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i • GROUNDWATER INVESTIGATION REPORT COUNTRY CLUB STORM DRAIN SYSTEM PROJECT I ' COUNTRY CLUB BOULEVARD AND PLYMOUTH ROAD STOCKTON, CALIFORNIA 1.0 INTRODUCTION ' This report provides the results of a groundwater investigation that was conducted by Condor Earth Technologies Inc (Condor) in order to identify potential sources of contamination (primarily gasoline additives/oxygenates) that have impacted the City of Stockton Municipal Utilities Department (MUD) storm drain system along Country Club Boulevard and Plymouth Road in Stockton, San Joaquin County, California (Figures 1 and 2, Appendix A) Groundwater investigation activities were conducted by Condor along this section of the MUD storm drain system on September 17 and 24, 2003 Condor ' prepared this report at the request of Mr Ali Gharegozloo of MUD This report includes a discussion of the project background, a description of the nearby underground storage tank(UST) sites and their associated contaminant plumes within the study area,description of the fieldwork conducted by Condor and other consultants along the storm drain line, laboratory analytical results, figures with direct push (Geoprobe and cone penetrometer testing [CPT]) boring locations, and liea discussion of the results All work conducted by Condor was performed under the supervision of a California Registered Geologist 2.0 PROJECT BACKGROUND ' In March of 2003, the City of Stockton began construction activities to install a sanitary sewer pipeline starting from the City's existing Smith Canal Sanitary Pump Station eastward under I-5, then northward along Plymouth Road, and then eastward again along Country Club Blvd for a total of 9,800 feet of pipe In April 2003, during the bore and hack operation under I-5, the contractor struck an existing storm drain line that runs north/south along the eastern side of 1-5 between I-5 and Plymouth Road 1 As part of the bore and hack operation, pumping and disposing of groundwater at the construction site was necessary To allow discharge of this groundwater to the City's sanitary sewer system, a discharge permit from the City's Municipal Utilities Department was obtained As a condition of the permit, ' periodic sampling of the discharge was required Prior to hitting the storm drain line, all testing of the permitted discharge showed no contamination After the contractor hit the storm drain line, the permitted discharge showed contamination for methyl tertiary-butyl ether(MTBE) and tertiary-butanol (TBA) ' At that time, it was unclear where the contamination had originated A subsequent investigation showed that water contained in the damaged storm drain line had leaked into the sanitary sewer line that was being constructed and had then traveled to the bore pit from which groundwater was being pumped Groundwater pumping was halted until a filter system could be brought onsite to strip the contaminants from the discharge At that time, it was believed the likely source of the MTBE and TBA was from contaminated groundwater leaking into the storm drain line As the storm drain line runs southward from Mendocino • ' �6� CONDOR