SITE INFORMATION AND CORRESPONDENCE FILE 2

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i 3✓ San Joaquin County DIRECTOR n,REHS Environmental Health Department Donna Hera M ASSISTANT DIRECTOR 2 y 600 East Main Street Laurie Cotulla, REHS ur { Stockton, California 95202-3029 PROGRAM COORDINATORS • Mike Huggins, REHS, RDI !' Margaret Lagorio,REHS Cq •. :-:'�j�P Website: www.sjgov.org/ehd Robert McClellon,REHS �/FOR Phone: (209) 468-3420 ,teff Carruesco,REHS, RDI Fax: (209) 464-0138 Kasey Foley,REHS July 6, 2009 Tbr 1-,o-A Mr. Sergio Morescalchi Atlantic Richfield Company PO Box 1257 San Ramon, CA 94583 Subject: 76 (Former BP) Service Station #11192 Site Code: RO# 087 1403 Country Club Blvd Global In#: T0607700329 Stockton CA, 95204 CUF#: 2413 The San Joaquin County Environmental Health Department (EHD) has reviewed Work Plan Addendum for Additional Site Assessment (Plan) dated March 26, 2009 and has the following comments. The Plan was submitted as required by the EHD since the originally approved work plan, dated October 2005, had not been enacted. The original plan called for installing six additional monitoring wells on and offsite,at multiple depths,to delineate contaminated ground water and was approved by the EHD in correspondence dated November 9, 2005. The more recent Plan proposed installation of only one monitoring well, MW-14 approximately 350 feet away from the site in the intermediate water bearing zone, screened from approximately 35 feet to 45 feet below ground surface (' bgs). Since the 2005 approval of the original work plan, the Shell investigation on the east side of Pershing Avenue (1267 Country Club Boulevard) has continued and monitoring wells "S-15" and "S-17" were installed on Elmwood Avenue, north of the Shell site, to address the down- gradient extent of the Shell plume. Discussion in the Plan states that knowledge of the 76/BP dissolved fuel oxygenate plume has changed,and some of the wells proposed in the original plan are no longer needed since the installation of the Shell monitoring wells provide delineation of the offsite ground water contamination in these areas. The EHD has reviewed the latest Shell ground water data,and the data for the 76/ BP station and notes the following. Shell monitoring well S-15 is screened from 35' bgs to 40' bgs,and ground water samples collected from this well since April 2008 have consistently contained total petroleum hydrocarbons as gasoline (TPHg), methyl tert-butyl ether (MtBE), and tert butyl- alcohol (TBA) at elevated concentrations. Additionally, Shell's deep monitoring well S-17 (screened from 58' to 73' bgs) and shallow monitoring well S-6 (screened from 9' to 24' bgs), also in this area, have occasionally contained the same constituents.