SITE INFORMATION AND CORRESPONDENCE

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Shell No. 204-7524-4404 - 2 - 30 September 2009 • 3011 W. Benjamin Holt Driveelockton petroleum hydrocarbons were detected in a grab groundwater sample (TPHg, 220 micrograms per Liter, or ug/L; and MTBE, 9.2 ug/L). The USTs system was replaced in 2004 (Gen 3) and the Site reopened as an operating Shell-branded (not Shell-owned) station. Groundwater monitoring sample results from a series of Site wells (MW-1, MW-2, MW-5, MW-11, and MW-12; Figure 2), conducted from November of 1996 through the present, show a series of increases and decreases in concentrations (peaks) that correlate to a MTBE plume moving in the downgradient direction towards 1-5. However, the declining trends in concentration have not been consistent, and have shown several minor increases/decreases. In April 2006, analysis of MW-11 groundwater reported an increase to 86 pg/L. Subsequent groundwater monitoring of MW-11 showed a gradual decline in MTBE concentrations to 24 ug/L in December 2007, the last monitoring event. All monitoring wells were properly abandoned on 6 August 2009. The recorded groundwater elevation varied from four to nine feet below mean sea level. The depth to water varied from four to eighteen feet below ground surface (the variation in depth to water was primarily due to some of the monitoring wells located in the raised off-ramp of the elevated 1-5). The direction of groundwater flow varied from North to Northeast at an average gradient of 0.003 feet/feet, towards 1-5. On 30 August 2006, the SJCEHD requested closure concurrence from the Regional Water Quality Control Board — Central Valley Region (Regional Water Board) Executive Officer. In a memo dated 15 December 2006 (attached to the non-concurrence letter), staff cited a lack of a stable plume or declining groundwater concentrations, an inadequate downgradient monitoring well network, and potential threats to sensitive receptors (public supply wells located 2,500 feet . east of 1-5). The non-concurrence letter requested the change of lead agency, and on 3 January 2007., the SJCEHD transferred lead agency status to the Regional Water Board. In a letter dated 24 January 2007 Regional Water Board staff (staff) notified Shell of the change in lead agency. Shell continued quarterly monitoring and reporting until December 2007, when monitoring was suspended with staff concurrence. .During a conference call on 26 April 2007, Shell's consultant Conestoga-Rovers & Associates (C-R&A) proposed a fate and transport modeling exercise with existing data for the groundwater plume, in lieu of an additional investigation workplan and a report. The rational for the model was that the MTBE groundwater plume had migrated offsite to the northeast underneath 1-5, complicating further investigation due to access issues with Caltrans, and that a model would substitute for the groundwater investigation. Staff agreed and C-R&A submitted the Fate and Transport Model (Model) on 31 December 2007. The Model used a two dimensional Microsoft Excel spreadsheet-based program (Bioscreen version 1.4) for groundwater provided as freeware from the US Environmental Protection Agency (USEPA), to estimate the fate (how much time will the plume persist) and transport (how far the plume will migrate) of the MTBE plume. The Model evaluated two separate Site data sets for a target final MTBE concentration of 5 ug/L, the Regional Water Board Water Quality Goal (WQG) for Taste and Odor Threshold, and to determine the MTBE concentrations and plume length. The MTBE data sets were the second quarter 2007 (2Q2007) maximum for that quarter monitoring datum (25 ug/L), which was run to the year 2017, and the second quarter 1997 (2Q1997) maximum site monitoring datum (29,000 ug/L), which was run to the year 2042.