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<br /> San Joaquin County
<br /> PIN
<br /> Environmental Health Department DIRECTOR
<br /> �. _ �...p Donna Heran,REHS
<br /> z: z 600 East Main Street
<br /> v: a 3029 95202
<br /> OGRAM COORDINATORS
<br /> Stockton, Californiaaorna -
<br /> Robert McClellon,REHS
<br /> Jeff Carruesco,REHS,RDI
<br /> Kasey
<br /> �' .:- P • Website:www.sjgov.org/ehd Linda Foley,REHS
<br /> Linda Turkatte,RENS
<br /> Phone: (209)468-3420
<br /> Fax: (209)464-0138
<br /> November 3, 2011
<br /> Ian Robb
<br /> Union Oil Company
<br /> 6101 Bollinger Canyon Road, Fifth Floor
<br /> San Ramon, CA 94583
<br /> Subject: Former UNOCAL#6981
<br /> 4707 Pacific Avenue
<br /> Stockton, CA
<br /> The San Joaquin County Environmental Health Department (EHD) has reviewed Hydrogeologic
<br /> Modeling Update and Request for Case Closure dated July 29, 2011, submitted on your behalf
<br /> by Stantec Consulting Corporation (Stantec) and has the following comments.
<br /> In correspondence dated May 5, 2011, the EHD requested submittal of a Case Closure
<br /> Summary Report that included a fate and transport hydrogeologic model using groundwater
<br /> analytical data from well VW-2, and that addressed all requirements of the Tri-Regional
<br /> Guidelines Appendix A.
<br /> The model update submitted was reported to have utilized groundwater data from wells VW-2,
<br /> VW-7, MW-2 and MW-16, covering a period beginning in 1990. The concern for closure of the
<br /> site is the projected degradation of the plume from this point in time forward, specifically for the
<br /> concentrations of contamination found in VW-2, which had not been sampled until recently. The
<br /> previously submitted model, dated December 17, 2009, made predictions of the life of the plume
<br /> from 2008-2018, using contaminant concentrations from VW-7, MW-2 and MW-16. The Tri-
<br /> Regional Guidelines Appendix A was not addressed in the submitted model update.
<br /> Please proceed with submittal of the previously requested Case Closure Summary Report,
<br /> including a fate and transport model for the contamination remaining in VW-2, and addressing
<br /> all requirements of the Tri-Regional Guidelines Appendix A. The EHD recommends utilizing
<br /> pre-remediation and/or post-remediation concentration trends to determine the natural
<br /> contaminant degradation rate. The Case Closure Summary Report, including the Tri-Regional
<br /> Guidelines Appendix A, is due for submittal no later than December 30, 2011.
<br /> If you have any questions please contact Lori Duncan at (209) 468-0337 or by email at
<br /> Iduncan@sjcehd.com.
<br /> Lori Duncan, REHS Nuel C. Henderson, Jr. PG
<br /> Senior Registered Environmental Health Specialist Engineering Geologist
<br /> c: Steve Strait, Stantec Consulting Corp., 15575 Los Gatos Blvd., Bldg C, Los Gatos CA, 95670
<br /> Ryan Zick, Target Corp., 33 South 6`h Street, CC-3715, Minneapolis, MN 55440
<br /> Jim Barton, CVRWQCB, 11020 Sun Center Drive, Suite 200, Rancho Cordova, CA 95670
<br />
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