SITE INFORMATION AND CORRESPONDENCE

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Frontier Transport • - 2 - • 28 December 2016 ~ 425 Larch Road Tracy, San Joaquin County 3. Please also include analysis for percent oxygen in the analytical suite for soil gas samples. Analysis of percent oxygen will aid in determining the presence of a bio-attenuation zone. 4. At a minimum, please collect at least one soil sample from each soil gas probe boring for laboratory analysis. Collection of soil data from these sample locations will aid in determining if a bio-attenuation zone is present at the Site. 5. Proposed well MW-30 should be moved due south of proposed well MW-29 and due west of existing well MW-28. Installation of proposed well MW-30 in this revised location will allow for lateral delineation to the west of MW-28. 6. The groundwater monitoring program detailed in the Addendum is acceptable. EMS proposes to perform quarterly to semi-annual groundwater monitoring of select wells. Groundwater samples are proposed to be analyzed for: TPH-G, BTEX, MTBE, DIPE, ETBE, TAME, TBA, 1,2-DCA, EDB, and naphthalene. The proposed sampling frequency of Site wells is as follows: Monitoring Well Sam ing Frequency Quarter) Semi-Annual first and thirdquarters) MW-1, MW-5, MW-17, MW-19 through MW-24, MW-2, MW-4, MW-8, MW-9 MW-27 through MW-31, DPE-3 The Fourth Quarter 2016 Quarterly Groundwater Monitoring Report is due 1 February 2017. 7. EMS did not provide well construction details for the three (3) proposed wells in the Addendum, however in the Work Plan, groundwater monitoring wells were proposed to be screened from 5 to 20 ft logs. The well construction details proposed in the Work Plan are acceptable. 8. In my letter dated 25 October 2016, 1 requested a scope of work for vertical delineation. In the Addendum, EMS provided analytical data for the existing deeper screened wells, MW-12 through MW-16, and MW-18, screened from 30 to 40 feet below ground surface (ft bgs). Wells MW-12, and MW-14 through MW16 were destroyed in 2014, after several years of petroleum hydrocarbons not being detected in these wells. Based on a review of data from these wells, groundwater pollution at the Site appears to have been adequately delineated vertically and I rescind the request for this scope of work. 9. In the memo attached to the 16 November 2015 staff letter, in the 15 April 2016 staff letter, and in the 25 October 2016 staff letter, I requested that all future reports include a table with all well and boring construction information, including at a minimum: well or boring name, coordinates (latitude and longitude), elevation, total depth, well diameter, screen interval, and filter pack interval. Existing and destroyed wells should be included on this table. A well construction details table was not included in the Addendum. Inclusion of this information will aid review. This is my fourth request that a well construction details table be included in all future reports and work plans. Please assure