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1 Biodegradation is accomplished through the consumption of organics (the contamination, in this case) by indigenous microorganisms. Consequently, to optimize biodegradation, an adequate microbial population must exist. This can be evaluated by performing a ' heterotrophic plate count. For groundwater, microbial populations typically range from 100 to 100,000 CFU/ml (Suthersan, 1997). Higher counts generally suggest a healthier population. Following insertion of the ORCO, the large increase in the heterotrophic plate count indicated ' an increase subsurface oxygen. This result typically would indicate that ORCO emplacement Would be effective in assisting and speeding the natural biodegradation process. ' 5.0 RECOMMENDATIONS ' Based on the mass balance calculations and the results of the ORCO test, JJW recommends the following: ' 1. Based on the results of the past year's quarterly sampling events, the overall history of the site, and generally low masses of contaminants, San Joaquin County Environmental Health Division may want to consider site closure, with a "no further action required" letter issued by ' the appropriate regulatory agencies. 2. If contaminate level are deemed too high by the San Joaquin County Environmental Health Division, then the next step would probably include ORCO emplacement in a number of direct- push holes prior to re-establishing quarterly monitoring. ' . 6.0 LIMITATIONS The lack of identification of contamination on a site does not preclude its existence. JJW ' Geosciences incorporates the current, standard of care when making judgments concerning the presence of contamination on a site. However, due to natural circumstances, it is not always possible to identify and/or accurately determine the presence of contamination. ' Additionally, changes in appropriate standards may occur, whether they result from legislation, the broadening of knowledge, or other reasons. Such changes may invalidate certain findings of this report. This report has been prepared for the exclusive use of the client and is applicable only for the subject site. JJW Geosciences is not responsible for interpretations by others of the data ' presented in this report. This report does not represent a legal opinion and no warranty is expressed or implied. This report is issued with the understanding that it is the responsibility of the property owner to ensure that the information and recommendations contained herein are brought to the attention of the appropriate regulatory agency. This work was performed in accordance with the generally accepted standards of care existing in Northern California at the time of the ' investigation. 1 1 4 JJW GEOSCIENCES Inc.