SITE INFORMATION AND CORRESPONDENCE FILE 2

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'..✓ Mr.Michael J.Infurna,Jr.—San Joaquin County Public Health Services—Environmental Health Division November 7,2002 observation of only a partial breakdown of MtBE to TBA is seen. Further degradation parameters were not reviewed or analyzed. This process, given the available data, would best describe the observed mass balance transfer from MtBE to TBA seen at the site. The EHD presents an alternative explanation for the observed changes in contaminant concentrations. The EHD presupposes an ongoing release at the site below tank test minimum release rates. GR disagrees with the EHD supposition based on the following: 1)Tosco has not distributed fuel containing MtBE in Northern California since January 1, 2001 (a copy of the Material Safety Data Sheet for unleaded gasoline is attached); 2) Tosco does not and has not utilized TBA as a fuel additive; 3) According to personal communication between Tosco and BP, who occupied the site prior to Tosco, BP did not/does not utilize TBA as a fuel additive; 4) The USTs and product piping at the site are composed of double walled fiberglass with interstitial monitoring devices in place. No alarm conditions have been experienced which would indicate a leaking tank or pipe; 5) The Santa Clara Valley Water District report which concluded that new double wall tanks leak referred only to vapor leaks of MtBE. As stated previously, Tosco fuel has not contained MtBE for the past 21 months, and concentrations of dissolved MtBE in groundwater at the site have been steadily decreasing. Additionally, Tosco now uses ethanol as an oxygenate additive in their fuel, If a new release had occurred, it would have been detected by interstitial alarms, or by an increase in ethanol concentrations in groundwater, a condition which has not been observed at the site. Ethanol has never been detected in groundwater samples collected from the site; 6) Laboratory analysis for TBA has only been performed since December of 2000, it is possible that TBA has been generated by the breakdown of MtBE over a long period of time, which has only recently been observed due to Tosco analyzing groundwater for TBA. The EHD has required that a full scan 8260 be performed on groundwater samples from wells MW-3 and MW-7, in order to determine if MtBE degredation products are present in groundwater. GR will analyze groundwater samples collected from MW-3 and MW-7 for full scan 8260B during the next scheduled quarterly monitoring event. WORK PLAN MODIFICATIONS As requested by the EHD, GR is providing notification of proposed modification to the Work Plan included in GR's Updated CAP (July 8, 2002). GR still intends to install a 10-point ozone sparge remediation system as an interim action to address hydrocarbon impact in the first encountered aquifer. As a standard procedure, GR will collect groundwater samples from at least two monitoring wells on a monthly basis during the routine operation and maintenance (O&M)visits to track the system progress. These data will be included in the Quarterly Monitoring and Sampling Reports as requested by the EHD. Additionally, GR proposes to install two shallow groundwater monitoring wells onsite, one of which was proposed in the July 8, 2002 Work Plan, and a second to replace abandoned well MW-2. The locations of the proposed ozone sparge points and monitoring wells are presented on the attached Figure 2. GR and Tosco wish to postpone the installation of the deep monitoring wells at this time, as allowed by the EHD in their 140245.08 3