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Fourth Quarter 1998 Groundwater Monitoring Report • Colberg Boat Works,401 North Stockton Street, Stockton, California Page 2 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 installation at the site The proposed work was documented by Apex in Workplan far Limited Subsurface Investigation and Workplan Addendum for Limited Subsurface Investigation, dated May 2, 1995 and January 24, 1997, respectively On July 28, 1997, Apex personnel supervised the drilling of six soil bonngs, and converting the bonngs into six groundwater morutoring 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 In Apnl 1998, Apex submitted a closure request for the former diesel tank location, which is on the west side of the subject site area and also recommended discontinuing analyses for oxygenate constituents with the exception of MTBE in wells MW-1, MW-2 and MW-3 Apex further recommended discontinuing analyses for TPHd in wells MW-1, MW-2 and MW-3 In September 1998, Apex submitted a report titled Workplan for Pilot Test and Feasibility Analysis for oxygen release compound (ORC) application to MW-3 to San Joaquin County Environmental Health Department This workplan has not yet received county approval GROUNDWATER MONITORING Groundwater Levels On October 22, 1998, Apex personnel collected groundwater-level measurements from the three 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 01 foot, referenced to the surveyed tap-of-casing elevations. Groundwater level measurements are summarized in Table 1 A potentiometric surface map of the shallow water-bearing zone on October 22, 1998 is shown on Figure 3 • Ki D TROJECT'SICOLOI 401-COLBERG BOAT WORKSIQMRIo981QMRTExT DOC