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r 1 Third Quarter 1997 Groundwater Monitoring Report Colberg Boat Works,401 North Stockton Street,Stockton,Calrfonua 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 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 of six soil borings, and converting the borings into six groundwater monitoring wells 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 The SJCEHD letter and the lab chromatograms are included in Appendix A GROUNDWATER MONITORING Groundwater Levels On October 31, 1997, Apex personnel collected groundwater-level measurements from the six groundwater monitoring wells (MW-1 through MW-6) 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-of-casing elevations Groundwater level measurements are summarized in Table 1 A potentiometric surface map of the shallow water- bearing zone on October 31, 1997 is shown on Figure 3 Groundwater Sampling and Analysis On October 31, 1997, Apex personnel collected groundwater samples from monitoring wells MW-1 through MW-6 in accordance to the Apex SOP included as Appendix B The samples were submitted, under chain-of-custody documentation, to California Laboratory Services of Rancho Cordova, California, a state-certified analytical laboratory The samples were analyzed 40 for concentrations of total petroleum hydrocarbons, as gasoline and diesel, by Modified EPA Method 8015, and benzene, toluene, ethylbenzene, and total xylenes by EPA Method 8020 The JY D 1 PROJECTICOLO! 001-COLBERG BOAT WORKSIQMR11971QMR1197 DOC