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Mr. Carl Navarra Page 3 of 3 Tracy, CA 7500 W. Eleventh Street 29 December 2008 that you propose to leave in place, noting why such contamination actually poses little risk to human health, the environment and groundwater quality. Submit a work plan to the EHD by 16 March 2009 to obtain data for the vapor intrusion evaluation; the ESL evaluation can be submitted on the same date, or as part of the report of findings for the vapor intrusion evaluation. Some monitoring wells, impacted by MTBE when last sampled, have not been sampled for several years. During the February 2009 monitoring event, in addition to the wells usually sampled, sample the following wells for laboratory analysis: MW-6, MW-9, MW-15, MW-16, MWFP-1, MWFP-3 and MWFP-4. You may put the following wells on annual sampling: MW-2, MW-5 and MW-12. You may propose a new sampling schedule in the report of findings for the ' first quarter 2009 event. Review of the last MTBE data in groundwater raises a concern that the main plume may be migrating east or west past MW-19, possibly on the east in view of the recent groundwater gradient toward the north-northwest, which may have brought the plume margin into MW-19. Submit a work plan to the EHD by 16 March 2009 to assess groundwater east and west of MW-11 and MW-19, and east of MW-18; the EHD recommends obtaining grab groundwater samples using direct push technology from the shallow sand unit. If you have any questions or comments you may contact Nuel Henderson, Engineering Geologist at (209) 468-3436. Sincerely, Nuel C. Henderson, Jr., PG Marg�Lgorio, REHS Engineering Geologist Program Coordinator c: Mr. James Barton, CVRWQCB, 11020 Sun Center Dr. #200, Rancho Cordova, CA 95670 Dr. Dai Watkins, TSJCI, 1120 Hollywood Ave., Ste 3, Oakland, CA 94602 j Closure Request Response Letter 1208 • i