SITE INFORMATION AND CORRESPONDENCE

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Mr. Dale Gillespie • 2 - • 23 April 2008 16 Cherokee Lane, Lodi ceasing the ozone injection into the aquifer. When groundwater monitoring revealed that onsite groundwater contaminant concentrations had increased in several onsite wells in February 2007, AGE restarted the ozone system in April 2007. In May 2007, the TPHg concentration in groundwater at off-site well MW-9 increased over an order of magnitude to 23,000 ug/L. Subsequent monitoring events conducted since May 2007 under active groundwater remediation show that the TPHg groundwater concentration has stabilized around 4,000 ug/L in offsite MW-9. However, the current remediation system has not effectively treated the offsite groundwater contamination to the point where petroleum hydrocarbons concentrations will continue to decline to Regional Board Water Quality Goals. Previously AGE stated in discussion with me that trenching under Cherokee Street, to extend the onsite ozone system to MW-9, was impractical due to the buried utilities in the street. Likewise a batch extraction of groundwater from MW-9, conducted in September 2006, was unsuccessful due to the slow recharge rate (0.3 gallons per minute). Therefore an in-situ chemical oxidation groundwater remediation may be warranted and will be considered. Groundwater monitoring indicates that the primary source of the contamination appears to be located between onsite MW-8 and offsite MW-9, extending under Cherokee Street. Injecting ORC® (weak oxidant) in a limited area around MW-9 may not be effective in this case. For that reason I strongly suggest that you prepare a workplan to conduct a more aggressive in-situ chemical oxidation (ISCO) remediation as a pilot study, by injecting a more reactive oxidant (e.g., modified Fenton's Reagent, etc.) on both sides of Cherokee Street, onsite near MW-8 and offsite near MW-9, to the most practical extent into the adjacent school yard. Schedule the injections so that the school is out of session (late May-early June) and monitor select wells on a monthly basis. Evaluate the data for two months and, if necessary, recommend and schedule a second injection before school resumes in the fall (late August-early September). Include the full list of metals (including hexavalent chromium) and full list of general minerals (including bromide/bromate) in the monitoring plan of the workplan, and use the Interstate Technologies and Regulatory Commission (ITRC) guidance for ISCO to design the pilot study. A copy of the ISCO-2 revised guidance may be downloaded from the Internet at: hftp://www.itrcweb.org/guidancedocument.asp?TID=l 3 3) In an email to AGE on 21 April 2008, 1 requested a rationale for the proposed on-site vapor well destruction and a figure showing the locations of the wells. AGE responded by email that the wells were no longer needed, and that destruction would "...aid in preparing the site for closure." The email included an attached onsite Figure 2 (enclosed), which shows seven vapor wells (VW-1 through VW-7), monitoring wells, an extraction well, and borings. While I concur that the on-site vapor wells are no longer needed, I question whether it is cost effective to destroy the vapor wells now and then destroy the remaining wells later when closure is approved. Please provide evidence that destroying the seven vapor wells now is more cost effective and necessary, as opposed to waiting and destroying all of the wells later.