SITE INFORMATION AND CORRESPONDENCE_FILE 2

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Mr. Russell Chapin 1766 W. Monte Diablo Avenue Page 2 of 3 to the ESLs and CHSSLs, the potential for vapor intrusion into structures must be evaluated. The EHD also noted at the Meeting that groundwater in shallow sand unit(s) southeast of your site should be assessed for contaminants. You then agreed that assessment of groundwater and evaluation of the potential for soil vapor intrusion was appropriate. Your agreement on the soil vapor intrusion issue appears to be affirmed in your letters of 27 August 2006 and 17 September 2006, but additional assessment of groundwater in the shallow sand unit toward the southeast was not noted in the letters. Your letter of 17 September 2006 indicates that you have directed your consultant, Advanced GeoEnvironmental, Inc. (AGE) to prepare a work plan "that includes assessment and criteria by the CVRWQCB for closure consideration" which appears to include assessing the potential for vapor intrusion and updating the vapor extraction system utilizing dual-phase extraction. You also indicate that "Should there be any regulatory objections that might cause further delay and add to the already excessive cost to this project" that you are "prepared to re- submit our letter (Nov. 04) Underground Tank Closure Appeal". You may, of course, appeal your case to the California State Water Resources Control Board (CSWRCB) at any time. The EHD will respond to your closure request with a technical presentation that shows closure of your site is not appropriate at this time. The requirement for evaluation of applicable ESLs, CHSSLs and vapor intrusion were brought to your attention so that they could be addressed while you continue to move your site toward closure by addressing the'all of EHD's concerns. These concerns are briefly noted above (paragraph 2) and discussed in more detail in EHD letters dated 03 March 2005, 25 January 2005 (addressed to Elizabeth Havens, SWRCB), 07 January 2005 and 04 October 2004. The EHD's concurrence will be based on an adequate technical presentation that addresses the EHD's concerns. To gain the EHD's concurrence with your next closure request, the EHD recommends that you and your consultants carefully review the referenced letters and prepare work plan(s) for any fieldwork needed to acquire data necessary to properly address these issues. Your letter of 17 September 2006 included an estimate of the residual masses of contaminants to be left on site, presumably dissolved, that included 36.9 pounds of total petroleum hydrocarbons quantified as gasoline (TPH-g). While concerned with the dissolved contaminant mass, the EHD is also concerned with the 5,733 pounds of TPH-g (sorbed) estimated by ATC Associates, Inc. (ATC) to be left on site (an estimate the EHD considered to be low as recent soil data had not been included in the estimate). This high sorbed mass appears to be the cause for persistently high dissolved contaminant concentrations and potential dissolved plume instability.