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CON 3ULTANTS INC E NVIRONMENTAL ❑ G EOTECHNICAL ❑ MATERIAL S ' Project No 58475-06-2413 November 5, 2002 ' Mr Saiyed S Ali California Department of Transportation Central Sierra Environmental Services Branch Post Office Box 2048 Stockton, California 95201 ' Subject STOCKTON MAINTENANCE STATION SAN JOAQUIN COUNTY, CALIFORNIA CONTRACT NO 43AO078 ' TASK ORDER NO 10-987901-MU GROUNDWATER MONITORING REPORT-THIRD QUARTER 2002 ' Dear Mr All In accordance with Caltrans Task Order No 10-987901-MU, dated February 22, 2002, Geocon Consultants, Inc has provided groundwater monitoring services at the Stockton Maintenance Station ' located at 1604 South B Street in San Joaquin County, California (the Site) The Site consists of a Caltrans maintenance facility utilized for the storage of vehicles and equipment used for the maintenance of California highways The scope of services provided by Geocon included depth to groundwater measurements, the sampling of fourteen monitoring wells, and the submittal of the water samples to a California-certified laboratory for analytical testing The site location is depicted on the Vicinity Map, Figure 1 BACKGROUND In December 1989, one 5,000-gallon diesel underground storage tank (UST) and one 10,000-gallon gasoline UST, two pump islands and associated product piping were removed from the Site Analytical results of soil samples collected from the UST excavation indicated total petroleum ' hydrocarbons as gasoline and diesel (TPHg and TPHd) concentrations up to 2,000 and 58 milligrams per kilogram (mg/kg), respectively In September 1993, one 115-gallon backup diesel generator UST was removed from the Site Soil discoloration and odors were not noted during the 1993 UST ' removal activities TPHd and benzene, toluene, ethylbenzene and total xylenes (BTEX) were not detected in the soil samples collected from the UST excavation and stockpile Permits and/or closure documentation for the 1993 UST removal were not made available by Caltrans or the San Joaquin County Environmental Health Department (SJCEHD) The former UST locations are presented on Figure 2 Twelve groundwater monitoring wells (MW-1 through MW-12) and two vapor extraction wells (VW-1 and VW-2) were installed at the Site between 1992 and 1996 Quarterly groundwater monitoring has been conducted at the Site since April 1992 for wells MW-1, MW-2 and MW-3, since May 1995 for wells MW-4 through MW-8 and VW-1, and since February 1996 for wells MW- ' 9 through MW-12 and VW-2 Maximum TPHg, TPHd and benzene concentrations of 54,000, 2,900 . and 13,700 micrograms per liter (µg/l), respectively, have been reported for the groundwater samples 11375 Sunrise Park Drive, Suite 100 ❑ Rancho Cordova, California 95742 ❑ Telephone (9161 852 9118 ❑ Fax 1916) 852 9132 1