SITE INFORMATION AND CORRESPONDENCE FILE 3

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San Joaquin County ` " Environmental Health Department DIRECTOR 2 Q � 600 East Main Street Donna Heran, REHS { Stockton , California 95202-3029 PROGRAM COORDINATORS Robert McClellan, REHS _ — Jeff Carruesco, REHS, RDI C9 � � FOR �\P Website: www.sjgov. org/ebd Kasey Foley, REHS ,.f- Phone : (209) 468-3420 Linda Turkatte, REHS i`XU Fax: (209) 464-0138 February 18 , 2011 Mr. Denis L. Brown Mr. David Hoover Shell Oil Products US California Fuel Supply Inc HSEQ / Science & Engineering 587 Ygnacio Valley Road 20945 S . Wilmington Ave . Walnut Creek, CA 94596 Carson , CA 90810 Subject: Former Shell Station, LOP Case #: 390870 2575 Country Club Blvd . APN : 123-020-12 Stockton , CA 95204 Global ID#: T0607732095 The San Joaquin County Environmental Health Department (EHD) has reviewed Feasibility Study (Study) by Conestoga-Rovers & Associates (CRA) dated October 5, 2010. The EHD had directed Shell in correspondence dated August 3 , 2010, to submit the study after it was decided that conducting a pilot test for sodium persulfate was not a viable remedial alternative to test. Conclusions in the study stated that since existing dissolved concentrations of sodium , aluminum , manganese and arsenic exceed water quality objectives (WOOS) , but not maximum contaminant levels ( MCLS ), the current 'beneficial use' status of the shallow groundwater at the site should modified to 'non-potable' status so clean up levels for this site will allow more contamination to remain in place without additional active remediation being conducted . Based on this premise, Shell concluded that monitored natural attenuation (MNA) would be an acceptable remedial technology for the site. The EHD advises that a beneficial status designation for groundwater is not Limited to MCLS or WQOs and proposals to evaluate residual groundwater contamination at this site must continue to use beneficial use guidelines. The EHD has evaluated the concentration trends in monitoring wells MW-5R , MW-8 , MW- 15 , MW- 18, and extraction well RW-1A for total petroleum hydrocarbons as gasoline (TPHg ) benzene , and tertiary butyl alcohol (TBA) since the groundwater extraction activities have ceased and cannot concur with Shell that a "strong" declining trend is being exhibited . The "strong" declining trend identified by Shell appears to have been greatly influenced by data collected during active remediation . Despite the fluctuations in the groundwater contaminant concentrations overall and the significant increase noted in RW- 1A, the EHD considers the groundwater concentration plume to be mostly stable and defined . In order to continue the evaluation of MNA as an effective and feasible alternative to active remediation , the EHD directs Shell to address the following concerns in a report due at the EHD by April 11 , 2011 : 1 . Provide a Human Health Risk Assessment (HHRA) and a vapor intrusion evaluation for the site and the adjacent school buildings .