SITE INFORMATION AND CORRESPONDENCE_FILE 2

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Mr. Larry Higinbotham Thrifty Station #172 Page 2 of 3 Remediation, Chapter 13, Chemical Oxidation (May 2004). Those site characteristics: a lack of free product and carbonate geology, soil permeability > 1 x 10-6 feet/sec, and highly soluble contaminants of concern (benzene and MTBE) provide the initial technical justification for proposing the method. Based on the information presented in the Plan, the EHD concurs with the conclusion that ozone injection is a potentially viable remedial option for this site, but cannot approve the pilot test without a waste discharge requirements (WDRs) evaluation by the Central Valley Regional Water Quality Control Board (CVRWQCB) and some additional technical information. To effectively decompose contaminants, ozone must have direct contact with the contaminants. Ozone degrades rapidly in the subsurface, its half-live variously estimated to be 20 to 40 minutes. During this limited window of time, various factors operate to minimize the potential for ozone contact with the chemicals of concern, for example limited relative permeability of the soil matrix to ozone and dissolved chemical migration, competing chemical reactions with naturally occurring organic matter (NOM), and reactive soil mineralogy. The NOM and reactive soil minerals should be characterized to more adequately evaluate site suitability for ozone injection. EHD recognizes that all the data for this evaluation may not be in hand at present, therefore the EHD is prepared to approve a work plan to acquire soil and groundwater samples to conduct bench-scale tests (BST) or a geochemical evaluation. If the test is conducted according to the guidance provided in Technical and Regulatory Guidance for In Situ Chemical oxidation of Contaminated Soil and Groundwater (January 2005) issued by the Interstate Technology & Regulatory Council In Situ Chemical Oxidation Team, data will be acquired that the CVRWQCB requires to evaluate the process for WDRs. The EHD cannot approve ozone injection without the WDR issue being addressed to the satisfaction of the CVRWQCB. If you propose and conduct the BST, the report of findings can include an evaluation of the potential effect of NOM and reactive minerals on ozone injection and an estimate of the ozone budget and duration required for the desired remediation. The Plan contains data that indicates that of the 87,646 pounds of contaminants originally estimated to be in place on the site, an estimated mass of 153,215 pounds have been removed. GHCI concluded that this successful SVE effort was substantial and appears to be approaching asymptotic concentrations. Recent contaminant mass removal rates were not included in the Plan and there were no additional residual mass calculations offered to support the conclusion that the removal rate was approaching asymptotic conditions. Current SVE removal rate data is needed so EHD can evaluate and concur with TOC's interpretation that the system has achieved asymptotic conditions and that continuation of the remedial effort is no longer cost effective. Submit a report to the EHD by 01 December 2006 evaluating the SVE performance with the various mass estimates included.