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California Department of Transportation March 13, 2001 Shop 10 Maintenance Station, Stockton, California Project No 400296-01 • 2 INTRODUCTION AND SCOPE OF SERVICES This report summarizes the results of the Third Quarter 2000 groundwater monitoring activities conducted September 13, 2000 at the Shop 10 Maintenance Station, located in Stockton, Califor- nia (Figure 1) The work conducted by Ninyo & Moore was in accordance with Task Order No 10-987901-NP and Caltrans Contract No 43AO012 Our scope of services include 1) attendance of a prework site visit, 2) preparation of a site safety plan, 3) measurement of the depth to static groundwater at selected wells, 4) purging of a minimum of three well volumes to labeled recon- ditioned 55-gallon drums, 5) collection and chemical analysis of groundwater samples, and 6) preparation of this report documenting our field activities and findings 3 SITE BACKGROUND According to a report entitled, Revised Report, Third Quarter 1998 Ground«ater Monitoring Re- II port by Professional Service Industries (PSI), dated March 19, 1999, four underground storage tanks (USTs) were removed from the site in August 1986 Subsequent to the removal, fourteen Isoil borings were drilled on-site and four were drilled off-site between 1987 and 1991 to deter- mine the extent of soil contamination Analytical results of soil samples collected indicated Imaximum concentrations of total petroleum hydrocarbons as gasoline (TPH-G) to be 3,800 mil- ligrams per kilogram (mg/kg) and total petroleum hydrocarbons as diesel (TPH-D) to be 4,500 Img/kg Groundwater monitoring wells currently active and sampled during quarterly groundwater monitoring for the site include MW-9, MW-11, MW-12, MW-13, MW-14, MW-16, MW-19, MW-20, MW-24, MW-25 and VM-1 Monitoring well VM-2 is normally sampled, however it has been buried and paved over since the last time it was sampled during the third quarter 1999 monitoring event Since 1988 several wells were installed and subsequently abandoned including MW-1, MW-2, MW-3, MW-4, MW-5, MW-7, MW-8, MW-10, MW-26 and VW-1 The ap- proximate locations of the active monitoring wells are shown in Figure 2 Quarterly groundwater Imonitoring has been conducted at the site in the wells since 1990 Historically, concentrations of • I I0290 01r shop]0 FV L 3Q2000 doc 2