SITE INFORMATION AND CORRESPONDENCE

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Ms Jennifer Sedlachek, Ex-10Nlobil - 2 - • 25 October 2006 75 Alpine Avenue. Stockton immediately west of the Site and the child daycare center, which could be accomplished by using the existing soil and groundwater data. 3. The deeper monitoring wells may be installed in a second phase after the groundwater flow direction and gradient are documented by the first phase of shallow monitoring wells. Since submittal of the Phase I Environmental Site Assessment on 24 August 2006. the eastern half of the Site has been developed and is now a landscaped, fenced and a raised paved area extending into the parking lot for the church/child care center. A fence separates the residence to the west from the parking lot. The western half of the Site remains undeveloped and controlled by the owner of the residence. although there was a For Sale sign for the property in September 2006. Due to the proximity of sensitive receptors, expediting the soil vapor intrusion investigation to provide the data for the risk assessment is a high priority for Regional Board staff. Mr Moise, ETIC and I also discussed the analytical methods and the investigation in the waste oil tank area. Please review Table 2 (enclosed) for the analyses. All work shall be done in accordance with Appendix A — Reports; Tri-Regional Board Staff Recommendations for Preliminary Investigations and Evaluation of Underground Tank Sites. dated 16 April 2004, which is available through the website listed in the header of this letter. The Workplan is approved with the following modifications: 1 All proposed monitoring and vapor wells shall be relocated within the constraints of the recent Site development to the greatest extent possible, by 29 December 2006. 2. Up to two additional soil vapor wells shall also be installed by 29 December 2006. to provide vapor migration data at the Site property boundaries for the risk assessment. Suggested additional locations are: the eastern boundary of the eastern half of the Site along EI Dorado Street, and the northern boundary of the western half of the Site, adjacent to the church/daycare center parking lot. 3. A Report of the investigation and the risk assessment will be submitted by 23 February 2007. A new Figure showing the actual locations of all wells and borings will be included in the Report. 4 The report shall include a conclusions and recommendations section for deeper borings and monitoring wells, to determine vertical extent of groundwater pollution. The deeper wells shall be installed no later than the 27 April 2007, with a report of the vertical delineation of the pollution due by 29 June 2007- 5. All requests for extensions shall be in writing, include a chronology of events and attempts to procure rights of entry and drilling contracts or other extenuating circumstances, and include a new schedule to conduct the work. 6. The EPA protocol allows BTEX to be analyzed for with EPA SW-86 Method 82060B or 8021 B. however. 8260B has lower detection limits, is subject to less interference in highly contaminated groundwater, and tends to be more economical by providing BTEX and MtBE data in the same analysis. Concerns about co-elution with some alkanes requires at least one confirmatory analysis with SW-86 Method 8260 per site. BTEX by Method 8021 is not capable of confirming the chemical identity of the analyte without at least one confirmatory analysis with SW-86 Method 8260 per site.