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WL18122121
<br /> C ON SU LTA NT S F NO
<br /> ENVIRONMENTAL ❑ GEOTECHNICAL ❑ MATERIALS
<br /> Project No 58475-06-24F
<br /> July 18, 2003
<br /> Mr Saiyed S Ali
<br /> California Department of Transportation
<br /> Central Sierra Environmental Services Branch
<br />' Post Office Box 2048
<br /> Stockton, California 95201
<br />' Subject SHOP 10 MAINTENANCE STATION
<br /> STOCKTON, SAN JOAQUIN COUNTY, CALIFORNIA
<br /> CONTRACT NO 43AO078
<br /> TASK ORDER NO 10-987901-MU
<br /> GROUNDWATER MONITORING REPORT- SECOND QUARTER 2003
<br />' Dear Mr Ali
<br /> In accordance with Caltrans Task Order No 10-987901-MU, dated February 22, 2002, Geocon
<br /> Consultants, Inc has provided groundwater monitoring services at the Shop 10 Maintenance Station
<br />' located at 1603 South B Street in Stockton, California (the Site) The Site consists of a maintenance
<br /> facility utilized for the storage of vehicles and equipment used for the maintenance of California
<br /> highways The scope of services provided by Geocon included depth to groundwater measurements,
<br /> the sampling of twelve onsite monitoring wells and the submittal of the water samples to a California-
<br /> certified laboratory for analytical testing The site location is depicted on the Vicinity Map, Figure I
<br />' BACKGROUND
<br /> In 1978, one 5,000-gallon underground storage tank (UST) with unknown contents was reportedly
<br />' removed from the Site due to a detected leak In 1989, three 5,000-gallon gasoline USTs, one 5,000-
<br /> gallon diesel UST and one 1,000-gallon waste oil UST were removed from the Site Maximum total
<br /> petroleum hydrocarbons as gasoline and diesel (TPI-Ig and TPHd) concentrations of 3,700 and 1,700
<br />' milligrams per kilogram (mg/kg), respectively, were detected in soil samples collected from beneath the
<br /> gasoline, diesel and waste oil USTs Between 1987 and 1996, twenty-one groundwater monitoring wells
<br /> were installed at the Site to determine the vertical and lateral extent of contamination Twelve wells are
<br /> currently located onsite and are included in the quarterly monitoring program Maximum TPHg, TPHd,
<br /> methyl tert-butyl ether (MTBE) and benzene concentrations of 231,000, 6,100, 96 and 28,000
<br /> micrograms per liter (µg/I), respectively, have been reported for water samples collected from the wells
<br />' Tert-butanol, tetrachloroethene, tert-butyl benzene 1,2-dichloroethane (1,2-DCA), iso-propylbenzene,
<br /> sec-butyl benzene, p-isopropyltoluene, naphthalene, n-propyl benzene, 1,2,4-trimethylbenzene and 1,3,5-
<br /> trtmethylbenzene have historically been detected in the groundwater samples collected from wells VM-1
<br /> and VM-2 1,2-DCA has also been detected in the groundwater samples collected from well MW-13 The
<br /> Site has been on a quarterly groundwater monitoring schedule since 1990 Wells MW-1 through MW-8,
<br /> MW-10, MW-26 and VW-1 have been abandoned The groundwater flow direction beneath the Site has
<br /> generally been directed to the east and northeast The former UST locations and approximate locations
<br /> of the groundwater monitoring wells are presented on Figure 2 A summary of historical analytical
<br /> groundwater data is tabulated in Appendix A
<br /> 11375 Sunrise Park Drive, Suite 100 11 Rancho Cordova, California 95742 0 Telephone{916] 852 9118 13 Fox [916 852 9132
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