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' California Department of Transportation February 24, 2000 <br /> Stockton Maintenance Station, Stockton, California Project No 103872-02 <br /> 2. INTRODUCTION AND SCOPE OF SERVICES <br /> This report summarizes the results of the Fourth Quarter 1999 groundwater monitoring activities <br /> conducted on January 5 and 6, 2000 at the Stockton Maintenance Station, located in Stockton, <br /> California (Figure 1) The work conducted by Ninyo & Moore was in accordance with Task Or- <br /> der No 10-911175-NB and Caltrans Contract No 43AO012 Our scope of services include 1) <br /> attendance of a prework site visit, 2) preparation of a site safety plan, 3) measurement of the <br /> depth to static groundwater at selected wells, 4) purging of a minimum of three well volumes to <br />' labeled reconditioned 55-gallon drums, 5) collection and chemical analysis of groundwater sam- <br /> ples, and 6) preparation of this report documenting our field activities and findings <br />' 3. SITE BACKGROUND <br /> According to a report entitled, Final Report, Fourth Quarter 1998 Groundwater Monitonnq Re- <br /> part by Professional Service Industries (PSI), dated February 19, 1999, one 5,000-gallon diesel <br /> underground storage tank (UST) and one 10,000-gallon unleaded gasoline UST, two pump is- <br /> lands and associated product piping were removed from the site in 1989 Subsequent to the <br /> removal, soil samples were collected to determine the extent of soil contamination Analytical <br />' results of soil samples collected indicated maximum concentrations of total petroleum hydrocar- <br /> bons as gasoline (TPH-G) to be 2,000 milligrams per kilogram (mg/kg) and total petroleum <br /> hydrocarbons as diesel (TPH-D) to be 58 mg/kg <br /> Twelve groundwater monitoring wells and two vapor extraction wells have been installed at the <br /> site The approximate locations of the monitoring and vapor extraction wells are shown in Figure <br /> t 2 Quarterly groundwater monitoring has been conducted at the site on wells MW-1, MW-2, and <br /> MW-3 since April 1992 Wells MW-4 through MW-8 and VW-I have been monitored since May <br /> 1995 Wells MW-9 through MW-12 and VW-2 have been monitored since February 1996 His- <br /> torically, high concentrations of TPH-G, TPH-D, and benzene, toluene, ethylbenzene, and total <br />' xylenes (BTEX) have been detected in the on-site monitoring wells <br />' uockta,doe 2 �g�lJl "&P' ®"M[� <br />