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Mr. Soon Kim Page 14 December 19, 1995 Intrinsic Bioremediation Demonstration Samples were collected from monitoring wells MW-DIS-2, 3,4, 9, 8S, and 8D by the minimum aeration protocol presented in the Appendix of the PAR/FRP(CH2M HELL, April i' 1995). In brief,the intent of this demonstration is to evaluate the geochemical indicators of natural biodegradation and assess the potential for self containment and abatement of the Disco Site gasoline plume without the expense of more aggressive remedial measures. Analytical Results The geochemical indicators summarized in Table 4 and presented as iso-concentration contour maps on Figures 4 through 9 include BTEX, nitrate, ferrous iron, sulfate,dissolved methane, and dissolved oxygen concentration in shallow groundwater. The interpretation of the iso-concentration contours for these parameters are based on a combination of measured values and historical information about the shape of the gasoline plume. Table 4 Summary of ITB Geochemical Indicators Del Monte Plant 33 Stockton, California Concentration (m ) Well Sample Dissolved Dissolved - Iron Nitrate Sulfate Date Methane Oxygen (Fe2+) I MW-DIS-2 10/25/95 0.0025 0.20 1.28 <0.02 7.88 MW-DIS-3 10/25/95 0.0016 0.40 0.0509 <0.02 7.99 MW-DIS-4 10/25/95 0.0009 1.80 9.54 6.78 10.30 MW-DIS-8S 10/25/95 0.0012 0.40 1.04 4.40 24.90 MW-DIS-813 10/25/95 0.0010 0.40 <0.025 3.08 10.60 MW-DIS-9 110/25/951 0.0007 0.80 0.0596 8.23 29.90 Note: i <0.02: Below Detection limit of 0.02 m /L I Figure 4 shows the ITB parameters associated with each of the wells monitored. The dashed lines in the central lower third indicate the"zone of significant contamination"based on 1 historic information, and the zone of source removal effected by the AS/SVE system with a 25 to 30 foot radius of influence. r