The primary monitoring parameters for an intrinsic bioremediation demonstration are electron acceptors and electron acceptor indicators such as dissolved oxygen, nitrate, sulfate, sulfide, ferrous iron, and methane. Evaluating the distribution and concentrations of these parameters within and adjacent to a hydrocarbon .plume provides 1) 'proof of the occurrence of contaminant biodegradation activity, 2) insight into the specific.processes responsible for such biodegradation (e.g., aerobic or anaerobic), and 3) data to support projections of biodegradation rate and future plume migration. PHS/EHD recommended inclusion of analytical method ASTM G22 for analyzing hydrocarbon utilizing bacteria. According to our laboratory, analytical method ASTM G22 measures "Resistance of Plastics to Bacteria" which does not appear to be an applicable monitoring parameter for the Disco Site. In general, analytical methods for microorganism enumeration in groundwater samples have a number of limitations. These methods only provide semi-quantitative data on the presence of select hydrocarbon degrading microorganisms, not on their hydrocarbon degrading activity. Also, because hydrocarbon degrading microorganisms tend to attach to surfaces, use of these methods on groundwater samples is particularly inconclusive. For these reasons, we do not recommend the use of analytical method ASTM G22 or microorganism enumeration methods. Generally, the minimum number of monitoring wells needed to conduct an intrinsic bioremediation demonstration include one background or uncontaminated well (preferably upgradient), one well within the dissolved contamination plume, and one well at the downgradient fringe of the plume. The monitoring wells that will be utilized for the demonstration study at the Disco Site are shown in Table 1. These wells will be monitored