SITE INFORMATION AND CORRESPONDENCE

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Remo Canepa Page 2 of 9 �I 6230 Pacific Avenue 4/17/2009 Stockton CA �i with which the EHD concurs. To confirm or refute the hypothesis, the EHD has reviewed site data to find additional evidence that a second release has occurred ; records reviewed include the file maintained by the EHD for installation , operation , inspections , and modifications of the active UST system on the subject site; the investigation history and findings for the site, and the remediation history of the site. Review of the EHD file for maintenance and operation of the active UST system did not reveal any items suggestive of a release since 1993 ; no significant violations have been issued, no emergency repairs permitted or reported, no evidence of fuel release during site inspections , and no reported alarms associated with actual releases. During the site investigation , impacted soil was noted between 35 and 56. 5 feet below surface grade (bsg) in boring B-1 , between 20 and 55 feet bsg in boring MW-1 , between 40 and 67 feet bsg in boring MW-2, and was reportedly present in borings advanced to approximately 55 feet bsg for vapor well installations (SV- 1 through SV-9), however, only samples from B- 1 , SB- 1 and SB-2 were submitted for laboratory analysis to quantify contaminant concentrations in soil. Condor Earth Technologies (CET) produced concentration contour maps of impacted soil at varying depth intervals for the UST and dispenser area and estimated the contaminant mass in soil at 13, 000 pounds of total petroleum hydrocarbons quantified as gasoline (TPHg ). An SVE system operated on the site from March 1994 to June 1995 and from March 1999 to January 2008 ; an estimated 11 ,058 pounds of TPHg has been removed by SVE. A groundwater extraction system (GWE) has been in operation on the site from November 2004 through the present; an estimated 756 pounds of TPHg has been removed via GWE though the first quarter of 2008 . The total mass estimated to be removed from the subsurface through SVE and GWE would be 11 , 814 pounds, or 90 .9% of the originally estimated mass. As the concentrations of dissolved contaminants have not been similarly reduced , it would appear that the original mass was greatly underestimated and/or a second release significantly increased it. The EHD prepared graphs of concentration trends over time, from 1994 through 2008, of TPHg , benzene and MTBE concentrations in monitoring wells MWA , MW-2, MW-3 and SV-4, the wells the F&B noted were impacted by n-butanes and pentanes . F&B actually included MW-7 instead of SV-4, but MW-7 is not significantly impacted and the laboratory sample number appears to be that of SV-4. The following graphs plot concentrations of TPHg , benzene and MTBE over time in the significantly impacted groundwater monitoring wells; older data is on the left, more recent data on the right. Data points obtained close in time to significant events on site, such as initiation of the SVE operation (March 1999) or the GWE operation (November 2004), are labeled to assist analysis of the effects of these remedial actions on contaminant concentrations. The EHD noted the following contaminant concentration trends : Second Release Evaluation 0409 f