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3 A • First 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 olk subsurface probes to collect soil and groundwater samples at the site The results of the su surface 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 for 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 o4 soil borings, and converting the borings 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 In a letter dated October 13, 1997, the SJCEHD requested the chromatograms for MW4/15 and MW4/20 be submitted for evaluation Apex included the lab chromatograms in "Third Quarter 1997 Groundwater Monitoring Report," dated November 17, 1997 GROUNDWATER MONITORING Groundwater Levels On January 22, 1998, the tap-of-casing (TOP) elevations of the six on-site monitoring wells (MW-1 through MW-6) were surveyed based on the City of Stockton Benchmark 237 The survey was conducted by Morrow Surveying (Morrow) of West Sacramento, California, a licensed land surveyor The elevation survey results are included in Appendix A The newly- surveyed TOP elevations are summarized in Table 1 On January 22, 1998, Apex personnel collected groundwater-level measurements from the six groundwater monitoring in accordance to the Apex Standard Operating Procedures (SOP) included as Appendix B All groundwater elevations were measured to the nearest 0 01 foot, referenced to the surveyed TOP elevations Groundwater level measurements are summarized in Table 1 A potentiometric surface map of the shallow water-bearing zone on January 22, 1998 is • shown on Figure 3 rYD1_PROJECT1CoL01001-COLBERC,BOA I WORK S\QMM2981QMR0298DOC i