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Additional Site Assessment Work Plan LANGSTON'S MARKET 15615 South 7" Street, Lathrop, California 1.0. INTRODUCTION At the request of Mr James Langston, Advanced GeoEnvironmental, Inc (AGE) has prepared the enclosed Monitoring Well Installation Work Plan for the Langston's Market at 15615 South 7`h Street, Lathrop, California The purpose of the work is to further assess high concentrations of petroleum hydrocarbons discovered in a grab ground water sample collected along the 7"'Street edge of the site during a November 2002 site investigation The location of the site is illustrated on Figure 1 A plan of the site is illustrated on Figure 2 An AGE-prepared work plan, dated August 2002, to install a monitoring well across 7"' Street east of the site was submitted to San Joaquin County Environmental Health Department(SJCEHD) and approved by letter dated 29 August 2002 However, due to difficulties obtaining the required well- installation permit from the City of Lathrop, AGE presently proposes to advance one soil boring at the originally-proposed monitoring well location, and another soil boring adjacent to the former dispenser area(Figure 2) This work plan was prepared at the request of Mr Langston to expedite the site closure process,and was prepared in accordance with Central Valley Regional Water Quality Control Board (RWQCB) guidelines for the investigation of UST sites 2.0. BACKGROUND Following is a brief summary of environmental activities at the subject site • June 1990 - A 4,000-gallon gasoline UST failed and approximately 1,200 gallons of unleaded gasoline were released to the subsurface • April 1992 - Soil and ground water samples collected from near the former UST location indicated that the gasoline release had reached ground water Between 1990 and 2000, eighteen (18) soil • April 1993 - Four ground water monitoring wells were installed at the site Significant concentrations of petroleum hydrocarbons were detected in ground water samples collected from the site • September 1995 - The area of the former USTs and dispenser are were excavated Approximately 3,000 cubic yards of Impacted soil was removed and disposed Sidewall and floor samples collected from the north and west of the excavation contained minor concentrations ofpetroleum hydrocarbons(<50 ppm) Excavation was limited to the east and south by roadways and utilities, remaining contamination in those directions were less than 100 ppm Monitoring wells MW-1 through MW-4 were abandoned prior to excavation activities and reinstalled at the completion excavation activities Advanced GeoEnvironmental,Inc