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r SITE CONCEPTUAL MODEL AND REMEDIAL ACTION PLAN 7 7-Eleven Store No 14117, 2725 Country Club Blvd ,Stockton CA June 20 2002 Bacterial species known to degrade MTBE include Gordonia, Hydrogenophaga, Nocardia, Rodococcus, Sphingomonas, Xanthobacter, Methylobactenum, Flavobacteria-Cytophaga, Alcaligenes, Mycobacterium, Rubrivivax, Arthrobacter, Acldovorax, Burkholderia, Variovorax, and Pseudomonas Generally, bacterial ' 1 populations are observed to consume other petroleum species (e g , benzene) before consuming MTBE and/or TBA ' Intrinsic biodegradation strategies for oxygenates usually consist of creating a large microbial population ' that then consumes all petroleum constituents, not just those most easily biodegraded Stimulation of intrinsic biodegradation is conducted through 1) Injection of oxygen (i e , via sparging or injection of oxygen-releasing compound [ORC]) and/or 2) injection of nutrient substances with or without additional ' bacterial colonies using sparge or other types of injection wells Some regulatory agencies do not approve the injection of bacterial and/or nutrients, due to background water quality concerns 431 Pilot Test Review of site groundwater analytical data (Appendix B) indicate that intrinsic biodegradation may already be occurring at the site, based on declines in dissolved MTBE levels and correlating increases in dissolved TBA levels It Is the increase in TBA relative to a decrease in MTBE that points to possible indigenous intrinsic biodegradation If both components had increased over time, a new ongoing release might be indicated Relatively low DO levels of less than 1 milligram per liter(mg/L) at the site (IT Corporation, April 2002) indicate that if intrinsic biodegradation is occurring, it is under non-aerobic ' conditions Intrinsic biodegradation potential was evaluated in conjunction with testing for DPE applicability ' The pilot test for the site was conducted on May 29, 2002, using well MW-2 as the extraction point, based on its location in the area of highest MTBE and TBA concentrations ' To evaluate potential indigenous bacterial populations, a grab groundwater sample was collected using a bailer from well MW-2 prior to initiation of the DPE test The sample was submitted to Sierra Foothill ' Laboratories for analysis by SM9215 for heterotrophic plate count(HPC) (an analysis of the total number of bacterial colonies present per milliliter) ' After collection of the HPC sample, the DPE test was initiated on well MW-2 A stinger tube was inserted to about 10 feet bg into the well (or about 3 feet below the top of the water surface), and vacuum was applied at 20 Inches of mercury using a vacuum truck Nearby monitoring wells MW-1 and MW-4 were observed for water level changes during the test In addition, extracted vapor levels were monitored with a flame-ionization detector(FID) (Appendix B) 1 14117Scm2 doc r