SITE INFORMATION AND CORRESPONDENCE FILE 3

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San Joaquin County Environmental Health Department DIRECTOR Donna Heran, REHS 600 East Main Street d PROGRAM COORDINATORS r�1III Stockton , California 95202 -3029 j .. Robert McClellon , REHS r. Jeff Carruesco, REHS, RDI Website: www s ov. or /ehd Kasey Foley, REHS 1 r II 4 � rFOR � �9 g �Linda Turkatte, REHS /Oeo � Phone: (209) 468-3420 Fax: (209) 464w0138 September 30, 2011 Ms . Stephanie McKenna Mr. Mark Springs Chevron Environmental Management Company 3535 Windham Circle 6111 Bollinger Canyon Road , Room 3652 Stockton , CA 95209 San Ramon , CA 94583 Subject: Chevron #9-4054 LOP Case#: 1780 2103 Country Club Blvd . AP#: 123-080-29 Stockton , CA 95204 Global ID#: T0607700063 The San Joaquin County Environmental Health Department (EHD ) has reviewed Feasibility Study ( FS ) dated August 12, 2011 , submitted by your consultant Arcadis . The FS was submitted in response to requirements set forth during phone and electronic mail discussions with Ms . Tonya Myers at Arcadis Consulting . In May 2011 , it was agreed that a FS would be submitted to the EHD by August 2011 - The submittal of the FS to Geotracker on August 12, 2011 , met the conditions of the discussion . Arcadis determined that active remediation was only needed in the B-zone and that monitored natural attenuation (MNA) would be adequate for the A-, C-, and D-zones identified at the site.. Four remedial alternatives, in conjunction with MNA were evaluated for effectiveness, long-term reliability, implementability, implementation risk, and reasonableness of cost. Arcadis concluded that MNA in the A- and C-zones with sulfate injection (Epsom salt) into the B-zone would be the preferred remedial alternative. After END app vor a,-a—piTo- e� p a�ld e-b submittt�included installation of one injection well and one dose-response well , five quarterly sulfate injection events, and five quarters of rebound testing (performance evaluation assessment) events . The EHD concurs with the following condition . The B-zone, off-site, down-gradient wells ( MW-9B , MW-12B , and MW-13B) contain the highest concentrations of dissolved petroleum hydrocarbons associated with this sites' off- site plume. As such , the groundwater contaminant plume is not laterally defined . A final remedial action plan cannot be approved until the site/plume is adequately characterized and defined . A site may enter into interim remedial action after it has been determined that remediation is needed , but it is still required that the site continue to investigate and define the extents of the groundwater plume concurrently with interim remedial actions . In order for the EHD to approve any remedial plan of the site, a work plan to continue the required investigation must be submitted , approved , and enacted concurrently with an interim remedial plan .