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ip <br /> Mr. Carl Navarra Page 4 of 4 <br /> 7500 W. Eleventh Street February 23, 2010 <br /> Tracy, CA <br /> the well may indicate that the plume of impacted groundwater is still migrating, and therefore <br /> cannot be considered stable. In the 28 December 2008 letter, the EHD had directed additional <br /> characterization of the down-gradient extent of the plume of MTBE-impacted groundwater. <br /> Plume stability must be demonstrated to obtain a site closure concurrence. TSJCI prepared <br /> Work Plan for Evaluation of MTBE Migration and Soil Gas Survey(WP), dated April 2009, which <br /> was approved by the EHD by letter dated 29 June 2009. Due to the high groundwater usage of <br /> the area, the EHD considers a high degree of confidence regarding the down-gradient <br /> delineation of the plume of impacted groundwater to be a priority. <br /> To further evaluate your request for site closure, the EHD directs you to prepare a site closure <br /> summary report (SCS) following the guidelines provided in the Tri Regional Guidelines, <br /> Appendix B. Include in the SCS the following: <br /> • Updated mass estimates of sorbed and dissolved contaminants proposed to be left in <br /> place contrasted with the estimated original or maximum contaminant mass; <br /> • An evaluation of the down-gradient extent of the MTBE-plume for which the EHD had <br /> approved a work plan by letter dated 28 June 2009 — the EHD recommends completing <br /> this phase of work and including the results in the SCR, if appropriate; <br /> • Reevaluation of the Tier li results considering impacted groundwater as a drinking water <br /> source for both the impacted soil and groundwater proposed to be left in place and for <br /> potential vapor intrusion evaluation; <br /> • A discussion and demonstration of the declining contaminant concentration trends and <br /> time needed to achieve background concentrations for the analytes and wells discussed <br /> above; and <br /> • The results of the first quarter 2010 groundwater monitoring event to better establish the <br /> concentration trends. <br /> Please note that most requests for a site closure that will leave significant contaminant masses <br /> in place involve plumes that have not migrated off-site, but most of your dissolved plume has left <br /> the site and now underlies Eleventh Street, Chrisman Avenue, the property at 7501 W. Eleventh <br /> Street and the arable field. This situation will require that the EHD conduct a public comment <br /> period with notice to the affected landowners should the EHD concur with your SCS. <br /> If you have any questions or comments you may contact Nuel Henderson, Engineering <br /> Geologist at (209)468-3436. <br /> Sincerely, L <br /> Nuel C. Henderson, Jr., PG Adrienne Ellsaesser, REHS <br /> Engineering Geologist Acting Program Coordinator <br /> c. Mr. James Barton, CVRWQCB, 11020 Sun Center Dr. #200, Rancho Cordova, CA 95670 <br /> Dr. Dai Watkins, TSJCI, 1120 Hollywood Ave., Ste 3, Oakland, CA 94602 <br /> Mr. Russ Zelmer, 7060 W. Durham Ferry Road, Tracy CA 95304 <br /> Site Closure Request Response Letter 0210 <br />