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WORKPLAN ADDITIONAL SOIL AND GROUNDWATER INVESTIGATION SURFACE WATER SAMPLING ' May 27, 1998 1.0 INTRODUCTION This work plan is for additional soil and groundwater investigation and surface water sampling at Herman & Helen's Marina located at Venice Island Ferry in Stockton, California (Figures 1 and 2, Appendix A). The purpose of the work described is to further investigate the extent of gasoline ' contamination associated with former underground storage tanks (USTs) at the site. This work plan was prepared by Condor Earth Technologies, Inc. (Condor) at the request of Mr. David M. Smith of Herman &Helen's Marina. ' In a telephone conversation on March 23, 1998, Mr. Ronald Rowe of the San Joaquin County Public Health Services, Environmental Health Division (PHS/EHD) indicated that based on his review of the Report—Additional Soil and Groundwater Investigation, prepared by Condor, dated December 11, 1997, he was requesting that quarterly groundwater monitoring continue at the site. Furthermore, he was requiring that a work plan be prepared for conducting quarterly surface water sampling and further ' investigating the gasoline oxygenate/additive plume to the east of site monitor well MW-2. Condor prepared a letter, dated March 23, 1998, documenting the conversation. This work plan is in direct response to Mr. Rowe's request and provides a description of the proposed fieldwork and laboratory analyses. 2.0 SITE BACKGROUND ' On October 30, 1991, Warren E. Gomes Excavating, Inc., of Rio Vista, California, excavated and removed three underground storage tanks(USTs)from the site(Figure 2,Appendix A). The USTs(TKI, TK2, and TK3)contained gasoline and diesel fuel. A small hole was found on the lower fill end of TK3 (diesel tank). Petroleum staining and odors were noted in the soil beneath the former locations of the USTs. Six soil samples were collected by Condor from the UST excavation at depths of 9 to 12 feet below the ground surface. Laboratory analyses indicated elevated concentrations of TPH-G, BTEX, and total extractable petroleum hydrocarbons quantified as diesel (TEPH) in the soil samples. Figure 2, Appendix A, indicates the locations of all geoprobe, Hydropunch, and monitor wells installed subsequent to the UST removal to investigate site soil and groundwater contamination. On August 22, 1995, three hydropunch borings were drilled at the site. Gasoline odors were noted in each borehole. Laboratory analyses indicated concentrations of TPH-G and BTEX in the soil and ' groundwater samples analyzed from each borehole. Based on the results of the August 1995, investigation, Condor recommended additional investigation be conducted to evaluate the extent of the hydrocarbon plume. On August 29, 1996, five Geoprobe boreholes were installed at the site. The results ' of the laboratory analyses indicated that elevated concentrations of TPH-G, BTEX, and methyl tertiary butyl ether (MTBE) were detected in soil and groundwater samples at the north portion of the site and that further investigation was necessary to evaluate the extent of soil and groundwater contamination. ' �� CONDOR