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, GROUNDWATER INVESTIGATION AND GROUNDWATER EXTRACTION WORK PLAN r Boyett Petroleum 419 S.Main Street Manteca,CA y 1.0 INTRODUCTION This work plan was prepared by Condor Earth Technologies, Inc. (Condor) to describe proposed additional groundwater investigation and limited batch groundwater extraction activities for the Boyett Petroleum facility located at 419 S. Main Street (site) in Manteca, California (Figures 1 and 2, Appendix A). In a letter dated April 14, 2006, Jeffrey Wong of the San Joaquin County Environmental Health Division (SJCEHD) described the results of a discussion with the California Regional Water Quality r Control Board(CRWQCB) regarding the No Further Action Request(NFAR) dated October 7, 2005. Mr. Wong stated the SJCEHD and the CRWQCB agreed that the site is not quite ready for closure. Mr. Wong requested a work plan to complete the lateral definition of the dissolved methyl tertiary-butyl ether (MTBE)plume toward the northwest, to provide a fate-and-transport model showing the path of travel of the plume before it reaches background levels, and to discuss and evaluate the risk of soil vapor intrusion into all nearby structures. He also recommended conducting limited batch groundwater extraction at monitoring wells MW-11 and EW-11 because the MTBE concentrations at these wells are still above the �+ MCL. Mr. Wong requested the work plan be submitted to the SJCEHD by June 1, 2006. Condor prepared this work plan at the request of Dale Boyett of Boyett Petroleum(client)in response to that letter. ••• 2.0 SITE BACKGROUND On November 20 and 21, 1996, soil sampling was conducted at the site by WHF, Inc. (WHF) under the direction of Robert McClellon of the SJCEHD. One soil sample was collected from beneath each of the site's three existing fuel dispensers at a depth of approximately two feet below the dispenser piping. Four discrete soil samples were collected to characterize approximately 44 cubic yards of stockpiled soil from demolition and retrofit activities at the site. The four discrete samples were composited into two soil �• samples for laboratory analyses. The soil samples collected from both the dispenser locations and the soil stockpile were analyzed for total petroleum hydrocarbons quantified as gasoline (TPH-G); for benzene, ethyl benzene, toluene, and total xylenes(BTEX); and MTBE. r On October 5, 1998, WHF completed two vertical soil borings, SB-1 and SB-2, to a maximum depth o 18 feet below ground surface (bgs) near the fuel dispenser island. Three soil samples were collected for laboratory analyses from each boring at depth intervals of 4 to 6 feet, 9 to 11 feet, and 16 feet. One groundwater sample was collected from each boring at a depth of 18 feet for laboratory analyses. On August 27 and 30, 1999, WHF completed four soil borings. The borings, which ranged in total depth from 26.5 to 36.5 feet bgs, were subsequently converted into monitoring wells MW-1 through MW-4. The depth to groundwater was reported to be approximately 18 feet bgs. Quarterly groundwater monitoring at the site began in the fourth quarter of 1999. r From December 20 through 22, 2000, WHF completed four soil borings. The borings, which ranged in total depth from approximately 20 to 25 feet bgs, were subsequently converted into monitoring wells r MW-5 through MW-8. The depth to groundwater was reported to be approximately 17 feet bgs. r iw CONDOR r