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Mr. Donald Rodgers - 2 - 9 October.2008 515 West Charter Way, StQton, San Joaquin County petroleum hydrocarbons. ORP generally decreased with the exception of MW-7S, which increased in ORP at 40 psig. The air sparging radius of influence (ROI) was calculated as 10 feet. The Report concludes that: 1. The well DO, BOD, and COD data show a high oxygen demand. 2. The two day pilot test did not provide enough time to evaluate DO distribution through the aquifer and oxygen uptake by aerobic bacteria; however, oxygen consumption is inferred by BOD and COD to be very rapid. 3. While the pilot study did not deliver adequate oxygen to evaluate biosparging as a remedy, biosparging should theoretically work at the site since bacteria populations are adequate, the dissolved iron concentration (3 mg/L) is not high enough to limit microbial biodegradation, generally DO levels (<2 mg/L) show groundwater conditions are anaerobic, and the injection of air (with nutrients nitrate and phosphate) into the aquifer should stimulate biodegradation. The Report recommends scaling up the biosparging system with 12 additional sparge wells spaced 10 feet apart, substitute pure oxygen for air as the injection gas, and run the biosparge system for one year under a new pilot study or as an interim remediation. Comment: The proposal to scale up the system from one to thirteen sparge points and then rerun the pilot test for one year is not approved. This proposal appears excessive and is not cost effective, in that the pilot study data results do not support full scale treatment by biosparging. Unless additional, conclusive supporting documentation can be supplied to show why biosparging will work at this site after it failed the first pilot study, it has not been shown to be cost-effective. However, other treatment options have been evaluated in the past, and one treatment technology was very effective in removing considerable mass of petroleum hydrocarbons from soil. Soil vapor extraction (SVE) was conducted from 2000 to 2004, and removed a reported 3,244 pounds of gasoline. The November 2007 Feasibility Study (FS), which recommended biosparging for groundwater treatment, also evaluated groundwater pump and treatment, air sparging (AS) with SVE to capture fugitive vapors, and ozone injection. The AS/SVE received the second highest FS grade (moderate to high for effective implementation, and moderate for cost) after biosparging. Since there are four existing vapor wells that might be used for SVE and one existing air sparging well; I recommend that consideration and evaluation of a pilot study for AS/SVE to, as the FS states, help evaluate the effectiveness of AS and to design a full scale AS system, since SVE is known to be effective. Please provide a new workplan to evaluate other remedial alternatives, such as AS/SVE. The workplan is due 1 December 2008. If you have any questions you may call me at (916) 464-4615, or email me at jbarton@waterboards.ca.gov. James L. L. Barton, P.G. Engineering Geologist cc: Mr. Mark Owens, UST Cleanup Fund, SWRCB, Sacramento Ms. Margaret Lagorio, San Joaquin County Environmental Health Department, Stockton Mr. Charles Metzinger, Shaw Environmental, 1326 North Market Blvd., Sacramento 95834