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' r ` GROUND ZERO ANALYSIS, INC. 1714 Main Street Escalon,California 95320-1927 Ece Telephone:(209)838-9$88FED Facsimile:(209)838-9883 Ay 61 ENVIR August 10, 2010 PER� 'EIV 7' Ml risER��CEs rH Ms. Lori Duncan San Joaquin County Environmental Health Department 600 East Main Street Stockton, CA 95202 Subject: Appendix A Addendum—Soil Sourced Vapor Intrusion Speedy Foods;8200-N. lfighway 99, Stockton,:CA Dear Ms. Duncan: Sections 15.0 and 16.1 of Ground.Zero's Appendix A Site Closure Request dated July 2, 2010, conclude that the chemicals of concern are not found in soil samples at concentrations that would pose a risk to human health or the environment. Published tables were used in the assessment of vapor intrusion from soil sourced contamination. The assessment was conservative and based on the environmental screening levels (ESLs) for residential land use (Table C-1) published in the San Francisco Bay RWQCB in the document Screening for Environmental Concerns at Sites with Contaminated Soil and Groundwater (revised May 2008). The published ESL tables include screening levels for the emission of subsurface vapors to building interiors. Ground Zero's Appendix A Site Closure Request did not assess the possibility of soil sourced vapor intrusion from the undeveloped area adjacent to the Speedy Food Mart. Soil samples were collected during the installation of monitoring wells: MW5, MW6, MW7, MWS, MW9B, MW10, MW11, MW12,MW15, MW16, EW2, and EW3 (off-pavement wells). These monitoring wells are located Y m the undeveloped area adjacent o theSpeedy Food Mart to the north, northeast, and east. With the exception of EW3 all soil samples were collected within or below the capillary :fringe. Laboratory analysis of all soil samples indicate that TPHg was not present above laboratory reporting limits suggesting the soil contamination was limited the area of the former underground storage tanks (USTs). MTBE was detected in MW6, MW 12, and EW2 in samples taken from within or below the capillary fringe. A soil sample was collected at 40 feet below grade surface (bgs) from EW3 with results indicating that there were no analyzed constituents above laboratory detection limits.