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k Second Quarter 1998 Groundwater Monitoring Report and Closure Request for Former Diesel Tank Site Colberg Boat Works,401 North Stockton Street,Stockton,Callfonua Page 2 BACKGROUND On May 16, 1986, Jim Thorpe Oil, Inc removed two 550-gallon diesel, one 8,000-gallon diesel, and one 1,000-gallon gasoline underground storage tanks (USTs) from the site The area around the former gasoline UST was over-excavated in 1988 In February 1993, Telic Engineering Corporation (TEC) of Stockton, California, performed a Phase I investigation of the subject site and surrounding area within a one-nule radius TEC's findings are summarized in their report Phase I Preliminary Hazardous Materials Site Assessment, dated July 21, 1993 On December 12 and 13, 1994, Apex supervised the advancement of 11 subsurface probes to collect soil and groundwater samples at the site The results of the subsurface investigation are summarized in the report Phase II Site Assessment Report, dated January 23, 1995 The results of the subsurface investigation indicated that areas around the former USTs were impacted by petroleum hydrocarbons Subsequently, Colberg Boat Works was directed by the San Joaquin County Environmental • Health Division (SJCEHD) to perform further investigations at the site Apex proposed additional subsurface investigation and groundwater monitoring well installation at the site The proposed work was documented by Apex in Workplan for Limited Subsurface Investigation and Workplan Addendum for Lammed Subsurface Investigation, dated May 2, 1995 and January 24, 1997, respectively On July 28, 1997, Apex personnel supervised the drilling of six soil borings, and converting the bonngs into six groundwater monitoring wells (Figure 2, MW-1 through MW-6) at the site The results of the work were documented by Apex in Results of Subsurface Investigation, dated August 21, 1997 GROUNDWATER MONITORING Groundwater Levels On April 30, 1998, Apex personnel collected groundwater-level measurements from the six groundwater monitoring wells in accordance to the Apex Standard Operating Procedures (SOP) included as Appendix A All groundwater elevations were measured to the nearest 0 O1 foot, referenced to the surveyed top-of-casing elevations Groundwater level measurements are summarized in Table 1 A potentiometric surface map of the shallow water-bearing zone on April 30, 1998 is shown on Figure 3 JY C 1 PROJECTICOLOI 001-COLBERG BOAT WORKSIQMR04981QMR0498 DOC