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Additional Site Assessment Report 1 • The Southland Corporation,Store#17334,4501 North Pershing Avenue,Stockton,CA January 15, 1998 f 1 0 INTRODUCTION This report is submitted by Fluor Daniel GTI, Inc (Fluor Daniel GTI) to summarize the results of site assessment conducted at Southland Store No 17334, 4501 North Pershing Avenue in Stockton, California (Figures 1 and 2) The scope of work for the site assessment Included the collection of background information,the drilling and sampling soil from one off-site and four on-site bonngs, Installing groundwater monrtonng wells within each of the borings, collection of groundwater samples , and preparation of this report summarizing the methods and results of the work performed The work scope was designed to fulfill the requirements of the San Joaquin County Public Health Services(SJCPHS) The work scope described in this report was completed at the site between September 23 and December 19, 1997 All work was performed in accordance with Fluor Daniel GTI's Work Plan for Additional Site Investigation,dated March 29, 1997,which was approved by the SJCPHS 2 0 BACKGROUND Based on review of the SJCPHS files,three sites adjacent to the subject site have had reported releases of gasoline-range petroleum hydrocarbons Cardlock Gasoline Station,4555 N Pershing Ave , located 100 feet west of subject site (upgradient of subject site) Shell Service Station,4445 N Pershing Ave , on southeast corner of Pershing and Rosemarie Lane (crossgradient of subject site) Exxon Service Station,4444 N Pershing Ave , on southwest corner of Pershing and Rosemarie Lane (crossgradient of subject site) Groundwater monitoring and sampling has been ongoing at the Exxon site since 1987,and conducted at the Cardlock and Shell sites since 1992 In 1988, Exxon installed a 30-foot-jeep groundwater monitoring well,MW-9,approximately 10 feet east and 10 feet south of Southland's tank pit(Figure 2) The depthto - groundwater in MW-9 has ranged from 30 feet BGS in 1990 to 20 feet BGS in April 1996 Seasonal water table fluctuations average 2 to 3 feet Historical groundwater flow direction at the three sites has been northeast,and the gradient at the Exxon sde on August 8, 1996 was 0 006 foot per foot On February 20, 1997, Fluor Daniel GTI supervised the advancement of four angled and three vertical geoprobe borings (GP-1 through GP-7) at the site Soil samples were collected from the bonngs at vertical depths of 15 feet to 22 feet below ground surface(BGS) Six bonngs(GP-1 through GP-6)were drilled beneath the three 10,000-gallon USTs at the site as required by the SJCPHS prior to tank lining permit approval In addition,groundwater grab samples were collected from bonngs GP-3, GP-4, and GP-7 ,rMsar rpt FLUOR DANIEL GTI